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'EUI64' -- Possible downref: Non-RFC (?) normative reference: ref. 'ISO10589' ** Obsolete normative reference: RFC 5549 (Obsoleted by RFC 8950) ** Obsolete normative reference: RFC 7752 (Obsoleted by RFC 9552) Summary: 2 errors (**), 0 flaws (~~), 35 warnings (==), 4 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 RIFT Working Group A. Przygienda, Ed. 3 Internet-Draft Juniper 4 Intended status: Standards Track A. Sharma 5 Expires: August 1, 2020 Comcast 6 P. Thubert 7 Cisco 8 Bruno. Rijsman 9 Individual 10 Dmitry. Afanasiev 11 Yandex 12 January 29, 2020 14 RIFT: Routing in Fat Trees 15 draft-ietf-rift-rift-10 17 Abstract 19 This document defines a specialized, dynamic routing protocol for 20 Clos and fat-tree network topologies optimized towards minimization 21 of configuration and operational complexity. The protocol 23 o deals with no configuration, fully automated construction of fat- 24 tree topologies based on detection of links, 26 o minimizes the amount of routing state held at each level, 28 o automatically prunes and load balances topology flooding exchanges 29 over a sufficient subset of links, 31 o supports automatic disaggregation of prefixes on link and node 32 failures to prevent black-holing and suboptimal routing, 34 o allows traffic steering and re-routing policies, 36 o allows loop-free non-ECMP forwarding, 38 o automatically re-balances traffic towards the spines based on 39 bandwidth available and finally 41 o provides mechanisms to synchronize a limited key-value data-store 42 that can be used after protocol convergence to e.g. bootstrap 43 higher levels of functionality on nodes. 45 Status of This Memo 47 This Internet-Draft is submitted in full conformance with the 48 provisions of BCP 78 and BCP 79. 50 Internet-Drafts are working documents of the Internet Engineering 51 Task Force (IETF). Note that other groups may also distribute 52 working documents as Internet-Drafts. The list of current Internet- 53 Drafts is at https://datatracker.ietf.org/drafts/current/. 55 Internet-Drafts are draft documents valid for a maximum of six months 56 and may be updated, replaced, or obsoleted by other documents at any 57 time. It is inappropriate to use Internet-Drafts as reference 58 material or to cite them other than as "work in progress." 60 This Internet-Draft will expire on August 1, 2020. 62 Copyright Notice 64 Copyright (c) 2020 IETF Trust and the persons identified as the 65 document authors. All rights reserved. 67 This document is subject to BCP 78 and the IETF Trust's Legal 68 Provisions Relating to IETF Documents 69 (https://trustee.ietf.org/license-info) in effect on the date of 70 publication of this document. Please review these documents 71 carefully, as they describe your rights and restrictions with respect 72 to this document. Code Components extracted from this document must 73 include Simplified BSD License text as described in Section 4.e of 74 the Trust Legal Provisions and are provided without warranty as 75 described in the Simplified BSD License. 77 Table of Contents 79 1. Authors . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 80 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 6 81 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 8 82 3. Reference Frame . . . . . . . . . . . . . . . . . . . . . . . 8 83 3.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 8 84 3.2. Topology . . . . . . . . . . . . . . . . . . . . . . . . 13 85 4. RIFT: Routing in Fat Trees . . . . . . . . . . . . . . . . . 15 86 4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 16 87 4.1.1. Properties . . . . . . . . . . . . . . . . . . . . . 16 88 4.1.2. Generalized Topology View . . . . . . . . . . . . . . 17 89 4.1.2.1. Terminology . . . . . . . . . . . . . . . . . . . 17 90 4.1.2.2. Clos as Crossed Crossbars . . . . . . . . . . . . 18 91 4.1.3. Fallen Leaf Problem . . . . . . . . . . . . . . . . . 28 92 4.1.4. Discovering Fallen Leaves . . . . . . . . . . . . . . 30 93 4.1.5. Addressing the Fallen Leaves Problem . . . . . . . . 31 94 4.2. Specification . . . . . . . . . . . . . . . . . . . . . . 32 95 4.2.1. Transport . . . . . . . . . . . . . . . . . . . . . . 33 96 4.2.2. Link (Neighbor) Discovery (LIE Exchange) . . . . . . 33 97 4.2.2.1. LIE FSM . . . . . . . . . . . . . . . . . . . . . 36 98 4.2.3. Topology Exchange (TIE Exchange) . . . . . . . . . . 46 99 4.2.3.1. Topology Information Elements . . . . . . . . . . 46 100 4.2.3.2. South- and Northbound Representation . . . . . . 46 101 4.2.3.3. Flooding . . . . . . . . . . . . . . . . . . . . 49 102 4.2.3.4. TIE Flooding Scopes . . . . . . . . . . . . . . . 56 103 4.2.3.5. 'Flood Only Node TIEs' Bit . . . . . . . . . . . 59 104 4.2.3.6. Initial and Periodic Database Synchronization . . 60 105 4.2.3.7. Purging and Roll-Overs . . . . . . . . . . . . . 60 106 4.2.3.8. Southbound Default Route Origination . . . . . . 61 107 4.2.3.9. Northbound TIE Flooding Reduction . . . . . . . . 61 108 4.2.3.10. Special Considerations . . . . . . . . . . . . . 66 109 4.2.4. Reachability Computation . . . . . . . . . . . . . . 67 110 4.2.4.1. Northbound SPF . . . . . . . . . . . . . . . . . 67 111 4.2.4.2. Southbound SPF . . . . . . . . . . . . . . . . . 68 112 4.2.4.3. East-West Forwarding Within a non-ToF Level . . . 68 113 4.2.4.4. East-West Links Within ToF Level . . . . . . . . 68 114 4.2.5. Automatic Disaggregation on Link & Node Failures . . 69 115 4.2.5.1. Positive, Non-transitive Disaggregation . . . . . 69 116 4.2.5.2. Negative, Transitive Disaggregation for Fallen 117 Leaves . . . . . . . . . . . . . . . . . . . . . 72 118 4.2.6. Attaching Prefixes . . . . . . . . . . . . . . . . . 74 119 4.2.7. Optional Zero Touch Provisioning (ZTP) . . . . . . . 83 120 4.2.7.1. Terminology . . . . . . . . . . . . . . . . . . . 84 121 4.2.7.2. Automatic SystemID Selection . . . . . . . . . . 85 122 4.2.7.3. Generic Fabric Example . . . . . . . . . . . . . 86 123 4.2.7.4. Level Determination Procedure . . . . . . . . . . 87 124 4.2.7.5. ZTP FSM . . . . . . . . . . . . . . . . . . . . . 88 125 4.2.7.6. Resulting Topologies . . . . . . . . . . . . . . 94 126 4.2.8. Stability Considerations . . . . . . . . . . . . . . 96 127 4.3. Further Mechanisms . . . . . . . . . . . . . . . . . . . 97 128 4.3.1. Overload Bit . . . . . . . . . . . . . . . . . . . . 97 129 4.3.2. Optimized Route Computation on Leaves . . . . . . . . 97 130 4.3.3. Mobility . . . . . . . . . . . . . . . . . . . . . . 97 131 4.3.3.1. Clock Comparison . . . . . . . . . . . . . . . . 99 132 4.3.3.2. Interaction between Time Stamps and Sequence 133 Counters . . . . . . . . . . . . . . . . . . . . 99 134 4.3.3.3. Anycast vs. Unicast . . . . . . . . . . . . . . . 100 135 4.3.3.4. Overlays and Signaling . . . . . . . . . . . . . 100 136 4.3.4. Key/Value Store . . . . . . . . . . . . . . . . . . . 100 137 4.3.4.1. Southbound . . . . . . . . . . . . . . . . . . . 100 138 4.3.4.2. Northbound . . . . . . . . . . . . . . . . . . . 101 139 4.3.5. Interactions with BFD . . . . . . . . . . . . . . . . 101 140 4.3.6. Fabric Bandwidth Balancing . . . . . . . . . . . . . 102 141 4.3.6.1. Northbound Direction . . . . . . . . . . . . . . 102 142 4.3.6.2. Southbound Direction . . . . . . . . . . . . . . 104 143 4.3.7. Label Binding . . . . . . . . . . . . . . . . . . . . 105 144 4.3.8. Leaf to Leaf Procedures . . . . . . . . . . . . . . . 105 145 4.3.9. Address Family and Multi Topology Considerations . . 105 146 4.3.10. Reachability of Internal Nodes in the Fabric . . . . 106 147 4.3.11. One-Hop Healing of Levels with East-West Links . . . 106 148 4.4. Security . . . . . . . . . . . . . . . . . . . . . . . . 106 149 4.4.1. Security Model . . . . . . . . . . . . . . . . . . . 106 150 4.4.2. Security Mechanisms . . . . . . . . . . . . . . . . . 108 151 4.4.3. Security Envelope . . . . . . . . . . . . . . . . . . 109 152 4.4.4. Weak Nonces . . . . . . . . . . . . . . . . . . . . . 112 153 4.4.5. Lifetime . . . . . . . . . . . . . . . . . . . . . . 113 154 4.4.6. Key Management . . . . . . . . . . . . . . . . . . . 113 155 4.4.7. Security Association Changes . . . . . . . . . . . . 113 156 5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 114 157 5.1. Normal Operation . . . . . . . . . . . . . . . . . . . . 114 158 5.2. Leaf Link Failure . . . . . . . . . . . . . . . . . . . . 115 159 5.3. Partitioned Fabric . . . . . . . . . . . . . . . . . . . 116 160 5.4. Northbound Partitioned Router and Optional East-West 161 Links . . . . . . . . . . . . . . . . . . . . . . . . . . 118 162 6. Implementation and Operation: Further Details . . . . . . . . 118 163 6.1. Considerations for Leaf-Only Implementation . . . . . . . 118 164 6.2. Considerations for Spine Implementation . . . . . . . . . 119 165 6.3. Adaptations to Other Proposed Data Center Topologies . . 119 166 6.4. Originating Non-Default Route Southbound . . . . . . . . 120 167 7. Security Considerations . . . . . . . . . . . . . . . . . . . 120 168 7.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 120 169 7.2. ZTP . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 170 7.3. Lifetime . . . . . . . . . . . . . . . . . . . . . . . . 121 171 7.4. Packet Number . . . . . . . . . . . . . . . . . . . . . . 121 172 7.5. Outer Fingerprint Attacks . . . . . . . . . . . . . . . . 121 173 7.6. TIE Origin Fingerprint DoS Attacks . . . . . . . . . . . 121 174 7.7. Host Implementations . . . . . . . . . . . . . . . . . . 122 175 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 122 176 8.1. Requested Multicast and Port Numbers . . . . . . . . . . 122 177 8.2. Requested Registries with Suggested Values . . . . . . . 122 178 8.2.1. Registry RIFT/common/AddressFamilyType . . . . . . . 123 179 8.2.1.1. Requested Entries . . . . . . . . . . . . . . . . 123 180 8.2.2. Registry RIFT/common/HierarchyIndications . . . . . . 123 181 8.2.2.1. Requested Entries . . . . . . . . . . . . . . . . 123 182 8.2.3. Registry RIFT/common/IEEE802_1ASTimeStampType . . . . 123 183 8.2.3.1. Requested Entries . . . . . . . . . . . . . . . . 123 184 8.2.4. Registry RIFT/common/IPAddressType . . . . . . . . . 124 185 8.2.4.1. Requested Entries . . . . . . . . . . . . . . . . 124 186 8.2.5. Registry RIFT/common/IPPrefixType . . . . . . . . . . 124 187 8.2.5.1. Requested Entries . . . . . . . . . . . . . . . . 124 188 8.2.6. Registry RIFT/common/IPv4PrefixType . . . . . . . . . 124 189 8.2.6.1. Requested Entries . . . . . . . . . . . . . . . . 124 190 8.2.7. Registry RIFT/common/IPv6PrefixType . . . . . . . . . 124 191 8.2.7.1. Requested Entries . . . . . . . . . . . . . . . . 124 192 8.2.8. Registry RIFT/common/PrefixSequenceType . . . . . . . 125 193 8.2.8.1. Requested Entries . . . . . . . . . . . . . . . . 125 194 8.2.9. Registry RIFT/common/RouteType . . . . . . . . . . . 125 195 8.2.9.1. Requested Entries . . . . . . . . . . . . . . . . 125 196 8.2.10. Registry RIFT/common/TIETypeType . . . . . . . . . . 125 197 8.2.10.1. Requested Entries . . . . . . . . . . . . . . . 126 198 8.2.11. Registry RIFT/common/TieDirectionType . . . . . . . . 126 199 8.2.11.1. Requested Entries . . . . . . . . . . . . . . . 126 200 8.2.12. Registry RIFT/encoding/Community . . . . . . . . . . 126 201 8.2.12.1. Requested Entries . . . . . . . . . . . . . . . 126 202 8.2.13. Registry RIFT/encoding/KeyValueTIEElement . . . . . . 126 203 8.2.13.1. Requested Entries . . . . . . . . . . . . . . . 127 204 8.2.14. Registry RIFT/encoding/LIEPacket . . . . . . . . . . 127 205 8.2.14.1. Requested Entries . . . . . . . . . . . . . . . 127 206 8.2.15. Registry RIFT/encoding/LinkCapabilities . . . . . . . 128 207 8.2.15.1. Requested Entries . . . . . . . . . . . . . . . 128 208 8.2.16. Registry RIFT/encoding/LinkIDPair . . . . . . . . . . 128 209 8.2.16.1. Requested Entries . . . . . . . . . . . . . . . 128 210 8.2.17. Registry RIFT/encoding/Neighbor . . . . . . . . . . . 129 211 8.2.17.1. Requested Entries . . . . . . . . . . . . . . . 129 212 8.2.18. Registry RIFT/encoding/NodeCapabilities . . . . . . . 129 213 8.2.18.1. Requested Entries . . . . . . . . . . . . . . . 129 214 8.2.19. Registry RIFT/encoding/NodeFlags . . . . . . . . . . 130 215 8.2.19.1. Requested Entries . . . . . . . . . . . . . . . 130 216 8.2.20. Registry RIFT/encoding/NodeNeighborsTIEElement . . . 130 217 8.2.20.1. Requested Entries . . . . . . . . . . . . . . . 130 218 8.2.21. Registry RIFT/encoding/NodeTIEElement . . . . . . . . 130 219 8.2.21.1. Requested Entries . . . . . . . . . . . . . . . 131 220 8.2.22. Registry RIFT/encoding/PacketContent . . . . . . . . 131 221 8.2.22.1. Requested Entries . . . . . . . . . . . . . . . 131 222 8.2.23. Registry RIFT/encoding/PacketHeader . . . . . . . . . 131 223 8.2.23.1. Requested Entries . . . . . . . . . . . . . . . 131 224 8.2.24. Registry RIFT/encoding/PrefixAttributes . . . . . . . 132 225 8.2.24.1. Requested Entries . . . . . . . . . . . . . . . 132 226 8.2.25. Registry RIFT/encoding/PrefixTIEElement . . . . . . . 132 227 8.2.25.1. Requested Entries . . . . . . . . . . . . . . . 133 228 8.2.26. Registry RIFT/encoding/ProtocolPacket . . . . . . . . 133 229 8.2.26.1. Requested Entries . . . . . . . . . . . . . . . 133 230 8.2.27. Registry RIFT/encoding/TIDEPacket . . . . . . . . . . 133 231 8.2.27.1. Requested Entries . . . . . . . . . . . . . . . 133 232 8.2.28. Registry RIFT/encoding/TIEElement . . . . . . . . . . 133 233 8.2.28.1. Requested Entries . . . . . . . . . . . . . . . 134 234 8.2.29. Registry RIFT/encoding/TIEHeader . . . . . . . . . . 134 235 8.2.29.1. Requested Entries . . . . . . . . . . . . . . . 135 236 8.2.30. Registry RIFT/encoding/TIEHeaderWithLifeTime . . . . 135 237 8.2.30.1. Requested Entries . . . . . . . . . . . . . . . 135 238 8.2.31. Registry RIFT/encoding/TIEID . . . . . . . . . . . . 135 239 8.2.31.1. Requested Entries . . . . . . . . . . . . . . . 136 240 8.2.32. Registry RIFT/encoding/TIEPacket . . . . . . . . . . 136 241 8.2.32.1. Requested Entries . . . . . . . . . . . . . . . 136 242 8.2.33. Registry RIFT/encoding/TIREPacket . . . . . . . . . . 136 243 8.2.33.1. Requested Entries . . . . . . . . . . . . . . . 136 244 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 136 245 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 137 246 10.1. Normative References . . . . . . . . . . . . . . . . . . 137 247 10.2. Informative References . . . . . . . . . . . . . . . . . 139 248 Appendix A. Sequence Number Binary Arithmetic . . . . . . . . . 141 249 Appendix B. Information Elements Schema . . . . . . . . . . . . 142 250 B.1. common.thrift . . . . . . . . . . . . . . . . . . . . . . 143 251 B.2. encoding.thrift . . . . . . . . . . . . . . . . . . . . . 149 252 Appendix C. Constants . . . . . . . . . . . . . . . . . . . . . 158 253 C.1. Configurable Protocol Constants . . . . . . . . . . . . . 158 254 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 160 256 1. Authors 258 This work is a product of a list of individuals which are all to be 259 considered major contributors independent of the fact whether their 260 name made it to the limited boilerplate author's list or not. 262 Tony Przygienda, Ed. | Alankar Sharma | Pascal Thubert 263 Juniper Networks | Comcast | Cisco 265 Bruno Rijsman | Ilya Vershkov | Dmitry Afanasiev 266 Individual | Mellanox | Yandex 268 Don Fedyk | Alia Atlas | John Drake 269 Individual | Individual | Juniper 271 Table 1: RIFT Authors 273 2. Introduction 275 Clos [CLOS] and Fat-Tree [FATTREE] topologies have gained prominence 276 in today's networking, primarily as result of the paradigm shift 277 towards a centralized data-center based architecture that is poised 278 to deliver a majority of computation and storage services in the 279 future. Today's current routing protocols were geared towards a 280 network with an irregular topology and low degree of connectivity 281 originally but given they were the only available options, 282 consequently several attempts to apply those protocols to Clos have 283 been made. Most successfully BGP [RFC4271] [RFC7938] has been 284 extended to this purpose, not as much due to its inherent suitability 285 but rather because the perceived capability to easily modify BGP and 286 the immanent difficulties with link-state [DIJKSTRA] based protocols 287 to optimize topology exchange and converge quickly in large scale 288 densely meshed topologies. The incumbent protocols precondition 289 normally extensive configuration or provisioning during bring up and 290 re-dimensioning. This tends to be viable only for a set of 291 organizations with according networking operation skills and budgets. 292 For many IP fabric builders a desirable protocol would be one that 293 auto-configures itself and deals with failures and mis-configurations 294 with a minimum of human intervention only. Such a solution would 295 allow local IP fabric bandwidth to be consumed in a 'standard 296 component' fashion, i.e. provision it much faster and operate it at 297 much lower costs than today, much like compute or storage is consumed 298 already. 300 In looking at the problem through the lens of data center 301 requirements, RIFT addresses challenges in IP fabric routing not 302 through an incremental modification of either a link-state 303 (distributed computation) or distance-vector (diffused computation) 304 but rather a mixture of both, colloquially best described as "link- 305 state towards the spine" and "distance vector towards the leaves". 306 In other words, "bottom" levels are flooding their link-state 307 information in the "northern" direction while each node generates 308 under normal conditions a "default route" and floods it in the 309 "southern" direction. This type of protocol allows naturally for 310 highly desirable aggregation. Alas, such aggregation could blackhole 311 traffic in cases of misconfiguration or while failures are being 312 resolved or even cause partial network partitioning and this has to 313 be addressed by some adequate mechanism. The approach RIFT takes is 314 described in Section 4.2.5 and is basically based on automatic, 315 sufficient disaggregation of prefixes in case of link and node 316 failures. 318 For the visually oriented reader, Figure 1 presents a first level 319 simplified view of the resulting information and routes on a RIFT 320 fabric. The top of the fabric is holding in its link-state database 321 the nodes below it and the routes to them. In the second row of the 322 database table we indicate that partial information of other nodes in 323 the same level is available as well. The details of how this is 324 achieved will be postponed for the moment. When we look at the 325 "bottom" of the fabric, the leaves, we see that the topology is 326 basically empty and they only hold a load balanced default route to 327 the next level under normal conditions. 329 The balance of this document details a dedicated IP fabric routing 330 protocol, fills in the specification details and ultimately includes 331 resulting security considerations. 333 . [A,B,C,D] 334 . [E] 335 . +-----+ +-----+ 336 . | E | | F | A/32 @ [C,D] 337 . +-+-+-+ +-+-+-+ B/32 @ [C,D] 338 . | | | | C/32 @ C 339 . | | +-----+ | D/32 @ D 340 . | | | | 341 . | +------+ | 342 . | | | | 343 . [A,B] +-+---+ | | +---+-+ [A,B] 344 . [D] | C +--+ +-+ D | [C] 345 . +-+-+-+ +-+-+-+ 346 . 0/0 @ [E,F] | | | | 0/0 @ [E,F] 347 . A/32 @ A | | +-----+ | A/32 @ A 348 . B/32 @ B | | | | B/32 @ B 349 . | +------+ | 350 . | | | | 351 . +-+---+ | | +---+-+ 352 . | A +--+ +-+ B | 353 . 0/0 @ [C,D] +-----+ +-----+ 0/0 @ [C,D] 355 Figure 1: RIFT information distribution 357 2.1. Requirements Language 359 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 360 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 361 document are to be interpreted as described in RFC 8174 [RFC8174]. 363 3. Reference Frame 365 3.1. Terminology 367 This section presents the terminology used in this document. It is 368 assumed that the reader is thoroughly familiar with the terms and 369 concepts used in OSPF [RFC2328] and IS-IS [ISO10589-Second-Edition], 370 [ISO10589] as well as the according graph theoretical concepts of 371 shortest path first (SPF) [DIJKSTRA] computation and DAGs. 373 Crossbar: Physical arrangement of ports in a switching matrix 374 without implying any further scheduling or buffering disciplines. 376 Clos/Fat Tree: This document uses the terms Clos and Fat Tree 377 interchangeably whereas it always refers to a folded spine-and- 378 leaf topology with possibly multiple Points of Delivery (PoDs) and 379 one or multiple Top of Fabric (ToF) planes. Several modifications 380 such as leaf-2-leaf shortcuts and multiple level shortcuts are 381 possible and described further in the document. 383 Directed Acyclic Graph (DAG): A finite directed graph with no 384 directed cycles (loops). If links in Clos are considered as 385 either being all directed towards the top or vice versa, each of 386 such two graphs is a DAG. 388 Folded Spine-and-Leaf: In case Clos fabric input and output stages 389 are analogous, the fabric can be "folded" to build a "superspine" 390 or top which we will call Top of Fabric (ToF) in this document. 392 Level: Clos and Fat Tree networks are topologically partially 393 ordered graphs and 'level' denotes the set of nodes at the same 394 height in such a network, where the bottom level (leaf) is the 395 level with lowest value. A node has links to nodes one level down 396 and/or one level up. Under some circumstances, a node may have 397 links to nodes at the same level. As footnote: Clos terminology 398 uses often the concept of "stage" but due to the folded nature of 399 the Fat Tree we do not use it to prevent misunderstandings. 401 Superspine vs. Aggregation and Spine vs. Edge/Leaf: 402 Traditional level names in 5-stages folded Clos for Level 2, 1 and 403 0 respectively. We normalize this language to talk about top-of- 404 fabric (ToF), top-of-pod (ToP) and leaves. 406 Zero Touch Provisioning (ZTP): Optional RIFT mechanism which allows 407 to derive node levels automatically based on minimum configuration 408 (only ToF property has to be provisioned on according nodes). 410 Point of Delivery (PoD): A self-contained vertical slice or subset 411 of a Clos or Fat Tree network containing normally only level 0 and 412 level 1 nodes. A node in a PoD communicates with nodes in other 413 PoDs via the Top-of-Fabric. We number PoDs to distinguish them 414 and use PoD #0 to denote "undefined" PoD. 416 Top of PoD (ToP): The set of nodes that provide intra-PoD 417 communication and have northbound adjacencies outside of the PoD, 418 i.e. are at the "top" of the PoD. 420 Top of Fabric (ToF): The set of nodes that provide inter-PoD 421 communication and have no northbound adjacencies, i.e. are at the 422 "very top" of the fabric. ToF nodes do not belong to any PoD and 423 are assigned "undefined" PoD value to indicate the equivalent of 424 "any" PoD. 426 Spine: Any nodes north of leaves and south of top-of-fabric nodes. 427 Multiple layers of spines in a PoD are possible. 429 Leaf: A node without southbound adjacencies. Its level is 0 (except 430 cases where it is deriving its level via ZTP and is running 431 without LEAF_ONLY which will be explained in Section 4.2.7). 433 Top-of-fabric Plane or Partition: In large fabrics top-of-fabric 434 switches may not have enough ports to aggregate all switches south 435 of them and with that, the ToF is 'split' into multiple 436 independent planes. Introduction and Section 4.1.2 explains the 437 concept in more detail. A plane is subset of ToF nodes that see 438 each other through south reflection or E-W links. 440 Radix: A radix of a switch is basically number of switching ports it 441 provides. It's sometimes called fanout as well. 443 North Radix: Ports cabled northbound to higher level nodes. 445 South Radix: Ports cabled southbound to lower level nodes. 447 South/Southbound and North/Northbound (Direction): 448 When describing protocol elements and procedures, we will be using 449 in different situations the directionality of the compass. I.e., 450 'south' or 'southbound' mean moving towards the bottom of the Clos 451 or Fat Tree network and 'north' and 'northbound' mean moving 452 towards the top of the Clos or Fat Tree network. 454 Northbound Link: A link to a node one level up or in other words, 455 one level further north. 457 Southbound Link: A link to a node one level down or in other words, 458 one level further south. 460 East-West Link: A link between two nodes at the same level. East- 461 West links are normally not part of Clos or "fat-tree" topologies. 463 Leaf shortcuts (L2L): East-West links at leaf level will need to be 464 differentiated from East-West links at other levels. 466 Routing on the host (RotH): Modern data center architecture variant 467 where servers/leaves are multi-homed and consecutively participate 468 in routing. 470 Northbound representation: Subset of topology information flooded 471 towards higher levels of the fabric. 473 Southbound representation: Subset of topology information sent 474 towards a lower level. 476 South Reflection: Often abbreviated just as "reflection" it defines 477 a mechanism where South Node TIEs are "reflected" from the level 478 south back up north to allow nodes in the same level without E-W 479 links to "see" each other's node TIEs. 481 TIE: This is an acronym for a "Topology Information Element". TIEs 482 are exchanged between RIFT nodes to describe parts of a network 483 such as links and address prefixes, in a fashion similar to ISIS 484 LSPs or OSPF LSAs. A TIE has always a direction and a type. We 485 will talk about North TIEs (sometimes abbreviated as N-TIEs) when 486 talking about TIEs in the northbound representation and South-TIEs 487 (sometimes abbreviated as S-TIEs) for the southbound equivalent. 488 TIEs have different types such as node and prefix TIEs. 490 Node TIE: This stands as acronym for a "Node Topology Information 491 Element" that contains all adjacencies the node discovered and 492 information about node itself. Node TIE should NOT be confused 493 with a N-TIE since "node" defines the type of TIE rather than its 494 direction. 496 Prefix TIE: This is an acronym for a "Prefix Topology Information 497 Element" and it contains all prefixes directly attached to this 498 node in case of a North TIE and in case of South TIE the necessary 499 default routes the node advertises southbound. 501 Key Value TIE: A South TIE that is carrying a set of key value pairs 502 [DYNAMO]. It can be used to distribute information in the 503 southbound direction within the protocol. 505 TIDE: Topology Information Description Element, equivalent to CSNP 506 in ISIS. 508 TIRE: Topology Information Request Element, equivalent to PSNP in 509 ISIS. It can both confirm received and request missing TIEs. 511 De-aggregation/Disaggregation: Process in which a node decides to 512 advertise more specific prefixes Southwards, either positively to 513 attract the corresponding traffic, or negatively to repel it. 514 Disaggregation is performed to prevent black-holing and suboptimal 515 routing to the more specific prefixes. 517 LIE: This is an acronym for a "Link Information Element", largely 518 equivalent to HELLOs in IGPs and exchanged over all the links 519 between systems running RIFT to form three way adjacencies. 521 Flood Repeater (FR): A node can designate one or more northbound 522 neighbor nodes to be flood repeaters. The flood repeaters are 523 responsible for flooding northbound TIEs further north. They are 524 similar to MPR in OSLR. The document sometimes calls them flood 525 leaders as well. 527 Bandwidth Adjusted Distance (BAD): Each RIFT node can calculate the 528 amount of northbound bandwidth available towards a node compared 529 to other nodes at the same level and can modify the route distance 530 accordingly to allow for the lower level to adjust their load 531 balancing towards spines. 533 Overloaded: Applies to a node advertising `overload` attribute as 534 set. The semantics closely follow the meaning of the same 535 attribute in [ISO10589-Second-Edition]. 537 Interface: A layer 3 entity over which RIFT control packets are 538 exchanged. 540 Three-Way Adjacency: RIFT tries to form a unique adjacency over an 541 interface and exchange local configuration and necessary ZTP 542 information. An adjacency is only advertised in node TIEs and 543 used for computations after it achieved three-way state, i.e. both 544 routers reflected each other in LIEs including relevant security 545 information. LIEs before three-way state is reached may carry ZTP 546 related information already. 548 Bi-directional Adjacency: Bidirectional adjacency is an adjacency 549 where nodes of both sides of the adjacency advertised it in the 550 node TIEs with the correct levels and system IDs. Bi- 551 directionality is used to check in different algorithms whether 552 the link should be included. 554 Neighbor: Once a three-way adjacency has been formed a neighborship 555 relationship contains the neighbor's properties. Multiple 556 adjacencies can be formed to a remote node via parallel interfaces 557 but such adjacencies are NOT sharing a neighbor structure. Saying 558 "neighbor" is thus equivalent to saying "a three-way adjacency". 560 Cost: The term signifies the weighted distance between two 561 neighbors. 563 Distance: Sum of costs (bound by infinite distance) between two 564 nodes. 566 Shortest-Path First (SPF): A well-known graph algorithm attributed 567 to Dijkstra that establishes a tree of shortest paths from a 568 source to destinations on the graph. We use SPF acronym due to 569 its familiarity as general term for the node reachability 570 calculations RIFT can employ to ultimately calculate routes of 571 which Dijkstra algorithm is one. 573 North SPF (N-SPF): A reachability calculation that is progressing 574 northbound, as example SPF that is using South Node TIEs only. 575 Normally it progresses a single hop only and installs default 576 routes. 578 South SPF (S-SPF): A reachability calculation that is progressing 579 southbound, as example SPF that is using North Node TIEs only. 581 Security Envelope RIFT packets are flooded within an authenticated 582 security envelope that allows to protect the integrity of 583 information a node accepts. 585 3.2. Topology 586 . +--------+ +--------+ ^ N 587 . |ToF 21| |ToF 22| | 588 .Level 2 ++-+--+-++ ++-+--+-++ <-*-> E/W 589 . | | | | | | | | | 590 . P111/2| |P121 | | | | S v 591 . ^ ^ ^ ^ | | | | 592 . | | | | | | | | 593 . +--------------+ | +-----------+ | | | +---------------+ 594 . | | | | | | | | 595 . South +-----------------------------+ | | ^ 596 . | | | | | | | All TIEs 597 . 0/0 0/0 0/0 +-----------------------------+ | 598 . v v v | | | | | 599 . | | +-+ +<-0/0----------+ | | 600 . | | | | | | | | 601 .+-+----++ optional +-+----++ ++----+-+ ++-----++ 602 .| | E/W link | | | | | | 603 .|Spin111+----------+Spin112| |Spin121| |Spin122| 604 .+-+---+-+ ++----+-+ +-+---+-+ ++---+--+ 605 . | | | South | | | | 606 . | +---0/0--->-----+ 0/0 | +----------------+ | 607 . 0/0 | | | | | | | 608 . | +---<-0/0-----+ | v | +--------------+ | | 609 . v | | | | | | | 610 .+-+---+-+ +--+--+-+ +-+---+-+ +---+-+-+ 611 .| | (L2L) | | | | Level 0 | | 612 .|Leaf111~~~~~~~~~~~~Leaf112| |Leaf121| |Leaf122| 613 .+-+-----+ +-+---+-+ +--+--+-+ +-+-----+ 614 . + + \ / + + 615 . Prefix111 Prefix112 \ / Prefix121 Prefix122 616 . multi-homed 617 . Prefix 618 .+---------- Pod 1 ---------+ +---------- Pod 2 ---------+ 620 Figure 2: A three level spine-and-leaf topology 621 .+--------+ +--------+ +--------+ +--------+ 622 .|ToF A1| |ToF B1| |ToF B2| |ToF A2| 623 .++-+-----+ ++-+-----+ ++-+-----+ ++-+-----+ 624 . | | | | | | | | 625 . | | | | | +---------------+ 626 . | | | | | | | | 627 . | | | +-------------------------+ | 628 . | | | | | | | | 629 . | +-----------------------+ | | | | 630 . | | | | | | | | 631 . | | +---------+ | +---------+ | | 632 . | | | | | | | | 633 . | +---------------------------------+ | | 634 . | | | | | | | | 635 .++-+-----+ ++-+-----+ +--+-+---+ +----+-+-+ 636 .|Spine111| |Spine112| |Spine121| |Spine122| 637 .+-+---+--+ ++----+--+ +-+---+--+ ++---+---+ 638 . | | | | | | | | 639 . | +--------+ | | +--------+ | 640 . | | | | | | | | 641 . | -------+ | | | +------+ | | 642 . | | | | | | | | 643 .+-+---+-+ +--+--+-+ +-+---+-+ +---+-+-+ 644 .|Leaf111| |Leaf112| |Leaf121| |Leaf122| 645 .+-------+ +-------+ +-------+ +-------+ 647 Figure 3: Topology with multiple planes 649 We will use topology in Figure 2 (called commonly a fat tree/network 650 in modern IP fabric considerations [VAHDAT08] as homonym to the 651 original definition of the term [FATTREE]) in all further 652 considerations. This figure depicts a generic "single plane fat- 653 tree" and the concepts explained using three levels apply by 654 induction to further levels and higher degrees of connectivity. 655 Further, this document will deal also with designs that provide only 656 sparser connectivity and "partitioned spines" as shown in Figure 3 657 and explained further in Section 4.1.2. 659 4. RIFT: Routing in Fat Trees 661 We present here a detailed outline of a protocol optimized for 662 Routing in Fat Trees (RIFT) that in most abstract terms has many 663 properties of a modified link-state protocol 664 [RFC2328][ISO10589-Second-Edition] when distributing information 665 northbound and distance vector [RFC4271] protocol when distributing 666 information southbound. While this is an unusual combination, it 667 does quite naturally exhibit the desirable properties we seek. 669 4.1. Overview 671 4.1.1. Properties 673 The most singular property of RIFT is that it floods flat link-state 674 information northbound only so that each level obtains the full 675 topology of levels south of it. Link-State information is, with some 676 exceptions, never flooded East-West or back South again. Exceptions 677 like south reflection is explained in detail in Section 4.2.5.1 and 678 east-west flooding at ToF level in multi-plane fabrics is outlined in 679 Section 4.1.2. In southbound direction, the protocol operates like a 680 "fully summarizing, unidirectional" path vector protocol or rather a 681 distance vector with implicit split horizon. Routing information, 682 normally just the default route, propagates one hop south and is 're- 683 advertised' by nodes at next lower level. However, RIFT uses 684 flooding in the southern direction as well to avoid the overhead of 685 building an update per adjacency. We omit describing the East-West 686 direction for the moment. 688 Those information flow constraints create not only an anisotropic 689 protocol (i.e. the information is not distributed "evenly" or 690 "clumped" but summarized along the N-S gradient) but also a "smooth" 691 information propagation where nodes do not receive the same 692 information from multiple directions at the same time. Normally, 693 accepting the same reachability on any link, without understanding 694 its topological significance, forces tie-breaking on some kind of 695 distance metric. And such tie-breaking leads ultimately in hop-by- 696 hop forwarding to shortest paths only. In constrast to that, RIFT, 697 under normal conditions, does not need to tie-break same reachability 698 information from multiple directions. Its computation principles 699 (south forwarding direction is always preferred) leads to valley-free 700 forwarding behavior. And since valley free routing is loop-free, it 701 can use all feasible paths which is another highly desirable property 702 if available bandwidth should be utilized to the maximum extent 703 possible. 705 To account for the "northern" and the "southern" information split 706 the link state database is partitioned accordingly into "north 707 representation" and "south representation" TIEs. In simplest terms 708 the North TIEs contain a link state topology description of lower 709 levels and and South TIEs carry simply default routes towards the 710 level above. This oversimplified view will be refined gradually in 711 following sections while introducing protocol procedures and state 712 machines at the same time. 714 4.1.2. Generalized Topology View 716 This section will shed some light on the topologies RIFT addresses, 717 including multi plane fabrics and their implications. Readers that 718 are only interested in single plane designs, i.e. all top-of-fabric 719 nodes being topologically equal and initially connected to all the 720 switches at the level below them, can skip the rest of Section 4.1.2 721 and resulting Section 4.2.5.2 as well. 723 It is quite difficult to visualize multi plane design, which are 724 effectively multi-dimensional switching matrices. To cope with that, 725 we will introduce a methodology allowing us to depict the 726 connectivity in two-dimensional pictures. Further, we will leverage 727 the fact that we are dealing basically with stacked crossbar fabrics 728 where ports align "on top of each other" in a regular fashion. 730 A word of caution to the reader; at this point it should be observed 731 that the language used to describe Clos variations, especially in 732 multi-plane designs, varies widely between sources. This description 733 follows the terminology introduced in Section 3.1. It is unavoidable 734 to have it present to be able to follow the rest of this section 735 correctly. 737 4.1.2.1. Terminology 739 This section describes the terminology and acronyms used in the rest 740 of the text. 742 P: Denotes the number of PoDs in a topology. 744 S: Denotes the number of ToF nodes in a topology. 746 K: Denotes the number of ports in radix of a switch pointing north or 747 south. Further, K_LEAF denotes number of ports pointing south, 748 i.e. towards leaves, and K_TOP for number of ports pointing north 749 towards a higher spine level. To simplify the visual aids, 750 notations and further considerations, K will be mostly set to 751 Radix/2. 753 ToF Plane: Set of ToFs that are aware of each other by means of 754 south reflection. We number planes by capital letters, e.g. 755 plane A. 757 N: Denote the number of independent ToF planes in a topology. 759 R: Denotes a redundancy factor, i.e. number of connections a spine 760 has towards a ToF plane. In single plane design K_TOP is equal to 761 R. 763 Fallen Leaf: A fallen leaf in a plane Z is a switch that lost all 764 connectivity northbound to Z. 766 4.1.2.2. Clos as Crossed Crossbars 768 The typical topology for which RIFT is defined is built of P number 769 of PoDs and connected together by S number of ToF nodes. A PoD node 770 has K number of ports (also called Radix). We consider half of them 771 (K=Radix/2) as connecting host devices from the south, and the other 772 half connecting to interleaved PoD Top-Level switches to the north. 773 Ratio K can be chosen differently without loss of generality when 774 port speeds differ or the fabric is oversubscribed but K=R/2 allows 775 for more readable representation whereby there are as many ports 776 facing north as south on any intermediate node. We represent a node 777 hence in a schematic fashion with ports "sticking out" to its north 778 and south rather than by the usual real-world front faceplate designs 779 of the day. 781 Figure 4 provides a view of a leaf node as seen from the north, i.e. 782 showing ports that connect northbound. For lack of a better symbol, 783 we have chosen to use the "o" as ASCII visualisation of a single 784 port. In this example, K_LEAF has 6 ports. Observe that the number 785 of PoDs is not related to Radix unless the ToF Nodes are constrained 786 to be the same as the PoD nodes in a particular deployment. 788 Top view 789 +---+ 790 | | 791 | o | e.g., Radix = 12, K_LEAF = 6 792 | | 793 | o | 794 | | ------------------------- 795 | o ------- Physical Port (Ethernet) ----+ 796 | | ------------------------- | 797 | o | | 798 | | | 799 | o | | 800 | | | 801 | o | | 802 | | | 803 +---+ | 805 || || || || || || || 806 +----+ +------------------------------------------------+ 807 | | | | 808 +----+ +------------------------------------------------+ 809 || || || || || || || 810 Side views 812 Figure 4: A Leaf Node, K_LEAF=6 814 The Radix of a PoD's topnode may be different than that of the leaf 815 node. Though, more often than not, a same type of node is used for 816 both, effectively forming a square (K*K). In general case, we could 817 have switches with K_TOP southern ports on nodes at the top of the 818 PoD which are not necessarily the same as K_LEAF. For instance, in 819 the representations below, we pick a 6 port K_LEAF and a 8 port 820 K_TOP. In order to form a crossbar, we need K_TOP Leaf Nodes as 821 illustrated in Figure 5. 823 +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ 824 | | | | | | | | | | | | | | | | 825 | o | | o | | o | | o | | o | | o | | o | | o | 826 | | | | | | | | | | | | | | | | 827 | o | | o | | o | | o | | o | | o | | o | | o | 828 | | | | | | | | | | | | | | | | 829 | o | | o | | o | | o | | o | | o | | o | | o | 830 | | | | | | | | | | | | | | | | 831 | o | | o | | o | | o | | o | | o | | o | | o | 832 | | | | | | | | | | | | | | | | 833 | o | | o | | o | | o | | o | | o | | o | | o | 834 | | | | | | | | | | | | | | | | 835 | o | | o | | o | | o | | o | | o | | o | | o | 836 | | | | | | | | | | | | | | | | 837 +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ 839 Figure 5: Southern View of a PoD, K_TOP=8 841 As further visualized in Figure 6 the K_TOP Leaf Nodes are fully 842 interconnected with the K_LEAF PoD-top nodes, providing connectivity 843 that can be represented as a crossbar when "looked at" from the 844 north. The result is that, in the absence of a failure, a packet 845 entering the PoD from the north on any port can be routed to any port 846 in the south of the PoD and vice versa. And that is precisely why it 847 makes sense to talk about a "switching matrix". 849 E<-*->W 851 +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ 852 | | | | | | | | | | | | | | | | 853 +--------------------------------------------------------+ 854 | o o o o o o o o | 855 +--------------------------------------------------------+ 856 +--------------------------------------------------------+ 857 | o o o o o o o o | 858 +--------------------------------------------------------+ 859 +--------------------------------------------------------+ 860 | o o o o o o o o | 861 +--------------------------------------------------------+ 862 +--------------------------------------------------------+ 863 | o o o o o o o o | 864 +--------------------------------------------------------+ 865 +--------------------------------------------------------+ 866 | o o o o o o o o |<-+ 867 +--------------------------------------------------------+ | 868 +--------------------------------------------------------+ | 869 | o o o o o o o o | | 870 +--------------------------------------------------------+ | 871 | | | | | | | | | | | | | | | | | 872 +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ | 873 ^ | 874 | | 875 | ---------- --------------------- | 876 +----- Leaf Node PoD top Node (Spine) --+ 877 ---------- --------------------- 879 Figure 6: Northern View of a PoD's Spines, K_TOP=8 881 Side views of this PoD is illustrated in Figure 7 and Figure 8. 883 Connecting to Spine 885 || || || || || || || || 886 +----------------------------------------------------------------+ N 887 | PoD top Node seen sideways | ^ 888 +----------------------------------------------------------------+ | 889 || || || || || || || || * 890 +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ | 891 | | | | | | | | | | | | | | | | v 892 +----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ S 893 || || || || || || || || 895 Connecting to Client nodes 897 Figure 7: Side View of a PoD, K_TOP=8, K_LEAF=6 899 Connecting to Spine 901 || || || || || || 902 +----+ +----+ +----+ +----+ +----+ +----+ N 903 | | | | | | | | | | | PoD top Nodes ^ 904 +----+ +----+ +----+ +----+ +----+ +----+ | 905 || || || || || || * 906 +------------------------------------------------+ | 907 | Leaf seen sideways | v 908 +------------------------------------------------+ S 909 || || || || || || 911 Connecting to Client nodes 913 Figure 8: Other side View of a PoD, K_TOP=8, K_LEAF=6, 90o turn in 914 E-W Plane 916 As next step, let us observe that a resulting PoD can be abstracted 917 as a bigger node with a number K of K_POD= K_TOP * K_LEAF, and the 918 design can recurse. 920 It will be critical at this point that, before progressing further, 921 the concept and the picture of "crossed crossbars" is clear. Else, 922 the following considerations might be difficult to comprehend. 924 To continue, the PoDs are interconnected with each other through a 925 Top-of-Fabric (ToF) node at the very top or the north edge of the 926 fabric. The resulting ToF is NOT partitioned if, and only if (IIF), 927 every PoD top level node (spine) is connected to every ToF Node. 929 This topology is also referred to as a single plane configuration and 930 is quite popular due to its simplicity. In order to reach a 1:1 931 connectivity ratio between the ToF and the leaves, it results that 932 there are K_TOP ToF nodes, because each port of a ToP node connects 933 to a different ToF node, and K_LEAF ToP nodes for the same reason. 934 Consequently, it will take (P * K_LEAF) ports on a ToF node to 935 connect to each of the K_LEAF ToP nodes of the P PoDs, as shown in 936 Figure 9. 938 [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] <-----+ 939 | | | | | | | | | 940 [=================================] | ----------- 941 | | | | | | | | +----- Top-of-Fabric 942 [ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] +----- Node -------+ 943 | ----------- | 944 | v 945 +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ <-----+ +-+ 946 | | | | | | | | | | | | | | | | | | 947 [ |o| |o| |o| |o| |o| |o| |o| |o| ] | | 948 [ |o| |o| |o| |o| |o| |o| |o| |o| ] ------------------------- | | 949 [ |o| |o| |o| |o| |o| |o| |o| |o<--- Physical Port (Ethernet) | | 950 [ |o| |o| |o| |o| |o| |o| |o| |o| ] ------------------------- | | 951 [ |o| |o| |o| |o| |o| |o| |o| |o| ] | | 952 [ |o| |o| |o| |o| |o| |o| |o| |o| ] | | 953 | | | | | | | | | | | | | | | | | | 954 [ |o| |o| |o| |o| |o| |o| |o| |o| ] | | 955 [ |o| |o| |o| |o| |o| |o| |o| |o| ] -------------- | | 956 [ |o| |o| |o| |o| |o| |o| |o| |o| ] <--- PoD top level | | 957 [ |o| |o| |o| |o| |o| |o| |o| |o| ] node (Spine) ---+ | | 958 [ |o| |o| |o| |o| |o| |o| |o| |o| ] -------------- | | | 959 [ |o| |o| |o| |o| |o| |o| |o| |o| ] | | | 960 | | | | | | | | | | | | | | | | -+ +- +-+ v | | 961 [ |o| |o| |o| |o| |o| |o| |o| |o| ] | | --| |--[ ]--| | 962 [ |o| |o| |o| |o| |o| |o| |o| |o| ] | ----- | --| |--[ ]--| | 963 [ |o| |o| |o| |o| |o| |o| |o| |o| ] +--- PoD ---+ --| |--[ ]--| | 964 [ |o| |o| |o| |o| |o| |o| |o| |o| ] | ----- | --| |--[ ]--| | 965 [ |o| |o| |o| |o| |o| |o| |o| |o| ] | | --| |--[ ]--| | 966 [ |o| |o| |o| |o| |o| |o| |o| |o| ] | | --| |--[ ]--| | 967 | | | | | | | | | | | | | | | | -+ +- +-+ | | 968 +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ 970 Figure 9: Fabric Spines and TOFs in Single Plane Design, 3 PoDs 972 The top view can be collapsed into a third dimension where the hidden 973 depth index is representing the PoD number. We can then show one PoD 974 as a class of PoDs and hence save one dimension in our 975 representation. The Spine Node expands in the depth and the vertical 976 dimensions, whereas the PoD top level Nodes are constrained, in 977 horizontal dimension. A port in the 2-D representation represents 978 effectively the class of all the ports at the same position in all 979 the PoDs that are projected in its position along the depth axis. 980 This is shown in Figure 10. 982 / / / / / / / / / / / / / / / / 983 / / / / / / / / / / / / / / / / 984 / / / / / / / / / / / / / / / / 985 / / / / / / / / / / / / / / / / ] 986 +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ ]] 987 | | | | | | | | | | | | | | | | ] --------------------------- 988 [ |o| |o| |o| |o| |o| |o| |o| |o| ] <-- PoD top level node (Spine) 989 [ |o| |o| |o| |o| |o| |o| |o| |o| ] --------------------------- 990 [ |o| |o| |o| |o| |o| |o| |o| |o| ]]]] 991 [ |o| |o| |o| |o| |o| |o| |o| |o| ]]] ^^ 992 [ |o| |o| |o| |o| |o| |o| |o| |o| ]] // PoDs 993 [ |o| |o| |o| |o| |o| |o| |o| |o| ] // (in depth) 994 | |/| |/| |/| |/| |/| |/| |/| |/ // 995 +-+ +-+ +-+/+-+/+-+ +-+ +-+ +-+ // 996 ^ 997 | ---------------- 998 +----- Top-of-Fabric Node 999 ---------------- 1001 Figure 10: Collapsed Northern View of a Fabric for Any Number of PoDs 1003 As simple as single plane deployment is it introduces a limit due to 1004 the bound on the available radix of the ToF nodes that has to be at 1005 least P * K_LEAF. Nevertheless, we will see that a distinct 1006 advantage of a connected or non-partitioned Top-of-Fabric is that all 1007 failures can be resolved by simple, non-transitive, positive 1008 disaggregation (i.e. nodes advertising more specific prefixes with 1009 the default to the level below them that is however not propagated 1010 further down the fabric) as described in Section 4.2.5.1 . In other 1011 words; non-partitioned ToF nodes can always reach nodes below or 1012 withdraw the routes from PoDs they cannot reach unambiguously. And 1013 with this, positive disaggregation can heal all failures and still 1014 allow all the ToF nodes to see each other via south reflection. 1015 Disaggregation will be explained in further detail in Section 4.2.5. 1017 In order to scale beyond the "single plane limit", the Top-of-Fabric 1018 can be partitioned by a N number of identically wired planes where N 1019 is an integer divider of K_LEAF. The 1:1 ratio and the desired 1020 symmetry are still served, this time with (K_TOP * N) ToF nodes, each 1021 of (P * K_LEAF / N) ports. N=1 represents a non-partitioned Spine 1022 and N=K_LEAF is a maximally partitioned Spine. Further, if R is any 1023 integer divisor of K_LEAF, then N=K_LEAF/R is a feasible number of 1024 planes and R a redundancy factor. If proves convenient for 1025 deployments to use a radix for the leaf nodes that is a power of 2 so 1026 they can pick a number of planes that is a lower power of 2. The 1027 example in Figure 11 splits the Spine in 2 planes with a redundancy 1028 factor R=3, meaning that there are 3 non-intersecting paths between 1029 any leaf node and any ToF node. A ToF node must have, in this case, 1030 at least 3*P ports, and be directly connected to 3 of the 6 PoD-ToP 1031 nodes (spines) in each PoD. 1033 +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ 1034 +-| |--| |--| |--| |--| |--| |--| |--| |-+ 1035 | | o | | o | | o | | o | | o | | o | | o | | o | | 1036 +-| |--| |--| |--| |--| |--| |--| |--| |-+ 1037 +-| |--| |--| |--| |--| |--| |--| |--| |-+ 1038 | | o | | o | | o | | o | | o | | o | | o | | o | | 1039 +-| |--| |--| |--| |--| |--| |--| |--| |-+ 1040 +-| |--| |--| |--| |--| |--| |--| |--| |-+ 1041 | | o | | o | | o | | o | | o | | o | | o | | o | | 1042 +-| |--| |--| |--| |--| |--| |--| |--| |-+ 1043 +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ 1045 Plane 1 1046 ----------- . ------------ . ------------ . ------------ . -------- 1047 Plane 2 1049 +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ 1050 +-| |--| |--| |--| |--| |--| |--| |--| |-+ 1051 | | o | | o | | o | | o | | o | | o | | o | | o | | 1052 +-| |--| |--| |--| |--| |--| |--| |--| |-+ 1053 +-| |--| |--| |--| |--| |--| |--| |--| |-+ 1054 | | o | | o | | o | | o | | o | | o | | o | | o | | 1055 +-| |--| |--| |--| |--| |--| |--| |--| |-+ 1056 +-| |--| |--| |--| |--| |--| |--| |--| |-+ 1057 | | o | | o | | o | | o | | o | | o | | o | | o | | 1058 +-| |--| |--| |--| |--| |--| |--| |--| |-+ 1059 +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ 1060 ^ 1061 | 1062 | ---------------- 1063 +----- Top-of-Fabric node 1064 "across" depth 1065 ---------------- 1067 Figure 11: Northern View of a Multi-Plane ToF Level, K_LEAF=6, N=2 1069 At the extreme end of the spectrum it is even possible to fully 1070 partition the spine with N = K_LEAF and R=1, while maintaining 1071 connectivity between each leaf node and each Top-of-Fabric node. In 1072 that case the ToF node connects to a single Port per PoD, so it 1073 appears as a single port in the projected view represented in 1074 Figure 12. The number of ports required on the Spine Node is more or 1075 equal to P, the number of PoDs. 1077 Plane 1 1078 +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ -+ 1079 +-| |--| |--| |--| |--| |--| |--| |--| |-+ | 1080 | | o | | o | | o | | o | | o | | o | | o | | o | | | 1081 +-| |--| |--| |--| |--| |--| |--| |--| |-+ | 1082 +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ | 1083 ----------- . ------------------- . ------------ . -------- | 1084 +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ | 1085 +-| |--| |--| |--| |--| |--| |--| |--| |-+ | 1086 | | o | | o | | o | | o | | o | | o | | o | | o | | | 1087 +-| |--| |--| |--| |--| |--| |--| |--| |-+ | 1088 +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ | 1089 ----------- . ------------ . ---- . ------------ . -------- | 1090 +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ | 1091 +-| |--| |--| |--| |--| |--| |--| |--| |-+ | 1092 | | o | | o | | o | | o | | o | | o | | o | | o | | | 1093 +-| |--| |--| |--| |--| |--| |--| |--| |-+ | 1094 +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ | 1095 ----------- . ------------ . ------------------- . -------- +<-+ 1096 +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ | | 1097 +-| |--| |--| |--| |--| |--| |--| |--| |-+ | | 1098 | | o | | o | | o | | o | | o | | o | | o | | o | | | | 1099 +-| |--| |--| |--| |--| |--| |--| |--| |-+ | | 1100 +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ | | 1101 ----------- . ------------ . ------------ . ---- . -------- | | 1102 +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ | | 1103 +-| |--| |--| |--| |--| |--| |--| |--| |-+ | | 1104 | | o | | o | | o | | o | | o | | o | | o | | o | | | | 1105 +-| |--| |--| |--| |--| |--| |--| |--| |-+ | | 1106 +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ | | 1107 ----------- . ------------ . ------------ . --------------- | | 1108 +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ | | 1109 +-| |--| |--| |--| |--| |--| |--| |--| |-+ | | 1110 | | o | | o | | o | | o | | o | | o | | o | | o | | | | 1111 +-| |--| |--| |--| |--| |--| |--| |--| |-+ | | 1112 +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ -+ | 1113 Plane 6 ^ | 1114 | | 1115 | ---------------- ------------- | 1116 +----- ToF Node Class of PoDs ---+ 1117 ---------------- ------------- 1119 Figure 12: Northern View of a Maximally Partitioned ToF Level, R=1 1121 4.1.3. Fallen Leaf Problem 1123 As mentioned earlier, RIFT exhibits an anisotropic behaviour tailored 1124 for fabrics with a North / South orientation and a high level of 1125 interleaving paths. A non-partitioned fabric makes a total loss of 1126 connectivity between a Top-of-Fabric node at the north and a leaf 1127 node at the south a very rare but yet possible occasion that is fully 1128 healed by positive disaggregation as described in Section 4.2.5.1. 1129 In large fabrics or fabrics built from switches with low radix, the 1130 ToF ends often being partitioned in planes which makes the occurrence 1131 of having a given leaf being only reachable from a subset of the ToF 1132 nodes more likely to happen. This makes some further considerations 1133 necessary. 1135 We define a "Fallen Leaf" as a leaf that can be reached by only a 1136 subset, but not all, of Top-of-Fabric nodes due to missing 1137 connectivity. If R is the redundancy factor, then it takes at least 1138 R breakages to reach a "Fallen Leaf" situation. 1140 In a maximally partitioned fabric, the redundancy factor is R= 1, so 1141 any breakage in the fabric may cause one or more fallen leaves. 1142 However, not all cases require disaggregation. The following cases 1143 do not require particular action in such scenario: 1145 If a southern link on a leaf node goes down, then connectivity to 1146 any node attached to the leaf is lost. There is no need to 1147 disaggregate since the connectivity is lost from all spine nodes 1148 to the leaf nodes in the same fashion. 1150 If a southern link on a leaf node goes down, then connectivity 1151 through that leaf is lost for all nodes. There is no need to 1152 disaggregate since the connectivity to this leaf is lost for all 1153 spine nodes in a same fashion. 1155 If a ToF Node goes down, then northern traffic towards it is 1156 routed via alternate ToF nodes in the same plane and there is no 1157 need to disaggregate routes. 1159 In a general manner, the mechanism of non-transitive positive 1160 disaggregation is sufficient when the disaggregating ToF nodes 1161 collectively connect to all the ToP nodes in the broken plane. This 1162 happens in the following case: 1164 If the breakage is the last northern link from a ToP node to a ToF 1165 node going down, then the fallen leaf problem affects only The ToF 1166 node, and the connectivity to all the nodes in the PoD is lost 1167 from that ToF node. This can be observed by other ToF nodes 1168 within the plane where the ToP node is located and positively 1169 disaggregated within that plane. 1171 On the other hand, there is a need to disaggregate the routes to 1172 Fallen Leaves in a transitive fashion, all the way to the other 1173 leaves in the following cases: 1175 o If the breakage is the last northern link from a leaf node within 1176 a plane (there is only one such link in a maximally partitioned 1177 fabric) that goes down, then connectivity to all unicast prefixes 1178 attached to the leaf node is lost within the plane where the link 1179 is located. Southern Reflection by a leaf node, e.g., between ToP 1180 nodes, if the PoD has only 2 levels, happens in between planes, 1181 allowing the ToP nodes to detect the problem within the PoD where 1182 it occurs and positively disaggregate. The breakage can be 1183 observed by the ToF nodes in the same plane through the North 1184 flooding of TIEs from the ToP nodes. The ToF nodes however need 1185 to be aware of all the affected prefixes for the negative, 1186 possibly transitive disaggregation to be fully effective (i.e. a 1187 node advertising in control plane that it cannot reach a certain 1188 more specific prefix than default whereas such disaggregation must 1189 in extreme condition propagate further down southbound). The 1190 problem can also be observed by the ToF nodes in the other planes 1191 through the flooding of North TIEs from the affected leaf nodes, 1192 together with non-node North TIEs which indicate the affected 1193 prefixes. To be effective in that case, the positive 1194 disaggregation must reach down to the nodes that make the plane 1195 selection, which are typically the ingress leaf nodes. The 1196 information is not useful for routing in the intermediate levels. 1198 o If the breakage is a ToP node in a maximally partitioned fabric - 1199 in which case it is the only ToP node serving the plane in that 1200 PoD - goes down, then the connectivity to all the nodes in the PoD 1201 is lost within the plane where the ToP node is located. 1202 Consequently, all leaves of the PoD fall in this plane. Since the 1203 Southern Reflection between the ToF nodes happens only within a 1204 plane, ToF nodes in other planes cannot discover fallen leaves in 1205 a different plane. They also cannot determine beyond their local 1206 plane whether a leaf node that was initially reachable has become 1207 unreachable. As the breakage can be observed by the ToF nodes in 1208 the plane where the breakage happened, the ToF nodes in the plane 1209 need to be aware of all the affected prefixes for the negative 1210 disaggregation to be fully effective. The problem can also be 1211 observed by the ToF nodes in the other planes through the flooding 1212 of North TIEs from the affected leaf nodes, if there are only 3 1213 levels and the ToP nodes are directly connected to the leaf nodes, 1214 and then again it can only be effective it is propagated 1215 transitively to the leaf, and useless above that level. 1217 For the sake of easy comprehension let us roll the abstractions back 1218 into a simple example and observe that in Figure 3 the loss of link 1219 Spine 122 to Leaf 122 will make Leaf 122 a fallen leaf for Top-of- 1220 Fabric plane B. Worse, if the cabling was never present in first 1221 place, plane B will not even be able to know that such a fallen leaf 1222 exists. Hence partitioning without further treatment results in two 1223 grave problems: 1225 o Leaf 111 trying to route to Leaf 122 MUST choose Spine 111 in 1226 plane A as its next hop since plane B will inevitably blackhole 1227 the packet when forwarding using default routes or do excessive 1228 bow tying. This information must be in its routing table. 1230 o Any kind of "flooding" or distance vector trying to deal with the 1231 problem by distributing host routes will be able to converge only 1232 using paths through leaves. The flooding of information on Leaf 1233 122 would have to go up to Top-of-Fabric A and then "loopback" 1234 over other leaves to ToF B leading in extreme cases to traffic for 1235 Leaf 122 when presented to plane B taking an "inverted fabric" 1236 path where leaves start to serve as TOFs, at least for the 1237 duration of a protocol's convergence. 1239 4.1.4. Discovering Fallen Leaves 1241 As illustrated later, and without further proof, the way to deal with 1242 fallen leaves in multi-plane designs, when aggregation is used, is 1243 that RIFT requires all the ToF nodes to share the same north topology 1244 database. This happens naturally in single plane design by the means 1245 of northbound flooding and south reflection but needs additional 1246 considerations in multi-plane fabrics. To satisfy this RIFT, in 1247 multi-plane designs, relies at the ToF level on ring interconnection 1248 of switches in multiple planes. Other solutions are possible but 1249 they either need more cabling or end up having much longer flooding 1250 paths and/or single points of failure. 1252 In detail, by reserving two ports on each Top-of-Fabric node it is 1253 possible to connect them together by interplane bi-directional rings 1254 as illustrated in Figure 13. The rings will be used to exchange full 1255 north topology information between planes. All ToFs having same 1256 north topology allows by the means of transitive, negative 1257 disaggregation described in Section 4.2.5.2 to efficiently fix any 1258 possible fallen leaf scenario. Somewhat as a side-effect, the 1259 exchange of information fulfills the ask to present full view of the 1260 fabric topology at the Top-of-Fabric level, without the need to 1261 collate it from multiple points by additional complexity of 1262 technologies like [RFC7752]. 1264 +---+ +---+ +---+ +---+ +---+ +---+ +--------+ 1265 | | | | | | | | | | | | | | 1266 | | | | | | | | 1267 +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ | 1268 +-| |--| |--| |--| |--| |--| |--| |-+ | 1269 | | o | | o | | o | | o | | o | | o | | o | | | Plane A 1270 +-| |--| |--| |--| |--| |--| |--| |-+ | 1271 +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ | 1272 | | | | | | | | 1273 +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ | 1274 +-| |--| |--| |--| |--| |--| |--| |-+ | 1275 | | o | | o | | o | | o | | o | | o | | o | | | Plane B 1276 +-| |--| |--| |--| |--| |--| |--| |-+ | 1277 +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ | 1278 | | | | | | | | 1279 ... | 1280 | | | | | | | | 1281 +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ | 1282 +-| |--| |--| |--| |--| |--| |--| |-+ | 1283 | | o | | o | | o | | o | | o | | o | | o | | | Plane X 1284 +-| |--| |--| |--| |--| |--| |--| |-+ | 1285 +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ +-o-+ | 1286 | | | | | | | | 1287 | | | | | | | | | | | | | | 1288 +---+ +---+ +---+ +---+ +---+ +---+ +--------+ 1289 Rings 1 2 3 4 5 6 7 1291 Figure 13: Connecting Top-of-Fabric Nodes Across Planes by Rings 1293 4.1.5. Addressing the Fallen Leaves Problem 1295 One consequence of the "Fallen Leaf" problem is that some prefixes 1296 attached to the fallen leaf become unreachable from some of the ToF 1297 nodes. RIFT proposes two methods to address this issue, the positive 1298 and the negative disaggregation. Both methods flood South TIEs to 1299 advertise the impacted prefix(es). 1301 When used for the operation of disaggregation, a positive South TIE, 1302 as usual, indicates reachability to a prefix of given length and all 1303 addresses subsumed by it. In contrast, a negative route 1304 advertisement indicates that the origin cannot route to the 1305 advertised prefix. 1307 The positive disaggregation is originated by a router that can still 1308 reach the advertised prefix, and the operation is not transitive. In 1309 other words, the receiver does not generate its own flooding south as 1310 a consequence of receiving positive disaggregation advertisements 1311 from a higher level node. The effect of a positive disaggregation is 1312 that the traffic to the impacted prefix will follow the longest match 1313 and will be limited to the northbound routers that advertised the 1314 more specific route. 1316 In contrast, the negative disaggregation can be transitive, and is 1317 propagated south when all the possible routes have been advertised as 1318 negative exceptions. A negative route advertisement is only 1319 actionable when the negative prefix is aggregated by a positive route 1320 advertisement for a shorter prefix. In such case, the negative 1321 advertisement "punches out a hole" in the positive route in the 1322 routing table, making the positive prefix reachable through the 1323 originator with the special consideration of the negative prefix 1324 removing certain next hop neighbors. 1326 When the ToF is not partitioned, the collective southern flooding of 1327 the positive disaggregation by the ToF nodes that can still reach the 1328 impacted prefix is in general enough to cover all the switches at the 1329 next level south, typically the ToP nodes. If all those switches are 1330 aware of the disaggregation, they collectively create a ceiling that 1331 intercepts all the traffic north and forwards it to the ToF nodes 1332 that advertised the more specific route. In that case, the positive 1333 disaggregation alone is sufficient to solve the fallen leaf problem. 1335 On the other hand, when the fabric is partitioned in planes, the 1336 positive disaggregation from ToF nodes in different planes do not 1337 reach the ToP switches in the affected plane and cannot solve the 1338 fallen leaves problem. In other words, a breakage in a plane can 1339 only be solved in that plane. Also, the selection of the plane for a 1340 packet typically occurs at the leaf level and the disaggregation must 1341 be transitive and reach all the leaves. In that case, the negative 1342 disaggregation is necessary. The details on the RIFT approach to 1343 deal with fallen leaves in an optimal way are specified in 1344 Section 4.2.5.2. 1346 4.2. Specification 1348 This section specifies the protocol in a normative fashion by either 1349 prescriptive procedures or behavior defined by Finite State Machines 1350 (FSM). 1352 Some FSM figures are provided as [DOT] description due to limitations 1353 of ASCII art. 1355 "On Entry" actions on FSM state are performed every time and right 1356 before the according state is entered, i.e. after any transitions 1357 from previous state. 1359 "On Exit" actions are performed every time and immediately when a 1360 state is exited, i.e. before any transitions towards target state are 1361 performed. 1363 Any attempt to transition from a state towards another on reception 1364 of an event where no action is specified MUST be considered an 1365 unrecoverable error. 1367 The FSMs and procedures are normative in the sense that an 1368 implementation MUST implement them either literally or an 1369 implementation MUST exhibit externally observable behavior that is 1370 identical to the execution of the specified FSMs. 1372 Where a FSM representation is inconvenient, i.e. the amount of 1373 procedures and kept state exceeds the amount of transitions, we defer 1374 to a more procedural description on data structures. 1376 4.2.1. Transport 1378 All packet formats are defined in Thrift [thrift] models in 1379 Appendix B. 1381 The serialized model is carried in an envelope within a UDP frame 1382 that provides security and allows validation/modification of several 1383 important fields without de-serialization for performance and 1384 security reasons. 1386 4.2.2. Link (Neighbor) Discovery (LIE Exchange) 1388 RIFT LIE exchange auto-discovers neighbors, negotiates ZTP parameters 1389 and discovers miscablings. It uses a three-way handshake mechanism 1390 which is a cleaned up version of [RFC5303]. Observe that for easier 1391 comprehension the terminology of one/two and three-way states does 1392 NOT align with OSPF or ISIS FSMs albeit they use roughly same 1393 mechanisms. The formation progresses under normal conditions from 1394 one-way to two-way and then three-way state at which point it is 1395 ready to exchange TIEs per Section 4.2.3. 1397 LIE exchange happens over well-known administratively locally scoped 1398 and configured or otherwise well-known IPv4 multicast address 1399 [RFC2365] and/or link-local multicast scope [RFC4291] for IPv6 1400 [RFC8200] using a configured or otherwise a well-known destination 1401 UDP port defined in Appendix C.1. LIEs SHOULD be sent with an IPv4 1402 Time to Live (TTL) / IPv6 Hop Limit (HL) of 1 to prevent RIFT 1403 information reaching beyond a single L3 next-hop in the topology. 1404 LIEs SHOULD be sent with network control precedence. 1406 Originating port of the LIE has no further significance other than 1407 identifying the origination point. LIEs are exchanged over all links 1408 running RIFT. 1410 An implementation MAY listen and send LIEs on IPv4 and/or IPv6 1411 multicast addresses. A node MUST NOT originate LIEs on an address 1412 family if it does not process received LIEs on that family. LIEs on 1413 same link are considered part of the same negotiation independent on 1414 the address family they arrive on. Observe further that the LIE 1415 source address may not identify the peer uniquely in unnumbered or 1416 link-local address cases so the response transmission MUST occur over 1417 the same interface the LIEs have been received on. A node MAY use 1418 any of the adjacency's source addresses it saw in LIEs on the 1419 specific interface during adjacency formation to send TIEs. That 1420 implies that an implementation MUST be ready to accept TIEs on all 1421 addresses it used as source of LIE frames. 1423 A three-way adjacency over any address family implies support for 1424 IPv4 forwarding if the `v4_forwarding_capable` flag is set to true 1425 and a node can use [RFC5549] type of forwarding in such a situation. 1426 It is expected that the whole fabric supports the same type of 1427 forwarding of address families on all the links. Operation of a 1428 fabric where only some of the links are supporting forwarding on an 1429 address family and others do not is outside the scope of this 1430 specification. 1432 The protocol does NOT support selective disabling of address 1433 families, disabling v4 forwarding capability or any local address 1434 changes in three-way state, i.e. if a link has entered three-way IPv4 1435 and/or IPv6 with a neighbor on an adjacency and it wants to stop 1436 supporting one of the families or change any of its local addresses 1437 or stop v4 forwarding, it has to tear down and rebuild the adjacency. 1438 It also has to remove any information it stored about the adjacency 1439 such as LIE source addresses seen. 1441 Unless ZTP as described in Section 4.2.7 is used, each node is 1442 provisioned with the level at which it is operating. It MAY be also 1443 provisioned with its PoD. If any of those values is undefined, then 1444 accordingly a default level and/or an "undefined" PoD are assumed. 1445 This means that leaves do not need to be configured at all if initial 1446 configuration values are all left at "undefined" value. Nodes above 1447 ToP MUST remain at "any" PoD value which has the same value as 1448 "undefined" PoD. This information is propagated in the LIEs 1449 exchanged. 1451 Further definitions of leaf flags are found in Section 4.2.7 given 1452 they have implications in terms of level and adjacency forming here. 1454 A node tries to form a three-way adjacency if and only if 1456 1. the node is in the same PoD or either the node or the neighbor 1457 advertises "undefined/any" PoD membership (PoD# = 0) AND 1459 2. the neighboring node is running the same MAJOR schema version AND 1461 3. the neighbor is not member of some PoD while the node has a 1462 northbound adjacency already joining another PoD AND 1464 4. the neighboring node uses a valid System ID AND 1466 5. the neighboring node uses a different System ID than the node 1467 itself 1469 6. the advertised MTUs match on both sides AND 1471 7. both nodes advertise defined level values AND 1473 8. [ 1475 i) the node is at level 0 and has no three way adjacencies 1476 already to nodes at Highest Adjacency Three-Way level (HAT as 1477 defined later in Section 4.2.7.1) with level different than 1478 the adjacent node OR 1480 ii) the node is not at level 0 and the neighboring node is at 1481 level 0 OR 1483 iii) both nodes are at level 0 AND both indicate support for 1484 Section 4.3.8 OR 1486 iv) neither node is at level 0 and the neighboring node is at 1487 most one level away 1489 ]. 1491 The rules checking PoD numbering MAY be optionally disregarded by a 1492 node if PoD detection is undesirable or has to be ignored. This will 1493 not affect the correctness of the protocol except preventing 1494 detection of certain miscabling cases. 1496 A node configured with "undefined" PoD membership MUST, after 1497 building first northbound three way adjacencies to a node being in a 1498 defined PoD, advertise that PoD as part of its LIEs. In case that 1499 adjacency is lost, from all available northbound three way 1500 adjacencies the node with the highest System ID and defined PoD is 1501 chosen. That way the northmost defined PoD value (normally the ToP 1502 nodes) can diffuse southbound towards the leaves "forcing" the PoD 1503 value on any node with "undefined" PoD. 1505 LIEs arriving with IPv4 Time to Live (TTL) / IPv6 Hop Limit (HL) 1506 larger than 1 MUST be ignored. 1508 A node SHOULD NOT send out LIEs without defined level in the header 1509 but in certain scenarios it may be beneficial for trouble-shooting 1510 purposes. 1512 4.2.2.1. LIE FSM 1514 This section specifies the precise, normative LIE FSM and can be 1515 omitted unless the reader is pursuing an implementation of the 1516 protocol. 1518 Initial state is `OneWay`. 1520 Event `MultipleNeighbors` occurs normally when more than two nodes 1521 see each other on the same link or a remote node is quickly 1522 reconfigured or rebooted without regressing to `OneWay` first. Each 1523 occurrence of the event SHOULD generate a clear, according 1524 notification to help operational deployments. 1526 The machine sends LIEs on several transitions to accelerate adjacency 1527 bring-up without waiting for the timer tic. 1529 Enter 1530 | 1531 V 1532 +-----------+ 1533 | OneWay |<----+ 1534 | | | HALChanged [StoreHAL] 1535 | Entry: | | HALSChanged [StoreHALS] 1536 | [CleanUp] | | HATChanged [StoreHAT] 1537 | | | HoldTimerExpired [-] 1538 | | | InstanceNameMismatch [-] 1539 | | | LevelChanged [UpdateLevel, PUSH SendLie] 1540 | | | LieReceived [ProcessLIE] 1541 | | | MTUMismatch [-] 1542 | | | NeighborAddressAdded [-] 1543 | | | NeighborChangedAddress [-] 1544 | | | NeighborChangedLevel [-] 1545 | | | NeighborChangedMinorFields [-] 1546 | | | NeighborDroppedReflection [-] 1547 | | | PODMismatch [-] 1548 | | | SendLIE [SendLIE] 1549 | | | TimerTick [PUSH SendLIE] 1550 | | | UnacceptableHeader 1551 | | | UpdateZTPOffer [SendOfferToZTPFSM] 1552 | |-----+ 1553 | | 1554 | |<--------------------- (ThreeWay) 1555 | |---------------------> 1556 | | ValidReflection [-] 1557 | | 1558 | |---------------------> (Multiple 1559 | | MultipleNeighbors Neighbors 1560 +-----------+ [StartMulNeighTimer] Wait) 1561 ^ | 1562 | | 1563 | | NewNeighbor [PUSH SendLIE] 1564 | V 1565 (TwoWay) 1567 LIE FSM 1569 (OneWay) 1570 | ^ 1571 | | HoldTimeExpired [-] 1572 | | InstanceNameMismatch [-] 1573 | | LevelChanged [StoreLevel] 1574 | | MTUMismatch [-] 1575 | | NeighborChangedAddress [-] 1576 | | NeighborChangedLevel [-] 1577 | | PODMismatch [-] 1578 | | UnacceptableHeader [-] 1579 V | 1580 +-----------+ 1581 | TwoWay |<----+ 1582 | | | HALChanged [StoreHAL] 1583 | | | HALSChanged [StoreHALS] 1584 | | | HATChanged [StoreHAT] 1585 | | | LevelChanged [StoreLevel] 1586 | | | LIERcvd [ProcessLIE] 1587 | | | SendLIE [SendLIE] 1588 | | | TimerTick [PUSH SendLIE, 1589 | | | IF HoldTimer expired 1590 | | | PUSH HoldTimerExpired] 1591 | | | UpdateZTPOffer [SendOfferToZTPFSM] 1592 | |-----+ 1593 | | 1594 | |<---------------------- 1595 | |----------------------> (Multiple 1596 | | NewNeighbor Neighbors 1597 | | [StartMulNeighTimer] Wait) 1598 | | MultipleNeighbors 1599 +-----------+ [StartMulNeighTimer] 1600 ^ | 1601 | | ValidReflection [-] 1602 | V 1603 (ThreeWay) 1605 LIE FSM (continued) 1607 (TwoWay) (OneWay) 1608 ^ | ^ 1609 | | | HoldTimerExpired [-] 1610 | | | InstanceNameMismatch [-] 1611 | | | LevelChanged [UpdateLevel] 1612 | | | MTUMismatch [-] 1613 | | | NeighborChangedAddress [-] 1614 | | | NeighborChangedLevel [-] 1615 NeighborDropped- | | | PODMismatch [-] 1616 Reflection [-] | | | UnacceptableHeader [-] 1617 | V | 1618 +-----------+ | 1619 | ThreeWay |-----+ 1620 | | 1621 | |<----+ 1622 | | | HALChanged [StoreHAL] 1623 | | | HALSChanged [StoreHALS] 1624 | | | HATChanged [StoreHAT] 1625 | | | LieReceived [ProcessLIE] 1626 | | | SendLIE [SendLIE] 1627 | | | TimerTick [PUSH SendLie, 1628 | | | IF HoldTimer expired 1629 | | | PUSH HoldTimerExpired] 1630 | | | UpdateZTPOffer [SendOfferToZTPFSM] 1631 | | | ValidReflection [-] 1632 | |-----+ 1633 | |----------------------> (Multiple 1634 | | MultipleNeighbors Neighbors 1635 +-----------+ [StartMulNeighTimer] Wait) 1637 LIE FSM (continued) 1639 (TwoWay) (ThreeWay) 1640 | | 1641 V V 1642 +------------+ 1643 | Multiple |<----+ 1644 | Neighbors | | HALChanged [StoreHAL] 1645 | Wait | | HALSChanged [StoreHALS] 1646 | | | HATChanged [StoreHAT] 1647 | | | MultipleNeighbors 1648 | | | [StartMultipleNeighborsTimer] 1649 | | | TimerTick [IF MulNeighTimer expired 1650 | | | PUSH MultipleNeighborsDone] 1651 | | | UpdateZTPOffer [SendOfferToZTP] 1652 | |-----+ 1653 | | 1654 | |<--------------------------- 1655 | |---------------------------> (OneWay) 1656 | | LevelChanged [StoreLevel] 1657 +------------+ MultipleNeighborsDone [-] 1659 LIE FSM (continued) 1661 Events 1663 o TimerTick: one second timer tic 1665 o LevelChanged: node's level has been changed by ZTP or 1666 configuration 1668 o HALChanged: best HAL computed by ZTP has changed 1670 o HATChanged: HAT computed by ZTP has changed 1672 o HALSChanged: set of HAL offering systems computed by ZTP has 1673 changed 1675 o LieRcvd: received LIE 1677 o NewNeighbor: new neighbor parsed 1679 o ValidReflection: received own reflection from neighbor 1681 o NeighborDroppedReflection: lost previous own reflection from 1682 neighbor 1684 o NeighborChangedLevel: neighbor changed advertised level 1686 o NeighborChangedAddress: neighbor changed IP address 1687 o UnacceptableHeader: unacceptable header seen 1689 o MTUMismatch: MTU mismatched 1691 o InstanceNameMismatch: Instance mismatched 1693 o PODMismatch: Unacceptable PoD seen 1695 o HoldtimeExpired: adjacency hold down expired 1697 o MultipleNeighbors: more than one neighbor seen on interface 1699 o MultipleNeighborsDone: cooldown for multiple neighbors expired 1701 o SendLie: send a LIE out 1703 o UpdateZTPOffer: update this node's ZTP offer 1705 Actions 1707 on MultipleNeighbors in OneWay finishes in MultipleNeighborsWait: 1708 start multiple neighbors timer as 4 * DEFAULT_LIE_HOLDTIME 1710 on NeighborDroppedReflection in ThreeWay finishes in TwoWay: no 1711 action 1713 on NeighborDroppedReflection in OneWay finishes in OneWay: no 1714 action 1716 on PODMismatch in TwoWay finishes in OneWay: no action 1718 on NewNeighbor in TwoWay finishes in MultipleNeighborsWait: PUSH 1719 SendLie event 1721 on LieRcvd in OneWay finishes in OneWay: PROCESS_LIE 1723 on UnacceptableHeader in ThreeWay finishes in OneWay: no action 1725 on UpdateZTPOffer in TwoWay finishes in TwoWay: send offer to ZTP 1726 FSM 1728 on NeighborChangedAddress in ThreeWay finishes in OneWay: no 1729 action 1731 on HALChanged in MultipleNeighborsWait finishes in 1732 MultipleNeighborsWait: store new HAL 1734 on NeighborChangedAddress in TwoWay finishes in OneWay: no action 1735 on MultipleNeighbors in TwoWay finishes in MultipleNeighborsWait: 1736 start multiple neighbors timer as 4 * DEFAULT_LIE_HOLDTIME 1738 on LevelChanged in ThreeWay finishes in OneWay: update level with 1739 event value 1741 on LieRcvd in ThreeWay finishes in ThreeWay: PROCESS_LIE 1743 on ValidReflection in OneWay finishes in ThreeWay: no action 1745 on NeighborChangedLevel in TwoWay finishes in OneWay: no action 1747 on MultipleNeighbors in ThreeWay finishes in 1748 MultipleNeighborsWait: start multiple neighbors timer as 4 * 1749 DEFAULT_LIE_HOLDTIME 1751 on InstanceNameMismatch in OneWay finishes in OneWay: no action 1753 on NewNeighbor in OneWay finishes in TwoWay: PUSH SendLie event 1755 on UpdateZTPOffer in OneWay finishes in OneWay: send offer to ZTP 1756 FSM 1758 on UpdateZTPOffer in ThreeWay finishes in ThreeWay: send offer to 1759 ZTP FSM 1761 on MTUMismatch in ThreeWay finishes in OneWay: no action 1763 on TimerTick in OneWay finishes in OneWay: PUSH SendLie event 1765 on SendLie in TwoWay finishes in TwoWay: SEND_LIE 1767 on ValidReflection in ThreeWay finishes in ThreeWay: no action 1769 on InstanceNameMismatch in TwoWay finishes in OneWay: no action 1771 on HoldtimeExpired in OneWay finishes in OneWay: no action 1773 on TimerTick in ThreeWay finishes in ThreeWay: PUSH SendLie event, 1774 if holdtime expired PUSH HoldtimeExpired event 1776 on HALChanged in TwoWay finishes in TwoWay: store new HAL 1778 on HoldtimeExpired in ThreeWay finishes in OneWay: no action 1780 on HALSChanged in TwoWay finishes in TwoWay: store HALS 1782 on HALSChanged in ThreeWay finishes in ThreeWay: store HALS 1783 on ValidReflection in TwoWay finishes in ThreeWay: no action 1785 on MultipleNeighborsDone in MultipleNeighborsWait finishes in 1786 OneWay: no action 1788 on NeighborAddressAdded in OneWay finishes in OneWay: no action 1790 on TimerTick in MultipleNeighborsWait finishes in 1791 MultipleNeighborsWait: decrement MultipleNeighbors timer, if 1792 expired PUSH MultipleNeighborsDone 1794 on MTUMismatch in OneWay finishes in OneWay: no action 1796 on MultipleNeighbors in MultipleNeighborsWait finishes in 1797 MultipleNeighborsWait: start multiple neighbors timer as 4 * 1798 DEFAULT_LIE_HOLDTIME 1800 on LieRcvd in TwoWay finishes in TwoWay: PROCESS_LIE 1802 on HATChanged in MultipleNeighborsWait finishes in 1803 MultipleNeighborsWait: store HAT 1805 on HoldtimeExpired in TwoWay finishes in OneWay: no action 1807 on NeighborChangedLevel in ThreeWay finishes in OneWay: no action 1809 on LevelChanged in OneWay finishes in OneWay: update level with 1810 event value, PUSH SendLie event 1812 on SendLie in OneWay finishes in OneWay: SEND_LIE 1814 on HATChanged in OneWay finishes in OneWay: store HAT 1816 on LevelChanged in TwoWay finishes in TwoWay: update level with 1817 event value 1819 on HATChanged in TwoWay finishes in TwoWay: store HAT 1821 on PODMismatch in ThreeWay finishes in OneWay: no action 1823 on LevelChanged in MultipleNeighborsWait finishes in OneWay: 1824 update level with event value 1826 on UnacceptableHeader in TwoWay finishes in OneWay: no action 1828 on NeighborChangedLevel in OneWay finishes in OneWay: no action 1830 on InstanceNameMismatch in ThreeWay finishes in OneWay: no action 1831 on HATChanged in ThreeWay finishes in ThreeWay: store HAT 1833 on HALChanged in OneWay finishes in OneWay: store new HAL 1835 on UnacceptableHeader in OneWay finishes in OneWay: no action 1837 on HALChanged in ThreeWay finishes in ThreeWay: store new HAL 1839 on UpdateZTPOffer in MultipleNeighborsWait finishes in 1840 MultipleNeighborsWait: send offer to ZTP FSM 1842 on NeighborChangedMinorFields in OneWay finishes in OneWay: no 1843 action 1845 on NeighborChangedAddress in OneWay finishes in OneWay: no action 1847 on MTUMismatch in TwoWay finishes in OneWay: no action 1849 on PODMismatch in OneWay finishes in OneWay: no action 1851 on SendLie in ThreeWay finishes in ThreeWay: SEND_LIE 1853 on TimerTick in TwoWay finishes in TwoWay: PUSH SendLie event, if 1854 holdtime expired PUSH HoldtimeExpired event 1856 on HALSChanged in OneWay finishes in OneWay: store HALS 1858 on HALSChanged in MultipleNeighborsWait finishes in 1859 MultipleNeighborsWait: store HALS 1861 on Entry into OneWay: CLEANUP 1863 Following words are used for well known procedures: 1865 1. PUSH Event: pushes an event to be executed by the FSM upon exit 1866 of this action 1868 2. CLEANUP: neighbor MUST be reset to unknown 1870 3. SEND_LIE: create a new LIE packet 1872 1. reflecting the neighbor if known and valid and 1874 2. setting the necessary `not_a_ztp_offer` variable if level was 1875 derived from last known neighbor on this interface and 1877 3. setting `you_are_not_flood_repeater` to computed value 1879 4. PROCESS_LIE: 1881 1. if lie has wrong major version OR our own system ID or 1882 invalid system ID then CLEANUP else 1884 2. if lie has non matching MTUs then CLEANUP, PUSH 1885 UpdateZTPOffer, PUSH MTUMismatch else 1887 3. if PoD rules do not allow adjacency forming then CLEANUP, 1888 PUSH PODMismatch, PUSH MTUMismatch else 1890 4. if lie has undefined level OR my level is undefined OR this 1891 node is leaf and remote level lower than HAT OR (lie's level 1892 is not leaf AND its difference is more than one from my 1893 level) then CLEANUP, PUSH UpdateZTPOffer, PUSH 1894 UnacceptableHeader else 1896 5. PUSH UpdateZTPOffer, construct temporary new neighbor 1897 structure with values from lie, if no current neighbor exists 1898 then set neighbor to new neighbor, PUSH NewNeighbor event, 1899 CHECK_THREE_WAY else 1901 1. if current neighbor system ID differs from lie's system 1902 ID then PUSH MultipleNeighbors else 1904 2. if current neighbor stored level differs from lie's level 1905 then PUSH NeighborChangedLevel else 1907 3. if current neighbor stored IPv4/v6 address differs from 1908 lie's address then PUSH NeighborChangedAddress else 1910 4. if any of neighbor's flood address port, name, local 1911 linkid changed then PUSH NeighborChangedMinorFields and 1913 5. CHECK_THREE_WAY 1915 5. CHECK_THREE_WAY: if current state is one-way do nothing else 1917 1. if lie packet does not contain neighbor then if current state 1918 is three-way then PUSH NeighborDroppedReflection else 1920 2. if packet reflects this system's ID and local port and state 1921 is three-way then PUSH event ValidReflection else PUSH event 1922 MultipleNeighbors 1924 4.2.3. Topology Exchange (TIE Exchange) 1926 4.2.3.1. Topology Information Elements 1928 Topology and reachability information in RIFT is conveyed by the 1929 means of TIEs which have good amount of commonalities with LSAs in 1930 OSPF. 1932 The TIE exchange mechanism uses the port indicated by each node in 1933 the LIE exchange and the interface on which the adjacency has been 1934 formed as destination. It SHOULD use TTL of 1 as well and set inter- 1935 network control precedence on according packets. 1937 TIEs contain sequence numbers, lifetimes and a type. Each type has 1938 ample identifying number space and information is spread across 1939 possibly many TIEs of a certain type by the means of a hash function 1940 that a node or deployment can individually determine. One extreme 1941 design choice is a prefix per TIE which leads to more BGP-like 1942 behavior where small increments are only advertised on route changes 1943 vs. deploying with dense prefix packing into few TIEs leading to more 1944 traditional IGP trade-off with fewer TIEs. An implementation may 1945 even rehash prefix to TIE mapping at any time at the cost of 1946 significant amount of re-advertisements of TIEs. 1948 More information about the TIE structure can be found in the schema 1949 in Appendix B. 1951 4.2.3.2. South- and Northbound Representation 1953 A central concept of RIFT is that each node represents itself 1954 differently depending on the direction in which it is advertising 1955 information. More precisely, a spine node represents two different 1956 databases over its adjacencies depending whether it advertises TIEs 1957 to the north or to the south/sideways. We call those differing TIE 1958 databases either south- or northbound (South TIEs and North TIEs) 1959 depending on the direction of distribution. 1961 The North TIEs hold all of the node's adjacencies and local prefixes 1962 while the South TIEs hold only all of the node's adjacencies, the 1963 default prefix with necessary disaggregated prefixes and local 1964 prefixes. We will explain this in detail further in Section 4.2.5. 1966 The TIE types are mostly symmetric in both directions and Table 2 1967 provides a quick reference to main TIE types including direction and 1968 their function. 1970 +--------------------+----------------------------------------------+ 1971 | TIE-Type | Content | 1972 +--------------------+----------------------------------------------+ 1973 | Node North TIE | node properties and adjacencies | 1974 +--------------------+----------------------------------------------+ 1975 | Node South TIE | same content as node North TIE | 1976 +--------------------+----------------------------------------------+ 1977 | Prefix North TIE | contains nodes' directly reachable prefixes | 1978 +--------------------+----------------------------------------------+ 1979 | Prefix South TIE | contains originated defaults and directly | 1980 | | reachable prefixes | 1981 +--------------------+----------------------------------------------+ 1982 | Positive | contains disaggregated prefixes | 1983 | Disaggregation | | 1984 | South TIE | | 1985 +--------------------+----------------------------------------------+ 1986 | Negative | contains special, negatively disaggregated | 1987 | Disaggregation | prefixes to support multi-plane designs | 1988 | South TIE | | 1989 +--------------------+----------------------------------------------+ 1990 | External Prefix | contains external prefixes | 1991 | North TIE | | 1992 +--------------------+----------------------------------------------+ 1993 | Key-Value North | contains nodes northbound KVs | 1994 | TIE | | 1995 +--------------------+----------------------------------------------+ 1996 | Key-Value South | contains nodes southbound KVs | 1997 | TIE | | 1998 +--------------------+----------------------------------------------+ 2000 Table 2: TIE Types 2002 As an example illustrating a databases holding both representations, 2003 consider the topology in Figure 2 with the optional link between 2004 spine 111 and spine 112 (so that the flooding on an East-West link 2005 can be shown). This example assumes unnumbered interfaces. First, 2006 here are the TIEs generated by some nodes. For simplicity, the key 2007 value elements which may be included in their South TIEs or North 2008 TIEs are not shown. 2010 ToF 21 South TIEs: 2011 Node South TIE: 2012 NodeElement(level=2, neighbors((Spine 111, level 1, cost 1), 2013 (Spine 112, level 1, cost 1), (Spine 121, level 1, cost 1), 2014 (Spine 122, level 1, cost 1))) 2015 Prefix South TIE: 2016 SouthPrefixesElement(prefixes(0/0, cost 1), (::/0, cost 1)) 2018 Spine 111 South TIEs: 2019 Node South TIE: 2020 NodeElement(level=1, neighbors((ToF 21, level 2, cost 1, 2021 links(...)), 2022 (ToF 22, level 2, cost 1, links(...)), 2023 (Spine 112, level 1, cost 1, links(...)), 2024 (Leaf111, level 0, cost 1, links(...)), 2025 (Leaf112, level 0, cost 1, links(...)))) 2026 Prefix South TIE: 2027 SouthPrefixesElement(prefixes(0/0, cost 1), (::/0, cost 1)) 2029 Spine 111 North TIEs: 2030 Node North TIE: 2031 NodeElement(level=1, 2032 neighbors((ToF 21, level 2, cost 1, links(...)), 2033 (ToF 22, level 2, cost 1, links(...)), 2034 (Spine 112, level 1, cost 1, links(...)), 2035 (Leaf111, level 0, cost 1, links(...)), 2036 (Leaf112, level 0, cost 1, links(...)))) 2037 Prefix North TIE: 2038 NorthPrefixesElement(prefixes(Spine 111.loopback) 2040 Spine 121 South TIEs: 2041 Node South TIE: 2042 NodeElement(level=1, neighbors((ToF 21,level 2,cost 1), 2043 (ToF 22, level 2, cost 1), (Leaf121, level 0, cost 1), 2044 (Leaf122, level 0, cost 1))) 2045 Prefix South TIE: 2046 SouthPrefixesElement(prefixes(0/0, cost 1), (::/0, cost 1)) 2048 Spine 121 North TIEs: 2049 Node North TIE: 2050 NodeElement(level=1, 2051 neighbors((ToF 21, level 2, cost 1, links(...)), 2052 (ToF 22, level 2, cost 1, links(...)), 2053 (Leaf121, level 0, cost 1, links(...)), 2054 (Leaf122, level 0, cost 1, links(...)))) 2055 Prefix North TIE: 2056 NorthPrefixesElement(prefixes(Spine 121.loopback) 2058 Leaf112 North TIEs: 2059 Node North TIE: 2060 NodeElement(level=0, 2061 neighbors((Spine 111, level 1, cost 1, links(...)), 2062 (Spine 112, level 1, cost 1, links(...)))) 2063 Prefix North TIE: 2064 NorthPrefixesElement(prefixes(Leaf112.loopback, Prefix112, 2065 Prefix_MH)) 2067 Figure 14: example TIES generated in a 2 level spine-and-leaf 2068 topology 2070 It may be here not necessarily obvious why the node South TIEs 2071 contain all the adjacencies of the according node. This will be 2072 necessary for algorithms given in Section 4.2.3.9 and Section 4.3.6. 2074 4.2.3.3. Flooding 2076 The mechanism used to distribute TIEs is the well-known (albeit 2077 modified in several respects to take advantage of fat tree topology) 2078 flooding mechanism used by today's link-state protocols. Although 2079 flooding is initially more demanding to implement it avoids many 2080 problems with update style used in diffused computation such as 2081 distance vector protocols. Since flooding tends to present an 2082 unscalable burden in large, densely meshed topologies (fat trees 2083 being unfortunately such a topology) we provide as solution a close 2084 to optimal global flood reduction and load balancing optimization in 2085 Section 4.2.3.9. 2087 As described before, TIEs themselves are transported over UDP with 2088 the ports indicated in the LIE exchanges and using the destination 2089 address on which the LIE adjacency has been formed. For unnumbered 2090 IPv4 interfaces same considerations apply as in equivalent OSPF case. 2092 4.2.3.3.1. Normative Flooding Procedures 2094 On reception of a TIE with an undefined level value in the packet 2095 header the node SHOULD issue a warning and indiscriminately discard 2096 the packet. 2098 This section specifies the precise, normative flooding mechanism and 2099 can be omitted unless the reader is pursuing an implementation of the 2100 protocol. 2102 Flooding Procedures are described in terms of a flooding state of an 2103 adjacency and resulting operations on it driven by packet arrivals. 2104 The FSM itself has basically just a single state and is not well 2105 suited to represent the behavior. An implementation MUST behave on 2106 the wire in the same way as the provided normative procedures of this 2107 paragraph. 2109 RIFT does not specify any kind of flood rate limiting since such 2110 specifications always assume particular points in available 2111 technology speeds and feeds and those points are shifting at faster 2112 and faster rate (speed of light holding for the moment). The encoded 2113 packets provide hints to react accordingly to losses or overruns. 2115 Flooding of all according topology exchange elements SHOULD be 2116 performed at highest feasible rate whereas the rate of transmission 2117 MUST be throttled by reacting to adequate features of the system such 2118 as e.g. queue lengths or congestion indications in the protocol 2119 packets. 2121 A node SHOULD NOT send out any topology information elements if the 2122 adjacancy is not in a "three-way" state. No further tightening of 2123 this rule is possible due to possible link buffering and re-ordering 2124 of LIEs and TIEs/TIDEs/TIREs. 2126 A node MUST drop any received TIEs/TIDEs/TIREs unless it is in three- 2127 way state. 2129 TIDEs and TIREs MUST NOT be re-flooded the way TIEs of other nodes 2130 are are MUST be always generated by the node itself and cross only to 2131 the neighboring node. 2133 4.2.3.3.1.1. FloodState Structure per Adjacency 2135 The structure contains conceptually the following elements. The word 2136 collection or queue indicates a set of elements that can be iterated: 2138 TIES_TX: Collection containing all the TIEs to transmit on the 2139 adjacency. 2141 TIES_ACK: Collection containing all the TIEs that have to be 2142 acknowledged on the adjacency. 2144 TIES_REQ: Collection containing all the TIE headers that have to be 2145 requested on the adjacency. 2147 TIES_RTX: Collection containing all TIEs that need retransmission 2148 with the according time to retransmit. 2150 Following words are used for well known procedures operating on this 2151 structure: 2153 TIE Describes either a full RIFT TIE or accordingly just the 2154 `TIEHeader` or `TIEID`. The according meaning is unambiguously 2155 contained in the context of the algorithm. 2157 is_flood_reduced(TIE): returns whether a TIE can be flood reduced or 2158 not. 2160 is_tide_entry_filtered(TIE): returns whether a header should be 2161 propagated in TIDE according to flooding scopes. 2163 is_request_filtered(TIE): returns whether a TIE request should be 2164 propagated to neighbor or not according to flooding scopes. 2166 is_flood_filtered(TIE): returns whether a TIE requested be flooded 2167 to neighbor or not according to flooding scopes. 2169 try_to_transmit_tie(TIE): 2171 A. if not is_flood_filtered(TIE) then 2173 1. remove TIE from TIES_RTX if present 2175 2. if TIE" with same key on TIES_ACK then 2177 a. if TIE" same or newer than TIE do nothing else 2179 b. remove TIE" from TIES_ACK and add TIE to TIES_TX 2181 3. else insert TIE into TIES_TX 2183 ack_tie(TIE): remove TIE from all collections and then insert TIE 2184 into TIES_ACK. 2186 tie_been_acked(TIE): remove TIE from all collections. 2188 remove_from_all_queues(TIE): same as `tie_been_acked`. 2190 request_tie(TIE): if not is_request_filtered(TIE) then 2191 remove_from_all_queues(TIE) and add to TIES_REQ. 2193 move_to_rtx_list(TIE): remove TIE from TIES_TX and then add to 2194 TIES_RTX using TIE retransmission interval. 2196 clear_requests(TIEs): remove all TIEs from TIES_REQ. 2198 bump_own_tie(TIE): for self-originated TIE originate an empty or re- 2199 generate with version number higher then the one in TIE. 2201 The collection SHOULD be served with following priorities if the 2202 system cannot process all the collections in real time: 2204 Elements on TIES_ACK should be processed with highest priority 2206 TIES_TX 2208 TIES_REQ and TIES_RTX 2210 4.2.3.3.1.2. TIDEs 2212 `TIEID` and `TIEHeader` space forms a strict total order (modulo 2213 incomparable sequence numbers in the very unlikely event that can 2214 occur if a TIE is "stuck" in a part of a network while the originator 2215 reboots and reissues TIEs many times to the point its sequence# rolls 2216 over and forms incomparable distance to the "stuck" copy) which 2217 implies that a comparison relation is possible between two elements. 2218 With that it is implicitly possible to compare TIEs, TIEHeaders and 2219 TIEIDs to each other whereas the shortest viable key is always 2220 implied. 2222 When generating and sending TIDEs an implementation SHOULD ensure 2223 that enough bandwidth is left to send elements of Floodstate 2224 structure. 2226 4.2.3.3.1.2.1. TIDE Generation 2228 As given by timer constant, periodically generate TIDEs by: 2230 NEXT_TIDE_ID: ID of next TIE to be sent in TIDE. 2232 TIDE_START: Begin of TIDE packet range. 2234 a. NEXT_TIDE_ID = MIN_TIEID 2236 b. while NEXT_TIDE_ID not equal to MAX_TIEID do 2238 1. TIDE_START = NEXT_TIDE_ID 2240 2. HEADERS = At most TIRDEs_PER_PKT headers in TIEDB starting at 2241 NEXT_TIDE_ID or higher that SHOULD be filtered by 2242 is_tide_entry_filtered and MUST either have a lifetime left > 2243 0 or have no content 2245 3. if HEADERS is empty then START = MIN_TIEID else START = first 2246 element in HEADERS 2248 4. if HEADERS' size less than TIRDEs_PER_PKT then END = 2249 MAX_TIEID else END = last element in HEADERS 2251 5. send sorted HEADERS as TIDE setting START and END as its 2252 range 2254 6. NEXT_TIDE_ID = END 2256 The constant `TIRDEs_PER_PKT` SHOULD be generated and used by the 2257 implementation to limit the amount of TIE headers per TIDE so the 2258 sent TIDE PDU does not exceed interface MTU. 2260 TIDE PDUs SHOULD be spaced on sending to prevent packet drops. 2262 4.2.3.3.1.2.2. TIDE Processing 2264 On reception of TIDEs the following processing is performed: 2266 TXKEYS: Collection of TIE Headers to be send after processing of 2267 the packet 2269 REQKEYS: Collection of TIEIDs to be requested after processing of 2270 the packet 2272 CLEARKEYS: Collection of TIEIDs to be removed from flood state 2273 queues 2275 LASTPROCESSED: Last processed TIEID in TIDE 2277 DBTIE: TIE in the LSDB if found 2279 a. LASTPROCESSED = TIDE.start_range 2281 b. for every HEADER in TIDE do 2283 1. DBTIE = find HEADER in current LSDB 2285 2. if HEADER < LASTPROCESSED then report error and reset 2286 adjacency and return 2288 3. put all TIEs in LSDB where (TIE.HEADER > LASTPROCESSED and 2289 TIE.HEADER < HEADER) into TXKEYS 2291 4. LASTPROCESSED = HEADER 2293 5. if DBTIE not found then 2295 I) if originator is this node then bump_own_tie 2297 II) else put HEADER into REQKEYS 2299 6. if DBTIE.HEADER < HEADER then 2301 I) if originator is this node then bump_own_tie else 2302 i. if this is a North TIE header from a northbound 2303 neighbor then override DBTIE in LSDB with HEADER 2305 ii. else put HEADER into REQKEYS 2307 7. if DBTIE.HEADER > HEADER then put DBTIE.HEADER into TXKEYS 2309 8. if DBTIE.HEADER = HEADER then 2311 I) if DBTIE has content already then put DBTIE.HEADER 2312 into CLEARKEYS 2314 II) else put HEADER into REQKEYS 2316 c. put all TIEs in LSDB where (TIE.HEADER > LASTPROCESSED and 2317 TIE.HEADER <= TIDE.end_range) into TXKEYS 2319 d. for all TIEs in TXKEYS try_to_transmit_tie(TIE) 2321 e. for all TIEs in REQKEYS request_tie(TIE) 2323 f. for all TIEs in CLEARKEYS remove_from_all_queues(TIE) 2325 4.2.3.3.1.3. TIREs 2327 4.2.3.3.1.3.1. TIRE Generation 2329 There is not much to say here. Elements from both TIES_REQ and 2330 TIES_ACK MUST be collected and sent out as fast as feasible as TIREs. 2331 When sending TIREs with elements from TIES_REQ the `lifetime` field 2332 MUST be set to 0 to force reflooding from the neighbor even if the 2333 TIEs seem to be same. 2335 4.2.3.3.1.3.2. TIRE Processing 2337 On reception of TIREs the following processing is performed: 2339 TXKEYS: Collection of TIE Headers to be send after processing of 2340 the packet 2342 REQKEYS: Collection of TIEIDs to be requested after processing of 2343 the packet 2345 ACKKEYS: Collection of TIEIDs that have been acked 2347 DBTIE: TIE in the LSDB if found 2349 a. for every HEADER in TIRE do 2350 1. DBTIE = find HEADER in current LSDB 2352 2. if DBTIE not found then do nothing 2354 3. if DBTIE.HEADER < HEADER then put HEADER into REQKEYS 2356 4. if DBTIE.HEADER > HEADER then put DBTIE.HEADER into TXKEYS 2358 5. if DBTIE.HEADER = HEADER then put DBTIE.HEADER into ACKKEYS 2360 b. for all TIEs in TXKEYS try_to_transmit_tie(TIE) 2362 c. for all TIEs in REQKEYS request_tie(TIE) 2364 d. for all TIEs in ACKKEYS tie_been_acked(TIE) 2366 4.2.3.3.1.4. TIEs Processing on Flood State Adjacency 2368 On reception of TIEs the following processing is performed: 2370 ACKTIE: TIE to acknowledge 2372 TXTIE: TIE to transmit 2374 DBTIE: TIE in the LSDB if found 2376 a. DBTIE = find TIE in current LSDB 2378 b. if DBTIE not found then 2380 1. if originator is this node then bump_own_tie with a short 2381 remaining lifetime 2383 2. else insert TIE into LSDB and ACKTIE = TIE 2385 else 2387 1. if DBTIE.HEADER = TIE.HEADER then 2389 i. if DBTIE has content already then ACKTIE = TIE 2391 ii. else process like the "DBTIE.HEADER < TIE.HEADER" case 2393 2. if DBTIE.HEADER < TIE.HEADER then 2395 i. if originator is this node then bump_own_tie 2397 ii. else insert TIE into LSDB and ACKTIE = TIE 2399 3. if DBTIE.HEADER > TIE.HEADER then 2401 i. if DBTIE has content already then TXTIE = DBTIE 2403 ii. else ACKTIE = DBTIE 2405 c. if TXTIE is set then try_to_transmit_tie(TXTIE) 2407 d. if ACKTIE is set then ack_tie(TIE) 2409 4.2.3.3.1.5. TIEs Processing When LSDB Received Newer Version on Other 2410 Adjacencies 2412 The Link State Database can be considered to be a switchboard that 2413 does not need any flooding procedures but can be given new versions 2414 of TIEs by a peer. Consecutively, a peer receives from the LSDB 2415 newer versions of TIEs received by other peers and processes them 2416 (without any filtering) just like receiving TIEs from its remote 2417 peer. This publisher model can be implemented in many ways. 2419 4.2.3.3.1.6. Sending TIEs 2421 On a periodic basis all TIEs with lifetime left > 0 MUST be sent out 2422 on the adjacency, removed from TIES_TX list and requeued onto 2423 TIES_RTX list. 2425 4.2.3.4. TIE Flooding Scopes 2427 In a somewhat analogous fashion to link-local, area and domain 2428 flooding scopes, RIFT defines several complex "flooding scopes" 2429 depending on the direction and type of TIE propagated. 2431 Every North TIE is flooded northbound, providing a node at a given 2432 level with the complete topology of the Clos or Fat Tree network that 2433 is reachable southwards of it, including all specific prefixes. This 2434 means that a packet received from a node at the same or lower level 2435 whose destination is covered by one of those specific prefixes will 2436 be routed directly towards the node advertising that prefix rather 2437 than sending the packet to a node at a higher level. 2439 A node's Node South TIEs, consisting of all node's adjacencies and 2440 prefix South TIEs limited to those related to default IP prefix and 2441 disaggregated prefixes, are flooded southbound in order to allow the 2442 nodes one level down to see connectivity of the higher level as well 2443 as reachability to the rest of the fabric. In order to allow an E-W 2444 disconnected node in a given level to receive the South TIEs of other 2445 nodes at its level, every *NODE* South TIE is "reflected" northbound 2446 to level from which it was received. It should be noted that East- 2447 West links are included in South TIE flooding (except at ToF level); 2448 those TIEs need to be flooded to satisfy algorithms in Section 4.2.4. 2449 In that way nodes at same level can learn about each other without a 2450 lower level, e.g. in case of leaf level. The precise, normative 2451 flooding scopes are given in Table 3. Those rules govern as well 2452 what SHOULD be included in TIDEs on the adjacency. Again, East-West 2453 flooding scopes are identical to South flooding scopes except in case 2454 of ToF East-West links (rings) which are basically performing 2455 northbound flooding. 2457 Node South TIE "south reflection" allows to support positive 2458 disaggregation on failures describes in Section 4.2.5 and flooding 2459 reduction in Section 4.2.3.9. 2461 +-----------+---------------------+----------------+-----------------+ 2462 | Type / | South | North | East-West | 2463 | Direction | | | | 2464 +-----------+---------------------+----------------+-----------------+ 2465 | node | flood if level of | flood if level | flood only if | 2466 | South TIE | originator is equal | of originator | this node | 2467 | | to this node | is higher than | is not ToF | 2468 | | | this node | | 2469 +-----------+---------------------+----------------+-----------------+ 2470 | non-node | flood self- | flood only if | flood only if | 2471 | South TIE | originated only | neighbor is | self-originated | 2472 | | | originator of | and this node | 2473 | | | TIE | is not ToF | 2474 +-----------+---------------------+----------------+-----------------+ 2475 | all North | never flood | flood always | flood only if | 2476 | TIEs | | | this node is | 2477 | | | | ToF | 2478 +-----------+---------------------+----------------+-----------------+ 2479 | TIDE | include at least | include at | if this node is | 2480 | | all non-self | least all node | ToF then | 2481 | | originated North | South TIEs and | include all | 2482 | | TIE headers and | all South TIEs | North TIEs, | 2483 | | self-originated | originated by | otherwise only | 2484 | | South TIE headers | peer and | self-originated | 2485 | | and | all North TIEs | TIEs | 2486 | | node South TIEs of | | | 2487 | | nodes at same | | | 2488 | | level | | | 2489 +-----------+---------------------+----------------+-----------------+ 2490 | TIRE as | request all North | request all | if this node is | 2491 | Request | TIEs and all peer's | South TIEs | ToF then apply | 2492 | | self-originated | | North scope | 2493 | | TIEs and | | rules, | 2494 | | all node South TIEs | | otherwise South | 2495 | | | | scope rules | 2496 +-----------+---------------------+----------------+-----------------+ 2497 | TIRE as | Ack all received | Ack all | Ack all | 2498 | Ack | TIEs | received TIEs | received TIEs | 2499 +-----------+---------------------+----------------+-----------------+ 2501 Table 3: Normative Flooding Scopes 2503 If the TIDE includes additional TIE headers beside the ones 2504 specified, the receiving neighbor must apply according filter to the 2505 received TIDE strictly and MUST NOT request the extra TIE headers 2506 that were not allowed by the flooding scope rules in its direction. 2508 As an example to illustrate these rules, consider using the topology 2509 in Figure 2, with the optional link between spine 111 and spine 112, 2510 and the associated TIEs given in Figure 14. The flooding from 2511 particular nodes of the TIEs is given in Table 4. 2513 +-----------+----------+--------------------------------------------+ 2514 | Router | Neighbor | TIEs | 2515 | floods to | | | 2516 +-----------+----------+--------------------------------------------+ 2517 | Leaf111 | Spine | Leaf111 North TIEs, Spine 111 node South | 2518 | | 112 | TIE | 2519 | Leaf111 | Spine | Leaf111 North TIEs, Spine 112 node South | 2520 | | 111 | TIE | 2521 | | | | 2522 | Spine 111 | Leaf111 | Spine 111 South TIEs | 2523 | Spine 111 | Leaf112 | Spine 111 South TIEs | 2524 | Spine 111 | Spine | Spine 111 South TIEs | 2525 | | 112 | | 2526 | Spine 111 | ToF 21 | Spine 111 North TIEs, Leaf111 | 2527 | | | North TIEs, Leaf112 North TIEs, ToF 22 | 2528 | | | node South TIE | 2529 | Spine 111 | ToF 22 | Spine 111 North TIEs, Leaf111 | 2530 | | | North TIEs, Leaf112 North TIEs, ToF 21 | 2531 | | | node South TIE | 2532 | | | | 2533 | ... | ... | ... | 2534 | ToF 21 | Spine | ToF 21 South TIEs | 2535 | | 111 | | 2536 | ToF 21 | Spine | ToF 21 South TIEs | 2537 | | 112 | | 2538 | ToF 21 | Spine | ToF 21 South TIEs | 2539 | | 121 | | 2540 | ToF 21 | Spine | ToF 21 South TIEs | 2541 | | 122 | | 2542 | ... | ... | ... | 2543 +-----------+----------+--------------------------------------------+ 2545 Table 4: Flooding some TIEs from example topology 2547 4.2.3.5. 'Flood Only Node TIEs' Bit 2549 RIFT includes an optional ECN mechanism to prevent "flooding inrush" 2550 on restart or bring-up with many southbound neighbors. A node MAY 2551 set on its LIEs the according bit to indicate to the neighbor that it 2552 should temporarily flood node TIEs only to it. It SHOULD only set it 2553 in the southbound direction. The receiving node SHOULD accommodate 2554 the request to lessen the flooding load on the affected node if south 2555 of the sender and SHOULD ignore the bit if northbound. 2557 Obviously this mechanism is most useful in southbound direction. The 2558 distribution of node TIEs guarantees correct behavior of algorithms 2559 like disaggregation or default route origination. Furthermore 2560 though, the use of this bit presents an inherent trade-off between 2561 processing load and convergence speed since suppressing flooding of 2562 northbound prefixes from neighbors will lead to blackholes. 2564 4.2.3.6. Initial and Periodic Database Synchronization 2566 The initial exchange of RIFT is modeled after ISIS with TIDE being 2567 equivalent to CSNP and TIRE playing the role of PSNP. The content of 2568 TIDEs and TIREs is governed by Table 3. 2570 4.2.3.7. Purging and Roll-Overs 2572 When a node exits the network, if "unpurged", residual stale TIEs may 2573 exist in the network until their lifetimes expire (which in case of 2574 RIFT is by default a rather long period to prevent ongoing re- 2575 origination of TIEs in very large topologies). RIFT does however not 2576 have a "purging mechanism" in the traditional sense based on sending 2577 specialized "purge" packets. In other routing protocols such 2578 mechanism has proven to be complex and fragile based on many years of 2579 experience. RIFT simply issues a new, empty version of the TIE with 2580 a short lifetime and relies on each node to age out and delete such 2581 TIE copy independently. Abundant amounts of memory are available 2582 today even on low-end platforms and hence keeping those relatively 2583 short-lived extra copies for a while is acceptable. The information 2584 will age out and in the meantime all computations will deliver 2585 correct results if a node leaves the network due to the new 2586 information distributed by its adjacent nodes breaking bi-directional 2587 connectivity checks in different computations. 2589 Once a RIFT node issues a TIE with an ID, it SHOULD preserve the ID 2590 as long as feasible (also when the protocol restarts), even if the 2591 TIE looses all content. The re-advertisement of empty TIE fulfills 2592 the purpose of purging any information advertised in previous 2593 versions. The originator is free to not re-originate the according 2594 empty TIE again or originate an empty TIE with relatively short 2595 lifetime to prevent large number of long-lived empty stubs polluting 2596 the network. Each node MUST timeout and clean up the according empty 2597 TIEs independently. 2599 Upon restart a node MUST, as any link-state implementation, be 2600 prepared to receive TIEs with its own system ID and supersede them 2601 with equivalent, newly generated, empty TIEs with a higher sequence 2602 number. As above, the lifetime can be relatively short since it only 2603 needs to exceed the necessary propagation and processing delay by all 2604 the nodes that are within the TIE's flooding scope. 2606 TIE sequence numbers are rolled over using the method described in 2607 Appendix A. First sequence number of any spontaneously originated 2608 TIE (i.e. not originated to override a detected older copy in the 2609 network) MUST be a reasonably unpredictable random number in the 2610 interval [0, 2^10-1] which will prevent otherwise identical TIE 2611 headers to remain "stuck" in the network with content different from 2612 TIE originated after reboot. 2614 4.2.3.8. Southbound Default Route Origination 2616 Under certain conditions nodes issue a default route in their South 2617 Prefix TIEs with costs as computed in Section 4.3.6.1. 2619 A node X that 2621 1. is NOT overloaded AND 2623 2. has southbound or East-West adjacencies 2625 originates in its south prefix TIE such a default route IIF 2627 1. all other nodes at X's' level are overloaded OR 2629 2. all other nodes at X's' level have NO northbound adjacencies OR 2631 3. X has computed reachability to a default route during N-SPF. 2633 The term "all other nodes at X's' level" describes obviously just the 2634 nodes at the same level in the PoD with a viable lower level 2635 (otherwise the node South TIEs cannot be reflected and the nodes in 2636 e.g. PoD 1 and PoD 2 are "invisible" to each other). 2638 A node originating a southbound default route MUST install a default 2639 discard route if it did not compute a default route during N-SPF. 2641 4.2.3.9. Northbound TIE Flooding Reduction 2643 Section 1.4 of the Optimized Link State Routing Protocol [RFC3626] 2644 (OLSR) introduces the concept of a "multipoint relay" (MPR) that 2645 minimize the overhead of flooding messages in the network by reducing 2646 redundant retransmissions in the same region. 2648 A similar technique is applied to RIFT to control northbound 2649 flooding. Important observations first: 2651 1. a node MUST flood self-originated North TIEs to all the reachable 2652 nodes at the level above which we call the node's "parents"; 2654 2. it is typically not necessary that all parents reflood the North 2655 TIEs to achieve a complete flooding of all the reachable nodes 2656 two levels above which we choose to call the node's 2657 "grandparents"; 2659 3. to control the volume of its flooding two hops North and yet keep 2660 it robust enough, it is advantageous for a node to select a 2661 subset of its parents as "Flood Repeaters" (FRs), which combined 2662 together deliver two or more copies of its flooding to all of its 2663 parents, i.e. the originating node's grandparents; 2665 4. nodes at the same level do NOT have to agree on a specific 2666 algorithm to select the FRs, but overall load balancing should be 2667 achieved so that different nodes at the same level should tend to 2668 select different parents as FRs; 2670 5. there are usually many solutions to the problem of finding a set 2671 of FRs for a given node; the problem of finding the minimal set 2672 is (similar to) a NP-Complete problem and a globally optimal set 2673 may not be the minimal one if load-balancing with other nodes is 2674 an important consideration; 2676 6. it is expected that there will be often sets of equivalent nodes 2677 at a level L, defined as having a common set of parents at L+1. 2678 Applying this observation at both L and L+1, an algorithm may 2679 attempt to split the larger problem in a sum of smaller separate 2680 problems; 2682 7. it is another expectation that there will be from time to time a 2683 broken link between a parent and a grandparent, and in that case 2684 the parent is probably a poor FR due to its lower reliability. 2685 An algorithm may attempt to eliminate parents with broken 2686 northbound adjacencies first in order to reduce the number of 2687 FRs. Albeit it could be argued that relying on higher fanout FRs 2688 will slow flooding due to higher replication load reliability of 2689 FR's links seems to be a more pressing concern. 2691 In a fully connected Clos Network, this means that a node selects one 2692 arbitrary parent as FR and then a second one for redundancy. The 2693 computation can be kept relatively simple and completely distributed 2694 without any need for synchronization amongst nodes. In a "PoD" 2695 structure, where the Level L+2 is partitioned in silos of equivalent 2696 grandparents that are only reachable from respective parents, this 2697 means treating each silo as a fully connected Clos Network and solve 2698 the problem within the silo. 2700 In terms of signaling, a node has enough information to select its 2701 set of FRs; this information is derived from the node's parents' Node 2702 South TIEs, which indicate the parent's reachable northbound 2703 adjacencies to its own parents, i.e. the node's grandparents. A node 2704 may send a LIE to a northbound neighbor with the optional boolean 2705 field `you_are_flood_repeater` set to false, to indicate that the 2706 northbound neighbor is not a flood repeater for the node that sent 2707 the LIE. In that case the northbound neighbor SHOULD NOT reflood 2708 northbound TIEs received from the node that sent the LIE. If the 2709 `you_are_flood_repeater` is absent or if `you_are_flood_repeater` is 2710 set to true, then the northbound neighbor is a flood repeater for the 2711 node that sent the LIE and MUST reflood northbound TIEs received from 2712 that node. 2714 This specification proposes a simple default algorithm that SHOULD be 2715 implemented and used by default on every RIFT node. 2717 o let |NA(Node) be the set of Northbound adjacencies of node Node 2718 and CN(Node) be the cardinality of |NA(Node); 2720 o let |SA(Node) be the set of Southbound adjacencies of node Node 2721 and CS(Node) be the cardinality of |SA(Node); 2723 o let |P(Node) be the set of node Node's parents; 2725 o let |G(Node) be the set of node Node's grandparents. Observe 2726 that |G(Node) = |P(|P(Node)); 2728 o let N be the child node at level L computing a set of FR; 2730 o let P be a node at level L+1 and a parent node of N, i.e. bi- 2731 directionally reachable over adjacency A(N, P); 2733 o let G be a grandparent node of N, reachable transitively via a 2734 parent P over adjacencies ADJ(N, P) and ADJ(P, G). Observe that N 2735 does not have enough information to check bidirectional 2736 reachability of A(P, G); 2738 o let R be a redundancy constant integer; a value of 2 or higher for 2739 R is RECOMMENDED; 2741 o let S be a similarity constant integer; a value in range 0 .. 2 2742 for S is RECOMMENDED, the value of 1 SHOULD be used. Two 2743 cardinalities are considered as equivalent if their absolute 2744 difference is less than or equal to S, i.e. 2746 o |a-b|<=S. 2748 o let RND be a 64-bit random number generated by the system once on 2749 startup. 2751 The algorithm consists of the following steps: 2753 1. Derive a 64-bits number by XOR'ing 'N's system ID with RND. 2755 2. Derive a 16-bits pseudo-random unsigned integer PR(N) from the 2756 resulting 64-bits number by splitting it in 16-bits-long words 2757 W1, W2, W3, W4 (where W1 are the least significant 16 bits of the 2758 64-bits number, and W4 are the most significant 16 bits) and then 2759 XOR'ing the circularly shifted resulting words together: 2761 A. (W1<<1) xor (W2<<2) xor (W3<<3) xor (W4<<4); 2763 where << is the circular shift operator. 2765 3. Sort the parents by decreasing number of northbound adjacencies 2766 (using decreasing system id of the parent as tie-breaker): 2767 sort |P(N) by decreasing CN(P), for all P in |P(N), as ordered 2768 array |A(N) 2770 4. Partition |A(N) in subarrays |A_k(N) of parents with equivalent 2771 cardinality of northbound adjacencies (in other words with 2772 equivalent number of grandparents they can reach): 2774 A. set k=0; // k is the ID of the subarrray 2776 B. set i=0; 2778 C. while i < CN(N) do 2780 i) set j=i; 2782 ii) while i < CN(N) and CN(|A(N)[j]) - CN(|A(N)[i]) <= S 2784 a. place |A(N)[i] in |A_k(N) // abstract action, 2785 maybe noop 2787 b. set i=i+1; 2789 iii) /* At this point j is the index in |A(N) of the first 2790 member of |A_k(N) and (i-j) is C_k(N) defined as the 2791 cardinality of |A_k(N) */ 2793 set k=k+1; 2795 /* At this point k is the total number of subarrays, initialized 2796 for the shuffling operation below */ 2798 5. shuffle individually each subarrays |A_k(N) of cardinality C_k(N) 2799 within |A(N) using the Durstenfeld variation of Fisher-Yates 2800 algorithm that depends on N's System ID: 2802 A. while k > 0 do 2804 i) for i from C_k(N)-1 to 1 decrementing by 1 do 2806 a. set j to PR(N) modulo i; 2808 b. exchange |A_k[j] and |A_k[i]; 2810 ii) set k=k-1; 2812 6. For each grandparent G, initialize a counter c(G) with the number 2813 of its south-bound adjacencies to elected flood repeaters (which 2814 is initially zero): 2816 A. for each G in |G(N) set c(G) = 0; 2818 7. Finally keep as FRs only parents that are needed to maintain the 2819 number of adjacencies between the FRs and any grandparent G equal 2820 or above the redundancy constant R: 2822 A. for each P in reshuffled |A(N); 2824 i) if there exists an adjacency ADJ(P, G) in |NA(P) such 2825 that c(G) < R then 2827 a. place P in FR set; 2829 b. for all adjacencies ADJ(P, G') in |NA(P) increment 2830 c(G') 2832 B. If any c(G) is still < R, it was not possible to elect a set 2833 of FRs that covers all grandparents with redundancy R 2835 Additional rules for flooding reduction: 2837 1. The algorithm MUST be re-evaluated by a node on every change of 2838 local adjacencies or reception of a parent South TIE with changed 2839 adjacencies. A node MAY apply a hysteresis to prevent excessive 2840 amount of computation during periods of network instability just 2841 like in case of reachability computation. 2843 2. Upon a change of the flood repeater set, a node SHOULD send out 2844 LIEs that grant flood repeater status to newly promoted nodes 2845 before it sends LIEs that revoke the status to the nodes that 2846 have been newly demoted. This is done to prevent transient 2847 behavior where the full coverage of grandparents is not 2848 guaranteed. Such a condition is sometimes unavoidable in case of 2849 lost LIEs but it will correct itself though at possible transient 2850 hit in flooding propagation speeds. 2852 3. A node MUST always flood its self-originated TIEs. 2854 4. A node receiving a TIE originated by a node for which it is not a 2855 flood repeater SHOULD NOT reflood such TIEs to its neighbors 2856 except for rules in Paragraph 6. 2858 5. The indication of flood reduction capability MUST be carried in 2859 the node TIEs and MAY be used to optimize the algorithm to 2860 account for nodes that will flood regardless. 2862 6. A node generates TIDEs as usual but when receiving TIREs or TIDEs 2863 resulting in requests for a TIE of which the newest received copy 2864 came on an adjacency where the node was not flood repeater it 2865 SHOULD ignore such requests on first and only first request. 2866 Normally, the nodes that received the TIEs as flooding repeaters 2867 should satisfy the requesting node and with that no further TIREs 2868 for such TIEs will be generated. Otherwise, the next set of 2869 TIDEs and TIREs MUST lead to flooding independent of the flood 2870 repeater status. This solves a very difficult incast problem on 2871 nodes restarting with a very wide fanout, especially northbound. 2872 To retrieve the full database they often end up processing many 2873 in-rushing copies whereas this approach load-balances the 2874 incoming database between adjacent nodes and flood repeaters 2875 should guarantee that two copies are sent by different nodes to 2876 ensure against any losses. 2878 4.2.3.10. Special Considerations 2880 First, due to the distributed, asynchronous nature of ZTP, it can 2881 create temporary convergence anomalies where nodes at higher levels 2882 of the fabric temporarily see themselves lower than they belong. 2883 Since flooding can begin before ZTP is "finished" and in fact must do 2884 so given there is no global termination criteria, information may end 2885 up in wrong layers. A special clause when changing level takes care 2886 of that. 2888 More difficult is a condition where a node (e.g. a leaf) floods a TIE 2889 north towards its grandparent, then its parent reboots, in fact 2890 partitioning the grandparent from leaf directly and then the leaf 2891 itself reboots. That can leave the grandparent holding the "primary 2892 copy" of the leaf's TIE. Normally this condition is resolved easily 2893 by the leaf re-originating its TIE with a higher sequence number than 2894 it sees in northbound TIEs, here however, when the parent comes back 2895 it won't be able to obtain leaf's North TIE from the grandparent 2896 easily and with that the leaf may not issue the TIE with a higher 2897 sequence number that can reach the granparent for a long time. 2898 Flooding procedures are extended to deal with the problem by the 2899 means of special clauses that override the database of a lower level 2900 with headers of newer TIEs seen in TIDEs coming from the north. 2902 4.2.4. Reachability Computation 2904 A node has three possible sources of relevant information for 2905 reachability computation. A node knows the full topology south of it 2906 from the received North Node TIEs or alternately north of it from the 2907 South Node TIEs. A node has the set of prefixes with their 2908 associated distances and bandwidths from corresponding prefix TIEs. 2910 To compute prefix reachability, a node runs conceptually a northbound 2911 and a southbound SPF. We call that N-SPF and S-SPF denoting the 2912 direction in which the computation front is progressing. 2914 Since neither computation can "loop", it is possible to compute non- 2915 equal-cost or even k-shortest paths [EPPSTEIN] and "saturate" the 2916 fabric to the extent desired but we use simple, familiar SPF 2917 algorithms and concepts here as example due to their prevalence in 2918 today's routing. 2920 4.2.4.1. Northbound SPF 2922 N-SPF MUST use exclusively northbound and East-West adjacencies in 2923 the computing node's node North TIEs (since if the node is a leaf it 2924 may not have generated a node South TIE) when starting SPF. Observe 2925 that N-SPF is really just a one hop variety since Node South TIEs are 2926 not re-flooded southbound beyond a single level (or East-West) and 2927 with that the computation cannot progress beyond adjacent nodes. 2929 Once progressing, we are using the next higher level's node South 2930 TIEs to find according adjacencies to verify backlink connectivity. 2931 Just as in case of IS-IS or OSPF, two unidirectional links MUST be 2932 associated together to confirm bidirectional connectivity. 2933 Particular care MUST be paid that the Node TIEs do not only contain 2934 the correct system IDs but matching levels as well. 2936 Default route found when crossing an E-W link SHOULD be used IIF 2938 1. the node itself does NOT have any northbound adjacencies AND 2940 2. the adjacent node has one or more northbound adjacencies 2941 This rule forms a "one-hop default route split-horizon" and prevents 2942 looping over default routes while allowing for "one-hop protection" 2943 of nodes that lost all northbound adjacencies except at Top-of-Fabric 2944 where the links are used exclusively to flood topology information in 2945 multi-plane designs. 2947 Other south prefixes found when crossing E-W link MAY be used IIF 2949 1. no north neighbors are advertising same or supersuming non- 2950 default prefix AND 2952 2. the node does not originate a non-default supersuming prefix 2953 itself. 2955 i.e. the E-W link can be used as a gateway of last resort for a 2956 specific prefix only. Using south prefixes across E-W link can be 2957 beneficial e.g. on automatic de-aggregation in pathological fabric 2958 partitioning scenarios. 2960 A detailed example can be found in Section 5.4. 2962 4.2.4.2. Southbound SPF 2964 S-SPF MUST use exclusively the southbound adjacencies in the node 2965 South TIEs, i.e. progresses towards nodes at lower levels. Observe 2966 that E-W adjacencies are NEVER used in the computation. This 2967 enforces the requirement that a packet traversing in a southbound 2968 direction must never change its direction. 2970 S-SPF MUST use northbound adjacencies in node North TIEs to verify 2971 backlink connectivity by checking for presence of the link beside 2972 correct SystemID and level. 2974 4.2.4.3. East-West Forwarding Within a non-ToF Level 2976 Using south prefixes over horizontal links MAY occur if the N-SPF 2977 includes East-West adjacencies in computation. It can protect 2978 against pathological fabric partitioning cases that leave only paths 2979 to destinations that would necessitate multiple changes of forwarding 2980 direction between north and south. 2982 4.2.4.4. East-West Links Within ToF Level 2984 E-W ToF links behave in terms of flooding scopes defined in 2985 Section 4.2.3.4 like northbound links and MUST be used exclusively 2986 for control plane information flooding. Even though a ToF node could 2987 be tempted to use those links during southbound SPF and carry traffic 2988 over them this MUST NOT be attempted since it may lead in, e.g. 2990 anycast cases to routing loops. An implementation MAY try to resolve 2991 the looping problem by following on the ring strictly tie-broken 2992 shortest-paths only but the details are outside this specification. 2993 And even then, the problem of proper capacity provisioning of such 2994 links when they become traffic-bearing in case of failures is vexing. 2996 4.2.5. Automatic Disaggregation on Link & Node Failures 2998 4.2.5.1. Positive, Non-transitive Disaggregation 3000 Under normal circumstances, node's South TIEs contain just the 3001 adjacencies and a default route. However, if a node detects that its 3002 default IP prefix covers one or more prefixes that are reachable 3003 through it but not through one or more other nodes at the same level, 3004 then it MUST explicitly advertise those prefixes in an South TIE. 3005 Otherwise, some percentage of the northbound traffic for those 3006 prefixes would be sent to nodes without according reachability, 3007 causing it to be black-holed. Even when not black-holing, the 3008 resulting forwarding could 'backhaul' packets through the higher 3009 level spines, clearly an undesirable condition affecting the blocking 3010 probabilities of the fabric. 3012 We refer to the process of advertising additional prefixes southbound 3013 as 'positive de-aggregation' or 'positive dis-aggregation'. Such 3014 dis-aggregation is non-transitive, i.e. its' effects are always 3015 contained to a single level of the fabric only. Naturally, multiple 3016 node or link failures can lead to several independent instances of 3017 positive dis-aggregation necessary to prevent looping or bow-tying 3018 the fabric. 3020 A node determines the set of prefixes needing de-aggregation using 3021 the following steps: 3023 1. A DAG computation in the southern direction is performed first, 3024 i.e. the North TIEs are used to find all of prefixes it can reach 3025 and the set of next-hops in the lower level for each of them. 3026 Such a computation can be easily performed on a fat tree by e.g. 3027 setting all link costs in the southern direction to 1 and all 3028 northern directions to infinity. We term set of those 3029 prefixes |R, and for each prefix, r, in |R, we define its set of 3030 next-hops to be |H(r). 3032 2. The node uses reflected South TIEs to find all nodes at the same 3033 level in the same PoD and the set of southbound adjacencies for 3034 each. The set of nodes at the same level is termed |N and for 3035 each node, n, in |N, we define its set of southbound adjacencies 3036 to be |A(n). 3038 3. For a given r, if the intersection of |H(r) and |A(n), for any n, 3039 is null then that prefix r must be explicitly advertised by the 3040 node in an South TIE. 3042 3. 3044 4. Identical set of de-aggregated prefixes is flooded on each of the 3045 node's southbound adjacencies. In accordance with the normal 3046 flooding rules for an South TIE, a node at the lower level that 3047 receives this South TIE SHOULD NOT propagate it south-bound or 3048 reflect the disaggregated prefixes back over its adjacencies to 3049 nodes at the level from which it was received. 3051 To summarize the above in simplest terms: if a node detects that its 3052 default route encompasses prefixes for which one of the other nodes 3053 in its level has no possible next-hops in the level below, it has to 3054 disaggregate it to prevent black-holing or suboptimal routing through 3055 such nodes. Hence a node X needs to determine if it can reach a 3056 different set of south neighbors than other nodes at the same level, 3057 which are connected to it via at least one common south neighbor. If 3058 it can, then prefix disaggregation may be required. If it can't, 3059 then no prefix disaggregation is needed. An example of 3060 disaggregation is provided in Section 5.3. 3062 A possible algorithm is described last: 3064 1. Create partial_neighbors = (empty), a set of neighbors with 3065 partial connectivity to the node X's level from X's perspective. 3066 Each entry in the set is a south neighbor of X and a list of 3067 nodes of X.level that can't reach that neighbor. 3069 2. A node X determines its set of southbound neighbors 3070 X.south_neighbors. 3072 3. For each South TIE originated from a node Y that X has which is 3073 at X.level, if Y.south_neighbors is not the same as 3074 X.south_neighbors but the nodes share at least one southern 3075 neighbor, for each neighbor N in X.south_neighbors but not in 3076 Y.south_neighbors, add (N, (Y)) to partial_neighbors if N isn't 3077 there or add Y to the list for N. 3079 4. If partial_neighbors is empty, then node X does not disaggregate 3080 any prefixes. If node X is advertising disaggregated prefixes in 3081 its South TIE, X SHOULD remove them and re-advertise its 3082 according South TIEs. 3084 A node X computes reachability to all nodes below it based upon the 3085 received North TIEs first. This results in a set of routes, each 3086 categorized by (prefix, path_distance, next-hop-set). Alternately, 3087 for clarity in the following procedure, these can be organized by 3088 next-hop-set as ( (next-hops), {(prefix, path_distance)}). If 3089 partial_neighbors isn't empty, then the following procedure describes 3090 how to identify prefixes to disaggregate. 3092 disaggregated_prefixes = { empty } 3093 nodes_same_level = { empty } 3094 for each South TIE 3095 if (South TIE.level == X.level and 3096 X shares at least one S-neighbor with X) 3097 add South TIE.originator to nodes_same_level 3098 end if 3099 end for 3101 for each next-hop-set NHS 3102 isolated_nodes = nodes_same_level 3103 for each NH in NHS 3104 if NH in partial_neighbors 3105 isolated_nodes = 3106 intersection(isolated_nodes, 3107 partial_neighbors[NH].nodes) 3108 end if 3109 end for 3111 if isolated_nodes is not empty 3112 for each prefix using NHS 3113 add (prefix, distance) to disaggregated_prefixes 3114 end for 3115 end if 3116 end for 3118 copy disaggregated_prefixes to X's South TIE 3119 if X's South TIE is different 3120 schedule South TIE for flooding 3121 end if 3123 Figure 15: Computation of Disaggregated Prefixes 3125 Each disaggregated prefix is sent with the according path_distance. 3126 This allows a node to send the same South TIE to each south neighbor. 3127 The south neighbor which is connected to that prefix will thus have a 3128 shorter path. 3130 Finally, to summarize the less obvious points partially omitted in 3131 the algorithms to keep them more tractable: 3133 1. all neighbor relationships MUST perform backlink checks. 3135 2. overload bits as introduced in Section 4.3.1 have to be respected 3136 during the computation. 3138 3. all the lower level nodes are flooded the same disaggregated 3139 prefixes since we don't want to build an South TIE per node and 3140 complicate things unnecessarily. The lower level node that can 3141 compute a southbound route to the prefix will prefer it to the 3142 disaggregated route anyway based on route preference rules. 3144 4. positively disaggregated prefixes do NOT have to propagate to 3145 lower levels. With that the disturbance in terms of new flooding 3146 is contained to a single level experiencing failures. 3148 5. disaggregated Prefix South TIEs are not "reflected" by the lower 3149 level, i.e. nodes within same level do NOT need to be aware 3150 which node computed the need for disaggregation. 3152 6. The fabric is still supporting maximum load balancing properties 3153 while not trying to send traffic northbound unless necessary. 3155 In case positive disaggregation is triggered and due to the very 3156 stable but un-synchronized nature of the algorithm the nodes may 3157 issue the necessary disaggregated prefixes at different points in 3158 time. This can lead for a short time to an "incast" behavior where 3159 the first advertising router based on the nature of longest prefix 3160 match will attract all the traffic. An implementation MAY hence 3161 choose different strategies to address this behavior if needed. 3163 To close this section it is worth to observe that in a single plane 3164 ToF this disaggregation prevents blackholing up to (K_LEAF * P) link 3165 failures in terms of Section 4.1.2 or in other terms, it takes at 3166 minimum that many link failures to partition the ToF into multiple 3167 planes. 3169 4.2.5.2. Negative, Transitive Disaggregation for Fallen Leaves 3171 As explained in Section 4.1.3 failures in multi-plane Top-of-Fabric 3172 or more than (K_LEAF * P) links failing in single plane design can 3173 generate fallen leaves. Such scenario cannot be addressed by 3174 positive disaggregation only and needs a further mechanism. 3176 4.2.5.2.1. Cabling of Multiple Top-of-Fabric Planes 3178 Let us return in this section to designs with multiple planes as 3179 shown in Figure 3. Figure 16 highlights how the ToF is cabled in 3180 case of two planes by the means of dual-rings to distribute all the 3181 North TIEs within both planes. For people familiar with traditional 3182 link-state routing protocols ToF level can be considered equivalent 3183 to area 0 in OSPF or level-2 in ISIS which need to be "connected" as 3184 well for the protocol to operate correctly. 3186 . ++==========++ ++==========++ 3187 . II II II II 3188 .+----++--+ +----++--+ +----++--+ +----++--+ 3189 .|ToF A1| |ToF B1| |ToF B2| |ToF A2| 3190 .++-+-++--+ ++-+-++--+ ++-+-++--+ ++-+-++--+ 3191 . | | II | | II | | II | | II 3192 . | | ++==========++ | | ++==========++ 3193 . | | | | | | | | 3194 . 3195 . ~~~ Highlighted ToF of the previous multi-plane figure ~~ 3197 Figure 16: Topologically connected planes 3199 As described in Section 4.1.3 failures in multi-plane fabrics can 3200 lead to blackholes which normal positive disaggregation cannot fix. 3201 The mechanism of negative, transitive disaggregation incorporated in 3202 RIFT provides the according solution. 3204 4.2.5.2.2. Transitive Advertisement of Negative Disaggregates 3206 A ToF node that discovers that it cannot reach a fallen leaf 3207 disaggregates all the prefixes of such leaves. It uses for that 3208 purpose negative prefix South TIEs that are, as usual, flooded 3209 southwards with the scope defined in Section 4.2.3.4. 3211 Transitively, a node explicitly loses connectivity to a prefix when 3212 none of its children advertises it and when the prefix is negatively 3213 disaggregated by all of its parents. When that happens, the node 3214 originates the negative prefix further down south. Since the 3215 mechanism applies recursively south the negative prefix may propagate 3216 transitively all the way down to the leaf. This is necessary since 3217 leaves connected to multiple planes by means of disjoint paths may 3218 have to choose the correct plane already at the very bottom of the 3219 fabric to make sure that they don't send traffic towards another leaf 3220 using a plane where it is "fallen" at which in point a blackhole is 3221 unavoidable. 3223 When the connectivity is restored, a node that disaggregated a prefix 3224 withdraws the negative disaggregation by the usual mechanism of re- 3225 advertising TIEs omitting the negative prefix. 3227 4.2.5.2.3. Computation of Negative Disaggregates 3229 The document omitted so far the description of the computation 3230 necessary to generate the correct set of negative prefixes. Negative 3231 prefixes can in fact be advertised due to two different triggers. We 3232 describe them consecutively. 3234 The first origination reason is a computation that uses all the node 3235 North TIEs to build the set of all reachable nodes by reachability 3236 computation over the complete graph and including ToF links. The 3237 computation uses the node itself as root. This is compared with the 3238 result of the normal southbound SPF as described in Section 4.2.4.2. 3239 The difference are the fallen leaves and all their attached prefixes 3240 are advertised as negative prefixes southbound if the node does not 3241 see the prefix being reachable within southbound SPF. 3243 The second mechanism hinges on the understanding how the negative 3244 prefixes are used within the computation as described in Figure 17. 3245 When attaching the negative prefixes at certain point in time the 3246 negative prefix may find itself with all the viable nodes from the 3247 shorter match nexthop being pruned. In other words, all its 3248 northbound neighbors provided a negative prefix advertisement. This 3249 is the trigger to advertise this negative prefix transitively south 3250 and normally caused by the node being in a plane where the prefix 3251 belongs to a fabric leaf that has "fallen" in this plane. Obviously, 3252 when one of the northbound switches withdraws its negative 3253 advertisement, the node has to withdraw its transitively provided 3254 negative prefix as well. 3256 4.2.6. Attaching Prefixes 3258 After SPF is run, it is necessary to attach the resulting 3259 reachability information in form of prefixes. For S-SPF, prefixes 3260 from an North TIE are attached to the originating node with that 3261 node's next-hop set and a distance equal to the prefix's cost plus 3262 the node's minimized path distance. The RIFT route database, a set 3263 of (prefix, prefix-type, attributes, path_distance, next-hop set), 3264 accumulates these results. 3266 In case of N-SPF prefixes from each South TIE need to also be added 3267 to the RIFT route database. The N-SPF is really just a stub so the 3268 computing node needs simply to determine, for each prefix in an South 3269 TIE that originated from adjacent node, what next-hops to use to 3270 reach that node. Since there may be parallel links, the next-hops to 3271 use can be a set; presence of the computing node in the associated 3272 Node South TIE is sufficient to verify that at least one link has 3273 bidirectional connectivity. The set of minimum cost next-hops from 3274 the computing node X to the originating adjacent node is determined. 3276 Each prefix has its cost adjusted before being added into the RIFT 3277 route database. The cost of the prefix is set to the cost received 3278 plus the cost of the minimum distance next-hop to that neighbor while 3279 taking into account its attributes such as mobility per 3280 Section 4.3.3. Then each prefix can be added into the RIFT route 3281 database with the next_hop_set; ties are broken based upon type first 3282 and then distance and further on `PrefixAttributes` and only the best 3283 combination is used for forwarding. RIFT route preferences are 3284 normalized by the according Thrift [thrift] model type. 3286 An example implementation for node X follows: 3288 for each South TIE 3289 if South TIE.level > X.level 3290 next_hop_set = set of minimum cost links to the 3291 South TIE.originator 3292 next_hop_cost = minimum cost link to 3293 South TIE.originator 3294 end if 3295 for each prefix P in the South TIE 3296 P.cost = P.cost + next_hop_cost 3297 if P not in route_database: 3298 add (P, P.cost, P.type, 3299 P.attributes, next_hop_set) to route_database 3300 end if 3301 if (P in route_database): 3302 if route_database[P].cost > P.cost or 3303 route_database[P].type > P.type: 3304 update route_database[P] with (P, P.type, P.cost, 3305 P.attributes, 3306 next_hop_set) 3307 else if route_database[P].cost == P.cost and 3308 route_database[P].type == P.type: 3309 update route_database[P] with (P, P.type, 3310 P.cost, P.attributes, 3311 merge(next_hop_set, route_database[P].next_hop_set)) 3312 else 3313 // Not preferred route so ignore 3314 end if 3315 end if 3316 end for 3317 end for 3319 Figure 17: Adding Routes from South TIE Positive and Negative 3320 Prefixes 3322 After the positive prefixes are attached and tie-broken, negative 3323 prefixes are attached and used in case of northbound computation, 3324 ideally from the shortest length to the longest. The nexthop 3325 adjacencies for a negative prefix are inherited from the longest 3326 positive prefix that aggregates it, and subsequently adjacencies to 3327 nodes that advertised negative for this prefix are removed. 3329 The rule of inheritance MUST be maintained when the nexthop list for 3330 a prefix is modified, as the modification may affect the entries for 3331 matching negative prefixes of immediate longer prefix length. For 3332 instance, if a nexthop is added, then by inheritance it must be added 3333 to all the negative routes of immediate longer prefixes length unless 3334 it is pruned due to a negative advertisement for the same next hop. 3335 Similarly, if a nexthop is deleted for a given prefix, then it is 3336 deleted for all the immediately aggregated negative routes. This 3337 will recurse in the case of nested negative prefix aggregations. 3339 The rule of inheritance must also be maintained when a new prefix of 3340 intermediate length is inserted, or when the immediately aggregating 3341 prefix is deleted from the routing table, making an even shorter 3342 aggregating prefix the one from which the negative routes now inherit 3343 their adjacencies. As the aggregating prefix changes, all the 3344 negative routes must be recomputed, and then again the process may 3345 recurse in case of nested negative prefix aggregations. 3347 Although these operations can be computationally expensive, the 3348 overall load on devices in the network is low because these 3349 computations are not run very often, as positive route advertisements 3350 are always preferred over negative ones. This prevents recursion in 3351 most cases because positive reachability information never inherits 3352 next hops. 3354 To make the negative disaggregation less abstract and provide an 3355 example let us consider a ToP node T1 with 4 ToF parents S1..S4 as 3356 represented in Figure 18: 3358 +----+ +----+ +----+ +----+ N 3359 | S1 | | S1 | | S1 | | S1 | ^ 3360 +----+ +----+ +----+ +----+ W< + >E 3361 | | | | v 3362 |+--------+ | | S 3363 ||+-----------------+ | 3364 |||+----------------+---------+ 3365 |||| 3366 +----+ 3367 | T1 | 3368 +----+ 3370 Figure 18: A ToP node with 4 parents 3372 If all ToF nodes can reach all the prefixes in the network; with 3373 RIFT, they will normally advertise a default route south. An 3374 abstract Routing Information Base (RIB), more commonly known as a 3375 routing table, stores all types of maintained routes including the 3376 negative ones and "tie-breaks" for the best one, whereas an abstract 3377 Forwarding table (FIB) retains only the ultimately computed 3378 "positive" routing instructions. In T1, those tables would look as 3379 illustrated in Figure 19: 3381 +---------+ 3382 | Default | 3383 +---------+ 3384 | 3385 | +--------+ 3386 +---> | Via S1 | 3387 | +--------+ 3388 | 3389 | +--------+ 3390 +---> | Via S2 | 3391 | +--------+ 3392 | 3393 | +--------+ 3394 +---> | Via S3 | 3395 | +---------+ 3396 | 3397 | +--------+ 3398 +---> | Via S4 | 3399 +--------+ 3401 Figure 19: Abstract RIB 3403 In case T1 receives a negative advertisement for prefix 2001:db8::/32 3404 from S1 a negative route is stored in the RIB (indicated by a ~ 3405 sign), while the more specific routes to the complementing ToF nodes 3406 are installed in FIB. RIB and FIB in T1 now look as illustrated in 3407 Figure 20 and Figure 21, respectively: 3409 +---------+ +-----------------+ 3410 | Default | <-------------- | ~2001:db8::/32 | 3411 +---------+ +-----------------+ 3412 | | 3413 | +--------+ | +--------+ 3414 +---> | Via S1 | +---> | Via S1 | 3415 | +--------+ +--------+ 3416 | 3417 | +--------+ 3418 +---> | Via S2 | 3419 | +--------+ 3420 | 3421 | +--------+ 3422 +---> | Via S3 | 3423 | +---------+ 3424 | 3425 | +--------+ 3426 +---> | Via S4 | 3427 +--------+ 3429 Figure 20: Abstract RIB after negative 2001:db8::/32 from S1 3431 The negative 2001:db8::/32 prefix entry inherits from ::/0, so the 3432 positive more specific routes are the complements to S1 in the set of 3433 next-hops for the default route. That entry is composed of S2, S3, 3434 and S4, or, in other words, it uses all entries the the default route 3435 with a "hole punched" for S1 into them. These are the next hops that 3436 are still available to reach 2001:db8::/32, now that S1 advertised 3437 that it will not forward 2001:db8::/32 anymore. Ultimately, those 3438 resulting next-hops are installed in FIB for the more specific route 3439 to 2001:db8::/32 as illustrated below: 3441 +---------+ +---------------+ 3442 | Default | | 2001:db8::/32 | 3443 +---------+ +---------------+ 3444 | | 3445 | +--------+ | 3446 +---> | Via S1 | | 3447 | +--------+ | 3448 | | 3449 | +--------+ | +--------+ 3450 +---> | Via S2 | +---> | Via S2 | 3451 | +--------+ | +--------+ 3452 | | 3453 | +--------+ | +--------+ 3454 +---> | Via S3 | +---> | Via S3 | 3455 | +--------+ | +--------+ 3456 | | 3457 | +--------+ | +--------+ 3458 +---> | Via S4 | +---> | Via S4 | 3459 +--------+ +--------+ 3461 Figure 21: Abstract FIB after negative 2001:db8::/32 from S1 3463 To illustrate matters further let us consider T1 receiving a negative 3464 advertisement for prefix 2001:db8:1::/48 from S2, which is stored in 3465 RIB again. After the update, the RIB in T1 is illustrated in 3466 Figure 22: 3468 +---------+ +----------------+ +------------------+ 3469 | Default | <----- | ~2001:db8::/32 | <------ | ~2001:db8:1::/48 | 3470 +---------+ +----------------+ +------------------+ 3471 | | | 3472 | +--------+ | +--------+ | 3473 +---> | Via S1 | +---> | Via S1 | | 3474 | +--------+ +--------+ | 3475 | | 3476 | +--------+ | +--------+ 3477 +---> | Via S2 | +---> | Via S2 | 3478 | +--------+ +--------+ 3479 | 3480 | +--------+ 3481 +---> | Via S3 | 3482 | +---------+ 3483 | 3484 | +--------+ 3485 +---> | Via S4 | 3486 +--------+ 3488 Figure 22: Abstract RIB after negative 2001:db8:1::/48 from S2 3490 Negative 2001:db8:1::/48 inherits from 2001:db8::/32 now, so the 3491 positive more specific routes are the complements to S2 in the set of 3492 next hops for 2001:db8::/32, which are S3 and S4, or, in other words, 3493 all entries of the parent with the negative holes "punched in" again. 3494 After the update, the FIB in T1 shows as illustrated in Figure 23: 3496 +---------+ +---------------+ +-----------------+ 3497 | Default | | 2001:db8::/32 | | 2001:db8:1::/48 | 3498 +---------+ +---------------+ +-----------------+ 3499 | | | 3500 | +--------+ | | 3501 +---> | Via S1 | | | 3502 | +--------+ | | 3503 | | | 3504 | +--------+ | +--------+ | 3505 +---> | Via S2 | +---> | Via S2 | | 3506 | +--------+ | +--------+ | 3507 | | | 3508 | +--------+ | +--------+ | +--------+ 3509 +---> | Via S3 | +---> | Via S3 | +---> | Via S3 | 3510 | +--------+ | +--------+ | +--------+ 3511 | | | 3512 | +--------+ | +--------+ | +--------+ 3513 +---> | Via S4 | +---> | Via S4 | +---> | Via S4 | 3514 +--------+ +--------+ +--------+ 3516 Figure 23: Abstract FIB after negative 2001:db8:1::/48 from S2 3518 Further, let us say that S3 stops advertising its service as default 3519 gateway. The entry is removed from RIB as usual. In order to update 3520 the FIB, it is necessary to eliminate the FIB entry for the default 3521 route, as well as all the FIB entries that were created for negative 3522 routes pointing to the RIB entry being removed (::/0). This is done 3523 recursively for 2001:db8::/32 and then for, 2001:db8:1::/48. The 3524 related FIB entries via S3 are removed, as illustrated in Figure 24. 3526 +---------+ +---------------+ +-----------------+ 3527 | Default | | 2001:db8::/32 | | 2001:db8:1::/48 | 3528 +---------+ +---------------+ +-----------------+ 3529 | | | 3530 | +--------+ | | 3531 +---> | Via S1 | | | 3532 | +--------+ | | 3533 | | | 3534 | +--------+ | +--------+ | 3535 +---> | Via S2 | +---> | Via S2 | | 3536 | +--------+ | +--------+ | 3537 | | | 3538 | | | 3539 | | | 3540 | | | 3541 | | | 3542 | +--------+ | +--------+ | +--------+ 3543 +---> | Via S4 | +---> | Via S4 | +---> | Via S4 | 3544 +--------+ +--------+ +--------+ 3546 Figure 24: Abstract FIB after loss of S3 3548 Say that at that time, S4 would also disaggregate prefix 3549 2001:db8:1::/48. This would mean that the FIB entry for 3550 2001:db8:1::/48 becomes a discard route, and that would be the signal 3551 for T1 to disaggregate prefix 2001:db8:1::/48 negatively in a 3552 transitive fashion with its own children. 3554 Finally, let us look at the case where S3 becomes available again as 3555 a default gateway, and a negative advertisement is received from S4 3556 about prefix 2001:db8:2::/48 as opposed to 2001:db8:1::/48. Again, a 3557 negative route is stored in the RIB, and the more specific route to 3558 the complementing ToF nodes are installed in FIB. Since 3559 2001:db8:2::/48 inherits from 2001:db8::/32, the positive FIB routes 3560 are chosen by removing S4 from S2, S3, S4. The abstract FIB in T1 3561 now shows as illustrated in Figure 25: 3563 +-----------------+ 3564 | 2001:db8:2::/48 | 3565 +-----------------+ 3566 | 3567 +---------+ +---------------+ +-----------------+ 3568 | Default | | 2001:db8::/32 | | 2001:db8:1::/48 | 3569 +---------+ +---------------+ +-----------------+ 3570 | | | | 3571 | +--------+ | | | +--------+ 3572 +---> | Via S1 | | | +---> | Via S2 | 3573 | +--------+ | | | +--------+ 3574 | | | | 3575 | +--------+ | +--------+ | | +--------+ 3576 +---> | Via S2 | +---> | Via S2 | | +---> | Via S3 | 3577 | +--------+ | +--------+ | +--------+ 3578 | | | 3579 | +--------+ | +--------+ | +--------+ 3580 +---> | Via S3 | +---> | Via S3 | +---> | Via S3 | 3581 | +--------+ | +--------+ | +--------+ 3582 | | | 3583 | +--------+ | +--------+ | +--------+ 3584 +---> | Via S4 | +---> | Via S4 | +---> | Via S4 | 3585 +--------+ +--------+ +--------+ 3587 Figure 25: Abstract FIB after negative 2001:db8:2::/48 from S4 3589 4.2.7. Optional Zero Touch Provisioning (ZTP) 3591 Each RIFT node can operate in zero touch provisioning (ZTP) mode, 3592 i.e. it has no configuration (unless it is a Top-of-Fabric at the top 3593 of the topology or the must operate in the topology as leaf and/or 3594 support leaf-2-leaf procedures) and it will fully configure itself 3595 after being attached to the topology. Configured nodes and nodes 3596 operating in ZTP can be mixed and will form a valid topology if 3597 achievable. 3599 The derivation of the level of each node happens based on offers 3600 received from its neighbors whereas each node (with possibly 3601 exceptions of configured leaves) tries to attach at the highest 3602 possible point in the fabric. This guarantees that even if the 3603 diffusion front reaches a node from "below" faster than from "above", 3604 it will greedily abandon already negotiated level derived from nodes 3605 topologically below it and properly peers with nodes above. 3607 The fabric is very consciously numbered from the top to allow for 3608 PoDs of different heights and minimize number of provisioning 3609 necessary, in this case just a TOP_OF_FABRIC flag on every node at 3610 the top of the fabric. 3612 This section describes the necessary concepts and procedures for ZTP 3613 operation. 3615 4.2.7.1. Terminology 3617 The interdependencies between the different flags and the configured 3618 level can be somewhat vexing at first and it may take multiple reads 3619 of the glossary to comprehend them. 3621 Automatic Level Derivation: Procedures which allow nodes without 3622 level configured to derive it automatically. Only applied if 3623 CONFIGURED_LEVEL is undefined. 3625 UNDEFINED_LEVEL: A "null" value that indicates that the level has 3626 not been determined and has not been configured. Schemas normally 3627 indicate that by a missing optional value without an available 3628 defined default. 3630 LEAF_ONLY: An optional configuration flag that can be configured on 3631 a node to make sure it never leaves the "bottom of the hierarchy". 3632 TOP_OF_FABRIC flag and CONFIGURED_LEVEL cannot be defined at the 3633 same time as this flag. It implies CONFIGURED_LEVEL value of 0. 3635 TOP_OF_FABRIC flag: Configuration flag that MUST be provided to all 3636 Top-of-Fabric nodes. LEAF_FLAG and CONFIGURED_LEVEL cannot be 3637 defined at the same time as this flag. It implies a 3638 CONFIGURED_LEVEL value. In fact, it is basically a shortcut for 3639 configuring same level at all Top-of-Fabric nodes which is 3640 unavoidable since an initial 'seed' is needed for other ZTP nodes 3641 to derive their level in the topology. The flag plays an 3642 important role in fabrics with multiple planes to enable 3643 successful negative disaggregation (Section 4.2.5.2). 3645 CONFIGURED_LEVEL: A level value provided manually. When this is 3646 defined (i.e. it is not an UNDEFINED_LEVEL) the node is not 3647 participating in ZTP. TOP_OF_FABRIC flag is ignored when this 3648 value is defined. LEAF_ONLY can be set only if this value is 3649 undefined or set to 0. 3651 DERIVED_LEVEL: Level value computed via automatic level derivation 3652 when CONFIGURED_LEVEL is equal to UNDEFINED_LEVEL. 3654 LEAF_2_LEAF: An optional flag that can be configured on a node to 3655 make sure it supports procedures defined in Section 4.3.8. In a 3656 strict sense it is a capability that implies LEAF_ONLY and the 3657 according restrictions. TOP_OF_FABRIC flag is ignored when set at 3658 the same time as this flag. 3660 LEVEL_VALUE: In ZTP case the original definition of "level" in 3661 Section 3.1 is both extended and relaxed. First, level is defined 3662 now as LEVEL_VALUE and is the first defined value of 3663 CONFIGURED_LEVEL followed by DERIVED_LEVEL. Second, it is 3664 possible for nodes to be more than one level apart to form 3665 adjacencies if any of the nodes is at least LEAF_ONLY. 3667 Valid Offered Level (VOL): A neighbor's level received on a valid 3668 LIE (i.e. passing all checks for adjacency formation while 3669 disregarding all clauses involving level values) persisting for 3670 the duration of the holdtime interval on the LIE. Observe that 3671 offers from nodes offering level value of 0 do not constitute VOLs 3672 (since no valid DERIVED_LEVEL can be obtained from those and 3673 consequently `not_a_ztp_offer` MUST be ignored). Offers from LIEs 3674 with `not_a_ztp_offer` being true are not VOLs either. If a node 3675 maintains parallel adjacencies to the neighbor, VOL on each 3676 adjacency is considered as equivalent, i.e. the newest VOL from 3677 any such adjacency updates the VOL received from the same node. 3679 Highest Available Level (HAL): Highest defined level value seen from 3680 all VOLs received. 3682 Highest Available Level Systems (HALS): Set of nodes offering HAL 3683 VOLs. 3685 Highest Adjacency Three Way (HAT): Highest neighbor level of all the 3686 formed three way adjacencies for the node. 3688 4.2.7.2. Automatic SystemID Selection 3690 RIFT nodes require a 64 bit SystemID which SHOULD be derived as 3691 EUI-64 MA-L derive according to [EUI64]. The organizationally 3692 governed portion of this ID (24 bits) can be used to generate 3693 multiple IDs if required to indicate more than one RIFT instance." 3695 As matter of operational concern, the router MUST ensure that such 3696 identifier is not changing very frequently (or at least not without 3697 sending all its TIEs with fairly short lifetimes) since otherwise the 3698 network may be left with large amounts of stale TIEs in other nodes 3699 (though this is not necessarily a serious problem if the procedures 3700 described in Section 7 are implemented). 3702 4.2.7.3. Generic Fabric Example 3704 ZTP forces us to think about miscabled or unusually cabled fabric and 3705 how such a topology can be forced into a "lattice" structure which a 3706 fabric represents (with further restrictions). Let us consider a 3707 necessary and sufficient physical cabling in Figure 26. We assume 3708 all nodes being in the same PoD. 3710 . +---+ 3711 . | A | s = TOP_OF_FABRIC 3712 . | s | l = LEAF_ONLY 3713 . ++-++ l2l = LEAF_2_LEAF 3714 . | | 3715 . +--+ +--+ 3716 . | | 3717 . +--++ ++--+ 3718 . | E | | F | 3719 . | +-+ | +-----------+ 3720 . ++--+ | ++-++ | 3721 . | | | | | 3722 . | +-------+ | | 3723 . | | | | | 3724 . | | +----+ | | 3725 . | | | | | 3726 . ++-++ ++-++ | 3727 . | I +-----+ J | | 3728 . | | | +-+ | 3729 . ++-++ +--++ | | 3730 . | | | | | 3731 . +---------+ | +------+ | 3732 . | | | | | 3733 . +-----------------+ | | 3734 . | | | | | 3735 . ++-++ ++-++ | 3736 . | X +-----+ Y +-+ 3737 . |l2l| | l | 3738 . +---+ +---+ 3740 Figure 26: Generic ZTP Cabling Considerations 3742 First, we must anchor the "top" of the cabling and that's what the 3743 TOP_OF_FABRIC flag at node A is for. Then things look smooth until 3744 we have to decide whether node Y is at the same level as I, J (and as 3745 consequence, X is south of it) or at the same level as X. This is 3746 unresolvable here until we "nail down the bottom" of the topology. 3747 To achieve that we choose to use in this example the leaf flags in X 3748 and Y. In case where Y would not have a leaf flag it will try to 3749 elect highest level offered and end up being in same level as I and 3750 J. 3752 4.2.7.4. Level Determination Procedure 3754 A node starting up with UNDEFINED_VALUE (i.e. without a 3755 CONFIGURED_LEVEL or any leaf or TOP_OF_FABRIC flag) MUST follow those 3756 additional procedures: 3758 1. It advertises its LEVEL_VALUE on all LIEs (observe that this can 3759 be UNDEFINED_LEVEL which in terms of the schema is simply an 3760 omitted optional value). 3762 2. It computes HAL as numerically highest available level in all 3763 VOLs. 3765 3. It chooses then MAX(HAL-1,0) as its DERIVED_LEVEL. The node then 3766 starts to advertise this derived level. 3768 4. A node that lost all adjacencies with HAL value MUST hold down 3769 computation of new DERIVED_LEVEL for a short period of time 3770 unless it has no VOLs from southbound adjacencies. After the 3771 holddown expired, it MUST discard all received offers, recompute 3772 DERIVED_LEVEL and announce it to all neighbors. 3774 5. A node MUST reset any adjacency that has changed the level it is 3775 offering and is in three-way state. 3777 6. A node that changed its defined level value MUST readvertise its 3778 own TIEs (since the new `PacketHeader` will contain a different 3779 level than before). Sequence number of each TIE MUST be 3780 increased. 3782 7. After a level has been derived the node MUST set the 3783 `not_a_ztp_offer` on LIEs towards all systems offering a VOL for 3784 HAL. 3786 8. A node that changed its level SHOULD flush from its link state 3787 database TIEs of all other nodes, otherwise stale information may 3788 persist on "direction reversal", i.e. nodes that seemed south 3789 are now north or east-west. This will not prevent the correct 3790 operation of the protocol but could be slightly confusing 3791 operationally. 3793 A node starting with LEVEL_VALUE being 0 (i.e. it assumes a leaf 3794 function by being configured with the appropriate flags or has a 3795 CONFIGURED_LEVEL of 0) MUST follow those additional procedures: 3797 1. It computes HAT per procedures above but does NOT use it to 3798 compute DERIVED_LEVEL. HAT is used to limit adjacency formation 3799 per Section 4.2.2. 3801 It MAY also follow modified procedures: 3803 1. It may pick a different strategy to choose VOL, e.g. use the VOL 3804 value with highest number of VOLs. Such strategies are only 3805 possible since the node always remains "at the bottom of the 3806 fabric" while another layer could "invert" the fabric by picking 3807 its preferred VOL in a different fashion than always trying to 3808 achieve the highest viable level. 3810 4.2.7.5. ZTP FSM 3812 This section specifies the precise, normative ZTP FSM and can be 3813 omitted unless the reader is pursuing an implementation of the 3814 protocol. 3816 Initial state is ComputeBestOffer. 3818 Enter 3819 | 3820 v 3821 +------------------+ 3822 | ComputeBestOffer | 3823 | |<----+ 3824 | Entry: | | BetterHAL [LEVEL_COMPUTE] 3825 | [LEVEL_COMPUTE] | | BetterHAT [LEVEL_COMPUTE] 3826 | | | ChangeLocalConfiguredLevel [StoreConfigLevel, 3827 | | | LEVEL_COMPUTE] 3828 | | | ChangeLocalHierarchyIndications 3829 | | | [StoreLeafFlags, 3830 | | | LEVEL_COMPUTE] 3831 | | | LostHAT [LEVEL_COMPUTE] 3832 | | | NeighborOffer [IF NoLevelOffered 3833 | | | THEN REMOVE_OFFER 3834 | | | ELSE IF OfferedLevel > Leaf 3835 | | | THEN UPDATE_OFFER 3836 | | | ELSE REMOVE_OFFER 3837 | | | ShortTic [RemoveExpiredOffers] 3838 | |-----+ 3839 | | 3840 | |<--------------------- 3841 | |---------------------> (UpdatingClients) 3842 | | ComputationDone [-] 3843 +------------------+ 3844 ^ | 3845 | | LostHAL [IF AnySouthBoundAdjacenciesPresent 3846 | | THEN UpdateHoldDownTimerToNormalValue 3847 | | ELSE FireHoldDownTimerImmediately] 3848 | V 3849 (HoldingDown) 3851 ZTP FSM FSM 3853 (ComputeBestOffer) 3854 | ^ 3855 | | ChangeLocalConfiguredLevel [StoreConfiguredLevel] 3856 | | ChangeLocalHierarchyIndications [StoreLeafFlags] 3857 | | HoldDownExpired [PURGE_OFFERS] 3858 V | 3859 +------------------+ 3860 | HoldingDown | 3861 | |<----+ 3862 | | | BetterHAL [-] 3863 | | | BetterHAT [-] 3864 | | | ComputationDone [-] 3865 | | | LostHAL [-] 3866 | | | LostHat [-] 3867 | | | NeighborOffer [IF NoLevelOffered 3868 | | | THEN REMOVE_OFFER 3869 | | | ELSE IF OfferedLevel > Leaf 3870 | | | THEN UPDATE_OFFER 3871 | | | ELSE REMOVE_OFFER 3872 | | | ShortTic [RemoveExpiredOffers, 3873 | | | IF HoldDownTimer expired 3874 | | | THEN PUSH HoldDownExpired] 3875 | |-----+ 3876 +------------------+ 3877 ^ 3878 | 3879 (UpdatingClients) 3881 ZTP FSM FSM (continued) 3883 (ComputeBestOffer) 3884 | ^ 3885 | | BetterHAL [-] 3886 | | BetterHAT [-] 3887 | | LostHAT [-] 3888 | | ChangeLocalHierarchyIndications [StoreLeafFlags] 3889 | | ChangeLocalConfiguredLevel [StoreConfigLevel] 3890 V | 3891 +------------------+ 3892 | UpdatingClients | 3893 | |<----+ 3894 | Entry: | | 3895 | [UpdateAllLIE- | | NeighborOffer [IF NoLevelOffered 3896 | FSMsWith- | | THEN REMOVE_OFFER 3897 | Computation- | | ELSE IF OfferedLevel > Leaf 3898 | Results] | | THEN UPDATE_OFFER 3899 | | | ELSE REMOVE_OFFER 3900 | | | ShortTic [RemoveExpiredOffers] 3901 | |-----+ 3902 +------------------+ 3903 | 3904 | LostHAL [IF AnySouthBoundAdjacenciesPresent 3905 | THEN UpdateHoldDownTimerToNormalValue 3906 | ELSE FireHoldDownTimerImmediately] 3907 V 3908 (HoldingDown) 3910 ZTP FSM FSM (continued) 3912 Events 3914 o ChangeLocalHierarchyIndications: node locally configured with new 3915 leaf flags 3917 o ChangeLocalConfiguredLevel: node locally configured with a defined 3918 level 3920 o NeighborOffer: a new neighbor offer with optional level and 3921 neighbor state 3923 o BetterHAL: better HAL computed internally 3925 o BetterHAT: better HAT computed internally 3927 o LostHAL: lost last HAL in computation 3929 o LostHAT: lost HAT in computation 3930 o ComputationDone: computation performed 3932 o HoldDownExpired: holddown expired 3934 o ShortTic: one second timer tick, to be ignored if transition does 3935 not exist 3937 Actions 3939 on ShortTic in HoldingDown finishes in HoldingDown: remove expired 3940 offers and if holddown timer expired PUSH_EVENT HoldDownExpired 3942 on ShortTic in ComputeBestOffer finishes in ComputeBestOffer: 3943 remove expired offers 3945 on HoldDownExpired in HoldingDown finishes in ComputeBestOffer: 3946 PURGE_OFFERS 3948 on ChangeLocalConfiguredLevel in HoldingDown finishes in 3949 ComputeBestOffer: store configured level 3951 on ShortTic in UpdatingClients finishes in UpdatingClients: remove 3952 expired offers 3954 on BetterHAT in ComputeBestOffer finishes in ComputeBestOffer: 3955 LEVEL_COMPUTE 3957 on BetterHAL in HoldingDown finishes in HoldingDown: no action 3959 on ChangeLocalHierarchyIndications in HoldingDown finishes in 3960 ComputeBestOffer: store leaf flags 3962 on BetterHAT in UpdatingClients finishes in ComputeBestOffer: no 3963 action 3965 on BetterHAL in UpdatingClients finishes in ComputeBestOffer: no 3966 action 3968 on ChangeLocalHierarchyIndications in UpdatingClients finishes in 3969 ComputeBestOffer: store leaf flags 3971 on LostHAL in HoldingDown finishes in HoldingDown: 3973 on LostHAT in ComputeBestOffer finishes in ComputeBestOffer: 3974 LEVEL_COMPUTE 3976 on LostHAT in HoldingDown finishes in HoldingDown: no action 3977 on BetterHAT in HoldingDown finishes in HoldingDown: no action 3979 on NeighborOffer in UpdatingClients finishes in UpdatingClients: 3981 if no level offered then REMOVE_OFFER 3983 else 3985 if offered level > leaf then UPDATE_OFFER 3987 else REMOVE_OFFER 3989 on LostHAL in ComputeBestOffer finishes in HoldingDown: if any 3990 southbound adjacencies present then update holddown timer to 3991 normal duration else fire holddown timer immediately 3993 on LostHAL in UpdatingClients finishes in HoldingDown: if any 3994 southbound adjacencies present then update holddown timer to 3995 normal duration else fire holddown timer immediately 3997 on ComputationDone in ComputeBestOffer finishes in 3998 UpdatingClients: no action 4000 on LostHAT in UpdatingClients finishes in ComputeBestOffer: no 4001 action 4003 on ComputationDone in HoldingDown finishes in HoldingDown: 4005 on ChangeLocalConfiguredLevel in ComputeBestOffer finishes in 4006 ComputeBestOffer: store configured level and LEVEL_COMPUTE 4008 on ChangeLocalConfiguredLevel in UpdatingClients finishes in 4009 ComputeBestOffer: store configured level 4011 on NeighborOffer in ComputeBestOffer finishes in ComputeBestOffer: 4013 if no level offered then REMOVE_OFFER 4015 else 4017 if offered level > leaf then UPDATE_OFFER 4019 else REMOVE_OFFER 4021 on NeighborOffer in HoldingDown finishes in HoldingDown: 4023 if no level offered then REMOVE_OFFER 4024 else 4026 if offered level > leaf then UPDATE_OFFER 4028 else REMOVE_OFFER 4030 on ChangeLocalHierarchyIndications in ComputeBestOffer finishes in 4031 ComputeBestOffer: store leaf flags and LEVEL_COMPUTE 4033 on BetterHAL in ComputeBestOffer finishes in ComputeBestOffer: 4034 LEVEL_COMPUTE 4036 on Entry into UpdatingClients: update all LIE FSMs with 4037 computation results 4039 on Entry into ComputeBestOffer: LEVEL_COMPUTE 4041 Following words are used for well known procedures: 4043 1. PUSH Event: pushes an event to be executed by the FSM upon exit 4044 of this action 4046 2. COMPARE_OFFERS: checks whether based on current offers and held 4047 last results the events BetterHAL/LostHAL/BetterHAT/LostHAT are 4048 necessary and returns them 4050 3. UPDATE_OFFER: store current offer with adjancency holdtime as 4051 lifetime and COMPARE_OFFERS, then PUSH according events 4053 4. LEVEL_COMPUTE: compute best offered or configured level and HAL/ 4054 HAT, if anything changed PUSH ComputationDone 4056 5. REMOVE_OFFER: remove the according offer and COMPARE_OFFERS, PUSH 4057 according events 4059 6. PURGE_OFFERS: REMOVE_OFFER for all held offers, COMPARE OFFERS, 4060 PUSH according events 4062 4.2.7.6. Resulting Topologies 4064 The procedures defined in Section 4.2.7.4 will lead to the RIFT 4065 topology and levels depicted in Figure 27. 4067 . +---+ 4068 . | As| 4069 . | 24| 4070 . ++-++ 4071 . | | 4072 . +--+ +--+ 4073 . | | 4074 . +--++ ++--+ 4075 . | E | | F | 4076 . | 23+-+ | 23+-----------+ 4077 . ++--+ | ++-++ | 4078 . | | | | | 4079 . | +-------+ | | 4080 . | | | | | 4081 . | | +----+ | | 4082 . | | | | | 4083 . ++-++ ++-++ | 4084 . | I +-----+ J | | 4085 . | 22| | 22| | 4086 . ++--+ +--++ | 4087 . | | | 4088 . +---------+ | | 4089 . | | | 4090 . ++-++ +---+ | 4091 . | X | | Y +-+ 4092 . | 0 | | 0 | 4093 . +---+ +---+ 4095 Figure 27: Generic ZTP Topology Autoconfigured 4097 In case we imagine the LEAF_ONLY restriction on Y is removed the 4098 outcome would be very different however and result in Figure 28. 4099 This demonstrates basically that auto configuration makes miscabling 4100 detection hard and with that can lead to undesirable effects in cases 4101 where leaves are not "nailed" by the accordingly configured flags and 4102 arbitrarily cabled. 4104 A node MAY analyze the outstanding level offers on its interfaces and 4105 generate warnings when its internal ruleset flags a possible 4106 miscabling. As an example, when a node's sees ZTP level offers that 4107 differ by more than one level from its chosen level (with proper 4108 accounting for leaf's being at level 0) this can indicate miscabling. 4110 . +---+ 4111 . | As| 4112 . | 24| 4113 . ++-++ 4114 . | | 4115 . +--+ +--+ 4116 . | | 4117 . +--++ ++--+ 4118 . | E | | F | 4119 . | 23+-+ | 23+-------+ 4120 . ++--+ | ++-++ | 4121 . | | | | | 4122 . | +-------+ | | 4123 . | | | | | 4124 . | | +----+ | | 4125 . | | | | | 4126 . ++-++ ++-++ +-+-+ 4127 . | I +-----+ J +-----+ Y | 4128 . | 22| | 22| | 22| 4129 . ++-++ +--++ ++-++ 4130 . | | | | | 4131 . | +-----------------+ | 4132 . | | | 4133 . +---------+ | | 4134 . | | | 4135 . ++-++ | 4136 . | X +--------+ 4137 . | 0 | 4138 . +---+ 4140 Figure 28: Generic ZTP Topology Autoconfigured 4142 4.2.8. Stability Considerations 4144 The autoconfiguration mechanism computes a global maximum of levels 4145 by diffusion. The achieved equilibrium can be disturbed massively by 4146 all nodes with highest level either leaving or entering the domain 4147 (with some finer distinctions not explained further). It is 4148 therefore recommended that each node is multi-homed towards nodes 4149 with respective HAL offerings. Fortunately, this is the natural 4150 state of things for the topology variants considered in RIFT. 4152 4.3. Further Mechanisms 4154 4.3.1. Overload Bit 4156 The overload Bit MUST be respected in all according reachability 4157 computations. A node with overload bit set SHOULD NOT advertise any 4158 reachability prefixes southbound except locally hosted ones. A node 4159 in overload SHOULD advertise all its locally hosted prefixes north 4160 and southbound. 4162 The leaf node SHOULD set the 'overload' bit on its node TIEs, since 4163 if the spine nodes were to forward traffic not meant for the local 4164 node, the leaf node does not have the topology information to prevent 4165 a routing/forwarding loop. 4167 4.3.2. Optimized Route Computation on Leaves 4169 Since the leaves do see only "one hop away" they do not need to run a 4170 "proper" SPF. Instead, they can gather the available prefix 4171 candidates from their neighbors and build the routing table 4172 accordingly. 4174 A leaf will have no North TIEs except its own and optionally from its 4175 East-West neighbors. A leaf will have South TIEs from its neighbors. 4177 Instead of creating a network graph from its North TIEs and 4178 neighbor's South TIEs and then running an SPF, a leaf node can simply 4179 compute the minimum cost and next_hop_set to each leaf neighbor by 4180 examining its local adjacencies, determining bi-directionality from 4181 the associated North TIE, and specifying the neighbor's next_hop_set 4182 set and cost from the minimum cost local adjacency to that neighbor. 4184 Then a leaf attaches prefixes as described in Section 4.2.6. 4186 4.3.3. Mobility 4188 It is a requirement for RIFT to maintain at the control plane a real 4189 time status of which prefix is attached to which port of which leaf, 4190 even in a context of mobility where the point of attachment may 4191 change several times in a subsecond period of time. 4193 There are two classical approaches to maintain such knowledge in an 4194 unambiguous fashion: 4196 time stamp: With this method, the infrastructure records the precise 4197 time at which the movement is observed. One key advantage of this 4198 technique is that it has no dependency on the mobile device. One 4199 drawback is that the infrastructure must be precisely synchronized 4200 to be able to compare time stamps as observed by the various 4201 points of attachment, e.g., using the variation of the Precision 4202 Time Protocol (PTP) IEEE Std. 1588 [IEEEstd1588], [IEEEstd8021AS] 4203 designed for bridged LANs IEEE Std. 802.1AS [IEEEstd8021AS]. Both 4204 the precision of the synchronization protocol and the resolution 4205 of the time stamp must beat the highest possible roaming time on 4206 the fabric. Another drawback is that the presence of the mobile 4207 device may be observed only asynchronously, e.g., after it starts 4208 using an IP protocol such as ARP [RFC0826], IPv6 Neighbor 4209 Discovery [RFC4861][RFC4862], or DHCP [RFC2131][RFC8415]. 4211 sequence counter: With this method, a mobile node notifies its point 4212 of attachment on arrival with a sequence counter that is 4213 incremented upon each movement. On the positive side, this method 4214 does not have a dependency on a precise sense of time, since the 4215 sequence of movements is kept in order by the device. The 4216 disadvantage of this approach is the lack of support for protocols 4217 that may be used by the mobile node to register its presence to 4218 the leaf node with the capability to provide a sequence counter. 4219 Well-known issues with wrapping sequence counters must be 4220 addressed properly, and many forms of sequence counters that vary 4221 in both wrapping rules and comparison rules. A particular 4222 knowledge of the source of the sequence counter is required to 4223 operate it, and the comparison between sequence counters from 4224 heterogeneous sources can be hard to impossible. 4226 RIFT supports a hybrid approach contained in an optional 4227 `PrefixSequenceType` prefix attribute that we call a `monotonic 4228 clock` consisting of a timestamp and optional sequence number. In 4229 case of presence of the attribute: 4231 o The leaf node MAY advertise a time stamp of the latest sighting of 4232 a prefix, e.g., by snooping IP protocols or the node using the 4233 time at which it advertised the prefix. RIFT transports the time 4234 stamp within the desired prefix North TIEs as 802.1AS timestamp. 4236 o RIFT may interoperate with the "update to 6LoWPAN Neighbor 4237 Discovery" [RFC8505], which provides a method for registering a 4238 prefix with a sequence counter called a Transaction ID (TID). 4239 RIFT transports in such case the TID in its native form. 4241 o RIFT also defines an abstract negative clock (ASNC) that compares 4242 as less than any other clock. By default, the lack of a 4243 `PrefixSequenceType` in a Prefix North TIE is interpreted as ASNC. 4244 We call this also an `undefined` clock. 4246 o Any prefix present on the fabric in multiple nodes that has the 4247 `same` clock is considered as anycast. ASNC is always considered 4248 smaller than any defined clock. 4250 o RIFT implementation assumes by default that all nodes are being 4251 synchronized to 200 milliseconds precision which is easily 4252 achievable even in very large fabrics using [RFC5905]. An 4253 implementation MAY provide a way to reconfigure a domain to a 4254 different value. We call this variable MAXIMUM_CLOCK_DELTA. 4256 4.3.3.1. Clock Comparison 4258 All monotonic clock values are comparable to each other using the 4259 following rules: 4261 1. ASNC is older than any other value except ASNC AND 4263 2. Clock with timestamp differing by more than MAXIMUM_CLOCK_DELTA 4264 are comparable by using the timestamps only AND 4266 3. Clocks with timestamps differing by less than MAXIMUM_CLOCK_DELTA 4267 are comparable by using their TIDs only AND 4269 4. An undefined TID is always older than any other TID AND 4271 5. TIDs are compared using rules of [RFC8505]. 4273 4.3.3.2. Interaction between Time Stamps and Sequence Counters 4275 For slow movements that occur less frequently than e.g. once per 4276 second, the time stamp that the RIFT infrastructure captures is 4277 enough to determine the freshest discovery. If the point of 4278 attachment changes faster than the maximum drift of the time stamping 4279 mechanism (i.e. MAXIMUM_CLOCK_DELTA), then a sequence counter is 4280 required to add resolution to the freshness evaluation, and it must 4281 be sized so that the counters stay comparable within the resolution 4282 of the time sampling mechanism. 4284 The sequence counter in [RFC8505] is encoded as one octet and wraps 4285 around using Appendix A. 4287 Within the resolution of MAXIMUM_CLOCK_DELTA the sequence counters 4288 captured during 2 sequential values of the time stamp SHOULD be 4289 comparable. This means with default values that a node may move up 4290 to 127 times during a 200 milliseconds period and the clocks remain 4291 still comparable thus allowing the infrastructure to assert the 4292 freshest advertisement with no ambiguity. 4294 4.3.3.3. Anycast vs. Unicast 4296 A unicast prefix can be attached to at most one leaf, whereas an 4297 anycast prefix may be reachable via more than one leaf. 4299 If a monotonic clock attribute is provided on the prefix, then the 4300 prefix with the `newest` clock value is strictly preferred. An 4301 anycast prefix does not carry a clock or all clock attributes MUST be 4302 the same under the rules of Section 4.3.3.1. 4304 Observe that it is important that in mobility events the leaf is re- 4305 flooding as quickly as possible the absence of the prefix that moved 4306 away. 4308 Observe further that without support for [RFC8505] movements on the 4309 fabric within intervals smaller than 100msec will be seen as anycast. 4311 4.3.3.4. Overlays and Signaling 4313 RIFT is agnostic whether any overlay technology like [MIP, LISP, 4314 VxLAN, NVO3] and the associated signaling is deployed over it. But 4315 it is expected that leaf nodes, and possibly Top-of-Fabric nodes can 4316 perform the correct encapsulation. 4318 In the context of mobility, overlays provide a classical solution to 4319 avoid injecting mobile prefixes in the fabric and improve the 4320 scalability of the solution. It makes sense on a data center that 4321 already uses overlays to consider their applicability to the mobility 4322 solution; as an example, a mobility protocol such as LISP may inform 4323 the ingress leaf of the location of the egress leaf in real time. 4325 Another possibility is to consider that mobility as an underlay 4326 service and support it in RIFT to an extent. The load on the fabric 4327 augments with the amount of mobility obviously since a move forces 4328 flooding and computation on all nodes in the scope of the move so 4329 tunneling from leaf to the Top-of-Fabric may be desired. 4331 4.3.4. Key/Value Store 4333 4.3.4.1. Southbound 4335 The protocol supports a southbound distribution of key-value pairs 4336 that can be used to e.g. distribute configuration information during 4337 topology bring-up. The KV South TIEs can arrive from multiple nodes 4338 and hence need tie-breaking per key. We use the following rules 4340 1. Only KV TIEs originated by nodes to which the receiver has a bi- 4341 directional adjacency are considered. 4343 2. Within all such valid KV South TIEs containing the key, the value 4344 of the KV South TIE for which the according node South TIE is 4345 present, has the highest level and within the same level has 4346 highest originating system ID is preferred. If keys in the most 4347 preferred TIEs are overlapping, the behavior is undefined. 4349 Observe that if a node goes down, the node south of it looses 4350 adjacencies to it and with that the KVs will be disregarded and on 4351 tie-break changes new KV re-advertised to prevent stale information 4352 being used by nodes further south. KV information in southbound 4353 direction is not result of independent computation of every node over 4354 same set of TIEs but a diffused computation. 4356 4.3.4.2. Northbound 4358 Certain use cases seem to necessitate distribution of essentially KV 4359 information that is generated in the leaves in the northbound 4360 direction. Such information is flooded in KV North TIEs. Since the 4361 originator of northbound KV is preserved during northbound flooding, 4362 overlapping keys could be used. However, to omit further protocol 4363 complexity, only the value of the key in TIE tie-broken in same 4364 fashion as southbound KV TIEs is used. 4366 4.3.5. Interactions with BFD 4368 RIFT MAY incorporate BFD [RFC5881] to react quickly to link failures. 4369 In such case following procedures are introduced: 4371 After RIFT three-way hello adjacency convergence a BFD session MAY 4372 be formed automatically between the RIFT endpoints without further 4373 configuration using the exchanged discriminators. The capability 4374 of the remote side to support BFD is carried on the LIEs. 4376 In case established BFD session goes Down after it was Up, RIFT 4377 adjacency SHOULD be re-initialized and subsequently started from 4378 Init after it sees a consecutive BFD Up. 4380 In case of parallel links between nodes each link MAY run its own 4381 independent BFD session or they may share a session. 4383 In case RIFT changes link identifiers or BFD capability indication 4384 both the LIE as well as the BFD sessions SHOULD be brought down 4385 and back up again. 4387 Multiple RIFT instances MAY choose to share a single BFD session 4388 (in such case it is undefined what discriminators are used albeit 4389 RIFT MAY advertise the same link ID for the same interface in 4390 multiple instances and with that "share" the discriminators). 4392 BFD TTL follows [RFC5082]. 4394 4.3.6. Fabric Bandwidth Balancing 4396 A well understood problem in fabrics is that in case of link losses 4397 it would be ideal to rebalance how much traffic is offered to 4398 switches in the next level based on the ingress and egress bandwidth 4399 they have. Current attempts rely mostly on specialized traffic 4400 engineering via controller or leaves being aware of complete topology 4401 with according cost and complexity. 4403 RIFT can support a very light weight mechanism that can deal with the 4404 problem in an approximate way based on the fact that RIFT is loop- 4405 free. 4407 4.3.6.1. Northbound Direction 4409 Every RIFT node SHOULD compute the amount of northbound bandwidth 4410 available through neighbors at higher level and modify distance 4411 received on default route from this neighbor. Those different 4412 distances SHOULD be used to support weighted ECMP forwarding towards 4413 higher level when using default route. We call such a distance 4414 Bandwidth Adjusted Distance or BAD. This is best illustrated by a 4415 simple example. 4417 . 100 x 100 100 MBits 4418 . | x | | 4419 . +-+---+-+ +-+---+-+ 4420 . | | | | 4421 . |Spin111| |Spin112| 4422 . +-+---+++ ++----+++ 4423 . |x || || || 4424 . || |+---------------+ || 4425 . || +---------------+| || 4426 . || || || || 4427 . || || || || 4428 . -----All Links 10 MBit------- 4429 . || || || || 4430 . || || || || 4431 . || +------------+| || || 4432 . || |+------------+ || || 4433 . |x || || || 4434 . +-+---+++ +--++-+++ 4435 . | | | | 4436 . |Leaf111| |Leaf112| 4437 . +-------+ +-------+ 4439 Figure 29: Balancing Bandwidth 4441 All links from leaves in Figure 29 are assumed to 10 MBit/s bandwidth 4442 while the uplinks one level further up are assumed to be 100 MBit/s. 4443 Further, in Figure 29 we assume that Leaf111 lost one of the parallel 4444 links to Spine 111 and with that wants to possibly push more traffic 4445 onto Spine 112. Leaf 112 has equal bandwidth to Spine 111 and Spine 4446 112 but Spine 111 lost one of its uplinks. 4448 The local modification of the received default route distance from 4449 upper level is achieved by running a relatively simple algorithm 4450 where the bandwidth is weighted exponentially while the distance on 4451 the default route represents a multiplier for the bandwidth weight 4452 for easy operational adjustments. 4454 On a node L use Node TIEs to compute for each non-overloaded 4455 northbound neighbor N three values: 4457 L_N_u: as sum of the bandwidth available to N 4459 N_u: as sum of the uplink bandwidth available on N 4461 T_N_u: as sum of L_N_u * OVERSUBSCRIPTION_CONSTANT + N_u 4463 For all T_N_u determine the according M_N_u as 4464 log_2(next_power_2(T_N_u)) and determine MAX_M_N_u as maximum value 4465 of all M_N_u. 4467 For each advertised default route from a node N modify the advertised 4468 distance D to BAD = D * (1 + MAX_M_N_u - M_N_u) and use BAD instead 4469 of distance D to weight balance default forwarding towards N. 4471 For the example above a simple table of values will help the 4472 understanding. We assume the default route distance is advertised 4473 with D=1 everywhere and OVERSUBSCRIPTION_CONSTANT = 1. 4475 +---------+-----------+-------+-------+-----+ 4476 | Node | N | T_N_u | M_N_u | BAD | 4477 +---------+-----------+-------+-------+-----+ 4478 | Leaf111 | Spine 111 | 110 | 7 | 2 | 4479 +---------+-----------+-------+-------+-----+ 4480 | Leaf111 | Spine 112 | 220 | 8 | 1 | 4481 +---------+-----------+-------+-------+-----+ 4482 | Leaf112 | Spine 111 | 120 | 7 | 2 | 4483 +---------+-----------+-------+-------+-----+ 4484 | Leaf112 | Spine 112 | 220 | 8 | 1 | 4485 +---------+-----------+-------+-------+-----+ 4487 Table 5: BAD Computation 4489 If a calculation produces a result exceeding the range of the type, 4490 e.g. bandwidth, the result is set to the highest possible value for 4491 that type. 4493 BAD is only computed for default routes. A node MAY compute and use 4494 BAD for any disaggregated prefixes or other RIFT routes. A node MAY 4495 use another algorithm than BAD to weight northbound traffic based on 4496 bandwidth given that the algorithm is distributed and un-synchronized 4497 and ultimately, its correct behavior does not depend on uniformity of 4498 balancing algorithms used in the fabric. E.g. it is conceivable that 4499 leaves could use real time link loads gathered by analytics to change 4500 the amount of traffic assigned to each default route next hop. 4502 Observe further that a change in available bandwidth will only affect 4503 at maximum two levels down in the fabric, i.e. blast radius of 4504 bandwidth changes is contained no matter its height. 4506 4.3.6.2. Southbound Direction 4508 Due to its loop free properties a node MAY take during S-SPF into 4509 account the available bandwidth on the nodes in lower levels and 4510 modify the amount of traffic offered to next level's "southbound" 4511 nodes based as what it sees is the total achievable maximum flow 4512 through those nodes. It is worth observing that such computations 4513 may work better if standardized but does not have to be necessarily. 4514 As long the packet keeps on heading south it will take one of the 4515 available paths and arrive at the intended destination. 4517 4.3.7. Label Binding 4519 A node MAY advertise on its LIEs a locally significant, downstream 4520 assigned, interface specific label. One use of such label is a hop- 4521 by-hop encapsulation allowing to easily distinguish forwarding planes 4522 served by a multiplicity of RIFT instances. 4524 4.3.8. Leaf to Leaf Procedures 4526 RIFT can optionally allow special leaf East-West adjacencies under 4527 additional set of rules. The leaf supporting those procedures MUST: 4529 advertise the LEAF_2_LEAF flag in node capabilities AND 4531 set the overload bit on all leaf's node TIEs AND 4533 flood only node's own north and south TIEs over E-W leaf 4534 adjacencies AND 4536 always use E-W leaf adjacency in both north as well as south 4537 computation AND 4539 install a discard route for any advertised aggregate in leaf's 4540 TIEs AND 4542 never form southbound adjacencies. 4544 This will allow the E-W leaf nodes to exchange traffic strictly for 4545 the prefixes advertised in each other's north prefix TIEs (since the 4546 southbound computation will find the reverse direction in the other 4547 node's TIE and install its north prefixes). 4549 4.3.9. Address Family and Multi Topology Considerations 4551 Multi-Topology (MT)[RFC5120] and Multi-Instance (MI)[RFC8202] is used 4552 today in link-state routing protocols to support several domains on 4553 the same physical topology. RIFT supports this capability by 4554 carrying transport ports in the LIE protocol exchanges. Multiplexing 4555 of LIEs can be achieved by either choosing varying multicast 4556 addresses or ports on the same address. 4558 BFD interactions in Section 4.3.5 are implementation dependent when 4559 multiple RIFT instances run on the same link. 4561 4.3.10. Reachability of Internal Nodes in the Fabric 4563 RIFT does not precondition that its nodes have reachable addresses 4564 albeit for operational purposes this is clearly desirable. Under 4565 normal operating conditions this can be easily achieved by e.g. 4566 injecting the node's loopback address into North and South Prefix 4567 TIEs or other implementation specific mechanisms. 4569 Things get more interesting in case a node looses all its northbound 4570 adjacencies but is not at the top of the fabric. That is outside the 4571 scope of this document and may be covered in a separate document. 4573 4.3.11. One-Hop Healing of Levels with East-West Links 4575 Based on the rules defined in Section 4.2.4, Section 4.2.3.8 and 4576 given presence of E-W links, RIFT can provide a one-hop protection of 4577 nodes that lost all their northbound links or in other complex link 4578 set failure scenarios except at Top-of-Fabric where the links are 4579 used exclusively to flood topology information in multi-plane 4580 designs. Section 5.4 explains the resulting behavior based on one 4581 such example. 4583 4.4. Security 4585 4.4.1. Security Model 4587 An inherent property of any security and ZTP architecture is the 4588 resulting trade-off in regard to integrity verification of the 4589 information distributed through the fabric vs. necessary provisioning 4590 and auto-configuration. At a minimum, in all approaches, the 4591 security of an established adjacency can be ensured. The stricter 4592 the security model the more provisioning must take over the role of 4593 ZTP. 4595 The most security conscious operators will want to have full control 4596 over which port on which router/switch is connected to the respective 4597 port on the "other side", which we will call the "port-association 4598 model" (PAM) achievable e.g. by configuring on each port pair a 4599 designated shared key or pair of private/public keys. In secure data 4600 center locations, operators may want to control which router/switch 4601 is connected to which other router/switch only or choose a "node- 4602 association model" (NAM) which allows, for example, simplified port 4603 sparing. In an even more relaxed environment, an operator may only 4604 be concerned that the router/switches share credentials ensuring that 4605 they belong to this particular data center network hence allowing the 4606 flexible sparing of whole routers/switches. We will define that case 4607 as the "fabric-association model" (FAM), equivalent to using a shared 4608 secret for the whole fabric. Such flexibility may make sense for 4609 leaf nodes such as servers where the addition and swapping of servers 4610 is more frequent than the rest of the data center network. 4611 Generally, leaves of the fabric tend to be less trusted than 4612 switches. The different models could be mixed throughout the fabric 4613 if the benefits outweigh the cost of increased complexity in 4614 provisioning. 4616 In each of the above cases, some configuration mechanism is needed to 4617 allow the operator to specify which connections are allowed, and some 4618 mechanism is needed to: 4620 a. specify the according level in the fabric, 4622 b. discover and report missing connections, 4624 c. discover and report unexpected connections, and prevent such 4625 adjacencies from forming. 4627 On the more relaxed configuration side of the spectrum, operators 4628 might only configure the level of each switch, but don't explicitly 4629 configure which connections are allowed. In this case, RIFT will 4630 only allow adjacencies to come up between nodes are that in adjacent 4631 levels. The operators with lowest security requirements may not use 4632 any configuration to specify which connections are allowed. Such 4633 fabrics could rely fully on ZTP for each router/switch to discover 4634 its level and would only allow adjacencies between adjacent levels to 4635 come up. Figure 30 illustrates the tradeoffs inherent in the 4636 different security models. 4638 Ultimately, some level of verification of the link quality may be 4639 required before an adjacency is allowed to be used for forwarding. 4640 For example, an implementation may require that a BFD session comes 4641 up before advertising the adjacency. 4643 For the above outlined cases, RIFT has two approaches to enforce that 4644 a local port is connected to the correct port on the correct remote 4645 router/switch. One approach is to piggy-back on RIFT's 4646 authentication mechanism. Assuming the provisioning model (e.g. the 4647 YANG model) is flexible enough, operators can choose to provision a 4648 unique authentication key for: 4650 a. each pair of ports in "port-association model" or 4652 b. each pair of switches in "node-association model" or 4653 c. each pair of levels or 4655 d. the entire fabric in "fabric-association model". 4657 The other approach is to rely on the system-id, port-id and level 4658 fields in the LIE message to validate an adjacency against the 4659 configured expected cabling topology, and optionally introduce some 4660 new rules in the FSM to allow the adjacency to come up if the 4661 expectations are met. 4663 ^ /\ | 4664 /|\ / \ | 4665 | / \ | 4666 | / PAM \ | 4667 Increasing / \ Increasing 4668 Integrity +----------+ Flexibility 4669 & / NAM \ & 4670 Increasing +--------------+ Less 4671 Provisioning / FAM \ Configuration 4672 | +------------------+ | 4673 | / Level Provisioning \ | 4674 | +----------------------+ \|/ 4675 | / Zero Configuration \ v 4676 +--------------------------+ 4678 Figure 30: Security Model 4680 4.4.2. Security Mechanisms 4682 RIFT Security goals are to ensure authentication, message integrity 4683 and prevention of replay attacks. Low processing overhead and 4684 efficient messaging are also a goal. Message confidentiality is a 4685 non-goal. 4687 The model in the previous section allows a range of security key 4688 types that are analogous to the various security association models. 4689 PAM and NAM allow security associations at the port or node level 4690 using symmetric or asymmetric keys that are pre-installed. FAM 4691 argues for security associations to be applied only at a group level 4692 or to be refined once the topology has been established. RIFT does 4693 not specify how security keys are installed or updated it specifies 4694 how the key can be used to achieve goals. 4696 The protocol has provisions for "weak" nonces to prevent replay 4697 attacks and includes authentication mechanisms comparable to 4698 [RFC5709] and [RFC7987]. 4700 4.4.3. Security Envelope 4702 RIFT MUST be carried in a mandatory secure envelope illustrated in 4703 Figure 31. Any value in the packet following a security fingerprint 4704 MUST be used only after the according fingerprint has been validated. 4706 Local configuration MAY allow to skip the checking of the envelope's 4707 integrity. 4709 0 1 2 3 4710 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 4712 UDP Header: 4713 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4714 | Source Port | RIFT destination port | 4715 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4716 | UDP Length | UDP Checksum | 4717 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4719 Outer Security Envelope Header: 4720 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4721 | RIFT MAGIC | Packet Number | 4722 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4723 | Reserved | RIFT Major | Outer Key ID | Fingerprint | 4724 | | Version | | Length | 4725 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4726 | | 4727 ~ Security Fingerprint covers all following content ~ 4728 | | 4729 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4730 | Weak Nonce Local | Weak Nonce Remote | 4731 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4732 | Remaining TIE Lifetime (all 1s in case of LIE) | 4733 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4735 TIE Origin Security Envelope Header: 4736 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4737 | TIE Origin Key ID | Fingerprint | 4738 | | Length | 4739 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4740 | | 4741 ~ Security Fingerprint covers all following content ~ 4742 | | 4743 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4745 Serialized RIFT Model Object 4746 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4747 | | 4748 ~ Serialized RIFT Model Object ~ 4749 | | 4750 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4752 Figure 31: Security Envelope 4754 RIFT MAGIC: 16 bits. Constant value of 0xA1F7 that allows to 4755 classify RIFT packets independent of used UDP port. 4757 Packet Number: 16 bits. An optional, per packet type monotonically 4758 growing number rolling over using sequence number arithmetic 4759 defined inAppendix A. A node SHOULD correctly set the number on 4760 subsequent packets or otherwise MUST set the value to 4761 `undefined_packet_number` as provided in the schema. This number 4762 can be used to detect losses and misordering in flooding for 4763 either operational purposes or in implementation to adjust 4764 flooding behavior to current link or buffer quality. This number 4765 MUST NOT be used to discard or validate the correctness of 4766 packets. 4768 RIFT Major Version: 8 bits. It allows to check whether protocol 4769 versions are compatible, i.e. the serialized object can be decoded 4770 at all. An implementation MUST drop packets with unexpected value 4771 and MAY report a problem. Must be same as in encoded model 4772 object, otherwise packet is dropped. 4774 Outer Key ID: 8 bits to allow key rollovers. This implies key type 4775 and used algorithm. Value 0 means that no valid fingerprint was 4776 computed. This key ID scope is local to the nodes on both ends of 4777 the adjacency. 4779 TIE Origin Key ID: 24 bits. This implies key type and used 4780 algorithm. Value 0 means that no valid fingerprint was computed. 4781 This key ID scope is global to the RIFT instance since it implies 4782 the originator of the TIE so the contained object does not have to 4783 be de-serialized to obtain it. 4785 Length of Fingerprint: 8 bits. Length in 32-bit multiples of the 4786 following fingerprint not including lifetime or weak nonces. It 4787 allows to navigate the structure when an unknown key type is 4788 present. To clarify a common corner case when this value is set 4789 to 0 it signifies an empty (0 bytes long) security fingerprint. 4791 Security Fingerprint: 32 bits * Length of Fingerprint. This is a 4792 signature that is computed over all data following after it. If 4793 the significant bits of fingerprint are fewer than the 32 bits 4794 padded length than the significant bits MUST be left aligned and 4795 remaining bits on the right padded with 0s. When using PKI the 4796 Security fingerprint originating node uses its private key to 4797 create the signature. The original packet can then be verified 4798 provided the public key is shared and current. 4800 Remaining TIE Lifetime: 32 bits. In case of anything but TIEs this 4801 field MUST be set to all ones and Origin Security Envelope Header 4802 MUST NOT be present in the packet. For TIEs this field represents 4803 the remaining lifetime of the TIE and Origin Security Envelope 4804 Header MUST be present in the packet. The value in the serialized 4805 model object MUST be ignored. 4807 Weak Nonce Local: 16 bits. Local Weak Nonce of the adjacency as 4808 advertised in LIEs. 4810 Weak Nonce Remote: 16 bits. Remote Weak Nonce of the adjacency as 4811 received in LIEs. 4813 TIE Origin Security Envelope Header: It MUST be present if and only 4814 if the Remaining TIE Lifetime field is NOT all ones. It carries 4815 through the originators key ID and according fingerprint of the 4816 object to protect TIE from modification during flooding. This 4817 ensures origin validation and integrity (but does not provide 4818 validation of a chain of trust). 4820 Observe that due to the schema migration rules per Appendix B the 4821 contained model can be always decoded if the major version matches 4822 and the envelope integrity has been validated. Consequently, 4823 description of the TIE is available to flood it properly including 4824 unknown TIE types. 4826 4.4.4. Weak Nonces 4828 The protocol uses two 16 bit nonces to salt generated signatures. We 4829 use the term "nonce" a bit loosely since RIFT nonces are not being 4830 changed on every packet as common in cryptography. For efficiency 4831 purposes they are changed at a frequency high enough to dwarf replay 4832 attacks attempts for all practical purposes. Therefore, we call them 4833 "weak" nonces. 4835 Any implementation including RIFT security MUST generate and wrap 4836 around local nonces properly. When a nonce increment leads to 4837 `undefined_nonce` value the value SHOULD be incremented again 4838 immediately. All implementation MUST reflect the neighbor's nonces. 4839 An implementation SHOULD increment a chosen nonce on every LIE FSM 4840 transition that ends up in a different state from the previous and 4841 MUST increment its nonce at least every 5 minutes (such 4842 considerations allow for efficient implementations without opening a 4843 significant security risk). When flooding TIEs, the implementation 4844 MUST use recent (i.e. within allowed difference) nonces reflected in 4845 the LIE exchange. The schema specifies maximum allowable nonce value 4846 difference on a packet compared to reflected nonces in the LIEs. Any 4847 packet received with nonces deviating more than the allowed delta 4848 MUST be discarded without further computation of signatures to 4849 prevent computation load attacks. 4851 In case where a secure implementation does not receive signatures or 4852 receives undefined nonces from neighbor indicating that it does not 4853 support or verify signatures, it is a matter of local policy how such 4854 packets are treated. Any secure implementation MAY choose to either 4855 refuse forming an adjacency with an implementation not advertising 4856 signatures or valid nonces or simply keep on signing local packets 4857 while accepting neighbor's packets without further security 4858 verification. 4860 As a necessary exception, an implementation MUST advertise 4861 `undefined_nonce` for remote nonce value when the FSM is not in two- 4862 way or three-way state and accept an `undefined_nonce` for its local 4863 nonce value on packets in any other state than three-way. 4865 As optional optimization, an implementation MAY send one LIE with 4866 previously negotiated neighbor's nonce to try to speed up a 4867 neighbor's transition from three-way to one-way and MUST revert to 4868 sending `undefined_nonce` after that. 4870 4.4.5. Lifetime 4872 Protecting lifetime on flooding may lead to excessive number of 4873 security fingerprint computation and hence an application generating 4874 such fingerprints on TIEs MAY round the value down to the next 4875 `rounddown_lifetime_interval` defined in the schema when sending TIEs 4876 albeit such optimization in presence of security hashes over 4877 advancing weak nonces may not be feasible. 4879 4.4.6. Key Management 4881 As outlined in the Security Model a private shared key or a public/ 4882 private key pair is used to Authenticate the adjacency. The actual 4883 method of key distribution and key synchronization is assumed to be 4884 out of band from RIFT's perspective. Both nodes in the adjacency 4885 must share the same keys and configuration of key type and algorithm 4886 for a key ID. Mismatched keys will obviously not inter-operate due 4887 to unverifiable security envelope. 4889 Key roll-over while the adjacency is active is allowed and the 4890 technique is well known and described in e.g. [RFC6518]. Key 4891 distribution procedures are out of scope for RIFT. 4893 4.4.7. Security Association Changes 4895 There in no mechanism to convert a security envelope for the same key 4896 ID from one algorithm to another once the envelope is operational. 4897 The recommended procedure to change to a new algorithm is to take the 4898 adjacency down and make the changes and then bring the adjacency up. 4900 Obviously, an implementation MAY choose to stop verifying security 4901 envelope for the duration of key change to keep the adjacency up but 4902 since this introduces a security vulnerability window, such roll-over 4903 is not recommended. 4905 5. Examples 4907 5.1. Normal Operation 4909 This section describes RIFT deployment in the example topology 4910 without any node or link failures. We disregard flooding reduction 4911 for simplicity's sake. 4913 As first step, the following bi-directional adjacencies will be 4914 created (and any other links that do not fulfill LIE rules in 4915 Section 4.2.2 disregarded): 4917 1. ToF 21 (PoD 0) to Spine 111, Spine 112, Spine 121, and Spine 122 4919 2. ToF 22 (PoD 0) to Spine 111, Spine 112, Spine 121, and Spine 122 4921 3. Spine 111 to Leaf 111, Leaf 112 4923 4. Spine 112 to Leaf 111, Leaf 112 4925 5. Spine 121 to Leaf 121, Leaf 122 4927 6. Spine 122 to Leaf 121, Leaf 122 4929 Consequently, North TIEs would be originated by Spine 111 and Spine 4930 112 and each set would be sent to both ToF 21 and ToF 22. North TIEs 4931 also would be originated by Leaf 111 (w/ Prefix 111) and Leaf 112 (w/ 4932 Prefix 112 and the multi-homed prefix) and each set would be sent to 4933 Spine 111 and Spine 112. Spine 111 and Spine 112 would then flood 4934 these North TIEs to ToF 21 and ToF 22. 4936 Similarly, North TIEs would be originated by Spine 121 and Spine 122 4937 and each set would be sent to both ToF 21 and ToF 22. North TIEs 4938 also would be originated by Leaf 121 (w/ Prefix 121 and the multi- 4939 homed prefix) and Leaf 122 (w/ Prefix 122) and each set would be sent 4940 to Spine 121 and Spine 122. Spine 121 and Spine 122 would then flood 4941 these North TIEs to ToF 21 and ToF 22. 4943 At this point both ToF 21 and ToF 22, as well as any controller to 4944 which they are connected, would have the complete network topology. 4945 At the same time, Spine 111/112/121/122 hold only the N-ties of level 4946 0 of their respective PoD. leaves hold only their own North TIEs. 4948 South TIEs with adjacencies and a default IP prefix would then be 4949 originated by ToF 21 and ToF 22 and each would be flooded to Spine 4950 111, Spine 112, Spine 121, and Spine 122. Spine 111, Spine 112, 4951 Spine 121, and Spine 122 would each send the South TIE from ToF 21 to 4952 ToF 22 and the South TIE from ToF 22 to ToF 21. (South TIEs are 4953 reflected up to level from which they are received but they are NOT 4954 propagated southbound.) 4956 A South TIE with a default IP prefix would be originated by Node 111 4957 and Spine 112 and each would be sent to Leaf 111 and Leaf 112. 4959 Similarly, an South TIE with a default IP prefix would be originated 4960 by Node 121 and Spine 122 and each would be sent to Leaf 121 and Leaf 4961 122. At this point IP connectivity with maximum possible ECMP has 4962 been established between the leaves while constraining the amount of 4963 information held by each node to the minimum necessary for normal 4964 operation and dealing with failures. 4966 5.2. Leaf Link Failure 4968 . | | | | 4969 .+-+---+-+ +-+---+-+ 4970 .| | | | 4971 .|Spin111| |Spin112| 4972 .+-+---+-+ ++----+-+ 4973 . | | | | 4974 . | +---------------+ X 4975 . | | | X Failure 4976 . | +-------------+ | X 4977 . | | | | 4978 .+-+---+-+ +--+--+-+ 4979 .| | | | 4980 .|Leaf111| |Leaf112| 4981 .+-------+ +-------+ 4982 . + + 4983 . Prefix111 Prefix112 4985 Figure 32: Single Leaf link failure 4987 In case of a failing leaf link between spine 112 and leaf 112 the 4988 link-state information will cause re-computation of the necessary SPF 4989 and the higher levels will stop forwarding towards prefix 112 through 4990 spine 112. Only spines 111 and 112, as well as both spines will see 4991 control traffic. Leaf 111 will receive a new South TIE from spine 4992 112 and reflect back to spine 111. 4994 Spine 111 will de-aggregate prefix 111 and prefix 112 but we will not 4995 describe it further here since de-aggregation is emphasized in the 4996 next example. It is worth observing however in this example that if 4997 leaf 111 would keep on forwarding traffic towards prefix 112 using 4998 the advertised south-bound default of spine 112 the traffic would end 4999 up on Top-of-Fabric 21 and ToF 22 and cross back into pod 1 using 5000 spine 111. This is arguably not as bad as black-holing present in 5001 the next example but clearly undesirable. Fortunately, de- 5002 aggregation prevents this type of behavior except for a transitory 5003 period of time. 5005 5.3. Partitioned Fabric 5007 . +--------+ +--------+ South TIE of ToF 21 5008 . | | | | received by 5009 . |ToF 21| |ToF 22| south reflection of 5010 . ++-+--+-++ ++-+--+-++ spines 112 and 111 5011 . | | | | | | | | 5012 . | | | | | | | 0/0 5013 . | | | | | | | | 5014 . | | | | | | | | 5015 . +--------------+ | +--- XXXXXX + | | | +---------------+ 5016 . | | | | | | | | 5017 . | +-----------------------------+ | | | 5018 . 0/0 | | | | | | | 5019 . | 0/0 0/0 +- XXXXXXXXXXXXXXXXXXXXXXXXX -+ | 5020 . | 1.1/16 | | | | | | 5021 . | | +-+ +-0/0-----------+ | | 5022 . | | | 1.1./16 | | | | 5023 .+-+----++ +-+-----+ ++-----0/0 ++----0/0 5024 .| | | | | 1.1/16 | 1.1/16 5025 .|Spin111| |Spin112| |Spin121| |Spin122| 5026 .+-+---+-+ ++----+-+ +-+---+-+ ++---+--+ 5027 . | | | | | | | | 5028 . | +---------------+ | | +----------------+ | 5029 . | | | | | | | | 5030 . | +-------------+ | | | +--------------+ | | 5031 . | | | | | | | | 5032 .+-+---+-+ +--+--+-+ +-+---+-+ +---+-+-+ 5033 .| | | | | | | | 5034 .|Leaf111| |Leaf112| |Leaf121| |Leaf122| 5035 .+-+-----+ ++------+ +-----+-+ +-+-----+ 5036 . + + + + 5037 . Prefix111 Prefix112 Prefix121 Prefix122 5038 . 1.1/16 5040 Figure 33: Fabric partition 5042 Figure 33 shows the arguably a more catastrophic but also a more 5043 interesting case. ToF 21 is completely severed from access to Prefix 5044 121 (we use in the figure 1.1/16 as example) by double link failure. 5045 However unlikely, if left unresolved, forwarding from leaf 111 and 5046 leaf 112 to prefix 121 would suffer 50% black-holing based on pure 5047 default route advertisements by ToF 21 and ToF 22. 5049 The mechanism used to resolve this scenario is hinging on the 5050 distribution of southbound representation by Top-of-Fabric 21 that is 5051 reflected by spine 111 and spine 112 to ToF 22. ToF 22, having 5052 computed reachability to all prefixes in the network, advertises with 5053 the default route the ones that are reachable only via lower level 5054 neighbors that ToF 21 does not show an adjacency to. That results in 5055 spine 111 and spine 112 obtaining a longest-prefix match to prefix 5056 121 which leads through ToF 22 and prevents black-holing through ToF 5057 21 still advertising the 0/0 aggregate only. 5059 The prefix 121 advertised by Top-of-Fabric 22 does not have to be 5060 propagated further towards leaves since they do no benefit from this 5061 information. Hence the amount of flooding is restricted to ToF 21 5062 reissuing its South TIEs and south reflection of those by spine 111 5063 and spine 112. The resulting SPF in ToF 22 issues a new prefix South 5064 TIEs containing 1.1/16. None of the leaves become aware of the 5065 changes and the failure is constrained strictly to the level that 5066 became partitioned. 5068 To finish with an example of the resulting sets computed using 5069 notation introduced in Section 4.2.5, Top-of-Fabric 22 constructs the 5070 following sets: 5072 |R = Prefix 111, Prefix 112, Prefix 121, Prefix 122 5074 |H (for r=Prefix 111) = Spine 111, Spine 112 5076 |H (for r=Prefix 112) = Spine 111, Spine 112 5078 |H (for r=Prefix 121) = Spine 121, Spine 122 5080 |H (for r=Prefix 122) = Spine 121, Spine 122 5082 |A (for ToF 21) = Spine 111, Spine 112 5084 With that and |H (for r=prefix 121) and |H (for r=prefix 122) being 5085 disjoint from |A (for Top-of-Fabric 21), ToF 22 will originate an 5086 South TIE with prefix 121 and prefix 122, that is flooded to spines 5087 112, 112, 121 and 122. 5089 5.4. Northbound Partitioned Router and Optional East-West Links 5091 . + + + 5092 . X N1 | N2 | N3 5093 . X | | 5094 .+--+----+ +--+----+ +--+-----+ 5095 .| |0/0> <0/0| |0/0> <0/0| | 5096 .| A01 +----------+ A02 +----------+ A03 | Level 1 5097 .++-+-+--+ ++--+--++ +---+-+-++ 5098 . | | | | | | | | | 5099 . | | +----------------------------------+ | | | 5100 . | | | | | | | | | 5101 . | +-------------+ | | | +--------------+ | 5102 . | | | | | | | | | 5103 . | +----------------+ | +-----------------+ | 5104 . | | | | | | | | | 5105 . | | +------------------------------------+ | | 5106 . | | | | | | | | | 5107 .++-+-+--+ | +---+---+ | +-+---+-++ 5108 .| | +-+ +-+ | | 5109 .| L01 | | L02 | | L03 | Level 0 5110 .+-------+ +-------+ +--------+ 5112 Figure 34: North Partitioned Router 5114 Figure 34 shows a part of a fabric where level 1 is horizontally 5115 connected and A01 lost its only northbound adjacency. Based on N-SPF 5116 rules in Section 4.2.4.1 A01 will compute northbound reachability by 5117 using the link A01 to A02 (whereas A02 will NOT use this link during 5118 N-SPF). Hence A01 will still advertise the default towards level 0 5119 and route unidirectionally using the horizontal link. 5121 As further consideration, the moment A02 looses link N2 the situation 5122 evolves again. A01 will have no more northbound reachability while 5123 still seeing A03 advertising northbound adjacencies in its south node 5124 tie. With that it will stop advertising a default route due to 5125 Section 4.2.3.8. 5127 6. Implementation and Operation: Further Details 5129 6.1. Considerations for Leaf-Only Implementation 5131 RIFT can and is intended to be stretched to the lowest level in the 5132 IP fabric to integrate ToRs or even servers. Since those entities 5133 would run as leaves only, it is worth to observe that a leaf only 5134 version is significantly simpler to implement and requires much less 5135 resources: 5137 1. Under normal conditions, the leaf needs to support a multipath 5138 default route only. In most catastrophic partitioning case it 5139 has to be capable of accommodating all the leaf routes in its own 5140 PoD to prevent black-holing. 5142 2. Leaf nodes hold only their own North TIEs and South TIEs of Level 5143 1 nodes they are connected to; so overall few in numbers. 5145 3. Leaf node does not have to support any type of de-aggregation 5146 computation or propagation. 5148 4. Leaf nodes do not have to support overload bit normally. 5150 5. Unless optional leaf-2-leaf procedures are desired default route 5151 origination and South TIE origination is unnecessary. 5153 6.2. Considerations for Spine Implementation 5155 In case of spines, i.e. nodes that will never act as Top of Fabric a 5156 full implementation is not required, specifically the node does not 5157 need to perform any computation of negative disaggregation except 5158 respecting northbound disaggregation advertised from the north. 5160 6.3. Adaptations to Other Proposed Data Center Topologies 5162 . +-----+ +-----+ 5163 . | | | | 5164 .+-+ S0 | | S1 | 5165 .| ++---++ ++---++ 5166 .| | | | | 5167 .| | +------------+ | 5168 .| | | +------------+ | 5169 .| | | | | 5170 .| ++-+--+ +--+-++ 5171 .| | | | | 5172 .| | A0 | | A1 | 5173 .| +-+--++ ++---++ 5174 .| | | | | 5175 .| | +------------+ | 5176 .| | +-----------+ | | 5177 .| | | | | 5178 .| +-+-+-+ +--+-++ 5179 .+-+ | | | 5180 . | L0 | | L1 | 5181 . +-----+ +-----+ 5183 Figure 35: Level Shortcut 5185 Strictly speaking, RIFT is not limited to Clos variations only. The 5186 protocol preconditions only a sense of 'compass rose direction' 5187 achieved by configuration (or derivation) of levels and other 5188 topologies are possible within this framework. So, conceptually, one 5189 could include leaf to leaf links and even shortcut between levels 5191 As an example, short cutting levels illustrated in Figure 35 will 5192 lead either to suboptimal routing when L0 sends traffic to L1 (since 5193 using S0's default route will lead to the traffic being sent back to 5194 A0 or A1) or the leaves need each other's routes installed to 5195 understand that only A0 and A1 should be used to talk to each other. 5197 Whether such modifications of topology constraints make sense is 5198 dependent on many technology variables and the exhausting treatment 5199 of the topic is definitely outside the scope of this document. 5201 6.4. Originating Non-Default Route Southbound 5203 Obviously, an implementation MAY choose to originate southbound 5204 instead of a strict default route (as described in Section 4.2.3.8) a 5205 shorter prefix P' but in such a scenario all addresses carried within 5206 the RIFT domain must be contained within P'. 5208 7. Security Considerations 5210 7.1. General 5212 One can consider attack vectors where a router may reboot many times 5213 while changing its system ID and pollute the network with many stale 5214 TIEs or TIEs are sent with very long lifetimes and not cleaned up 5215 when the routes vanishes. Those attack vectors are not unique to 5216 RIFT. Given large memory footprints available today those attacks 5217 should be relatively benign. Otherwise a node SHOULD implement a 5218 strategy of discarding contents of all TIEs that were not present in 5219 the SPF tree over a certain, configurable period of time. Since the 5220 protocol, like all modern link-state protocols, is self-stabilizing 5221 and will advertise the presence of such TIEs to its neighbors, they 5222 can be re-requested again if a computation finds that it sees an 5223 adjacency formed towards the system ID of the discarded TIEs. 5225 7.2. ZTP 5227 Section 4.2.7 presents many attack vectors in untrusted environments, 5228 starting with nodes that oscillate their level offers to the 5229 possibility of a node offering a three-way adjacency with the highest 5230 possible level value with a very long holdtime trying to put itself 5231 "on top of the lattice" and with that gaining access to the whole 5232 southbound topology. Session authentication mechanisms are necessary 5233 in environments where this is possible and RIFT provides the 5234 according security envelope to ensure this if desired. 5236 7.3. Lifetime 5238 Traditional IGP protocols are vulnerable to lifetime modification and 5239 replay attacks that can be somewhat mitigated by using techniques 5240 like [RFC7987]. RIFT removes this attack vector by protecting the 5241 lifetime behind a signature computed over it and additional nonce 5242 combination which makes even the replay attack window very small and 5243 for practical purposes irrelevant since lifetime cannot be 5244 artificially shortened by the attacker. 5246 7.4. Packet Number 5248 Optional packet number is carried in the security envelope without 5249 any encryption protection and is hence vulnerable to replay and 5250 modification attacks. Contrary to nonces this number must change on 5251 every packet and would present a very high cryptographic load if 5252 signed. The attack vector packet number present is relatively 5253 benign. Changing the packet number by a man-in-the-middle attack 5254 will only affect operational validation tools and possibly some 5255 performance optimizations on flooding. It is expected that an 5256 implementation detecting too many "fake losses" or "misorderings" due 5257 to the attack on the packet number would simply suppress its further 5258 processing. 5260 7.5. Outer Fingerprint Attacks 5262 A node can try to inject LIE packets observing a conversation on the 5263 wire by using the outer key ID albeit it cannot generate valid hashes 5264 in case it changes the integrity of the message so the only possible 5265 attack is DoS due to excessive LIE validation. 5267 A node can try to replay previous LIEs with changed state that it 5268 recorded but the attack is hard to replicate since the nonce 5269 combination must match the ongoing exchange and is then limited to a 5270 single flap only since both nodes will advance their nonces in case 5271 the adjacency state changed. Even in the most unlikely case the 5272 attack length is limited due to both sides periodically increasing 5273 their nonces. 5275 7.6. TIE Origin Fingerprint DoS Attacks 5277 A compromised node can attempt to generate "fake TIEs" using other 5278 nodes' TIE origin key identifiers. Albeit the ultimate validation of 5279 the origin fingerprint will fail in such scenarios and not progress 5280 further than immediately peering nodes, the resulting denial of 5281 service attack seems unavoidable since the TIE origin key id is only 5282 protected by the, here assumed to be compromised, node. 5284 7.7. Host Implementations 5286 It can be reasonably expected that with the proliferation of RotH 5287 servers, rather than dedicated networking devices, will constitute 5288 significant amount of RIFT devices. Given their normally far wider 5289 software envelope and access granted to them, such servers are also 5290 far more likely to be compromised and present an attack vector on the 5291 protocol. Hijacking of prefixes to attract traffic is a trust 5292 problem and cannot be addressed within the protocol if the trust 5293 model is breached, i.e. the server presents valid credentials to form 5294 an adjacency and issue TIEs. However, in a move devious way, the 5295 servers can present DoS (or even DDos) vectors of issuing too many 5296 LIE packets, flood large amount of North TIEs and similar anomalies. 5297 A prudent implementation hosting leaves should implement thresholds 5298 and raise warnings when leaf is advertising number of TIEs in excess 5299 of those. 5301 8. IANA Considerations 5303 This specification requests multicast address assignments and 5304 standard port numbers. Additionally registries for the schema are 5305 requested and suggested values provided that reflect the numbers 5306 allocated in the given schema. 5308 8.1. Requested Multicast and Port Numbers 5310 This document requests allocation in the 'IPv4 Multicast Address 5311 Space' registry the suggested value of 224.0.0.120 as 5312 'ALL_V4_RIFT_ROUTERS' and in the 'IPv6 Multicast Address Space' 5313 registry the suggested value of FF02::A1F7 as 'ALL_V6_RIFT_ROUTERS'. 5315 This document requests allocation in the 'Service Name and Transport 5316 Protocol Port Number Registry' the allocation of a suggested value of 5317 914 on udp for 'RIFT_LIES_PORT' and suggested value of 915 for 5318 'RIFT_TIES_PORT'. 5320 8.2. Requested Registries with Suggested Values 5322 This section requests registries that help govern the schema via 5323 usual IANA registry procedures. A top level 'RIFT' registry should 5324 hold the according registries requested in following sections with 5325 their pre-defined values. IANA is requested to store the schema 5326 version introducing the allocated value as well as, optionally, its 5327 description when present. This will allow to assign different values 5328 to an entry depending on schema version. Alternately, IANA is 5329 requested to consider a root RIFT/2 registry to store RIFT schema 5330 major version 2 values and may be requested in the future to create a 5331 RIFT/3 registry under that. In any case, IANA is requested to store 5332 the schema version in the entries since that will allow to 5333 distinguish between minor versions in the same major schema version. 5334 All values not suggested as to be considered `Unassigned`. The range 5335 of every registry is a 16-bit integer. Allocation of new values is 5336 always performed via `Expert Review` action. 5338 8.2.1. Registry RIFT/common/AddressFamilyType 5340 Address family type. 5342 8.2.1.1. Requested Entries 5344 Name Value Schema Version Description 5345 Illegal 0 2.0 5346 AddressFamilyMinValue 1 2.0 5347 IPv4 2 2.0 5348 IPv6 3 2.0 5349 AddressFamilyMaxValue 4 2.0 5351 8.2.2. Registry RIFT/common/HierarchyIndications 5353 Flags indicating node configuration in case of ZTP. 5355 8.2.2.1. Requested Entries 5357 Name Value Schema Version Description 5358 leaf_only 0 2.0 5359 leaf_only_and_leaf_2_leaf_procedures 1 2.0 5360 top_of_fabric 2 2.0 5362 8.2.3. Registry RIFT/common/IEEE802_1ASTimeStampType 5364 Timestamp per IEEE 802.1AS, all values MUST be interpreted in 5365 implementation as unsigned. 5367 8.2.3.1. Requested Entries 5369 Name Value Schema Version Description 5370 AS_sec 1 2.0 5371 AS_nsec 2 2.0 5373 8.2.4. Registry RIFT/common/IPAddressType 5375 IP address type. 5377 8.2.4.1. Requested Entries 5379 Name Value Schema Version Description 5380 ipv4address 1 2.0 Content is IPv4 5381 ipv6address 2 2.0 Content is IPv6 5383 8.2.5. Registry RIFT/common/IPPrefixType 5385 Prefix advertisement. 5387 @note: for interface addresses the protocol can propagate the address 5388 part beyond the subnet mask and on reachability computation that has 5389 to be normalized. The non-significant bits can be used for 5390 operational purposes. 5392 8.2.5.1. Requested Entries 5394 Name Value Schema Version Description 5395 ipv4prefix 1 2.0 5396 ipv6prefix 2 2.0 5398 8.2.6. Registry RIFT/common/IPv4PrefixType 5400 IPv4 prefix type. 5402 8.2.6.1. Requested Entries 5404 Name Value Schema Version Description 5405 address 1 2.0 5406 prefixlen 2 2.0 5408 8.2.7. Registry RIFT/common/IPv6PrefixType 5410 IPv6 prefix type. 5412 8.2.7.1. Requested Entries 5414 Name Value Schema Version Description 5415 address 1 2.0 5416 prefixlen 2 2.0 5418 8.2.8. Registry RIFT/common/PrefixSequenceType 5420 Sequence of a prefix in case of move. 5422 8.2.8.1. Requested Entries 5424 Name Value Schema Description 5425 Version 5426 timestamp 1 2.0 5427 transactionid 2 2.0 Transaction ID set by client in e.g. 5428 in 6LoWPAN. 5430 8.2.9. Registry RIFT/common/RouteType 5432 RIFT route types. 5434 @note: route types which MUST be ordered on their preference PGP 5435 prefixes are most preferred attracting traffic north (towards spine) 5436 and then south normal prefixes are attracting traffic south (towards 5437 leaves), i.e. prefix in NORTH PREFIX TIE is preferred over SOUTH 5438 PREFIX TIE. 5440 @note: The only purpose of those values is to introduce an ordering 5441 whereas an implementation can choose internally any other values as 5442 long the ordering is preserved 5444 8.2.9.1. Requested Entries 5446 Name Value Schema Version Description 5447 Illegal 0 2.0 5448 RouteTypeMinValue 1 2.0 5449 Discard 2 2.0 5450 LocalPrefix 3 2.0 5451 SouthPGPPrefix 4 2.0 5452 NorthPGPPrefix 5 2.0 5453 NorthPrefix 6 2.0 5454 NorthExternalPrefix 7 2.0 5455 SouthPrefix 8 2.0 5456 SouthExternalPrefix 9 2.0 5457 NegativeSouthPrefix 10 2.0 5458 RouteTypeMaxValue 11 2.0 5460 8.2.10. Registry RIFT/common/TIETypeType 5462 Type of TIE. 5464 This enum indicates what TIE type the TIE is carrying. In case the 5465 value is not known to the receiver, the TIE MUST be re-flooded. This 5466 allows for future extensions of the protocol within the same major 5467 schema with types opaque to some nodes UNLESS the flooding scope is 5468 not the same as prefix TIE, then a major version revision MUST be 5469 performed. 5471 8.2.10.1. Requested Entries 5473 Name Value Schema Description 5474 Version 5475 Illegal 0 2.0 5476 TIETypeMinValue 1 2.0 5477 NodeTIEType 2 2.0 5478 PrefixTIEType 3 2.0 5479 PositiveDisaggregationPrefixTIEType 4 2.0 5480 NegativeDisaggregationPrefixTIEType 5 2.0 5481 PGPrefixTIEType 6 2.0 5482 KeyValueTIEType 7 2.0 5483 ExternalPrefixTIEType 8 2.0 5484 PositiveExternalDisaggregationPrefixTIEType 9 2.0 5485 TIETypeMaxValue 10 2.0 5487 8.2.11. Registry RIFT/common/TieDirectionType 5489 Direction of TIEs. 5491 8.2.11.1. Requested Entries 5493 Name Value Schema Version Description 5494 Illegal 0 2.0 5495 South 1 2.0 5496 North 2 2.0 5497 DirectionMaxValue 3 2.0 5499 8.2.12. Registry RIFT/encoding/Community 5501 Prefix community. 5503 8.2.12.1. Requested Entries 5505 Name Value Schema Version Description 5506 top 1 2.0 Higher order bits 5507 bottom 2 2.0 Lower order bits 5509 8.2.13. Registry RIFT/encoding/KeyValueTIEElement 5511 Generic key value pairs. 5513 8.2.13.1. Requested Entries 5515 Name Value Schema Version Description 5516 keyvalues 1 2.0 5518 8.2.14. Registry RIFT/encoding/LIEPacket 5520 RIFT LIE Packet. 5522 @note: this node's level is already included on the packet header 5524 8.2.14.1. Requested Entries 5526 Name Value Schema Description 5527 Version 5528 name 1 2.0 Node or adjacency name. 5529 local_id 2 2.0 Local link ID. 5530 flood_port 3 2.0 UDP port to which we can 5531 receive flooded TIEs. 5532 link_mtu_size 4 2.0 Layer 3 MTU, used to 5533 discover to mismatch. 5534 link_bandwidth 5 2.0 Local link bandwidth on 5535 the interface. 5536 neighbor 6 2.0 Reflects the neighbor once 5537 received to provide 5538 3-way connectivity. 5539 pod 7 2.0 Node's PoD. 5540 node_capabilities 10 2.0 Node capabilities shown in 5541 the LIE. The capabilities 5542 MUST match the capabilities 5543 shown in the Node TIEs, 5544 otherwise 5545 the behavior is 5546 unspecified. A node 5547 detecting the mismatch 5548 SHOULD generate according 5549 error. 5550 link_capabilities 11 2.0 Capabilities of this link. 5551 holdtime 12 2.0 Required holdtime of the 5552 adjacency, i.e. how much 5553 time 5554 MUST expire without LIE for 5555 the adjacency to drop. 5556 label 13 2.0 Unsolicited, downstream 5557 assigned locally 5558 significant label 5559 value for the adjacency. 5560 not_a_ztp_offer 21 2.0 Indicates that the level 5561 on the LIE MUST NOT be used 5562 to derive a ZTP level by 5563 the receiving node. 5564 you_are_flood_repeater 22 2.0 Indicates to northbound 5565 neighbor that it should 5566 be reflooding this node's 5567 N-TIEs to achieve flood 5568 reduction and 5569 balancing for northbound 5570 flooding. To be ignored if 5571 received from a 5572 northbound adjacency. 5573 you_are_sending_too_quickly 23 2.0 Can be optionally set to 5574 indicate to neighbor that 5575 packet losses are seen on 5576 reception based on packet 5577 numbers or the rate is too 5578 high. The receiver SHOULD 5579 temporarily slow down 5580 flooding rates. 5581 instance_name 24 2.0 Instance name in case 5582 multiple RIFT instances 5583 running on same interface. 5585 8.2.15. Registry RIFT/encoding/LinkCapabilities 5587 Link capabilities. 5589 8.2.15.1. Requested Entries 5591 Name Value Schema Description 5592 Version 5593 bfd 1 2.0 Indicates that the link is 5594 supporting BFD. 5595 v4_forwarding_capable 2 2.0 5597 8.2.16. Registry RIFT/encoding/LinkIDPair 5599 LinkID pair describes one of parallel links between two nodes. 5601 8.2.16.1. Requested Entries 5602 Name Value Schema Description 5603 Version 5604 local_id 1 2.0 Node-wide unique value for 5605 the local link. 5606 remote_id 2 2.0 Received remote link ID for 5607 this link. 5608 platform_interface_index 10 2.0 Describes the local 5609 interface index of the link. 5610 platform_interface_name 11 2.0 Describes the local 5611 interface name. 5612 trusted_outer_security_key 12 2.0 Indication whether the link 5613 is secured, i.e. protected 5614 by outer key, absence 5615 of this element means no 5616 indication, undefined outer 5617 key means not secured. 5618 bfd_up 13 2.0 Indication whether the link 5619 is protected by established 5620 BFD session. 5622 8.2.17. Registry RIFT/encoding/Neighbor 5624 Neighbor structure. 5626 8.2.17.1. Requested Entries 5628 Name Value Schema Version Description 5629 originator 1 2.0 System ID of the originator. 5630 remote_id 2 2.0 ID of remote side of the link. 5632 8.2.18. Registry RIFT/encoding/NodeCapabilities 5634 Capabilities the node supports. 5636 @note: The schema may add to this field future capabilities to 5637 indicate whether it will support interpretation of future schema 5638 extensions on the same major revision. Such fields MUST be optional 5639 and have an implicit or explicit false default value. If a future 5640 capability changes route selection or generates blackholes if some 5641 nodes are not supporting it then a major version increment is 5642 unavoidable. 5644 8.2.18.1. Requested Entries 5645 Name Value Schema Description 5646 Version 5647 protocol_minor_version 1 2.0 Must advertise supported minor 5648 version dialect that way. 5649 flood_reduction 2 2.0 Can this node participate in 5650 flood reduction. 5651 hierarchy_indications 3 2.0 Does this node restrict itself 5652 to be top-of-fabric or 5653 leaf only (in ZTP) and does it 5654 support leaf-2-leaf procedures. 5656 8.2.19. Registry RIFT/encoding/NodeFlags 5658 Indication flags of the node. 5660 8.2.19.1. Requested Entries 5662 Name Value Schema Description 5663 Version 5664 overload 1 2.0 Indicates that node is in overload, do not 5665 transit traffic through it. 5667 8.2.20. Registry RIFT/encoding/NodeNeighborsTIEElement 5669 neighbor of a node 5671 8.2.20.1. Requested Entries 5673 Name Value Schema Description 5674 Version 5675 level 1 2.0 level of neighbor 5676 cost 3 2.0 5677 link_ids 4 2.0 can carry description of multiple parallel 5678 links in a TIE 5679 bandwidth 5 2.0 total bandwidth to neighbor, this will be 5680 normally sum of the 5681 bandwidths of all the parallel links. 5683 8.2.21. Registry RIFT/encoding/NodeTIEElement 5685 Description of a node. 5687 It may occur multiple times in different TIEs but if either 5689 capabilities values do not match or 5691 flags values do not match or 5692 neighbors repeat with different values 5694 the behavior is undefined and a warning SHOULD be generated. 5695 Neighbors can be distributed across multiple TIEs however if the sets 5696 are disjoint. Miscablings SHOULD be repeated in every node TIE, 5697 otherwise the behavior is undefined. 5699 @note: Observe that absence of fields implies defined defaults. 5701 8.2.21.1. Requested Entries 5703 Name Value Schema Description 5704 Version 5705 level 1 2.0 Level of the node. 5706 neighbors 2 2.0 Node's neighbors. If neighbor systemID 5707 repeats in other node TIEs of 5708 same node the behavior is undefined. 5709 capabilities 3 2.0 Capabilities of the node. 5710 flags 4 2.0 Flags of the node. 5711 name 5 2.0 Optional node name for easier 5712 operations. 5713 pod 6 2.0 PoD to which the node belongs. 5714 miscabled_links 10 2.0 If any local links are miscabled, the 5715 indication is flooded. 5717 8.2.22. Registry RIFT/encoding/PacketContent 5719 Content of a RIFT packet. 5721 8.2.22.1. Requested Entries 5723 Name Value Schema Version Description 5724 lie 1 2.0 5725 tide 2 2.0 5726 tire 3 2.0 5727 tie 4 2.0 5729 8.2.23. Registry RIFT/encoding/PacketHeader 5731 Common RIFT packet header. 5733 8.2.23.1. Requested Entries 5734 Name Value Schema Description 5735 Version 5736 major_version 1 2.0 Major version of protocol. 5737 minor_version 2 2.0 Minor version of protocol. 5738 sender 3 2.0 Node sending the packet, in case of 5739 LIE/TIRE/TIDE also 5740 the originator of it. 5741 level 4 2.0 Level of the node sending the packet, 5742 required on everything except 5743 LIEs. Lack of presence on LIEs indicates 5744 UNDEFINED_LEVEL and is used 5745 in ZTP procedures. 5747 8.2.24. Registry RIFT/encoding/PrefixAttributes 5749 Attributes of a prefix. 5751 8.2.24.1. Requested Entries 5753 Name Value Schema Description 5754 Version 5755 metric 2 2.0 Distance of the prefix. 5756 tags 3 2.0 Generic unordered set of route tags, 5757 can be redistributed to other 5758 protocols or use 5759 within the context of real time 5760 analytics. 5761 monotonic_clock 4 2.0 Monotonic clock for mobile 5762 addresses. 5763 loopback 6 2.0 Indicates if the interface is a node 5764 loopback. 5765 directly_attached 7 2.0 Indicates that the prefix is 5766 directly attached, i.e. should be 5767 routed to even if 5768 the node is in overload. * 5769 from_link 10 2.0 In case of locally originated 5770 prefixes, i.e. interface addresses 5771 this can describe 5772 which link the address belongs to. 5774 8.2.25. Registry RIFT/encoding/PrefixTIEElement 5776 TIE carrying prefixes 5778 8.2.25.1. Requested Entries 5780 Name Value Schema Description 5781 Version 5782 prefixes 1 2.0 Prefixes with the associated attributes. 5783 If the same prefix repeats in multiple TIEs of 5784 same node behavior is 5785 unspecified. 5787 8.2.26. Registry RIFT/encoding/ProtocolPacket 5789 RIFT packet structure. 5791 8.2.26.1. Requested Entries 5793 Name Value Schema Version Description 5794 header 1 2.0 5795 content 2 2.0 5797 8.2.27. Registry RIFT/encoding/TIDEPacket 5799 TIDE with sorted TIE headers, if headers are unsorted, behavior is 5800 undefined. 5802 8.2.27.1. Requested Entries 5804 Name Value Schema Version Description 5805 start_range 1 2.0 First TIE header in the tide 5806 packet. 5807 end_range 2 2.0 Last TIE header in the tide packet. 5808 headers 3 2.0 _Sorted_ list of headers. 5810 8.2.28. Registry RIFT/encoding/TIEElement 5812 Single element in a TIE. 5814 Schema enum `common.TIETypeType` in TIEID indicates which elements 5815 MUST be present in the TIEElement. In case of mismatch the 5816 unexpected elements MUST be ignored. In case of lack of expected 5817 element the TIE an error MUST be reported and the TIE MUST be 5818 ignored. 5820 This type can be extended with new optional elements for new 5821 `common.TIETypeType` values without breaking the major but if it is 5822 necessary to understand whether all nodes support the new type a node 5823 capability must be added as well. 5825 8.2.28.1. Requested Entries 5827 Name Valu Schem Description 5828 e a Ver 5829 sion 5830 node 1 2.0 Used in case of enum comm 5831 on.TIETypeType.NodeTIEType 5832 . 5833 prefixes 2 2.0 Used in case of enum comm 5834 on.TIETypeType.PrefixTIETy 5835 pe. 5836 positive_disaggregation_prefixe 3 2.0 Positive prefixes (always 5837 s southbound). 5838 It MUST NOT be advertised 5839 within a North TIE and 5840 ignored otherwise 5841 negative_disaggregation_prefixe 5 2.0 Transitive, negative 5842 s prefixes (always 5843 southbound) which 5844 MUST be aggregated and 5845 propagated 5846 according to the 5847 specification 5848 southwards towards lower 5849 levels to heal 5850 pathological upper level 5851 partitioning, otherwise 5852 blackholes may occur in 5853 multiplane fabrics. 5854 It MUST NOT be advertised 5855 within a North TIE. 5856 external_prefixes 6 2.0 Externally reimported 5857 prefixes. 5858 positive_external_disaggregatio 7 2.0 Positive external 5859 n_prefixes disaggregated prefixes 5860 (always southbound). 5861 It MUST NOT be advertised 5862 within a North TIE and 5863 ignored otherwise. 5864 keyvalues 9 2.0 Key-Value store elements. 5866 8.2.29. Registry RIFT/encoding/TIEHeader 5868 Header of a TIE. 5870 @note: TIEID space is a total order achieved by comparing the 5871 elements in sequence defined and comparing each value as an unsigned 5872 integer of according length. 5874 @note: After sequence number the lifetime received on the envelope 5875 must be used for comparison before further fields. 5877 @note: `origination_time` and `origination_lifetime` are disregarded 5878 for comparison purposes and carried purely for debugging/security 5879 purposes if present. 5881 8.2.29.1. Requested Entries 5883 Name Value Schema Description 5884 Version 5885 tieid 2 2.0 ID of the tie. 5886 seq_nr 3 2.0 Sequence number of the tie. 5887 origination_time 10 2.0 Absolute timestamp when the TIE 5888 was generated. This can be used on 5889 fabrics with 5890 synchronized clock to prevent 5891 lifetime modification attacks. 5892 origination_lifetime 12 2.0 Original lifetime when the TIE 5893 was generated. This can be used on 5894 fabrics with 5895 synchronized clock to prevent 5896 lifetime modification attacks. 5898 8.2.30. Registry RIFT/encoding/TIEHeaderWithLifeTime 5900 Header of a TIE as described in TIRE/TIDE. 5902 8.2.30.1. Requested Entries 5904 Name Value Schema Description 5905 Version 5906 header 1 2.0 5907 remaining_lifetime 2 2.0 Remaining lifetime that expires 5908 down to 0 just like in ISIS. 5909 TIEs with lifetimes differing by 5910 less than `lifetime_diff2ignore` 5911 MUST be 5912 considered EQUAL. 5914 8.2.31. Registry RIFT/encoding/TIEID 5916 ID of a TIE. 5918 @note: TIEID space is a total order achieved by comparing the 5919 elements in sequence defined and comparing each value as an unsigned 5920 integer of according length. 5922 8.2.31.1. Requested Entries 5924 Name Value Schema Version Description 5925 direction 1 2.0 direction of TIE 5926 originator 2 2.0 indicates originator of the TIE 5927 tietype 3 2.0 type of the tie 5928 tie_nr 4 2.0 number of the tie 5930 8.2.32. Registry RIFT/encoding/TIEPacket 5932 TIE packet 5934 8.2.32.1. Requested Entries 5936 Name Value Schema Version Description 5937 header 1 2.0 5938 element 2 2.0 5940 8.2.33. Registry RIFT/encoding/TIREPacket 5942 TIRE packet 5944 8.2.33.1. Requested Entries 5946 Name Value Schema Version Description 5947 headers 1 2.0 5949 9. Acknowledgments 5951 A new routing protocol in its complexity is not a product of a parent 5952 but of a village as the author list shows already. However, many 5953 more people provided input, fine-combed the specification based on 5954 their experience in design or implementation. This section will make 5955 an inadequate attempt in recording their contribution. 5957 Many thanks to Naiming Shen for some of the early discussions around 5958 the topic of using IGPs for routing in topologies related to Clos. 5959 Russ White to be especially acknowledged for the key conversation on 5960 epistemology that allowed to tie current asynchronous distributed 5961 systems theory results to a modern protocol design presented here. 5962 Adrian Farrel, Joel Halpern, Jeffrey Zhang, Krzysztof Szarkowicz, 5963 Nagendra Kumar, Melchior Aelmans provided thoughtful comments that 5964 improved the readability of the document and found good amount of 5965 corners where the light failed to shine. Kris Price was first to 5966 mention single router, single arm default considerations. Jeff 5967 Tantsura helped out with some initial thoughts on BFD interactions 5968 while Jeff Haas corrected several misconceptions about BFD's finer 5969 points. Artur Makutunowicz pointed out many possible improvements 5970 and acted as sounding board in regard to modern protocol 5971 implementation techniques RIFT is exploring. Barak Gafni formalized 5972 first time clearly the problem of partitioned spine and fallen leaves 5973 on a (clean) napkin in Singapore that led to the very important part 5974 of the specification centered around multiple Top-of-Fabric planes 5975 and negative disaggregation. Igor Gashinsky and others shared many 5976 thoughts on problems encountered in design and operation of large- 5977 scale data center fabrics. Xu Benchong found a delicate error in the 5978 flooding procedures while implementing. 5980 10. References 5982 10.1. Normative References 5984 [EUI64] IEEE, "Guidelines for Use of Extended Unique Identifier 5985 (EUI), Organizationally Unique Identifier (OUI), and 5986 Company ID (CID)", IEEE EUI, 5987 . 5989 [ISO10589] 5990 ISO "International Organization for Standardization", 5991 "Intermediate system to Intermediate system intra-domain 5992 routeing information exchange protocol for use in 5993 conjunction with the protocol for providing the 5994 connectionless-mode Network Service (ISO 8473), ISO/IEC 5995 10589:2002, Second Edition.", Nov 2002. 5997 [RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982, 5998 DOI 10.17487/RFC1982, August 1996, 5999 . 6001 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, 6002 DOI 10.17487/RFC2328, April 1998, 6003 . 6005 [RFC2365] Meyer, D., "Administratively Scoped IP Multicast", BCP 23, 6006 RFC 2365, DOI 10.17487/RFC2365, July 1998, 6007 . 6009 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 6010 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 6011 DOI 10.17487/RFC4271, January 2006, 6012 . 6014 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 6015 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 6016 2006, . 6018 [RFC5082] Gill, V., Heasley, J., Meyer, D., Savola, P., Ed., and C. 6019 Pignataro, "The Generalized TTL Security Mechanism 6020 (GTSM)", RFC 5082, DOI 10.17487/RFC5082, October 2007, 6021 . 6023 [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi 6024 Topology (MT) Routing in Intermediate System to 6025 Intermediate Systems (IS-ISs)", RFC 5120, 6026 DOI 10.17487/RFC5120, February 2008, 6027 . 6029 [RFC5303] Katz, D., Saluja, R., and D. Eastlake 3rd, "Three-Way 6030 Handshake for IS-IS Point-to-Point Adjacencies", RFC 5303, 6031 DOI 10.17487/RFC5303, October 2008, 6032 . 6034 [RFC5549] Le Faucheur, F. and E. Rosen, "Advertising IPv4 Network 6035 Layer Reachability Information with an IPv6 Next Hop", 6036 RFC 5549, DOI 10.17487/RFC5549, May 2009, 6037 . 6039 [RFC5709] Bhatia, M., Manral, V., Fanto, M., White, R., Barnes, M., 6040 Li, T., and R. Atkinson, "OSPFv2 HMAC-SHA Cryptographic 6041 Authentication", RFC 5709, DOI 10.17487/RFC5709, October 6042 2009, . 6044 [RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 6045 (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, 6046 DOI 10.17487/RFC5881, June 2010, 6047 . 6049 [RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch, 6050 "Network Time Protocol Version 4: Protocol and Algorithms 6051 Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010, 6052 . 6054 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 6055 S. Ray, "North-Bound Distribution of Link-State and 6056 Traffic Engineering (TE) Information Using BGP", RFC 7752, 6057 DOI 10.17487/RFC7752, March 2016, 6058 . 6060 [RFC7987] Ginsberg, L., Wells, P., Decraene, B., Przygienda, T., and 6061 H. Gredler, "IS-IS Minimum Remaining Lifetime", RFC 7987, 6062 DOI 10.17487/RFC7987, October 2016, 6063 . 6065 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 6066 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 6067 May 2017, . 6069 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 6070 (IPv6) Specification", STD 86, RFC 8200, 6071 DOI 10.17487/RFC8200, July 2017, 6072 . 6074 [RFC8202] Ginsberg, L., Previdi, S., and W. Henderickx, "IS-IS 6075 Multi-Instance", RFC 8202, DOI 10.17487/RFC8202, June 6076 2017, . 6078 [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. 6079 Perkins, "Registration Extensions for IPv6 over Low-Power 6080 Wireless Personal Area Network (6LoWPAN) Neighbor 6081 Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, 6082 . 6084 [thrift] Apache Software Foundation, "Thrift Interface Description 6085 Language", . 6087 10.2. Informative References 6089 [CLOS] Yuan, X., "On Nonblocking Folded-Clos Networks in Computer 6090 Communication Environments", IEEE International Parallel & 6091 Distributed Processing Symposium, 2011. 6093 [DIJKSTRA] 6094 Dijkstra, E., "A Note on Two Problems in Connexion with 6095 Graphs", Journal Numer. Math. , 1959. 6097 [DOT] Ellson, J. and L. Koutsofios, "Graphviz: open source graph 6098 drawing tools", Springer-Verlag , 2001. 6100 [DYNAMO] De Candia et al., G., "Dynamo: amazon's highly available 6101 key-value store", ACM SIGOPS symposium on Operating 6102 systems principles (SOSP '07), 2007. 6104 [EPPSTEIN] 6105 Eppstein, D., "Finding the k-Shortest Paths", 1997. 6107 [FATTREE] Leiserson, C., "Fat-Trees: Universal Networks for 6108 Hardware-Efficient Supercomputing", 1985. 6110 [IEEEstd1588] 6111 IEEE, "IEEE Standard for a Precision Clock Synchronization 6112 Protocol for Networked Measurement and Control Systems", 6113 IEEE Standard 1588, 6114 . 6116 [IEEEstd8021AS] 6117 IEEE, "IEEE Standard for Local and Metropolitan Area 6118 Networks - Timing and Synchronization for Time-Sensitive 6119 Applications in Bridged Local Area Networks", 6120 IEEE Standard 802.1AS, 6121 . 6123 [ISO10589-Second-Edition] 6124 International Organization for Standardization, 6125 "Intermediate system to Intermediate system intra-domain 6126 routeing information exchange protocol for use in 6127 conjunction with the protocol for providing the 6128 connectionless-mode Network Service (ISO 8473)", Nov 2002. 6130 [RFC0826] Plummer, D., "An Ethernet Address Resolution Protocol: Or 6131 Converting Network Protocol Addresses to 48.bit Ethernet 6132 Address for Transmission on Ethernet Hardware", STD 37, 6133 RFC 826, DOI 10.17487/RFC0826, November 1982, 6134 . 6136 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", 6137 RFC 2131, DOI 10.17487/RFC2131, March 1997, 6138 . 6140 [RFC3626] Clausen, T., Ed. and P. Jacquet, Ed., "Optimized Link 6141 State Routing Protocol (OLSR)", RFC 3626, 6142 DOI 10.17487/RFC3626, October 2003, 6143 . 6145 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 6146 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 6147 DOI 10.17487/RFC4861, September 2007, 6148 . 6150 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 6151 Address Autoconfiguration", RFC 4862, 6152 DOI 10.17487/RFC4862, September 2007, 6153 . 6155 [RFC6518] Lebovitz, G. and M. Bhatia, "Keying and Authentication for 6156 Routing Protocols (KARP) Design Guidelines", RFC 6518, 6157 DOI 10.17487/RFC6518, February 2012, 6158 . 6160 [RFC7938] Lapukhov, P., Premji, A., and J. Mitchell, Ed., "Use of 6161 BGP for Routing in Large-Scale Data Centers", RFC 7938, 6162 DOI 10.17487/RFC7938, August 2016, 6163 . 6165 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 6166 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 6167 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 6168 RFC 8415, DOI 10.17487/RFC8415, November 2018, 6169 . 6171 [VAHDAT08] 6172 Al-Fares, M., Loukissas, A., and A. Vahdat, "A Scalable, 6173 Commodity Data Center Network Architecture", SIGCOMM , 6174 2008. 6176 [Wikipedia] 6177 Wikipedia, 6178 "https://en.wikipedia.org/wiki/Serial_number_arithmetic", 6179 2016. 6181 Appendix A. Sequence Number Binary Arithmetic 6183 The only reasonably reference to a cleaner than [RFC1982] sequence 6184 number solution is given in [Wikipedia]. It basically converts the 6185 problem into two complement's arithmetic. Assuming a straight two 6186 complement's subtractions on the bit-width of the sequence number the 6187 according >: and =: relations are defined as: 6189 U_1, U_2 are 12-bits aligned unsigned version number 6191 D_f is ( U_1 - U_2 ) interpreted as two complement signed 12-bits 6192 D_b is ( U_2 - U_1 ) interpreted as two complement signed 12-bits 6194 U_1 >: U_2 IIF D_f > 0 AND D_b < 0 6195 U_1 =: U_2 IIF D_f = 0 6197 The >: relationship is anti-symmetric but not transitive. Observe 6198 that this leaves >: of the numbers having maximum two complement 6199 distance, e.g. ( 0 and 0x800 ) undefined in our 12-bits case since 6200 D_f and D_b are both -0x7ff. 6202 A simple example of the relationship in case of 3-bit arithmetic 6203 follows as table indicating D_f/D_b values and then the relationship 6204 of U_1 to U_2: 6206 U2 / U1 0 1 2 3 4 5 6 7 6207 0 +/+ +/- +/- +/- -/- -/+ -/+ -/+ 6208 1 -/+ +/+ +/- +/- +/- -/- -/+ -/+ 6209 2 -/+ -/+ +/+ +/- +/- +/- -/- -/+ 6210 3 -/+ -/+ -/+ +/+ +/- +/- +/- -/- 6211 4 -/- -/+ -/+ -/+ +/+ +/- +/- +/- 6212 5 +/- -/- -/+ -/+ -/+ +/+ +/- +/- 6213 6 +/- +/- -/- -/+ -/+ -/+ +/+ +/- 6214 7 +/- +/- +/- -/- -/+ -/+ -/+ +/+ 6216 U2 / U1 0 1 2 3 4 5 6 7 6217 0 = > > > ? < < < 6218 1 < = > > > ? < < 6219 2 < < = > > > ? < 6220 3 < < < = > > > ? 6221 4 ? < < < = > > > 6222 5 > ? < < < = > > 6223 6 > > ? < < < = > 6224 7 > > > ? < < < = 6226 Appendix B. Information Elements Schema 6228 This section introduces the schema for information elements. The IDL 6229 is Thrift [thrift]. 6231 On schema changes that 6233 1. change field numbers or 6235 2. add new *required* fields or 6237 3. remove any fields or 6239 4. change lists into sets, unions into structures or 6241 5. change multiplicity of fields or 6243 6. changes name of any field or type or 6245 7. change data types of any field or 6247 8. adds, changes or removes a default value of any *existing* field 6248 or 6250 9. removes or changes any defined constant or constant value or 6252 10. changes any enumeration type except extending `common.TIEType` 6253 (use of enumeration types is generally discouraged) 6255 major version of the schema MUST increase. All other changes MUST 6256 increase minor version within the same major. 6258 Observe however that introducing an optional field does not cause a 6259 major version increase even if the fields inside the structure are 6260 optional with defaults. 6262 All signed integer as forced by Thrift [thrift] support must be cast 6263 for internal purposes to equivalent unsigned values without 6264 discarding the signedness bit. An implementation SHOULD try to avoid 6265 using the signedness bit when generating values. 6267 The schema is normative. 6269 B.1. common.thrift 6271 /** 6272 Thrift file with common definitions for RIFT 6273 */ 6275 namespace py common 6276 namespace rs models 6278 /** @note MUST be interpreted in implementation as unsigned 64 bits. 6279 * The implementation SHOULD NOT use the MSB. 6280 */ 6281 typedef i64 SystemIDType 6282 typedef i32 IPv4Address 6283 /** this has to be long enough to accomodate prefix */ 6284 typedef binary IPv6Address 6285 /** @note MUST be interpreted in implementation as unsigned */ 6286 typedef i16 UDPPortType 6287 /** @note MUST be interpreted in implementation as unsigned */ 6288 typedef i32 TIENrType 6289 /** @note MUST be interpreted in implementation as unsigned */ 6290 typedef i32 MTUSizeType 6291 /** @note MUST be interpreted in implementation as unsigned 6292 rolling over number */ 6293 typedef i16 SeqNrType 6294 /** @note MUST be interpreted in implementation as unsigned */ 6295 typedef i32 LifeTimeInSecType 6296 /** @note MUST be interpreted in implementation as unsigned */ 6297 typedef i8 LevelType 6298 /** optional, recommended monotonically increasing number 6299 _per packet type per adjacency_ 6300 that can be used to detect losses/misordering/restarts. 6301 @note MUST be interpreted in implementation as unsigned 6302 rolling over number */ 6303 typedef i16 PacketNumberType 6304 /** @note MUST be interpreted in implementation as unsigned */ 6305 typedef i32 PodType 6306 /** @note MUST be interpreted in implementation as unsigned. 6307 This is carried in the 6308 security envelope and MUST fit into 8 bits. */ 6309 typedef i8 VersionType 6310 /** @note MUST be interpreted in implementation as unsigned */ 6311 typedef i16 MinorVersionType 6312 /** @note MUST be interpreted in implementation as unsigned */ 6313 typedef i32 MetricType 6314 /** @note MUST be interpreted in implementation as unsigned 6315 and unstructured */ 6316 typedef i64 RouteTagType 6317 /** @note MUST be interpreted in implementation as unstructured 6318 label value */ 6319 typedef i32 LabelType 6320 /** @note MUST be interpreted in implementation as unsigned */ 6321 typedef i32 BandwithInMegaBitsType 6322 /** @note Key Value key ID type */ 6323 typedef string KeyIDType 6324 /** node local, unique identification for a link (interface/tunnel 6325 * etc. Basically anything RIFT runs on). This is kept 6326 * at 32 bits so it aligns with BFD [RFC5880] discriminator size. 6327 */ 6328 typedef i32 LinkIDType 6329 typedef string KeyNameType 6330 typedef i8 PrefixLenType 6331 /** timestamp in seconds since the epoch */ 6332 typedef i64 TimestampInSecsType 6333 /** security nonce. 6334 @note MUST be interpreted in implementation as rolling 6335 over unsigned value */ 6336 typedef i16 NonceType 6337 /** LIE FSM holdtime type */ 6338 typedef i16 TimeIntervalInSecType 6339 /** Transaction ID type for prefix mobility as specified by RFC6550, 6340 value MUST be interpreted in implementation as unsigned */ 6341 typedef i8 PrefixTransactionIDType 6342 /** Timestamp per IEEE 802.1AS, all values MUST be interpreted in 6343 implementation as unsigned. */ 6344 struct IEEE802_1ASTimeStampType { 6345 1: required i64 AS_sec; 6346 2: optional i32 AS_nsec; 6347 } 6348 /** generic counter type */ 6349 typedef i64 CounterType 6350 /** Platform Interface Index type, i.e. index of interface on hardware, 6351 can be used e.g. with RFC5837 */ 6352 typedef i32 PlatformInterfaceIndex 6354 /** Flags indicating node configuration in case of ZTP. 6355 */ 6356 enum HierarchyIndications { 6357 /** forces level to `leaf_level` and enables according procedures */ 6358 leaf_only = 0, 6359 /** forces level to `leaf_level` and enables according procedures */ 6360 leaf_only_and_leaf_2_leaf_procedures = 1, 6361 /** forces level to `top_of_fabric` and enables according 6362 procedures */ 6363 top_of_fabric = 2, 6364 } 6366 const PacketNumberType undefined_packet_number = 0 6367 /** This MUST be used when node is configured as top of fabric in ZTP. 6368 This is kept reasonably low to alow for fast ZTP convergence on 6369 failures. */ 6370 const LevelType top_of_fabric_level = 24 6371 /** default bandwidth on a link */ 6372 const BandwithInMegaBitsType default_bandwidth = 100 6373 /** fixed leaf level when ZTP is not used */ 6374 const LevelType leaf_level = 0 6375 const LevelType default_level = leaf_level 6376 const PodType default_pod = 0 6377 const LinkIDType undefined_linkid = 0 6379 /** default distance used */ 6380 const MetricType default_distance = 1 6381 /** any distance larger than this will be considered infinity */ 6382 const MetricType infinite_distance = 0x7FFFFFFF 6383 /** represents invalid distance */ 6384 const MetricType invalid_distance = 0 6385 const bool overload_default = false 6386 const bool flood_reduction_default = true 6387 /** default LIE FSM holddown time */ 6388 const TimeIntervalInSecType default_lie_holdtime = 3 6389 /** default ZTP FSM holddown time */ 6390 const TimeIntervalInSecType default_ztp_holdtime = 1 6391 /** by default LIE levels are ZTP offers */ 6392 const bool default_not_a_ztp_offer = false 6393 /** by default everyone is repeating flooding */ 6394 const bool default_you_are_flood_repeater = true 6395 /** 0 is illegal for SystemID */ 6396 const SystemIDType IllegalSystemID = 0 6397 /** empty set of nodes */ 6398 const set empty_set_of_nodeids = {} 6399 /** default lifetime of TIE is one week */ 6400 const LifeTimeInSecType default_lifetime = 604800 6401 /** default lifetime when TIEs are purged is 5 minutes */ 6402 const LifeTimeInSecType purge_lifetime = 300 6403 /** round down interval when TIEs are sent with security hashes 6404 to prevent excessive computation. **/ 6405 const LifeTimeInSecType rounddown_lifetime_interval = 60 6406 /** any `TieHeader` that has a smaller lifetime difference 6407 than this constant is equal (if other fields equal). This 6408 constant MUST be larger than `purge_lifetime` to avoid 6409 retransmissions */ 6410 const LifeTimeInSecType lifetime_diff2ignore = 400 6412 /** default UDP port to run LIEs on */ 6413 const UDPPortType default_lie_udp_port = 914 6414 /** default UDP port to receive TIEs on, that can be peer specific */ 6415 const UDPPortType default_tie_udp_flood_port = 915 6417 /** default MTU link size to use */ 6418 const MTUSizeType default_mtu_size = 1400 6419 /** default link being BFD capable */ 6420 const bool bfd_default = true 6422 /** undefined nonce, equivalent to missing nonce */ 6423 const NonceType undefined_nonce = 0; 6424 /** outer security key id, MUST be interpreted as in implementation 6425 as unsigned */ 6426 typedef i8 OuterSecurityKeyID 6427 /** security key id, MUST be interpreted as in implementation 6428 as unsigned */ 6429 typedef i32 TIESecurityKeyID 6430 /** undefined key */ 6431 const TIESecurityKeyID undefined_securitykey_id = 0; 6432 /** Maximum delta (negative or positive) that a mirrored nonce can 6433 deviate from local value to be considered valid. If nonces are 6434 changed every minute on both sides this opens statistically 6435 a `maximum_valid_nonce_delta` minutes window of identical LIEs, 6436 TIE, TI(x)E replays. 6437 The interval cannot be too small since LIE FSM may change 6438 states fairly quickly during ZTP without sending LIEs*/ 6439 const i16 maximum_valid_nonce_delta = 5; 6440 /** Direction of TIEs. */ 6441 enum TieDirectionType { 6442 Illegal = 0, 6443 South = 1, 6444 North = 2, 6445 DirectionMaxValue = 3, 6446 } 6448 /** Address family type. */ 6449 enum AddressFamilyType { 6450 Illegal = 0, 6451 AddressFamilyMinValue = 1, 6452 IPv4 = 2, 6453 IPv6 = 3, 6454 AddressFamilyMaxValue = 4, 6455 } 6457 /** IPv4 prefix type. */ 6458 struct IPv4PrefixType { 6459 1: required IPv4Address address; 6460 2: required PrefixLenType prefixlen; 6461 } 6463 /** IPv6 prefix type. */ 6464 struct IPv6PrefixType { 6465 1: required IPv6Address address; 6466 2: required PrefixLenType prefixlen; 6467 } 6469 /** IP address type. */ 6470 union IPAddressType { 6471 /** Content is IPv4 */ 6472 1: optional IPv4Address ipv4address; 6473 /** Content is IPv6 */ 6474 2: optional IPv6Address ipv6address; 6475 } 6477 /** Prefix advertisement. 6479 @note: for interface 6480 addresses the protocol can propagate the address part beyond 6481 the subnet mask and on reachability computation that has to 6482 be normalized. The non-significant bits can be used 6483 for operational purposes. 6484 */ 6485 union IPPrefixType { 6486 1: optional IPv4PrefixType ipv4prefix; 6487 2: optional IPv6PrefixType ipv6prefix; 6489 } 6491 /** Sequence of a prefix in case of move. 6492 */ 6493 struct PrefixSequenceType { 6494 1: required IEEE802_1ASTimeStampType timestamp; 6495 /** Transaction ID set by client in e.g. in 6LoWPAN. */ 6496 2: optional PrefixTransactionIDType transactionid; 6497 } 6499 /** Type of TIE. 6501 This enum indicates what TIE type the TIE is carrying. 6502 In case the value is not known to the receiver, 6503 the TIE MUST be re-flooded. This allows for 6504 future extensions of the protocol within the same major schema 6505 with types opaque to some nodes UNLESS the flooding scope is not 6506 the same as prefix TIE, then a major version revision MUST 6507 be performed. 6508 */ 6509 enum TIETypeType { 6510 Illegal = 0, 6511 TIETypeMinValue = 1, 6512 /** first legal value */ 6513 NodeTIEType = 2, 6514 PrefixTIEType = 3, 6515 PositiveDisaggregationPrefixTIEType = 4, 6516 NegativeDisaggregationPrefixTIEType = 5, 6517 PGPrefixTIEType = 6, 6518 KeyValueTIEType = 7, 6519 ExternalPrefixTIEType = 8, 6520 PositiveExternalDisaggregationPrefixTIEType = 9, 6521 TIETypeMaxValue = 10, 6522 } 6524 /** RIFT route types. 6526 @note: route types which MUST be ordered on their preference 6527 PGP prefixes are most preferred attracting 6528 traffic north (towards spine) and then south 6529 normal prefixes are attracting traffic south 6530 (towards leaves), i.e. prefix in NORTH PREFIX TIE 6531 is preferred over SOUTH PREFIX TIE. 6533 @note: The only purpose of those values is to introduce an 6534 ordering whereas an implementation can choose internally 6535 any other values as long the ordering is preserved 6536 */ 6538 enum RouteType { 6539 Illegal = 0, 6540 RouteTypeMinValue = 1, 6541 /** First legal value. */ 6542 /** Discard routes are most preferred */ 6543 Discard = 2, 6545 /** Local prefixes are directly attached prefixes on the 6546 * system such as e.g. interface routes. 6547 */ 6548 LocalPrefix = 3, 6549 /** Advertised in S-TIEs */ 6550 SouthPGPPrefix = 4, 6551 /** Advertised in N-TIEs */ 6552 NorthPGPPrefix = 5, 6553 /** Advertised in N-TIEs */ 6554 NorthPrefix = 6, 6555 /** Externally imported north */ 6556 NorthExternalPrefix = 7, 6557 /** Advertised in S-TIEs, either normal prefix or positive 6558 disaggregation */ 6559 SouthPrefix = 8, 6560 /** Externally imported south */ 6561 SouthExternalPrefix = 9, 6562 /** Negative, transitive prefixes are least preferred */ 6563 NegativeSouthPrefix = 10, 6564 RouteTypeMaxValue = 11, 6565 } 6567 B.2. encoding.thrift 6569 /** 6570 Thrift file for packet encodings for RIFT 6571 */ 6573 include "common.thrift" 6575 /** Represents protocol encoding schema major version */ 6576 const common.VersionType protocol_major_version = 2 6577 /** Represents protocol encoding schema minor version */ 6578 const common.MinorVersionType protocol_minor_version = 0 6580 /** Common RIFT packet header. */ 6581 struct PacketHeader { 6582 /** Major version of protocol. */ 6583 1: required common.VersionType major_version = 6584 protocol_major_version; 6585 /** Minor version of protocol. */ 6586 2: required common.VersionType minor_version = 6587 protocol_minor_version; 6588 /** Node sending the packet, in case of LIE/TIRE/TIDE 6589 also the originator of it. */ 6590 3: required common.SystemIDType sender; 6591 /** Level of the node sending the packet, required on everything 6592 except LIEs. Lack of presence on LIEs indicates UNDEFINED_LEVEL 6593 and is used in ZTP procedures. 6594 */ 6595 4: optional common.LevelType level; 6596 } 6598 /** Prefix community. */ 6599 struct Community { 6600 /** Higher order bits */ 6601 1: required i32 top; 6602 /** Lower order bits */ 6603 2: required i32 bottom; 6604 } 6606 /** Neighbor structure. */ 6607 struct Neighbor { 6608 /** System ID of the originator. */ 6609 1: required common.SystemIDType originator; 6610 /** ID of remote side of the link. */ 6611 2: required common.LinkIDType remote_id; 6612 } 6614 /** Capabilities the node supports. 6616 @note: The schema may add to this 6617 field future capabilities to indicate whether it will support 6618 interpretation of future schema extensions on the same major 6619 revision. Such fields MUST be optional and have an implicit or 6620 explicit false default value. If a future capability changes route 6621 selection or generates blackholes if some nodes are not supporting 6622 it then a major version increment is unavoidable. 6623 */ 6624 struct NodeCapabilities { 6625 /** Must advertise supported minor version dialect that way. */ 6626 1: required common.MinorVersionType protocol_minor_version = 6627 protocol_minor_version; 6628 /** Can this node participate in flood reduction. */ 6629 2: optional bool flood_reduction = 6630 common.flood_reduction_default; 6632 /** Does this node restrict itself to be top-of-fabric or 6633 leaf only (in ZTP) and does it support leaf-2-leaf 6634 procedures. */ 6635 3: optional common.HierarchyIndications hierarchy_indications; 6636 } 6638 /** Link capabilities. */ 6639 struct LinkCapabilities { 6640 /** Indicates that the link is supporting BFD. */ 6641 1: optional bool bfd = 6642 common.bfd_default; 6643 /** Indicates whether the interface will support v4 forwarding. 6645 @note: This MUST be set to true when LIEs from a v4 address are 6646 sent and MAY be set to true in LIEs on v6 address. If v4 6647 and v6 LIEs indicate contradicting information the 6648 behavior is unspecified. */ 6649 2: optional bool v4_forwarding_capable = 6650 true; 6651 } 6653 /** RIFT LIE Packet. 6655 @note: this node's level is already included on the packet header 6656 */ 6657 struct LIEPacket { 6658 /** Node or adjacency name. */ 6659 1: optional string name; 6660 /** Local link ID. */ 6661 2: required common.LinkIDType local_id; 6662 /** UDP port to which we can receive flooded TIEs. */ 6663 3: required common.UDPPortType flood_port = 6664 common.default_tie_udp_flood_port; 6665 /** Layer 3 MTU, used to discover to mismatch. */ 6666 4: optional common.MTUSizeType link_mtu_size = 6667 common.default_mtu_size; 6668 /** Local link bandwidth on the interface. */ 6669 5: optional common.BandwithInMegaBitsType 6670 link_bandwidth = common.default_bandwidth; 6671 /** Reflects the neighbor once received to provide 6672 3-way connectivity. */ 6673 6: optional Neighbor neighbor; 6674 /** Node's PoD. */ 6675 7: optional common.PodType pod = 6676 common.default_pod; 6677 /** Node capabilities shown in LIE. The capabilities 6678 MUST match the capabilities shown in the Node TIEs, otherwise 6679 the behavior is unspecified. A node detecting the mismatch 6680 SHOULD generate according error. */ 6681 10: required NodeCapabilities node_capabilities; 6682 /** Capabilities of this link. */ 6683 11: optional LinkCapabilities link_capabilities; 6684 /** Required holdtime of the adjacency, i.e. how much time 6685 MUST expire without LIE for the adjacency to drop. */ 6686 12: required common.TimeIntervalInSecType 6687 holdtime = common.default_lie_holdtime; 6688 /** Unsolicited, downstream assigned locally significant label 6689 value for the adjacency. */ 6690 13: optional common.LabelType label; 6691 /** Indicates that the level on the LIE MUST NOT be used 6692 to derive a ZTP level by the receiving node. */ 6693 21: optional bool not_a_ztp_offer = 6694 common.default_not_a_ztp_offer; 6695 /** Indicates to northbound neighbor that it should 6696 be reflooding this node's N-TIEs to achieve flood reduction and 6697 balancing for northbound flooding. To be ignored if received 6698 from a northbound adjacency. */ 6699 22: optional bool you_are_flood_repeater = 6700 common.default_you_are_flood_repeater; 6701 /** Can be optionally set to indicate to neighbor that packet losses 6702 are seen on reception based on packet numbers or the rate is 6703 too high. The receiver SHOULD temporarily slow down 6704 flooding rates. 6705 */ 6706 23: optional bool you_are_sending_too_quickly = 6707 false; 6708 /** Instance name in case multiple RIFT instances running on same 6709 interface. */ 6710 24: optional string instance_name; 6711 } 6713 /** LinkID pair describes one of parallel links between two nodes. */ 6714 struct LinkIDPair { 6715 /** Node-wide unique value for the local link. */ 6716 1: required common.LinkIDType local_id; 6717 /** Received remote link ID for this link. */ 6718 2: required common.LinkIDType remote_id; 6720 /** Describes the local interface index of the link. */ 6721 10: optional common.PlatformInterfaceIndex platform_interface_index; 6722 /** Describes the local interface name. */ 6723 11: optional string platform_interface_name; 6724 /** Indication whether the link is secured, i.e. protected by 6725 outer key, absence of this element means no indication, 6726 undefined outer key means not secured. */ 6727 12: optional common.OuterSecurityKeyID 6728 trusted_outer_security_key; 6729 /** Indication whether the link is protected by established 6730 BFD session. */ 6731 13: optional bool bfd_up; 6732 } 6734 /** ID of a TIE. 6736 @note: TIEID space is a total order achieved by comparing 6737 the elements in sequence defined and comparing each 6738 value as an unsigned integer of according length. 6739 */ 6740 struct TIEID { 6741 /** direction of TIE */ 6742 1: required common.TieDirectionType direction; 6743 /** indicates originator of the TIE */ 6744 2: required common.SystemIDType originator; 6745 /** type of the tie */ 6746 3: required common.TIETypeType tietype; 6747 /** number of the tie */ 6748 4: required common.TIENrType tie_nr; 6749 } 6751 /** Header of a TIE. 6753 @note: TIEID space is a total order achieved by comparing 6754 the elements in sequence defined and comparing each 6755 value as an unsigned integer of according length. 6757 @note: After sequence number the lifetime received on the envelope 6758 must be used for comparison before further fields. 6760 @note: `origination_time` and `origination_lifetime` are disregarded 6761 for comparison purposes and carried purely for 6762 debugging/security purposes if present. 6763 */ 6764 struct TIEHeader { 6765 /** ID of the tie. */ 6766 2: required TIEID tieid; 6767 /** Sequence number of the tie. */ 6768 3: required common.SeqNrType seq_nr; 6770 /** Absolute timestamp when the TIE 6771 was generated. This can be used on fabrics with 6772 synchronized clock to prevent lifetime modification attacks. */ 6773 10: optional common.IEEE802_1ASTimeStampType origination_time; 6774 /** Original lifetime when the TIE 6775 was generated. This can be used on fabrics with 6776 synchronized clock to prevent lifetime modification attacks. */ 6777 12: optional common.LifeTimeInSecType origination_lifetime; 6778 } 6780 /** Header of a TIE as described in TIRE/TIDE. 6781 */ 6782 struct TIEHeaderWithLifeTime { 6783 1: required TIEHeader header; 6784 /** Remaining lifetime that expires down to 0 just like in ISIS. 6785 TIEs with lifetimes differing by less than 6786 `lifetime_diff2ignore` MUST be considered EQUAL. */ 6787 2: required common.LifeTimeInSecType remaining_lifetime; 6788 } 6790 /** TIDE with sorted TIE headers, if headers are unsorted, behavior 6791 is undefined. */ 6792 struct TIDEPacket { 6793 /** First TIE header in the tide packet. */ 6794 1: required TIEID start_range; 6795 /** Last TIE header in the tide packet. */ 6796 2: required TIEID end_range; 6797 /** _Sorted_ list of headers. */ 6798 3: required list headers; 6799 } 6801 /** TIRE packet */ 6802 struct TIREPacket { 6803 1: required set headers; 6804 } 6806 /** neighbor of a node */ 6807 struct NodeNeighborsTIEElement { 6808 /** level of neighbor */ 6809 1: required common.LevelType level; 6810 /** Cost to neighbor. 6812 @note: All parallel links to same node 6813 incur same cost, in case the neighbor has multiple 6814 parallel links at different cost, the largest distance 6815 (highest numerical value) MUST be advertised. 6817 @note: any neighbor with cost <= 0 MUST be ignored 6818 in computations */ 6819 3: optional common.MetricType cost 6820 = common.default_distance; 6821 /** can carry description of multiple parallel links in a TIE */ 6822 4: optional set link_ids; 6823 /** total bandwith to neighbor, this will be normally sum of the 6824 bandwidths of all the parallel links. */ 6825 5: optional common.BandwithInMegaBitsType 6826 bandwidth = common.default_bandwidth; 6827 } 6829 /** Indication flags of the node. */ 6830 struct NodeFlags { 6831 /** Indicates that node is in overload, do not transit traffic 6832 through it. */ 6833 1: optional bool overload = common.overload_default; 6834 } 6836 /** Description of a node. 6838 It may occur multiple times in different TIEs but if either 6839 6840 capabilities values do not match or 6841 flags values do not match or 6842 neighbors repeat with different values 6843 6845 the behavior is undefined and a warning SHOULD be generated. 6846 Neighbors can be distributed across multiple TIEs however if 6847 the sets are disjoint. Miscablings SHOULD be repeated in every 6848 node TIE, otherwise the behavior is undefined. 6850 @note: Observe that absence of fields implies defined defaults. 6851 */ 6852 struct NodeTIEElement { 6853 /** Level of the node. */ 6854 1: required common.LevelType level; 6855 /** Node's neighbors. If neighbor systemID repeats in other 6856 node TIEs of same node the behavior is undefined. */ 6857 2: required map neighbors; 6859 /** Capabilities of the node. */ 6860 3: required NodeCapabilities capabilities; 6861 /** Flags of the node. */ 6862 4: optional NodeFlags flags; 6863 /** Optional node name for easier operations. */ 6864 5: optional string name; 6865 /** PoD to which the node belongs. */ 6866 6: optional common.PodType pod; 6868 /** If any local links are miscabled, the indication is flooded. */ 6869 10: optional set miscabled_links; 6871 } 6873 /** Attributes of a prefix. */ 6874 struct PrefixAttributes { 6875 /** Distance of the prefix. */ 6876 2: required common.MetricType metric 6877 = common.default_distance; 6878 /** Generic unordered set of route tags, can be redistributed 6879 to other protocols or use within the context of real time 6880 analytics. */ 6881 3: optional set tags; 6882 /** Monotonic clock for mobile addresses. */ 6883 4: optional common.PrefixSequenceType monotonic_clock; 6884 /** Indicates if the interface is a node loopback. */ 6885 6: optional bool loopback = false; 6886 /** Indicates that the prefix is directly attached, i.e. should be 6887 routed to even if the node is in overload. */ 6888 7: optional bool directly_attached = true; 6890 /** In case of locally originated prefixes, i.e. interface 6891 addresses this can describe which link the address 6892 belongs to. */ 6893 10: optional common.LinkIDType from_link; 6894 } 6896 /** TIE carrying prefixes */ 6897 struct PrefixTIEElement { 6898 /** Prefixes with the associated attributes. 6899 If the same prefix repeats in multiple TIEs of same node 6900 behavior is unspecified. */ 6901 1: required map prefixes; 6902 } 6904 /** Generic key value pairs. */ 6905 struct KeyValueTIEElement { 6906 /** @note: if the same key repeats in multiple TIEs of same node 6907 or with different values, behavior is unspecified */ 6908 1: required map keyvalues; 6909 } 6911 /** Single element in a TIE. 6913 Schema enum `common.TIETypeType` 6914 in TIEID indicates which elements MUST be present 6915 in the TIEElement. In case of mismatch the unexpected 6916 elements MUST be ignored. In case of lack of expected 6917 element the TIE an error MUST be reported and the TIE 6918 MUST be ignored. 6920 This type can be extended with new optional elements 6921 for new `common.TIETypeType` values without breaking 6922 the major but if it is necessary to understand whether 6923 all nodes support the new type a node capability must 6924 be added as well. 6925 */ 6926 union TIEElement { 6927 /** Used in case of enum common.TIETypeType.NodeTIEType. */ 6928 1: optional NodeTIEElement node; 6929 /** Used in case of enum common.TIETypeType.PrefixTIEType. */ 6930 2: optional PrefixTIEElement prefixes; 6931 /** Positive prefixes (always southbound). 6932 It MUST NOT be advertised within a North TIE and 6933 ignored otherwise. 6934 */ 6935 3: optional PrefixTIEElement positive_disaggregation_prefixes; 6936 /** Transitive, negative prefixes (always southbound) which 6937 MUST be aggregated and propagated 6938 according to the specification 6939 southwards towards lower levels to heal 6940 pathological upper level partitioning, otherwise 6941 blackholes may occur in multiplane fabrics. 6942 It MUST NOT be advertised within a North TIE. 6943 */ 6944 5: optional PrefixTIEElement negative_disaggregation_prefixes; 6945 /** Externally reimported prefixes. */ 6946 6: optional PrefixTIEElement external_prefixes; 6947 /** Positive external disaggregated prefixes (always southbound). 6948 It MUST NOT be advertised within a North TIE and 6949 ignored otherwise. 6950 */ 6951 7: optional PrefixTIEElement 6952 positive_external_disaggregation_prefixes; 6953 /** Key-Value store elements. */ 6954 9: optional KeyValueTIEElement keyvalues; 6955 } 6957 /** TIE packet */ 6958 struct TIEPacket { 6959 1: required TIEHeader header; 6960 2: required TIEElement element; 6961 } 6963 /** Content of a RIFT packet. */ 6964 union PacketContent { 6965 1: optional LIEPacket lie; 6966 2: optional TIDEPacket tide; 6967 3: optional TIREPacket tire; 6968 4: optional TIEPacket tie; 6969 } 6971 /** RIFT packet structure. */ 6972 struct ProtocolPacket { 6973 1: required PacketHeader header; 6974 2: required PacketContent content; 6975 } 6977 Appendix C. Constants 6979 C.1. Configurable Protocol Constants 6981 This section gathers constants that are provided in the schema files 6982 and in the document. 6984 +----------------+--------------+-----------------------------------+ 6985 | | Type | Value | 6986 +----------------+--------------+-----------------------------------+ 6987 | LIE IPv4 | Default | 224.0.0.120 or all-rift-routers | 6988 | Multicast | Value, | to be assigned in IPv4 | 6989 | Address | Configurable | Multicast Address Space Registry | 6990 | | | in Local Network Control Block | 6991 +----------------+--------------+-----------------------------------+ 6992 | LIE IPv6 | Default | FF02::A1F7 or all-rift-routers to | 6993 | Multicast | Value, | be assigned in IPv6 Multicast | 6994 | Address | Configurable | Address Assignments | 6995 +----------------+--------------+-----------------------------------+ 6996 | LIE | Default | 914 | 6997 | Destination | Value, | | 6998 | Port | Configurable | | 6999 +----------------+--------------+-----------------------------------+ 7000 | Level value | Constant | 24 | 7001 | for | | | 7002 | TOP_OF_FABRIC | | | 7003 | flag | | | 7004 +----------------+--------------+-----------------------------------+ 7005 | Default LIE | Default | 3 seconds | 7006 | Holdtime | Value, | | 7007 | | Configurable | | 7008 +----------------+--------------+-----------------------------------+ 7009 | TIE | Default | 1 second | 7010 | Retransmission | Value | | 7011 | Interval | | | 7012 +----------------+--------------+-----------------------------------+ 7013 | TIDE | Default | 5 seconds | 7014 | Generation | Value, | | 7015 | Interval | Configurable | | 7016 +----------------+--------------+-----------------------------------+ 7017 | MIN_TIEID | Constant | TIE Key with minimal values: | 7018 | signifies | | TIEID(originator=0, | 7019 | start of TIDEs | | tietype=TIETypeMinValue, | 7020 | | | tie_nr=0, direction=South) | 7021 +----------------+--------------+-----------------------------------+ 7022 | MAX_TIEID | Constant | TIE Key with maximal values: | 7023 | signifies end | | TIEID(originator=MAX_UINT64, | 7024 | of TIDEs | | tietype=TIETypeMaxValue, | 7025 | | | tie_nr=MAX_UINT64, | 7026 | | | direction=North) | 7027 +----------------+--------------+-----------------------------------+ 7029 Table 6: all_constants 7031 Authors' Addresses 7033 Tony Przygienda (editor) 7034 Juniper 7035 1137 Innovation Way 7037 Sunnyvale, CA 7039 USA 7041 Email: prz@juniper.net 7043 Alankar Sharma 7044 Comcast 7045 1800 Bishops Gate Blvd 7046 Mount Laurel, NJ 08054 7047 US 7049 Email: Alankar_Sharma@comcast.com 7051 Pascal Thubert 7052 Cisco Systems, Inc 7053 Building D 7054 45 Allee des Ormes - BP1200 7055 MOUGINS - Sophia Antipolis 06254 7056 FRANCE 7058 Phone: +33 497 23 26 34 7059 Email: pthubert@cisco.com 7061 Bruno Rijsman 7062 Individual 7064 Email: brunorijsman@gmail.com 7066 Dmitry Afanasiev 7067 Yandex 7069 Email: fl0w@yandex-team.ru