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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group K. Patel 3 Internet-Draft Arrcus, Inc. 4 Intended status: Standards Track A. Lindem 5 Expires: January 27, 2021 Cisco Systems 6 S. Zandi 7 LinkedIn 8 W. Henderickx 9 Nokia 10 July 26, 2020 12 Shortest Path Routing Extensions for BGP Protocol 13 draft-ietf-lsvr-bgp-spf-10 15 Abstract 17 Many Massively Scaled Data Centers (MSDCs) have converged on 18 simplified layer 3 routing. Furthermore, requirements for 19 operational simplicity have led many of these MSDCs to converge on 20 BGP as their single routing protocol for both their fabric routing 21 and their Data Center Interconnect (DCI) routing. This document 22 describes a solution which leverages BGP Link-State distribution and 23 the Shortest Path First (SPF) algorithm similar to Internal Gateway 24 Protocols (IGPs) such as OSPF. 26 Status of This Memo 28 This Internet-Draft is submitted in full conformance with the 29 provisions of BCP 78 and BCP 79. 31 Internet-Drafts are working documents of the Internet Engineering 32 Task Force (IETF). Note that other groups may also distribute 33 working documents as Internet-Drafts. The list of current Internet- 34 Drafts is at https://datatracker.ietf.org/drafts/current/. 36 Internet-Drafts are draft documents valid for a maximum of six months 37 and may be updated, replaced, or obsoleted by other documents at any 38 time. It is inappropriate to use Internet-Drafts as reference 39 material or to cite them other than as "work in progress." 41 This Internet-Draft will expire on January 27, 2021. 43 Copyright Notice 45 Copyright (c) 2020 IETF Trust and the persons identified as the 46 document authors. All rights reserved. 48 This document is subject to BCP 78 and the IETF Trust's Legal 49 Provisions Relating to IETF Documents 50 (https://trustee.ietf.org/license-info) in effect on the date of 51 publication of this document. Please review these documents 52 carefully, as they describe your rights and restrictions with respect 53 to this document. Code Components extracted from this document must 54 include Simplified BSD License text as described in Section 4.e of 55 the Trust Legal Provisions and are provided without warranty as 56 described in the Simplified BSD License. 58 Table of Contents 60 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 61 1.1. BGP Shortest Path First (SPF) Motivation . . . . . . . . 4 62 1.2. Requirements Language . . . . . . . . . . . . . . . . . . 5 63 2. BGP Peering Models . . . . . . . . . . . . . . . . . . . . . 5 64 2.1. BGP Single-Hop Peering on Network Node Connections . . . 5 65 2.2. BGP Peering Between Directly Connected Network Nodes . . 5 66 2.3. BGP Peering in Route-Reflector or Controller Topology . . 6 67 3. BGP-LS Shortest Path Routing (SPF) SAFI . . . . . . . . . . . 6 68 4. Extensions to BGP-LS . . . . . . . . . . . . . . . . . . . . 6 69 4.1. Node NLRI Usage . . . . . . . . . . . . . . . . . . . . . 7 70 4.1.1. Node NLRI Attribute SPF Capability TLV . . . . . . . 7 71 4.1.2. BGP-LS Node NLRI Attribute SPF Status TLV . . . . . . 8 72 4.2. Link NLRI Usage . . . . . . . . . . . . . . . . . . . . . 8 73 4.2.1. BGP-LS Link NLRI Attribute Prefix-Length TLVs . . . . 9 74 4.2.2. BGP-LS Link NLRI Attribute SPF Status TLV . . . . . . 9 75 4.3. Prefix NLRI Usage . . . . . . . . . . . . . . . . . . . . 10 76 4.3.1. BGP-LS Prefix NLRI Attribute SPF Status TLV . . . . . 10 77 4.4. BGP-LS Attribute Sequence-Number TLV . . . . . . . . . . 10 78 5. Decision Process with SPF Algorithm . . . . . . . . . . . . . 11 79 5.1. Phase-1 BGP NLRI Selection . . . . . . . . . . . . . . . 12 80 5.2. Dual Stack Support . . . . . . . . . . . . . . . . . . . 13 81 5.3. SPF Calculation based on BGP-LS NLRI . . . . . . . . . . 13 82 5.4. NEXT_HOP Manipulation . . . . . . . . . . . . . . . . . . 16 83 5.5. IPv4/IPv6 Unicast Address Family Interaction . . . . . . 16 84 5.6. NLRI Advertisement and Convergence . . . . . . . . . . . 17 85 5.6.1. Link/Prefix Failure Convergence . . . . . . . . . . . 17 86 5.6.2. Node Failure Convergence . . . . . . . . . . . . . . 17 87 5.7. Error Handling . . . . . . . . . . . . . . . . . . . . . 18 88 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 89 7. Security Considerations . . . . . . . . . . . . . . . . . . . 18 90 8. Management Considerations . . . . . . . . . . . . . . . . . . 18 91 8.1. Configuration . . . . . . . . . . . . . . . . . . . . . . 18 92 8.2. Operational Data . . . . . . . . . . . . . . . . . . . . 19 93 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19 94 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 19 95 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 96 11.1. Normative References . . . . . . . . . . . . . . . . . . 20 97 11.2. Information References . . . . . . . . . . . . . . . . . 21 98 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22 100 1. Introduction 102 Many Massively Scaled Data Centers (MSDCs) have converged on 103 simplified layer 3 routing. Furthermore, requirements for 104 operational simplicity have led many of these MSDCs to converge on 105 BGP [RFC4271] as their single routing protocol for both their fabric 106 routing and their Data Center Interconnect (DCI) routing. 107 Requirements and procedures for using BGP are described in [RFC7938]. 108 This document describes an alternative solution which leverages BGP- 109 LS [RFC7752] and the Shortest Path First algorithm similar to 110 Internal Gateway Protocols (IGPs) such as OSPF [RFC2328]. 112 [RFC4271] defines the Decision Process that is used to select routes 113 for subsequent advertisement by applying the policies in the local 114 Policy Information Base (PIB) to the routes stored in its Adj-RIBs- 115 In. The output of the Decision Process is the set of routes that are 116 announced by a BGP speaker to its peers. These selected routes are 117 stored by a BGP speaker in the speaker's Adj-RIBs-Out according to 118 policy. 120 [RFC7752] describes a mechanism by which link-state and TE 121 information can be collected from networks and shared with external 122 components using BGP. This is achieved by defining NLRI advertised 123 within the BGP-LS/BGP-LS-SPF AFI/SAFI. The BGP-LS extensions defined 124 in [RFC7752] makes use of the Decision Process defined in [RFC4271]. 126 This document augments [RFC7752] by replacing its use of the existing 127 Decision Process. Rather than reusing the BGP-LS SAFI, the BGP-LS- 128 SPF SAFI is introduced to insure backward compatibility. The Phase 1 129 and 2 decision functions of the Decision Process are replaced with 130 the Shortest Path First (SPF) algorithm also known as the Dijkstra 131 algorithm. The Phase 3 decision function is also simplified since it 132 is no longer dependent on the previous phases. This solution avails 133 the benefits of both BGP and SPF-based IGPs. These include TCP based 134 flow-control, no periodic link-state refresh, and completely 135 incremental NLRI advertisement. These advantages can reduce the 136 overhead in MSDCs where there is a high degree of Equal Cost Multi- 137 Path (ECMPs) and the topology is very stable. Additionally, using an 138 SPF-based computation can support fast convergence and the 139 computation of Loop-Free Alternatives (LFAs) [RFC5286] in the event 140 of link failures. Furthermore, a BGP based solution lends itself to 141 multiple peering models including those incorporating route- 142 reflectors [RFC4456] or controllers. 144 Support for Multiple Topology Routing (MTR) as described in [RFC4915] 145 is an area for further study dependent on deployment requirements. 147 1.1. BGP Shortest Path First (SPF) Motivation 149 Given that [RFC7938] already describes how BGP could be used as the 150 sole routing protocol in an MSDC, one might question the motivation 151 for defining an alternate BGP deployment model when a mature solution 152 exists. For both alternatives, BGP offers the operational benefits 153 of a single routing protocol. However, BGP SPF offers some unique 154 advantages above and beyond standard BGP distance-vector routing. 156 A primary advantage is that all BGP speakers in the BGP SPF routing 157 domain will have a complete view of the topology. This will allow 158 support for ECMP, IP fast-reroute (e.g., Loop-Free Alternatives), 159 Shared Risk Link Groups (SRLGs), and other routing enhancements 160 without advertisement of addition BGP paths or other extensions. In 161 short, the advantages of an IGP such as OSPF [RFC2328] are availed in 162 BGP. 164 With the simplified BGP decision process as defined in Section 5.1, 165 NLRI changes can be disseminated throughout the BGP routing domain 166 much more rapidly (equivalent to IGPs with the proper 167 implementation). 169 Another primary advantage is a potential reduction in NLRI 170 advertisement. With standard BGP distance-vector routing, a single 171 link failure may impact 100s or 1000s prefixes and result in the 172 withdrawal or re-advertisement of the attendant NLRI. With BGP SPF, 173 only the BGP speakers corresponding to the link NLRI need withdraw 174 the corresponding BGP-LS Link NLRI. This advantage will contribute 175 to both faster convergence and better scaling. 177 With controller and route-reflector peering models, BGP SPF 178 advertisement and distributed computation require a minimal number of 179 sessions and copies of the NLRI since only the latest version of the 180 NLRI from the originator is required. Given that verification of the 181 adjacencies is done outside of BGP (see Section 2), each BGP speaker 182 will only need as many sessions and copies of the NLRI as required 183 for redundancy (e.g., one for the SPF computation and another for 184 backup). Functions such as Optimized Route Reflection (ORR) are 185 supported without extension by virtue of the primary advantages. 186 Additionally, a controller could inject topology that is learned 187 outside the BGP routing domain. 189 Given that controllers are already consuming BGP-LS NLRI [RFC7752], 190 reusing for the BGP-LS SPF leverages the existing controller 191 implementations. 193 Another potential advantage of BGP SPF is that both IPv6 and IPv4 can 194 be supported in the same address family using the same topology. 195 Although not described in this version of the document, multi- 196 topology extensions can be used to support separate IPv4, IPv6, 197 unicast, and multicast topologies while sharing the same NLRI. 199 Finally, the BGP SPF topology can be used as an underlay for other 200 BGP address families (using the existing model) and realize all the 201 above advantages. A simplified peering model using IPv6 link-local 202 addresses as next-hops can be deployed similar to [RFC5549]. 204 1.2. Requirements Language 206 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 207 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 208 "OPTIONAL" in this document are to be interpreted as described in BCP 209 14 [RFC2119] [RFC8174] when, and only when, they appear in all 210 capitals, as shown here. 212 2. BGP Peering Models 214 Depending on the requirements, scaling, and capabilities of the BGP 215 speakers, various peering models are supported. The only requirement 216 is that all BGP speakers in the BGP SPF routing domain receive link- 217 state NLRI on a timely basis, run an SPF calculation, and update 218 their data plane appropriately. The content of the Link NLRI is 219 described in Section 4.2. 221 2.1. BGP Single-Hop Peering on Network Node Connections 223 The simplest peering model is the one described in section 5.2.1 of 224 [RFC7938]. In this model, EBGP single-hop sessions are established 225 over direct point-to-point links interconnecting the SPF domain 226 nodes. For the purposes of BGP SPF, Link NLRI is only advertised if 227 a single-hop BGP session has been established and the Link-State/SPF 228 address family capability has been exchanged [RFC4790] on the 229 corresponding session. If the session goes down, the corresponding 230 Link NLRI will be withdrawn. Topologically, this would be equivalent 231 to the peering model in [RFC7938] where there is a BGP session on 232 every link in the data center switch fabric. 234 2.2. BGP Peering Between Directly Connected Network Nodes 236 In this model, BGP speakers peer with all directly connected network 237 nodes but the sessions may be multi-hop and the direct connection 238 discovery and liveliness detection for those connections are 239 independent of the BGP protocol. How this is accomplished is outside 240 the scope of this document. Consequently, there will be a single 241 session even if there are multiple direct connections between BGP 242 speakers. For the purposes of BGP SPF, Link NLRI is advertised as 243 long as a BGP session has been established, the Link-State/SPF 244 address family capability has been exchanged [RFC4790] and the 245 corresponding link is considered is up and considered operational. 246 This is much like the previous peering model only peering is on a 247 single loopback address and the switch fabric links can be 248 unnumbered. However, there will be the same number of sessions as 249 with the previous peering model unless there are parallel links 250 between switches in the fabric. 252 2.3. BGP Peering in Route-Reflector or Controller Topology 254 In this model, BGP speakers peer solely with one or more Route 255 Reflectors [RFC4456] or controllers. As in the previous model, 256 direct connection discovery and liveliness detection for those 257 connections are done outside the BGP protocol. More specifically, 258 the Liveliness detection is done using BFD protocol described in 259 [RFC5880]. For the purposes of BGP SPF, Link NLRI is advertised as 260 long as the corresponding link is up and considered operational. 262 This peering model, known as sparse peering, allows for many fewer 263 BGP sessions and, consequently, instances of the same NLRI received 264 from multiple peers. It is discussed in greater detail in 265 [I-D.ietf-lsvr-applicability]. 267 3. BGP-LS Shortest Path Routing (SPF) SAFI 269 In order to replace the Phase 1 and 2 decision functions of the 270 existing Decision Process with an SPF-based Decision Process and 271 streamline the Phase 3 decision functions in a backward compatible 272 manner, this draft introduces the BGP-LS-SFP SAFI for BGP-LS SPF 273 operation. The BGP-LS-SPF (AFI 16388 / SAFI TBD1) [RFC4790] is 274 allocated by IANA as specified in the Section 6. A BGP speaker using 275 the BGP-LS SPF extensions described herein MUST exchange the AFI/SAFI 276 using Multiprotocol Extensions Capability Code [RFC4760] with other 277 BGP speakers in the SPF routing domain. 279 4. Extensions to BGP-LS 281 [RFC7752] describes a mechanism by which link-state and TE 282 information can be collected from networks and shared with external 283 components using BGP protocol. It describes both the definition of 284 BGP-LS NLRI that describes links, nodes, and prefixes comprising IGP 285 link-state information and the definition of a BGP path attribute 286 (BGP-LS attribute) that carries link, node, and prefix properties and 287 attributes, such as the link and prefix metric or auxiliary Router- 288 IDs of nodes, etc. 290 The BGP protocol will be used in the Protocol-ID field specified in 291 table 1 of [I-D.ietf-idr-bgpls-segment-routing-epe]. The local and 292 remote node descriptors for all NLRI will be the BGP Router-ID (TLV 293 516) and either the AS Number (TLV 512) [RFC7752] or the BGP 294 Confederation Member (TLV 517) [RFC8402]. However, if the BGP 295 Router-ID is known to be unique within the BGP Routing domain, it can 296 be used as the sole descriptor. 298 4.1. Node NLRI Usage 300 The BGP Node NLRI will be advertised unconditionally by all routers 301 in the BGP SPF routing domain. 303 4.1.1. Node NLRI Attribute SPF Capability TLV 305 The SPF capability is a new Node Attribute TLV that will be added to 306 those defined in table 7 of [RFC7752]. The new attribute TLV will 307 only be applicable when BGP is specified in the Node NLRI Protocol ID 308 field. The TBD TLV type will be defined by IANA. The new Node 309 Attribute TLV will contain a single-octet SPF algorithm as defined in 310 [RFC8402]. 312 0 1 2 3 313 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 1 314 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 315 | Type | Length | 316 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 317 | SPF Algorithm | 318 +-+-+-+-+-+-+-+-+ 320 The SPF Algorithm may take the following values: 322 0 - Normal Shortest Path First (SPF) algorithm based on link 323 metric. This is the standard shortest path algorithm as 324 computed by the IGP protocol. Consistent with the deployed 325 practice for link-state protocols, Algorithm 0 permits any 326 node to overwrite the SPF path with a different path based on 327 its local policy. 328 1 - Strict Shortest Path First (SPF) algorithm based on link 329 metric. The algorithm is identical to Algorithm 0 but Algorithm 330 1 requires that all nodes along the path will honor the SPF 331 routing decision. Local policy at the node claiming support for 332 Algorithm 1 MUST NOT alter the SPF paths computed by Algorithm 1. 334 Note that usage of Strict Shortest Path First (SPF) algorithm is 335 defined in the IGP algorithm registry but usage is restricted to 336 [I-D.ietf-idr-bgpls-segment-routing-epe]. Hence, its usage for BGP- 337 LS SPF is out of scope. 339 When computing the SPF for a given BGP routing domain, only BGP nodes 340 advertising the SPF capability attribute will be included the 341 Shortest Path Tree (SPT). 343 4.1.2. BGP-LS Node NLRI Attribute SPF Status TLV 345 A BGP-LS Attribute TLV to BGP-LS Node NLRI is defined to indicate the 346 status of the node with respect to the BGP SPF calculation. This 347 will be used to rapidly take a node out of service or to indicate the 348 node is not to be used for transit (i.e., non-local) traffic. If the 349 SPF Status TLV is not included with the Node NLRI, the node is 350 considered to be up and is available for transit traffic. 352 0 1 2 3 353 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 1 354 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 355 | TBD Type | Length | 356 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 357 | SPF Status | 358 +-+-+-+-+-+-+-+-+ 360 BGP Status Values: 0 - Reserved 361 1 - Node Unreachable with respect to BGP SPF 362 2 - Node does not support transit with respect 363 to BGP SPF 364 3-254 - Undefined 365 255 - Reserved 367 4.2. Link NLRI Usage 369 The criteria for advertisement of Link NLRI are discussed in 370 Section 2. 372 Link NLRI is advertised with local and remote node descriptors as 373 described above and unique link identifiers dependent on the 374 addressing. For IPv4 links, the links local IPv4 (TLV 259) and 375 remote IPv4 (TLV 260) addresses will be used. For IPv6 links, the 376 local IPv6 (TLV 261) and remote IPv6 (TLV 262) addresses will be 377 used. For unnumbered links, the link local/remote identifiers (TLV 378 258) will be used. For links supporting having both IPv4 and IPv6 379 addresses, both sets of descriptors may be included in the same Link 380 NLRI. The link identifiers are described in table 5 of [RFC7752]. 382 The link IGP metric attribute TLV (TLV 1095) as well as any others 383 required for non-SPF purposes SHOULD be advertised. The metric value 384 in this TLV is variable length dependent on specific protocol usage 385 (refer to section 3.3.2.4 in [RFC7752]). For simplicity, the BGP-LS 386 SPF metric length will be 4 octets. Algorithms such as setting the 387 metric inversely to the link speed as done in the OSPF MIB [RFC4750] 388 MAY be supported. However, this is beyond the scope of this 389 document. 391 4.2.1. BGP-LS Link NLRI Attribute Prefix-Length TLVs 393 Two BGP-LS Attribute TLVs to BGP-LS Link NLRI are defined to 394 advertise the prefix length associated with the IPv4 and IPv6 link 395 prefixes. The prefix length is used for the optional installation of 396 prefixes corresponding to Link NLRI as defined in Section 5.3. 398 0 1 2 3 399 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 1 400 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 401 | TBD IPv4 or IPv6 Type | Length | 402 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 403 | Prefix-Length | 404 +-+-+-+-+-+-+-+-+ 406 Prefix-length - A one-octet length restricted to 1-32 for IPv4 407 Link NLRI endpoint prefixes and 1-128 for IPv6 408 Link NLRI endpoint prefixes. 410 4.2.2. BGP-LS Link NLRI Attribute SPF Status TLV 412 A BGP-LS Attribute TLV to BGP-LS Link NLRI is defined to indicate the 413 status of the link with respect to the BGP SPF calculation. This 414 will be used to expedite convergence for link failures as discussed 415 in Section 5.6.1. If the SPF Status TLV is not included with the 416 Link NLRI, the link is considered up and available. 418 0 1 2 3 419 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 1 420 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 421 | TBD Type | Length | 422 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 423 | SPF Status | 424 +-+-+-+-+-+-+-+-+ 426 BGP Status Values: 0 - Reserved 427 1 - Link Unreachable with respect to BGP SPF 428 2-254 - Undefined 429 255 - Reserved 431 4.3. Prefix NLRI Usage 433 Prefix NLRI is advertised with a local node descriptor as described 434 above and the prefix and length used as the descriptors (TLV 265) as 435 described in [RFC7752]. The prefix metric attribute TLV (TLV 1155) 436 as well as any others required for non-SPF purposes SHOULD be 437 advertised. For loopback prefixes, the metric should be 0. For non- 438 loopback prefixes, the setting of the metric is a local matter and 439 beyond the scope of this document. 441 4.3.1. BGP-LS Prefix NLRI Attribute SPF Status TLV 443 A BGP-LS Attribute TLV to BGP-LS Prefix NLRI is defined to indicate 444 the status of the prefix with respect to the BGP SPF calculation. 445 This will be used to expedite convergence for prefix unreachability 446 as discussed in Section 5.6.1. If the SPF Status TLV is not included 447 with the Prefix NLRI, the prefix is considered reachable. 449 0 1 2 3 450 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 1 451 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 452 | TBD Type | Length | 453 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 454 | SPF Status | 455 +-+-+-+-+-+-+-+-+ 457 BGP Status Values: 0 - Reserved 458 1 - Prefix down with respect to SPF 459 2-254 - Undefined 460 255 - Reserved 462 4.4. BGP-LS Attribute Sequence-Number TLV 464 A new BGP-LS Attribute TLV to BGP-LS NLRI types is defined to assure 465 the most recent version of a given NLRI is used in the SPF 466 computation. The TBD TLV type will be defined by IANA. The new BGP- 467 LS Attribute TLV will contain an 8-octet sequence number. The usage 468 of the Sequence Number TLV is described in Section 5.1. 470 0 1 2 3 471 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 1 472 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 473 | Type | Length | 474 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 475 | Sequence Number (High-Order 32 Bits) | 476 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 477 | Sequence Number (Low-Order 32 Bits) | 478 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 480 Sequence Number 482 The 64-bit strictly increasing sequence number is incremented for 483 every version of BGP-LS NLRI originated. BGP speakers implementing 484 this specification MUST use available mechanisms to preserve the 485 sequence number's strictly increasing property for the deployed life 486 of the BGP speaker (including cold restarts). One mechanism for 487 accomplishing this would be to use the high-order 32 bits of the 488 sequence number as a wrap/boot count that is incremented anytime the 489 BGP router loses its sequence number state or the low-order 32 bits 490 wrap. 492 When incrementing the sequence number for each self-originated NLRI, 493 the sequence number should be treated as an unsigned 64-bit value. 494 If the lower-order 32-bit value wraps, the higher-order 32-bit value 495 should be incremented and saved in non-volatile storage. If by some 496 chance the BGP Speaker is deployed long enough that there is a 497 possibility that the 64-bit sequence number may wrap or a BGP Speaker 498 completely loses its sequence number state (e.g., the BGP speaker 499 hardware is replaced or experiences a cold-start), the phase 1 500 decision function (see Section 5.1) rules will insure convergence, 501 albeit, not immediately. 503 5. Decision Process with SPF Algorithm 505 The Decision Process described in [RFC4271] takes place in three 506 distinct phases. The Phase 1 decision function of the Decision 507 Process is responsible for calculating the degree of preference for 508 each route received from a BGP speaker's peer. The Phase 2 decision 509 function is invoked on completion of the Phase 1 decision function 510 and is responsible for choosing the best route out of all those 511 available for each distinct destination, and for installing each 512 chosen route into the Loc-RIB. The combination of the Phase 1 and 2 513 decision functions is characterized as a Path Vector algorithm. 515 The SPF based Decision process replaces the BGP best-path Decision 516 process described in [RFC4271]. This process starts with selecting 517 only those Node NLRI whose SPF capability TLV matches with the local 518 BGP speaker's SPF capability TLV value. Since Link-State NLRI always 519 contains the local descriptor [RFC7752], it will only be originated 520 by a single BGP speaker in the BGP routing domain. These selected 521 Node NLRI and their Link/Prefix NLRI are used to build a directed 522 graph during the SPF computation. The best paths for BGP prefixes 523 are installed as a result of the SPF process. 525 When BGP-LS-SPF NLRI is received, all that is required is to 526 determine whether it is the best-path by examining the Node-ID and 527 sequence number as described in Section 5.1. If the received best- 528 path NLRI had changed, it will be advertised to other BGP-LS-SPF 529 peers. If the attributes have changed (other than the sequence 530 number), a BGP SPF calculation will be scheduled. However, a changed 531 NLRI MAY be advertised to other peers almost immediately and 532 propagation of changes can approach IGP convergence times. To 533 accomplish this, the MinRouteAdvertisementIntervalTimer and 534 MinASOriginationIntervalTimer [RFC4271] are not applicable to the 535 BGP-LS-SPF SAFI. Rather, SPF calculations SHOULD be triggered and 536 dampened consistent with the SPF back-off algorithm specified in 537 [RFC8405]. 539 The Phase 3 decision function of the Decision Process [RFC4271] is 540 also simplified since under normal SPF operation, a BGP speaker would 541 advertise the NLRI selected for the SPF to all BGP peers with the 542 BGP-LS/BGP-LS-SPF AFI/SAFI. Application of policy would not be 543 prevented however its usage to best-path process would be limited as 544 the SPF relies solely on link metrics. 546 5.1. Phase-1 BGP NLRI Selection 548 The rules for NLRI selection are greatly simplified from [RFC4271]. 550 1. If the NLRI is received from the BGP speaker originating the NLRI 551 (as determined by the comparing BGP Router ID in the NLRI Node 552 identifiers with the BGP speaker Router ID), then it is preferred 553 over the same NLRI from non-originators. This rule will assure 554 that stale NLRI is updated even if a BGP-LS router loses its 555 sequence number state due to a cold-start. 557 2. If the Sequence-Number TLV is present in the BGP-LS Attribute, 558 then the NLRI with the most recent, i.e., highest sequence number 559 is selected. BGP-LS NLRI with a Sequence-Number TLV will be 560 considered more recent than NLRI without a BGP-LS Attribute or a 561 BGP-LS Attribute that doesn't include the Sequence-Number TLV. 563 3. The final tie-breaker is the NLRI from the BGP Speaker with the 564 numerically largest BGP Router ID. 566 When a BGP speaker completely loses its sequence number state, i.e., 567 due to a cold start, or in the unlikely possibility that that 568 sequence number wraps, the BGP routing domain will still converge. 569 This is due to the fact that BGP speakers adjacent to the router will 570 always accept self-originated NLRI from the associated speaker as 571 more recent (rule # 1). When BGP speaker reestablishes a connection 572 with its peers, any existing session will be taken down and stale 573 NLRI will be replaced by the new NLRI and stale NLRI will be 574 discarded independent of whether or not BGP graceful restart is 575 deployed, [RFC4724]. The adjacent BGP speaker will update their NLRI 576 advertisements in turn until the BGP routing domain has converged. 578 The modified SPF Decision Process performs an SPF calculation rooted 579 at the BGP speaker using the metrics from Link and Prefix NLRI 580 Attribute TLVs [RFC7752]. As a result, any attributes that would 581 influence the Decision process defined in [RFC4271] like ORIGIN, 582 MULTI_EXIT_DISC, and LOCAL_PREF attributes are ignored by the SPF 583 algorithm. Furthermore, the NEXT_HOP attribute value is preserved 584 but otherwise ignored during the SPF or best-path. 586 5.2. Dual Stack Support 588 The SPF-based decision process operates on Node, Link, and Prefix 589 NLRIs that support both IPv4 and IPv6 addresses. Whether to run a 590 single SPF instance or multiple SPF instances for separate AFs is a 591 matter of a local implementation. Normally, IPv4 next-hops are 592 calculated for IPv4 prefixes and IPv6 next-hops are calculated for 593 IPv6 prefixes. However, an interesting use-case is deployment of 594 [RFC5549] where IPv6 next-hops are calculated for both IPv4 and IPv6 595 prefixes. As stated in Section 1, support for Multiple Topology 596 Routing (MTR) is an area for future study. 598 5.3. SPF Calculation based on BGP-LS NLRI 600 This section details the BGP-LS SPF local routing information base 601 (RIB) calculation. The router will use BGP-LS Node, Link, and Prefix 602 NLRI to populate the local RIB using the following algorithm. This 603 calculation yields the set of intra-area routes associated with the 604 BGP-LS domain. A router calculates the shortest-path tree using 605 itself as the root. Variations and optimizations of the algorithm 606 are valid as long as it yields the same set of routes. The algorithm 607 below supports Equal Cost Multi-Path (ECMP) routes. Weighted Unequal 608 Cost Multi-Path are out of scope. The organization of this section 609 owes heavily to section 16 of [RFC2328]. 611 The following abstract data structures are defined in order to 612 specify the algorithm. 614 o Local Route Information Base (RIB) - This is abstract contains 615 reachability information (i.e., next hops) for all prefixes (both 616 IPv4 and IPv6) as well as the Node NLRI reachability. 617 Implementations may choose to implement this as separate RIBs for 618 each address family and/or Node NLRI. 620 o Link State NLRI Database (LSNDB) - Database of BGP-LS NLRI that 621 facilitates access to all Node, Link, and Prefix NLRI as well as 622 all the Link and Prefix NLRI corresponding to a given Node NLRI. 623 Other optimization, such as, resolving bi-directional connectivity 624 associations between Link NLRI are possible but of scope of this 625 document. 627 o Candidate List - This is a list of candidate Node NLRI with the 628 lowest cost Node NLRI at the front of the list. It is typically 629 implemented as a heap but other concrete data structures have also 630 been used. 632 The algorithm is comprised of the steps below: 634 1. The current local RIB is invalidated. The local RIB is rebuilt 635 during the course of the SPF computation. The existing routing 636 entries are preserved for comparison to determine changes that 637 need to be installed in the global RIB. 639 2. The computing router's Node NLRI is installed in the local RIB 640 with a cost of 0 and as the sole entry in the candidate list. 642 3. The Node NLRI with the lowest cost is removed from the candidate 643 list for processing. If the BGP-LS Node attribute includes an 644 SPF Status TLV (Section 4.1.2) indicating the node is 645 unreachable, the Node NLRI is ignored and the next lowest cost 646 Node NLRI is selected from candidate list. The Node 647 corresponding to this NLRI will be referred to as the Current 648 Node. If the candidate list is empty, the SPF calculation has 649 completed and the algorithm proceeds to step 6. 651 4. All the Prefix NLRI with the same Node Identifiers as the Current 652 Node will be considered for installation. The cost for each 653 prefix is the metric advertised in the Prefix NLRI added to the 654 cost to reach the Current Node. 656 * If the BGP-LS Prefix attribute includes an SPF Status TLV 657 indicating the prefix is unreachable, the BGP-LS Prefix NLRI 658 is considered unreachable and the next BGP-LS Prefix NLRI is 659 examined. 661 * If the prefix is in the local RIB and the cost is greater than 662 the Current route's metric, the Prefix NLRI does not 663 contribute to the route and is ignored. 665 * If the prefix is in the local RIB and the cost is less than 666 the current route's metric, the Prefix is installed with the 667 Current Node's next-hops replacing the local RIB route's next- 668 hops and the metric being updated. 670 * If the prefix is in the local RIB and the cost is same as the 671 current route's metric, the Prefix is installed with the 672 Current Node's next-hops being merged with local RIB route's 673 next-hops. 675 5. All the Link NLRI with the same Node Identifiers as the Current 676 Node will be considered for installation. Each link will be 677 examined and will be referred to in the following text as the 678 Current Link. The cost of the Current Link is the advertised 679 metric in the Link NLRI added to the cost to reach the Current 680 Node. 682 * Optionally, the prefix(es) associated with the Current Link 683 are installed into the local RIB using the same rules as were 684 used for Prefix NLRI in the previous steps. 686 * If the current Node NLRI attributes includes the SPF status 687 TLV (Section 4.1.2) and the status indicates that the Node 688 doesn't support transit, the next link for the current node is 689 processed. 691 * The Current Link's endpoint Node NLRI is accessed (i.e., the 692 Node NLRI with the same Node identifiers as the Link 693 endpoint). If it exists, it will be referred to as the 694 Endpoint Node NLRI and the algorithm will proceed as follows: 696 + If the BGP-LS Link NLRI attribute includes an SPF Status 697 TLV indicating the link is down, the BGP-LS Link NLRI is 698 considered down and the next BGP-LS Link NLRI is examined. 700 + All the Link NLRI corresponding the Endpoint Node NLRI will 701 be searched for a back-link NLRI pointing to the current 702 node. Both the Node identifiers and the Link endpoint 703 identifiers in the Endpoint Node's Link NLRI must match for 704 a match. If there is no corresponding Link NLRI 705 corresponding to the Endpoint Node NLRI, the Endpoint Node 706 NLRI fails the bi-directional connectivity test and is not 707 processed further. 709 + If the Endpoint Node NLRI is not on the candidate list, it 710 is inserted based on the link cost and BGP Identifier (the 711 latter being used as a tie-breaker). 713 + If the Endpoint Node NLRI is already on the candidate list 714 with a lower cost, it need not be inserted again. 716 + If the Endpoint Node NLRI is already on the candidate list 717 with a higher cost, it must be removed and reinserted with 718 a lower cost. 720 * Return to step 3 to process the next lowest cost Node NLRI on 721 the candidate list. 723 6. The local RIB is examined and changes (adds, deletes, 724 modifications) are installed into the global RIB. 726 5.4. NEXT_HOP Manipulation 728 A BGP speaker that supports SPF extensions MAY interact with peers 729 that don't support SPF extensions. If the BGP-LS address family is 730 advertised to a peer not supporting the SPF extensions described 731 herein, then the BGP speaker MUST conform to the NEXT_HOP rules 732 specified in [RFC4271] when announcing the Link-State address family 733 routes to those peers. 735 All BGP peers that support SPF extensions would locally compute the 736 Loc-RIB next-hops as a result of the SPF process. Consequently, the 737 NEXT_HOP attribute is always ignored on receipt. However, BGP 738 speakers SHOULD set the NEXT_HOP address according to the NEXT_HOP 739 attribute rules specified in [RFC4271]. 741 5.5. IPv4/IPv6 Unicast Address Family Interaction 743 While the BGP-LS SPF address family and the IPv4/IPv6 unicast address 744 families install routes into the same device routing tables, they 745 will operate independently much the same as OSPF and IS-IS would 746 operate today (i.e., "Ships-in-the-Night" mode). There will be no 747 implicit route redistribution between the BGP address families. 748 However, implementation specific redistribution mechanisms SHOULD be 749 made available with the restriction that redistribution of BGP-LS SPF 750 routes into the IPv4 address family applies only to IPv4 routes and 751 redistribution of BGP-LS SPF route into the IPv6 address family 752 applies only to IPv6 routes. 754 Given the fact that SPF algorithms are based on the assumption that 755 all routers in the routing domain calculate the precisely the same 756 SPF tree and install the same set of routes, it is RECOMMENDED that 757 BGP-LS SPF IPv4/IPv6 routes be given priority by default when 758 installed into their respective RIBs. In common implementations the 759 prioritization is governed by route preference or administrative 760 distance with lower being more preferred. 762 5.6. NLRI Advertisement and Convergence 764 5.6.1. Link/Prefix Failure Convergence 766 A local failure will prevent a link from being used in the SPF 767 calculation due to the IGP bi-directional connectivity requirement. 768 Consequently, local link failures should always be given priority 769 over updates (e.g., withdrawing all routes learned on a session) in 770 order to ensure the highest priority propagation and optimal 771 convergence. 773 An IGP such as OSPF [RFC2328] will stop using the link as soon as the 774 Router-LSA for one side of the link is received. With normal BGP 775 advertisement, the link would continue to be used until the last copy 776 of the BGP-LS Link NLRI is withdrawn. In order to avoid this delay, 777 the originator of the Link NLRI will advertise a more recent version 778 of the BGP-LS Link NLRI including the SPF Status TLV Section 4.2.2 779 indicating the link is down with respect to BGP SPF. After some 780 configurable period of time, e.g., 2-3 seconds, the BGP-LS Link NLRI 781 can be withdrawn with no consequence. If the link becomes available 782 in that period, the originator of the BGP-LS LINK NLRI will simply 783 advertise a more recent version of the BGP-LS Link NLRI without the 784 SPF Status TLV in the BGP-LS Link Attributes. 786 Similarly, when a prefix becomes unreachable, a more recent version 787 of the BGP-LS Prefix NLRI will be advertised with the SPF Status TLV 788 Section 4.3.1 indicating the prefix is unreachable in the BGP-LS 789 Prefix Attributes and the prefix will be considered unreachable with 790 respect to BGP SPF. After some configurable period of time, e.g., 791 2-3 seconds, the BGP-LS Prefix NLRI can be withdrawn with no 792 consequence. If the prefix becomes reachable in that period, the 793 originator of the BGP-LS Prefix NLRI will simply advertise a more 794 recent version of the BGP-LS Prefix NLRI without the SPF Status TLV 795 in the BGP-LS Prefix Attributes. 797 5.6.2. Node Failure Convergence 799 With BGP without graceful restart [RFC4724], all the NLRI advertised 800 by node are implicitly withdrawn when a session failure is detected. 801 If fast failure detection such as BFD is utilized, and the node is on 802 the fastest converging path, the most recent versions of BGP-LS NLRI 803 may be withdrawn while these versions are in-flight on longer paths. 804 This will result the older version of the NLRI being used until the 805 new versions arrive and, potentially, unnecessary route flaps. 806 Therefore, BGP-LS SPF NLRI SHOULD always be retained before being 807 implicitly withdrawn for a brief configurable interval, e.g., 2-3 808 seconds. This will not delay convergence since the adjacent nodes 809 will detect the link failure and advertise a more recent NLRI 810 indicating the link is down with respect to BGP SPF Section 5.6.1 and 811 the BGP-SPF calculation will failure the bi-directional connectivity 812 check. 814 5.7. Error Handling 816 When a BGP speaker receives a BGP Update containing a malformed SPF 817 Capability TLV in the Node NLRI BGP-LS Attribute [RFC7752], it MUST 818 ignore the received TLV and the Node NLRI and not pass it to other 819 BGP peers as specified in [RFC7606]. When discarding a Node NLRI 820 with malformed TLV, a BGP speaker SHOULD log an error for further 821 analysis. 823 6. IANA Considerations 825 This document defines an AFI/SAFI for BGP-LS SPF operation and 826 requests IANA to assign the BGP-LS/BGP-LS-SPF (AFI 16388 / SAFI TBD1) 827 as described in [RFC4760]. 829 This document also defines five attribute TLVs for BGP-LS NLRI. We 830 request IANA to assign types for the SPF capability TLV, Sequence 831 Number TLV, IPv4 Link Prefix-Length TLV, IPv6 Link Prefix-Length TLV, 832 and SPF Status TLV from the "BGP-LS Node Descriptor, Link Descriptor, 833 Prefix Descriptor, and Attribute TLVs" Registry. 835 7. Security Considerations 837 This extension to BGP does not change the underlying security issues 838 inherent in the existing [RFC4271], [RFC4724], and [RFC7752]. 840 8. Management Considerations 842 This section includes unique management considerations for the BGP-LS 843 SPF address family. 845 8.1. Configuration 847 In addition to configuration of the BGP-LS SPF address family, 848 implementations SHOULD support the configuration of the 849 INITIAL_SPF_DELAY, SHORT_SPF_DELAY, LONG_SPF_DELAY, TIME_TO_LEARN, 850 and HOLDDOWN_INTERVAL as documented in [RFC8405]. 852 8.2. Operational Data 854 In order to troubleshoot SPF issues, implementations SHOULD support 855 an SPF log including entries for previous SPF computations, Each SPF 856 log entry would include the BGP-LS NLRI SPF triggering the SPF, SPF 857 scheduled time, SPF start time, SPF end time, and SPF type if 858 different types of SPF are supported. Since the size of the log will 859 be finite, implementations SHOULD also maintain counters for the 860 total number of SPF computations of each type and the total number of 861 SPF triggering events. Additionally, to troubleshoot SPF scheduling 862 and back-off [RFC8405], the current SPF back-off state, remaining 863 time-to-learn, remaining holddown, last trigger event time, last SPF 864 time, and next SPF time should be available. 866 9. Acknowledgements 868 The authors would like to thank Sue Hares, Jorge Rabadan, Boris 869 Hassanov, Dan Frost, Matt Anderson, Fred Baker, and Lukas Krattiger 870 for their review and comments. Thanks to Pushpasis Sarkar for 871 discussions on preventing a BGP SPF Router from being used for non- 872 local traffic (i.e., transit traffic). 874 The authors extend special thanks to Eric Rosen for fruitful 875 discussions on BGP-LS SPF convergence as compared to IGPs. 877 10. Contributors 879 In addition to the authors listed on the front page, the following 880 co-authors have contributed to the document. 882 Derek Yeung 883 Arrcus, Inc. 884 derek@arrcus.com 886 Gunter Van De Velde 887 Nokia 888 gunter.van_de_velde@nokia.com 890 Abhay Roy 891 Arrcus, Inc. 892 abhay@arrcus.com 894 Venu Venugopal 895 Cisco Systems 896 venuv@cisco.com 898 Chaitanya Yadlapalli 899 AT&T 900 cy098d@att.com 902 11. References 904 11.1. Normative References 906 [I-D.ietf-idr-bgpls-segment-routing-epe] 907 Previdi, S., Talaulikar, K., Filsfils, C., Patel, K., Ray, 908 S., and J. Dong, "BGP-LS extensions for Segment Routing 909 BGP Egress Peer Engineering", draft-ietf-idr-bgpls- 910 segment-routing-epe-19 (work in progress), May 2019. 912 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 913 Requirement Levels", BCP 14, RFC 2119, 914 DOI 10.17487/RFC2119, March 1997, 915 . 917 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 918 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 919 DOI 10.17487/RFC4271, January 2006, 920 . 922 [RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K. 923 Patel, "Revised Error Handling for BGP UPDATE Messages", 924 RFC 7606, DOI 10.17487/RFC7606, August 2015, 925 . 927 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 928 S. Ray, "North-Bound Distribution of Link-State and 929 Traffic Engineering (TE) Information Using BGP", RFC 7752, 930 DOI 10.17487/RFC7752, March 2016, 931 . 933 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 934 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 935 May 2017, . 937 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 938 Decraene, B., Litkowski, S., and R. Shakir, "Segment 939 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 940 July 2018, . 942 [RFC8405] Decraene, B., Litkowski, S., Gredler, H., Lindem, A., 943 Francois, P., and C. Bowers, "Shortest Path First (SPF) 944 Back-Off Delay Algorithm for Link-State IGPs", RFC 8405, 945 DOI 10.17487/RFC8405, June 2018, 946 . 948 11.2. Information References 950 [I-D.ietf-lsvr-applicability] 951 Patel, K., Lindem, A., Zandi, S., and G. Dawra, "Usage and 952 Applicability of Link State Vector Routing in Data 953 Centers", draft-ietf-lsvr-applicability-05 (work in 954 progress), March 2020. 956 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, 957 DOI 10.17487/RFC2328, April 1998, 958 . 960 [RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route 961 Reflection: An Alternative to Full Mesh Internal BGP 962 (IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006, 963 . 965 [RFC4724] Sangli, S., Chen, E., Fernando, R., Scudder, J., and Y. 966 Rekhter, "Graceful Restart Mechanism for BGP", RFC 4724, 967 DOI 10.17487/RFC4724, January 2007, 968 . 970 [RFC4750] Joyal, D., Ed., Galecki, P., Ed., Giacalone, S., Ed., 971 Coltun, R., and F. Baker, "OSPF Version 2 Management 972 Information Base", RFC 4750, DOI 10.17487/RFC4750, 973 December 2006, . 975 [RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, 976 "Multiprotocol Extensions for BGP-4", RFC 4760, 977 DOI 10.17487/RFC4760, January 2007, 978 . 980 [RFC4790] Newman, C., Duerst, M., and A. Gulbrandsen, "Internet 981 Application Protocol Collation Registry", RFC 4790, 982 DOI 10.17487/RFC4790, March 2007, 983 . 985 [RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P. 986 Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", 987 RFC 4915, DOI 10.17487/RFC4915, June 2007, 988 . 990 [RFC5286] Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for 991 IP Fast Reroute: Loop-Free Alternates", RFC 5286, 992 DOI 10.17487/RFC5286, September 2008, 993 . 995 [RFC5549] Le Faucheur, F. and E. Rosen, "Advertising IPv4 Network 996 Layer Reachability Information with an IPv6 Next Hop", 997 RFC 5549, DOI 10.17487/RFC5549, May 2009, 998 . 1000 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 1001 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 1002 . 1004 [RFC7938] Lapukhov, P., Premji, A., and J. Mitchell, Ed., "Use of 1005 BGP for Routing in Large-Scale Data Centers", RFC 7938, 1006 DOI 10.17487/RFC7938, August 2016, 1007 . 1009 Authors' Addresses 1011 Keyur Patel 1012 Arrcus, Inc. 1014 Email: keyur@arrcus.com 1015 Acee Lindem 1016 Cisco Systems 1017 301 Midenhall Way 1018 Cary, NC 27513 1019 USA 1021 Email: acee@cisco.com 1023 Shawn Zandi 1024 LinkedIn 1025 222 2nd Street 1026 San Francisco, CA 94105 1027 USA 1029 Email: szandi@linkedin.com 1031 Wim Henderickx 1032 Nokia 1033 Antwerp 1034 Belgium 1036 Email: wim.henderickx@nokia.com