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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Outdated reference: A later version (-29) exists of draft-ietf-lsvr-bgp-spf-01 == Outdated reference: A later version (-17) exists of draft-acee-idr-lldp-peer-discovery-03 == Outdated reference: A later version (-12) exists of draft-xu-idr-neighbor-autodiscovery-08 == Outdated reference: A later version (-03) exists of draft-ymbk-lsvr-lsoe-00 -- Obsolete informational reference (is this intentional?): RFC 7752 (Obsoleted by RFC 9552) Summary: 0 errors (**), 0 flaws (~~), 5 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 LSVR K. Patel 3 Internet-Draft Arrcus, Inc. 4 Intended status: Informational A. Lindem 5 Expires: January 26, 2019 Cisco Systems 6 S. Zandi 7 G. Dawra 8 Linkedin 9 July 25, 2018 11 Usage and Applicability of Link State Vector Routing in Data Centers 12 draft-keyupate-ietf-applicability-00.txt 14 Abstract 16 This document discusses the usage and applicability of Link State 17 Vector Routing (LSVR) extensions in the CLOS architecture of Data 18 Center Networks. The document is intended to provide a simplified 19 guide for the deployment of LSVR extensions. 21 Status of This Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at http://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on January 26, 2019. 38 Copyright Notice 40 Copyright (c) 2018 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents 45 (http://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 56 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 2 57 3. Recommended Reading . . . . . . . . . . . . . . . . . . . . . 3 58 4. Common Deployment Scenario . . . . . . . . . . . . . . . . . 3 59 5. Justification for BGP SPF Extension . . . . . . . . . . . . . 4 60 6. LSVR Applicability to CLOS Networks . . . . . . . . . . . . . 4 61 6.1. Usage of BGP-LS SAFI . . . . . . . . . . . . . . . . . . 5 62 6.1.1. Relationship to Other BGP AFI/SAFI Tuples . . . . . . 5 63 6.2. Peering Models . . . . . . . . . . . . . . . . . . . . . 5 64 6.2.1. Bi-Connected Graph Heuristic . . . . . . . . . . . . 6 65 6.3. BGP Peer Discovery . . . . . . . . . . . . . . . . . . . 6 66 6.3.1. BGP Peer Discovery Requirements . . . . . . . . . . . 6 67 6.3.2. BGP Peer Discovery Alternatives . . . . . . . . . . . 7 68 6.3.3. Data Center Interconnect (DCI) Applicability . . . . 7 69 6.4. Non-CLOS/FAT Tree Topology Applicability . . . . . . . . 8 70 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 71 8. Security Considerations . . . . . . . . . . . . . . . . . . . 8 72 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 73 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 74 10.1. Normative References . . . . . . . . . . . . . . . . . . 8 75 10.2. Informative References . . . . . . . . . . . . . . . . . 9 76 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 78 1. Introduction 80 This document complements [I-D.ietf-lsvr-bgp-spf] by discussing the 81 applicability of the technology in a simple and fairly common 82 deployment scenario, which is described in Section 4. 84 After describing the deployment scenario, Section 5 will describe the 85 reasons for BGP modifications for such deployments. 87 Once the control plane routing protocol requirements are described, 88 Section 6 will cover the LSVR protocol enhancements to BGP to meet 89 these requirements and their applicability to Data Center CLOS 90 networks. 92 2. Requirements Language 94 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 95 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 96 "OPTIONAL" in this document are to be interpreted as described in BCP 97 14 [RFC2119] [RFC8174] when, and only when, they appear in all 98 capitals, as shown here. 100 3. Recommended Reading 102 This document assumes knowledge of existing data center networks and 103 data center network topologies [CLOS]. This document also assumes 104 knowledge of data center routing protocols like BGP [RFC4271], BGP- 105 SPF [I-D.ietf-lsvr-bgp-spf], OSPF [RFC2328], as well as, data center 106 OAM protocols like LLDP [RFC4957] and BFD [RFC5580]. 108 4. Common Deployment Scenario 110 Within a Data Center, a common network design to interconnect servers 111 is done using the CLOS topology [CLOS]. The CLOS topology is fully 112 non-blocking and the topology is realized using Equal Cost Multipath 113 (ECMP). In a CLOS topology, the minimum number of parallel paths 114 between two servers is determined by the width of a tier-1 stage as 115 shown in the figure 1. 117 The following example illustrates multistage CLOS topology. 119 Tier-1 120 +-----+ 121 |NODE | 122 +->| 12 |--+ 123 | +-----+ | 124 Tier-2 | | Tier-2 125 +-----+ | +-----+ | +-----+ 126 +------------>|NODE |--+->|NODE |--+--|NODE |-------------+ 127 | +-----| 9 |--+ | 10 | +--| 11 |-----+ | 128 | | +-----+ +-----+ +-----+ | | 129 | | | | 130 | | +-----+ +-----+ +-----+ | | 131 | +-----+---->|NODE |--+ |NODE | +--|NODE |-----+-----+ | 132 | | | +---| 6 |--+->| 7 |--+--| 8 |---+ | | | 133 | | | | +-----+ | +-----+ | +-----+ | | | | 134 | | | | | | | | | | 135 +-----+ +-----+ | +-----+ | +-----+ +-----+ 136 |NODE | |NODE | Tier-3 +->|NODE |--+ Tier-3 |NODE | |NODE | 137 | 1 | | 2 | | 3 | | 4 | | 5 | 138 +-----+ +-----+ +-----+ +-----+ +-----+ 139 | | | | | | | | 140 A O B O <- Servers -> Z O O O 142 Figure 1: Illustration of the basic CLOS 144 5. Justification for BGP SPF Extension 146 Many data centers use BGP as a routing protocol to create an overlay 147 as well as an underlay network for their CLOS Topologies to simplify 148 layer-3 routing and operations [RFC7938]. However, BGP is a path- 149 vector routing protocol. Since it does not create a fabric topology, 150 it uses hop-by-hop EBGP peering to facilitate hop-by-hop routing to 151 create the underlay network and to resolve any overlay next hops. 152 The hop-by-hop BGP peering paradigm imposes several restrictions 153 within a CLOS. It severely prohibits a deployment of Route 154 Reflectors/Route Controllers as the EBGP sessions are inline with the 155 data path. The BGP best path algorithm is prefix-based and it 156 prevents announcements of prefixes to other BGP speakers until the 157 best path decision process is performed for the prefix at each 158 intermediate hop. These restrictions significantly delay the overall 159 convergence of the underlay network within a CLOS. 161 The LSVR SPF modifications allow BGP to overcome these limitations. 162 Furthermore, using the BGP-LS NLRI format [RFC7752] allows the LSVR 163 data to be advertised for nodes, links, and prefixes in the BGP 164 routing domain and used for SPF computations. 166 6. LSVR Applicability to CLOS Networks 168 With the BGP SPF extensions [I-D.ietf-lsvr-bgp-spf], the BGP best 169 path computation and route computation are replaced with OSPF-like 170 algorithms [RFC2328] both to determine whether an BGP-LS NLRI has 171 changed and needs to be re-advertised and to compute the routing 172 table. These modifications will significantly improve convergence of 173 the underlay while affording the operational benefits of a single 174 routing protocol [RFC7938]. 176 Data center controllers typically require visibility to the BGP 177 topology to compute traffic-engineered paths. These controllers 178 learn the topology and other relevant information via the BGP-LS 179 address family [RFC7752] which is totally independent of the underlay 180 address families (usually IPv4/IPv6 unicast). Furthermore, in 181 traditional BGP underlays, all the BGP routers will need to advertise 182 their BGP-LS information independently. With the BGP SPF extensions, 183 controllers can learn the topology using the same BGP advertisements 184 used to compute the underlay routes. Furthermore, these data center 185 controllers can avail the convergence advantages of the BGP SPF 186 extensions. The placement of controllers can be outside of the 187 forwarding path or within the forwarding path. 189 Alternatively, as each and every router in the BGP SPF domain will 190 have a complete view of the topology, the operator can also choose to 191 configure BGP sessions in hop-by-hop peering model described in 193 [RFC7938] along with BFD [RFC5580]. In doing so, while the hop-by- 194 hop peering model lacks inherent benefits of the controller-based 195 model, BGP updates need not be serialized by BGP best path algorithm 196 in either of these models. This helps overall network convergence. 198 6.1. Usage of BGP-LS SAFI 200 The BGP SPF extensions [I-D.ietf-lsvr-bgp-spf] define a new BGP-LS 201 SAFI for announcement of BGP SPF link-state. The NLRI format and its 202 associated attributes follow the format of BGP-LS for node, link, and 203 prefix announcements. Whether the peering model within a CLOS 204 follows hop-by-hop peering described in [RFC7938] or any controller- 205 based or route-reflector peering, an operator can exchange BGP SPF 206 SAFI routes over the BGP peering by simply configuring BGP SPF SAFI 207 between the necessary BGP speakers. 209 The BGP-LS SPF SAFI can also co-exist with BGP IP Unicast SAFI which 210 could exchange overlapping IP routes. The routes received by these 211 SAFIs are evaluated, stored, and announced separately according to 212 the rules of [RFC4760]. The tie-breaking of route installation is a 213 matter of the local policies and preferences of the network operator. 215 Finally, as the BGP SPF peering is done following the procedures 216 described in [RFC4271], all the existing transport security 217 mechanisms including [RFC5925] are available for the BGP-LS SPF SAFI. 219 6.1.1. Relationship to Other BGP AFI/SAFI Tuples 221 Normally, the BGP-LS AFI/SAFI is used solely to compute the underlay 222 and is given preference over other AFI/SAFIs. Other BGP SAFIs, e.g., 223 IPv6/IPv6 Unicast VPN would use the BGP-SPF computed routes for next 224 hop resolution. However, if BGP-LS NLRI is also being advertised for 225 controller consumption, there is no need to replicate the Node, Link, 226 and Prefix NLRI in BGP-NLRI. Rather, additional NLRI attributes can 227 be advertised in the BGP-LS SPF AFI/SAFI as required. 229 6.2. Peering Models 231 As previously stated, BGP SPF can be deployed using the existing 232 peering model where there is a single hop BGP session on each and 233 every link in the data center fabric [RFC7938]. This provides for 234 both the advertisement of routes and the determination of link and 235 neighboring switch availability. With BGP SPF, the underlay will 236 converge faster due to changes in the decision process which will 237 allow NLRI changes to be advertised faster after detecting a change. 239 Alternately, BFD [RFC5580] can be used to swiftly determine the 240 availability of links and the BGP peering model can be significantly 241 sparser than the data center fabric. BGP SPF sessions then only be 242 established with enough peers to provide a bi-connected graph. If 243 IEBGP is used, then the BGP routers at tier N-1 will act as route- 244 reflectors for the routers at tier N. 246 6.2.1. Bi-Connected Graph Heuristic 248 With this heuristic, discovery of BGP peers is assumed Section 6.3. 249 Additionally, it assumed that the direction of the peering can be 250 ascertained. In the context of a data center fabric, direction is 251 either northbound (toward the spine), southbound (toward the Top-Of- 252 Rack (TOR) switches) or east-west (same level in hierarchy. The 253 determination of the direction is beyond the scope of this document. 254 However, it would be reasonable to assume a technique where the TOR 255 switches can be identified and the number of hops to the TOR is used 256 to determine the direction. 258 In this heuristic, BGP speakers allow passive session establishment 259 for southbound BGP sessions. For northbound sessions, BGP speakers 260 will attempt to maintain two northbound BGP sessions with different 261 switches (in data center fabrics there is normally a single layer-3 262 connection anyway). For east-west sessions, passive BGP session 263 establishment is allowed. However, BGP speaker will never actively 264 establish an east-west BGP session unless it can't establish two 265 northbound BGP sessions. 267 6.3. BGP Peer Discovery 269 6.3.1. BGP Peer Discovery Requirements 271 The most basic requirement is to be able to discover the address of a 272 single-hop peer without pre-configuration. This is being 273 accomplished today with using IPv6 Router Advertisements (RA) 274 [RFC4861] and assuming that a BGP sessions is desired with any 275 discovered peer. Beyond the basic requirement, it is useful to have 276 to following information relating to the BGP session: 278 o Autonomous System (AS) and BGP Identifier of a potential peer. 279 The latter can be used for debugging and to decrease the 280 likelihood of BGP session establishment collisions. 282 o Security capabilities supported and for cryptographic 283 authentication, the security capabilities and possibly a key-chain 284 [RFC8177] to be used. 286 o Session Policy Identifier - A group number or name used to 287 associate common session parameters with the peer. For example, 288 in a data center, BGP sessions with a Top of Rack (ToR) device 289 could have parameters than BGP sessions between leaf and spine. 291 In a data center fabric, it is often useful to know whether a peer is 292 southbound (towards the servers) or northbound (towards the spine or 293 super-spine) Section 6.2.1. A potential requirement would also be to 294 determine this dynamically. One mechanism, without specifying all 295 the details, might be for the ToRs to be identified when installed 296 and for the others switches in the fabric to determine their level 297 based on the distance from the closest ToR. 299 If there are multiple links between BGP speakers or the links between 300 BGP speakers are unnumbered, it is also useful to be able to 301 establish multi-hop sessions using the loopback addresses. This will 302 often require the discovery protocol to install route(s) toward the 303 potential peer loopback addresses prior to BGP session establishment. 305 Finally, a simple BGP discovery protocol could also be used to 306 establish a multi-hop session with one or more controllers by 307 advertising connectivity to one or more controllers. However, once 308 the multi-hop session actually traverses multiple nodes, it is 309 bordering a distance-vector routing protocol and possibly this is not 310 a good requirement for the discovery protocol. 312 6.3.2. BGP Peer Discovery Alternatives 314 While BGP peer discovery is not part of [I-D.ietf-lsvr-bgp-spf], 315 there are, at least, three proposals for BGP peer discovery. At 316 least one of these mechanisms will be adopted and will be applicable 317 to deployments other than the data center. It is strongly 318 RECOMMENDED that the accepted mechanism be used in conjunction with 319 BGP SPF in data centers. The BGP discovery mechanism should 320 discovery both peer addresses and endpoints for BFD discovery. 321 Additionally, it would be great if there were a heuristic for 322 determining whether the peer is at a tier above or below the 323 discovering BGP speaker (refer to Section 6.2.1). 325 The BGP discovery mechanisms under consideration are 326 [I-D.acee-idr-lldp-peer-discovery], 327 [I-D.xu-idr-neighbor-autodiscovery], and [I-D.ymbk-lsvr-lsoe]. 329 6.3.3. Data Center Interconnect (DCI) Applicability 331 Since BGP SPF is to be used for the routing underlay and DCI gateway 332 boxes typically have direct or very simple connectivity, BGP external 333 sessions would typically not include the BGP SPF SAFI. 335 6.4. Non-CLOS/FAT Tree Topology Applicability 337 The BGP SPF extensions [I-D.ietf-lsvr-bgp-spf] can be used in other 338 topologies and avail the inherent convergence improvements. 339 Additionally, sparse peering techniques may be utilized Section 6.2. 340 However, determining whether or to establish a BGP session is more 341 complex and the heuristic described in Section 6.2.1 cannot be used. 342 In such topologies, other techniques such as those described in 343 [I-D.li-dynamic-flooding] may be employed. One potential deployment 344 would be the underlay for a Service Provider (SP) backbone where 345 usage of a single protocol, i.e., BGP, is desired. 347 7. IANA Considerations 349 No IANA updates are requested by this document. 351 8. Security Considerations 353 This document introduces no new security considerations above and 354 beyond those already specified in the [RFC4271] and 355 [I-D.ietf-lsvr-bgp-spf]. 357 9. Acknowledgements 359 The authors would like to thank Alvaro Retana and Yan Filyurin for 360 the review and comments. 362 10. References 364 10.1. Normative References 366 [I-D.ietf-lsvr-bgp-spf] 367 Patel, K., Lindem, A., Zandi, S., and W. Henderickx, 368 "Shortest Path Routing Extensions for BGP Protocol", 369 draft-ietf-lsvr-bgp-spf-01 (work in progress), May 2018. 371 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 372 Requirement Levels", BCP 14, RFC 2119, 373 DOI 10.17487/RFC2119, March 1997, . 376 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 377 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 378 May 2017, . 380 10.2. Informative References 382 [CLOS] "A Study of Non-Blocking Switching Networks", The Bell 383 System Technical Journal, Vol. 32(2), DOI 384 10.1002/j.1538-7305.1953.tb01433.x, March 1953. 386 [I-D.acee-idr-lldp-peer-discovery] 387 Lindem, A., Patel, K., Zandi, S., Haas, J., and X. Xu, 388 "BGP Logical Link Discovery Protocol (LLDP) Peer 389 Discovery", draft-acee-idr-lldp-peer-discovery-03 (work in 390 progress), June 2018. 392 [I-D.li-dynamic-flooding] 393 Li, T. and P. Psenak, "Dynamic Flooding on Dense Graphs", 394 draft-li-dynamic-flooding-05 (work in progress), June 395 2018. 397 [I-D.xu-idr-neighbor-autodiscovery] 398 Xu, X., Bi, K., Tantsura, J., Triantafillis, N., and K. 399 Talaulikar, "BGP Neighbor Autodiscovery", draft-xu-idr- 400 neighbor-autodiscovery-08 (work in progress), May 2018. 402 [I-D.ymbk-lsvr-lsoe] 403 Bush, R. and K. Patel, "Link State Over Ethernet", draft- 404 ymbk-lsvr-lsoe-00 (work in progress), March 2018. 406 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, 407 DOI 10.17487/RFC2328, April 1998, . 410 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 411 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 412 DOI 10.17487/RFC4271, January 2006, . 415 [RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, 416 "Multiprotocol Extensions for BGP-4", RFC 4760, 417 DOI 10.17487/RFC4760, January 2007, . 420 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 421 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 422 DOI 10.17487/RFC4861, September 2007, . 425 [RFC4957] Krishnan, S., Ed., Montavont, N., Njedjou, E., Veerepalli, 426 S., and A. Yegin, Ed., "Link-Layer Event Notifications for 427 Detecting Network Attachments", RFC 4957, 428 DOI 10.17487/RFC4957, August 2007, . 431 [RFC5580] Tschofenig, H., Ed., Adrangi, F., Jones, M., Lior, A., and 432 B. Aboba, "Carrying Location Objects in RADIUS and 433 Diameter", RFC 5580, DOI 10.17487/RFC5580, August 2009, 434 . 436 [RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP 437 Authentication Option", RFC 5925, DOI 10.17487/RFC5925, 438 June 2010, . 440 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 441 S. Ray, "North-Bound Distribution of Link-State and 442 Traffic Engineering (TE) Information Using BGP", RFC 7752, 443 DOI 10.17487/RFC7752, March 2016, . 446 [RFC7938] Lapukhov, P., Premji, A., and J. Mitchell, Ed., "Use of 447 BGP for Routing in Large-Scale Data Centers", RFC 7938, 448 DOI 10.17487/RFC7938, August 2016, . 451 [RFC8177] Lindem, A., Ed., Qu, Y., Yeung, D., Chen, I., and J. 452 Zhang, "YANG Data Model for Key Chains", RFC 8177, 453 DOI 10.17487/RFC8177, June 2017, . 456 Authors' Addresses 458 Keyur Patel 459 Arrcus, Inc. 460 2077 Gateway Pl 461 San Jose, CA 95110 462 USA 464 Email: keyur@arrcus.com 465 Acee Lindem 466 Cisco Systems 467 301 Midenhall Way 468 Cary, NC 95110 469 USA 471 Email: acee@cisco.com 473 Shawn Zandi 474 Linkedin 475 222 2nd Street 476 San Francisco, CA 94105 477 USA 479 Email: szandi@linkedin.com 481 Gaurav Dawra 482 Linkedin 483 222 2nd Street 484 San Francisco, CA 94105 485 USA 487 Email: gdawra@linkedin.com