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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: June 12, 2020 Cisco Systems 6 S. Zandi 7 LinkedIn 8 W. Henderickx 9 Nokia 10 December 10, 2019 12 Shortest Path Routing Extensions for BGP Protocol 13 draft-ietf-lsvr-bgp-spf-07 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 June 12, 2020. 43 Copyright Notice 45 Copyright (c) 2019 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. Algorithms such 384 as setting the metric inversely to the link speed as done in the OSPF 385 MIB [RFC4750] MAY be supported. However, this is beyond the scope of 386 this document. 388 4.2.1. BGP-LS Link NLRI Attribute Prefix-Length TLVs 390 Two BGP-LS Attribute TLVs to BGP-LS Link NLRI are defined to 391 advertise the prefix length associated with the IPv4 and IPv6 link 392 prefixes. The prefix length is used for the optional installation of 393 prefixes corresponding to Link NLRI as defined in Section 5.3. 395 0 1 2 3 396 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 1 397 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 398 | TBD IPv4 or IPv6 Type | Length | 399 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 400 | Prefix-Length | 401 +-+-+-+-+-+-+-+-+ 403 Prefix-length - A one-octet length restricted to 1-32 for IPv4 404 Link NLRI endpoint prefixes and 1-128 for IPv6 405 Link NLRI endpoint prefixes. 407 4.2.2. BGP-LS Link NLRI Attribute SPF Status TLV 409 A BGP-LS Attribute TLV to BGP-LS Link NLRI is defined to indicate the 410 status of the link with respect to the BGP SPF calculation. This 411 will be used to expedite convergence for link failures as discussed 412 in Section 5.6.1. If the SPF Status TLV is not included with the 413 Link NLRI, the link is considered up and available. 415 0 1 2 3 416 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 1 417 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 418 | TBD Type | Length | 419 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 420 | SPF Status | 421 +-+-+-+-+-+-+-+-+ 423 BGP Status Values: 0 - Reserved 424 1 - Link Unreachable with respect to BGP SPF 425 2-254 - Undefined 426 255 - Reserved 428 4.3. Prefix NLRI Usage 430 Prefix NLRI is advertised with a local node descriptor as described 431 above and the prefix and length used as the descriptors (TLV 265) as 432 described in [RFC7752]. The prefix metric attribute TLV (TLV 1155) 433 as well as any others required for non-SPF purposes SHOULD be 434 advertised. For loopback prefixes, the metric should be 0. For non- 435 loopback prefixes, the setting of the metric is a local matter and 436 beyond the scope of this document. 438 4.3.1. BGP-LS Prefix NLRI Attribute SPF Status TLV 440 A BGP-LS Attribute TLV to BGP-LS Prefix NLRI is defined to indicate 441 the status of the prefix with respect to the BGP SPF calculation. 442 This will be used to expedite convergence for prefix unreachability 443 as discussed in Section 5.6.1. If the SPF Status TLV is not included 444 with the Prefix NLRI, the prefix is considered reachable. 446 0 1 2 3 447 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 1 448 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 449 | TBD Type | Length | 450 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 451 | SPF Status | 452 +-+-+-+-+-+-+-+-+ 454 BGP Status Values: 0 - Reserved 455 1 - Prefix down with respect to SPF 456 2-254 - Undefined 457 255 - Reserved 459 4.4. BGP-LS Attribute Sequence-Number TLV 461 A new BGP-LS Attribute TLV to BGP-LS NLRI types is defined to assure 462 the most recent version of a given NLRI is used in the SPF 463 computation. The TBD TLV type will be defined by IANA. The new BGP- 464 LS Attribute TLV will contain an 8-octet sequence number. The usage 465 of the Sequence Number TLV is described in Section 5.1. 467 0 1 2 3 468 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 1 469 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 470 | Type | Length | 471 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 472 | Sequence Number (High-Order 32 Bits) | 473 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 474 | Sequence Number (Low-Order 32 Bits) | 475 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 477 Sequence Number 479 The 64-bit strictly increasing sequence number is incremented for 480 every version of BGP-LS NLRI originated. BGP speakers implementing 481 this specification MUST use available mechanisms to preserve the 482 sequence number's strictly increasing property for the deployed life 483 of the BGP speaker (including cold restarts). One mechanism for 484 accomplishing this would be to use the high-order 32 bits of the 485 sequence number as a wrap/boot count that is incremented anytime the 486 BGP router loses its sequence number state or the low-order 32 bits 487 wrap. 489 When incrementing the sequence number for each self-originated NLRI, 490 the sequence number should be treated as an unsigned 64-bit value. 491 If the lower-order 32-bit value wraps, the higher-order 32-bit value 492 should be incremented and saved in non-volatile storage. If by some 493 chance the BGP Speaker is deployed long enough that there is a 494 possibility that the 64-bit sequence number may wrap or a BGP Speaker 495 completely loses its sequence number state (e.g., the BGP speaker 496 hardware is replaced or experiences a cold-start), the phase 1 497 decision function (see Section 5.1) rules will insure convergence, 498 albeit, not immediately. 500 5. Decision Process with SPF Algorithm 502 The Decision Process described in [RFC4271] takes place in three 503 distinct phases. The Phase 1 decision function of the Decision 504 Process is responsible for calculating the degree of preference for 505 each route received from a BGP speaker's peer. The Phase 2 decision 506 function is invoked on completion of the Phase 1 decision function 507 and is responsible for choosing the best route out of all those 508 available for each distinct destination, and for installing each 509 chosen route into the Loc-RIB. The combination of the Phase 1 and 2 510 decision functions is characterized as a Path Vector algorithm. 512 The SPF based Decision process replaces the BGP best-path Decision 513 process described in [RFC4271]. This process starts with selecting 514 only those Node NLRI whose SPF capability TLV matches with the local 515 BGP speaker's SPF capability TLV value. Since Link-State NLRI always 516 contains the local descriptor [RFC7752], it will only be originated 517 by a single BGP speaker in the BGP routing domain. These selected 518 Node NLRI and their Link/Prefix NLRI are used to build a directed 519 graph during the SPF computation. The best paths for BGP prefixes 520 are installed as a result of the SPF process. 522 When BGP-LS-SPF NLRI is received, all that is required is to 523 determine whether it is the best-path by examining the Node-ID and 524 sequence number as described in Section 5.1. If the received best- 525 path NLRI had changed, it will be advertised to other BGP-LS-SPF 526 peers. If the attributes have changed (other than the sequence 527 number), a BGP SPF calculation will be scheduled. However, a changed 528 NLRI MAY be advertised to other peers almost immediately and 529 propagation of changes can approach IGP convergence times. To 530 accomplish this, the MinRouteAdvertisementIntervalTimer and 531 MinASOriginationIntervalTimer [RFC4271] are not applicable to the 532 BGP-LS-SPF SAFI. Rather, SPF calculations SHOULD be triggered and 533 dampened consistent with the SPF back-off algorithm specified in 534 [RFC8405]. 536 The Phase 3 decision function of the Decision Process [RFC4271] is 537 also simplified since under normal SPF operation, a BGP speaker would 538 advertise the NLRI selected for the SPF to all BGP peers with the 539 BGP-LS/BGP-LS-SPF AFI/SAFI. Application of policy would not be 540 prevented however its usage to best-path process would be limited as 541 the SPF relies solely on link metrics. 543 5.1. Phase-1 BGP NLRI Selection 545 The rules for NLRI selection are greatly simplified from [RFC4271]. 547 1. If the NLRI is received from the BGP speaker originating the NLRI 548 (as determined by the comparing BGP Router ID in the NLRI Node 549 identifiers with the BGP speaker Router ID), then it is preferred 550 over the same NLRI from non-originators. This rule will assure 551 that stale NLRI is updated even if a BGP-LS router loses its 552 sequence number state due to a cold-start. 554 2. If the Sequence-Number TLV is present in the BGP-LS Attribute, 555 then the NLRI with the most recent, i.e., highest sequence number 556 is selected. BGP-LS NLRI with a Sequence-Number TLV will be 557 considered more recent than NLRI without a BGP-LS Attribute or a 558 BGP-LS Attribute that doesn't include the Sequence-Number TLV. 560 3. The final tie-breaker is the NLRI from the BGP Speaker with the 561 numerically largest BGP Router ID. 563 When a BGP speaker completely loses its sequence number state, i.e., 564 due to a cold start, or in the unlikely possibility that that 565 sequence number wraps, the BGP routing domain will still converge. 566 This is due to the fact that BGP speakers adjacent to the router will 567 always accept self-originated NLRI from the associated speaker as 568 more recent (rule # 1). When BGP speaker reestablishes a connection 569 with its peers, any existing session will be taken down and stale 570 NLRI will be replaced by the new NLRI and stale NLRI will be 571 discarded independent of whether or not BGP graceful restart is 572 deployed, [RFC4724]. The adjacent BGP speaker will update their NLRI 573 advertisements in turn until the BGP routing domain has converged. 575 The modified SPF Decision Process performs an SPF calculation rooted 576 at the BGP speaker using the metrics from Link and Prefix NLRI 577 Attribute TLVs [RFC7752]. As a result, any attributes that would 578 influence the Decision process defined in [RFC4271] like ORIGIN, 579 MULTI_EXIT_DISC, and LOCAL_PREF attributes are ignored by the SPF 580 algorithm. Furthermore, the NEXT_HOP attribute value is preserved 581 but otherwise ignored during the SPF or best-path. 583 5.2. Dual Stack Support 585 The SPF-based decision process operates on Node, Link, and Prefix 586 NLRIs that support both IPv4 and IPv6 addresses. Whether to run a 587 single SPF instance or multiple SPF instances for separate AFs is a 588 matter of a local implementation. Normally, IPv4 next-hops are 589 calculated for IPv4 prefixes and IPv6 next-hops are calculated for 590 IPv6 prefixes. However, an interesting use-case is deployment of 591 [RFC5549] where IPv6 next-hops are calculated for both IPv4 and IPv6 592 prefixes. As stated in Section 1, support for Multiple Topology 593 Routing (MTR) is an area for future study. 595 5.3. SPF Calculation based on BGP-LS NLRI 597 This section details the BGP-LS SPF local routing information base 598 (RIB) calculation. The router will use BGP-LS Node, Link, and Prefix 599 NLRI to populate the local RIB using the following algorithm. This 600 calculation yields the set of intra-area routes associated with the 601 BGP-LS domain. A router calculates the shortest-path tree using 602 itself as the root. Variations and optimizations of the algorithm 603 are valid as long as it yields the same set of routes. The algorithm 604 below supports Equal Cost Multi-Path (ECMP) routes. Weighted Unequal 605 Cost Multi-Path are out of scope. The organization of this section 606 owes heavily to section 16 of [RFC2328]. 608 The following abstract data structures are defined in order to 609 specify the algorithm. 611 o Local Route Information Base (RIB) - This is abstract contains 612 reachability information (i.e., next hops) for all prefixes (both 613 IPv4 and IPv6) as well as the Node NLRI reachability. 614 Implementations may choose to implement this as separate RIBs for 615 each address family and/or Node NLRI. 617 o Link State NLRI Database (LSNDB) - Database of BGP-LS NLRI that 618 facilitates access to all Node, Link, and Prefix NLRI as well as 619 all the Link and Prefix NLRI corresponding to a given Node NLRI. 620 Other optimization, such as, resolving bi-directional connectivity 621 associations between Link NLRI are possible but of scope of this 622 document. 624 o Candidate List - This is a list of candidate Node NLRI with the 625 lowest cost Node NLRI at the front of the list. It is typically 626 implemented as a heap but other concrete data structures have also 627 been used. 629 The algorithm is comprised of the steps below: 631 1. The current local RIB is invalidated. The local RIB is built 632 again during the course of the SPF computation. The existing 633 routing entries are preserved for comparison to determine changes 634 that need to be installed in the global RIB. 636 2. The computing router's Node NLRI is installed in the local RIB 637 with a cost of 0 and as the sole entry in the candidate list. 639 3. The Node NLRI with the lowest cost is removed from the candidate 640 list for processing. If the BGP-LS Node attribute includes an 641 SPF Status TLV (Section 4.1.2) indicating the node is 642 unreachable, the Node NLRI is ignored and the next lowest cost 643 Node NLRI is selected from candidate list. The Node 644 corresponding to this NLRI will be referred to as the Current 645 Node. If the candidate list is empty, the SPF calculation has 646 completed and the algorithm proceeds to step 6. 648 4. All the Prefix NLRI with the same Node Identifiers as the Current 649 Node will be considered for installation. The cost for each 650 prefix is the metric advertised in the Prefix NLRI added to the 651 cost to reach the Current Node. 653 * If the BGP-LS Prefix attribute includes an SPF Status TLV 654 indicating the prefix is unreachable, the BGP-LS Prefix NLRI 655 is considered unreachable and the next BGP-LS Prefix NLRI is 656 examined. 658 * If the prefix is in the local RIB and the cost is greater than 659 the Current route's metric, the Prefix NLRI does not 660 contribute to the route and is ignored. 662 * If the prefix is in the local RIB and the cost is less than 663 the current route's metric, the Prefix is installed with the 664 Current Node's next-hops replacing the local RIB route's next- 665 hops and the metric being updated. 667 * If the prefix is in the local RIB and the cost is same as the 668 current route's metric, the Prefix is installed with the 669 Current Node's next-hops being merged with local RIB route's 670 next-hops. 672 5. All the Link NLRI with the same Node Identifiers as the Current 673 Node will be considered for installation. Each link will be 674 examined and will be referred to in the following text as the 675 Current Link. The cost of the Current Link is the advertised 676 metric in the Link NLRI added to the cost to reach the Current 677 Node. 679 * Optionally, the prefix(es) associated with the Current Link 680 are installed into the local RIB using the same rules as were 681 used for Prefix NLRI in the previous steps. 683 * If the current Node NLRI attributes includes the SPF status 684 TLV (Section 4.1.2) and the status indicates that the Node 685 doesn't support transit, the next link for the current node is 686 processed. 688 * The Current Link's endpoint Node NLRI is accessed (i.e., the 689 Node NLRI with the same Node identifiers as the Link 690 endpoint). If it exists, it will be referred to as the 691 Endpoint Node NLRI and the algorithm will proceed as follows: 693 + If the BGP-LS Link NLRI attribute includes an SPF Status 694 TLV indicating the link is down, the BGP-LS Link NLRI is 695 considered down and the next BGP-LS Link NLRI is examined. 697 + All the Link NLRI corresponding the Endpoint Node NLRI will 698 be searched for a back-link NLRI pointing to the current 699 node. Both the Node identifiers and the Link endpoint 700 identifiers in the Endpoint Node's Link NLRI must match for 701 a match. If there is no corresponding Link NLRI 702 corresponding to the Endpoint Node NLRI, the Endpoint Node 703 NLRI fails the bi-directional connectivity test and is not 704 processed further. 706 + If the Endpoint Node NLRI is not on the candidate list, it 707 is inserted based on the link cost and BGP Identifier (the 708 latter being used as a tie-breaker). 710 + If the Endpoint Node NLRI is already on the candidate list 711 with a lower cost, it need not be inserted again. 713 + If the Endpoint Node NLRI is already on the candidate list 714 with a higher cost, it must be removed and reinserted with 715 a lower cost. 717 * Return to step 3 to process the next lowest cost Node NLRI on 718 the candidate list. 720 6. The local RIB is examined and changes (adds, deletes, 721 modifications) are installed into the global RIB. 723 5.4. NEXT_HOP Manipulation 725 A BGP speaker that supports SPF extensions MAY interact with peers 726 that don't support SPF extensions. If the BGP-LS address family is 727 advertised to a peer not supporting the SPF extensions described 728 herein, then the BGP speaker MUST conform to the NEXT_HOP rules 729 specified in [RFC4271] when announcing the Link-State address family 730 routes to those peers. 732 All BGP peers that support SPF extensions would locally compute the 733 Loc-RIB next-hops as a result of the SPF process. Consequently, the 734 NEXT_HOP attribute is always ignored on receipt. However, BGP 735 speakers SHOULD set the NEXT_HOP address according to the NEXT_HOP 736 attribute rules specified in [RFC4271]. 738 5.5. IPv4/IPv6 Unicast Address Family Interaction 740 While the BGP-LS SPF address family and the IPv4/IPv6 unicast address 741 families install routes into the same device routing tables, they 742 will operate independently much the same as OSPF and IS-IS would 743 operate today (i.e., "Ships-in-the-Night" mode). There will be no 744 implicit route redistribution between the BGP address families. 745 However, implementation specific redistribution mechanisms SHOULD be 746 made available with the restriction that redistribution of BGP-LS SPF 747 routes into the IPv4 address family applies only to IPv4 routes and 748 redistribution of BGP-LS SPF route into the IPv6 address family 749 applies only to IPv6 routes. 751 Given the fact that SPF algorithms are based on the assumption that 752 all routers in the routing domain calculate the precisely the same 753 SPF tree and install the same set of routes, it is RECOMMENDED that 754 BGP-LS SPF IPv4/IPv6 routes be given priority by default when 755 installed into their respective RIBs. In common implementations the 756 prioritization is governed by route preference or administrative 757 distance with lower being more preferred. 759 5.6. NLRI Advertisement and Convergence 761 5.6.1. Link/Prefix Failure Convergence 763 A local failure will prevent a link from being used in the SPF 764 calculation due to the IGP bi-directional connectivity requirement. 765 Consequently, local link failures should always be given priority 766 over updates (e.g., withdrawing all routes learned on a session) in 767 order to ensure the highest priority propagation and optimal 768 convergence. 770 An IGP such as OSPF [RFC2328] will stop using the link as soon as the 771 Router-LSA for one side of the link is received. With normal BGP 772 advertisement, the link would continue to be used until the last copy 773 of the BGP-LS Link NLRI is withdrawn. In order to avoid this delay, 774 the originator of the Link NLRI will advertise a more recent version 775 of the BGP-LS Link NLRI including the SPF Status TLV Section 4.2.2 776 indicating the link is down with respect to BGP SPF. After some 777 configurable period of time, e.g., 2-3 seconds, the BGP-LS Link NLRI 778 can be withdrawn with no consequence. If the link becomes available 779 in that period, the originator of the BGP-LS LINK NLRI will simply 780 advertise a more recent version of the BGP-LS Link NLRI without the 781 SPF Status TLV in the BGP-LS Link Attributes. 783 Similarly, when a prefix becomes unreachable, a more recent version 784 of the BGP-LS Prefix NLRI will be advertised with the SPF Status TLV 785 Section 4.3.1 indicating the prefix is unreachable in the BGP-LS 786 Prefix Attributes and the prefix will be considered unreachable with 787 respect to BGP SPF. After some configurable period of time, e.g., 788 2-3 seconds, the BGP-LS Prefix NLRI can be withdrawn with no 789 consequence. If the prefix becomes reachable in that period, the 790 originator of the BGP-LS Prefix NLRI will simply advertise a more 791 recent version of the BGP-LS Prefix NLRI without the SPF Status TLV 792 in the BGP-LS Prefix Attributes. 794 5.6.2. Node Failure Convergence 796 With BGP without graceful restart [RFC4724], all the NLRI advertised 797 by node are implicitly withdrawn when a session failure is detected. 798 If fast failure detection such as BFD is utilized and the node is on 799 the fastest converging path, the most recent versions of BGP-LS NLRI 800 may be withdrawn while these versions are in-flight on longer paths. 801 This will result the older version of the NLRI being used until the 802 new versions arrive and, potentially, unnecessary route flaps. 803 Therefore, BGP-LS SPF NLRI SHOULD always be retained before being 804 implicitly withdrawn for a brief configurable interval, e.g., 2-3 805 seconds. This will not delay convergence since the adjacent nodes 806 will detect the link failure and advertise a more recent NLRI 807 indicating the link is down with respect to BGP SPF Section 5.6.1 and 808 the BGP-SPF calculation will failure the bi-directional connectivity 809 check. 811 5.7. Error Handling 813 When a BGP speaker receives a BGP Update containing a malformed SPF 814 Capability TLV in the Node NLRI BGP-LS Attribute [RFC7752], it MUST 815 ignore the received TLV and the Node NLRI and not pass it to other 816 BGP peers as specified in [RFC7606]. When discarding a Node NLRI 817 with malformed TLV, a BGP speaker SHOULD log an error for further 818 analysis. 820 6. IANA Considerations 822 This document defines an AFI/SAFI for BGP-LS SPF operation and 823 requests IANA to assign the BGP-LS/BGP-LS-SPF (AFI 16388 / SAFI TBD1) 824 as described in [RFC4750]. 826 This document also defines five attribute TLVs for BGP-LS NLRI. We 827 request IANA to assign types for the SPF capability TLV, Sequence 828 Number TLV, IPv4 Link Prefix-Length TLV, IPv6 Link Prefix-Length TLV, 829 and SPF Status TLV from the "BGP-LS Node Descriptor, Link Descriptor, 830 Prefix Descriptor, and Attribute TLVs" Registry. 832 7. Security Considerations 834 This extension to BGP does not change the underlying security issues 835 inherent in the existing [RFC4271], [RFC4724], and [RFC7752]. 837 8. Management Considerations 839 This section includes unique management considerations for the BGP-LS 840 SPF address family. 842 8.1. Configuration 844 In addition to configuration of the BGP-LS SPF address family, 845 implementations SHOULD support the configuration of the 846 INITIAL_SPF_DELAY, SHORT_SPF_DELAY, LONG_SPF_DELAY, TIME_TO_LEARN, 847 and HOLDDOWN_INTERVAL as documented in [RFC8405]. 849 8.2. Operational Data 851 In order to troubleshoot SPF issues, implementations SHOULD support 852 an SPF log including entries for previous SPF computations, Each SPF 853 log entry would include the BGP-LS NLRI SPF triggering the SPF, SPF 854 scheduled time, SPF start time, SPF end time, and SPF type if 855 different types of SPF are supported. Since the size of the log will 856 be finite, implementations SHOULD also maintain counters for the 857 total number of SPF computations of each type and the total number of 858 SPF triggering events. Additionally, to troubleshoot SPF scheduling 859 and back-off [RFC8405], the current SPF back-off state, remaining 860 time-to-learn, remaining holddown, last trigger event time, last SPF 861 time, and next SPF time should be available. 863 9. Acknowledgements 865 The authors would like to thank Sue Hares, Jorge Rabadan, Boris 866 Hassanov, Dan Frost, Matt Anderson, and Fred Baker for their review 867 and comments. Thanks to Chaitanya Yadlapalli and Pushpais Sarkar for 868 discussions on preventing a BGP SPF Router from being used for non- 869 local traffic (i.e., transit traffic). 871 The authors extend special thanks to Eric Rosen for fruitful 872 discussions on BGP-LS SPF convergence as compared to IGPs. 874 10. Contributors 876 In addition to the authors listed on the front page, the following 877 co-authors have contributed to the document. 879 Derek Yeung 880 Arrcus, Inc. 881 derek@arrcus.com 883 Gunter Van De Velde 884 Nokia 885 gunter.van_de_velde@nokia.com 887 Abhay Roy 888 Cisco Systems 889 akr@cisco.com 891 Venu Venugopal 892 Cisco Systems 893 venuv@cisco.com 895 11. References 897 11.1. Normative References 899 [I-D.ietf-idr-bgpls-segment-routing-epe] 900 Previdi, S., Talaulikar, K., Filsfils, C., Patel, K., Ray, 901 S., and J. Dong, "BGP-LS extensions for Segment Routing 902 BGP Egress Peer Engineering", draft-ietf-idr-bgpls- 903 segment-routing-epe-19 (work in progress), May 2019. 905 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 906 Requirement Levels", BCP 14, RFC 2119, 907 DOI 10.17487/RFC2119, March 1997, 908 . 910 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 911 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 912 DOI 10.17487/RFC4271, January 2006, 913 . 915 [RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K. 916 Patel, "Revised Error Handling for BGP UPDATE Messages", 917 RFC 7606, DOI 10.17487/RFC7606, August 2015, 918 . 920 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 921 S. Ray, "North-Bound Distribution of Link-State and 922 Traffic Engineering (TE) Information Using BGP", RFC 7752, 923 DOI 10.17487/RFC7752, March 2016, 924 . 926 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 927 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 928 May 2017, . 930 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 931 Decraene, B., Litkowski, S., and R. Shakir, "Segment 932 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 933 July 2018, . 935 [RFC8405] Decraene, B., Litkowski, S., Gredler, H., Lindem, A., 936 Francois, P., and C. Bowers, "Shortest Path First (SPF) 937 Back-Off Delay Algorithm for Link-State IGPs", RFC 8405, 938 DOI 10.17487/RFC8405, June 2018, 939 . 941 11.2. Information References 943 [I-D.ietf-lsvr-applicability] 944 Patel, K., Lindem, A., Zandi, S., and G. Dawra, "Usage and 945 Applicability of Link State Vector Routing in Data 946 Centers", draft-ietf-lsvr-applicability-04 (work in 947 progress), November 2019. 949 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, 950 DOI 10.17487/RFC2328, April 1998, 951 . 953 [RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route 954 Reflection: An Alternative to Full Mesh Internal BGP 955 (IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006, 956 . 958 [RFC4724] Sangli, S., Chen, E., Fernando, R., Scudder, J., and Y. 959 Rekhter, "Graceful Restart Mechanism for BGP", RFC 4724, 960 DOI 10.17487/RFC4724, January 2007, 961 . 963 [RFC4750] Joyal, D., Ed., Galecki, P., Ed., Giacalone, S., Ed., 964 Coltun, R., and F. Baker, "OSPF Version 2 Management 965 Information Base", RFC 4750, DOI 10.17487/RFC4750, 966 December 2006, . 968 [RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, 969 "Multiprotocol Extensions for BGP-4", RFC 4760, 970 DOI 10.17487/RFC4760, January 2007, 971 . 973 [RFC4790] Newman, C., Duerst, M., and A. Gulbrandsen, "Internet 974 Application Protocol Collation Registry", RFC 4790, 975 DOI 10.17487/RFC4790, March 2007, 976 . 978 [RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P. 979 Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", 980 RFC 4915, DOI 10.17487/RFC4915, June 2007, 981 . 983 [RFC5286] Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for 984 IP Fast Reroute: Loop-Free Alternates", RFC 5286, 985 DOI 10.17487/RFC5286, September 2008, 986 . 988 [RFC5549] Le Faucheur, F. and E. Rosen, "Advertising IPv4 Network 989 Layer Reachability Information with an IPv6 Next Hop", 990 RFC 5549, DOI 10.17487/RFC5549, May 2009, 991 . 993 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 994 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 995 . 997 [RFC7938] Lapukhov, P., Premji, A., and J. Mitchell, Ed., "Use of 998 BGP for Routing in Large-Scale Data Centers", RFC 7938, 999 DOI 10.17487/RFC7938, August 2016, 1000 . 1002 Authors' Addresses 1004 Keyur Patel 1005 Arrcus, Inc. 1007 Email: keyur@arrcus.com 1009 Acee Lindem 1010 Cisco Systems 1011 301 Midenhall Way 1012 Cary, NC 27513 1013 USA 1015 Email: acee@cisco.com 1017 Shawn Zandi 1018 LinkedIn 1019 222 2nd Street 1020 San Francisco, CA 94105 1021 USA 1023 Email: szandi@linkedin.com 1025 Wim Henderickx 1026 Nokia 1027 Antwerp 1028 Belgium 1030 Email: wim.henderickx@nokia.com