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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-22) exists of draft-ietf-idr-tunnel-encaps-15 ** Obsolete normative reference: RFC 7752 (Obsoleted by RFC 9552) == Outdated reference: A later version (-06) exists of draft-farrel-spring-sr-domain-interconnect-05 == Outdated reference: A later version (-18) exists of draft-ietf-idr-bgp-ls-segment-routing-ext-16 Summary: 1 error (**), 0 flaws (~~), 4 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 BESS Working Group A. Farrel 3 Internet-Draft Old Dog Consulting 4 Intended status: Standards Track J. Drake 5 Expires: September 12, 2020 E. Rosen 6 Juniper Networks 7 K. Patel 8 Arrcus, Inc. 9 L. Jalil 10 Verizon 11 March 11, 2020 13 Gateway Auto-Discovery and Route Advertisement for Segment Routing 14 Enabled Domain Interconnection 15 draft-ietf-bess-datacenter-gateway-05 17 Abstract 19 Data centers are critical components of the infrastructure used by 20 network operators to provide services to their customers. Data 21 centers are attached to the Internet or a backbone network by gateway 22 routers. One data center typically has more than one gateway for 23 commercial, load balancing, and resiliency reasons. 25 Segment Routing is a popular protocol mechanism for use within a data 26 center, but also for steering traffic that flows between two data 27 center sites. In order that one data center site may load balance 28 the traffic it sends to another data center site, it needs to know 29 the complete set of gateway routers at the remote data center, the 30 points of connection from those gateways to the backbone network, and 31 the connectivity across the backbone network. 33 Segment Routing may also be operated in other domains, such as access 34 networks. Those domains also need to be connected across backbone 35 networks through gateways. 37 This document defines a mechanism using the BGP Tunnel Encapsulation 38 attribute to allow each gateway router to advertise the routes to the 39 prefixes in the Segment Routing domains to which it provides access, 40 and also to advertise on behalf of each other gateway to the same 41 Segment Routing domain. 43 Status of This Memo 45 This Internet-Draft is submitted in full conformance with the 46 provisions of BCP 78 and BCP 79. 48 Internet-Drafts are working documents of the Internet Engineering 49 Task Force (IETF). Note that other groups may also distribute 50 working documents as Internet-Drafts. The list of current Internet- 51 Drafts is at https://datatracker.ietf.org/drafts/current/. 53 Internet-Drafts are draft documents valid for a maximum of six months 54 and may be updated, replaced, or obsoleted by other documents at any 55 time. It is inappropriate to use Internet-Drafts as reference 56 material or to cite them other than as "work in progress." 58 This Internet-Draft will expire on September 12, 2020. 60 Copyright Notice 62 Copyright (c) 2020 IETF Trust and the persons identified as the 63 document authors. All rights reserved. 65 This document is subject to BCP 78 and the IETF Trust's Legal 66 Provisions Relating to IETF Documents 67 (https://trustee.ietf.org/license-info) in effect on the date of 68 publication of this document. Please review these documents 69 carefully, as they describe your rights and restrictions with respect 70 to this document. Code Components extracted from this document must 71 include Simplified BSD License text as described in Section 4.e of 72 the Trust Legal Provisions and are provided without warranty as 73 described in the Simplified BSD License. 75 Table of Contents 77 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 78 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 5 79 3. SR Domain Gateway Auto-Discovery . . . . . . . . . . . . . . 5 80 4. Relationship to BGP Link State and Egress Peer Engineering . 7 81 5. Advertising an SR Domain Route Externally . . . . . . . . . . 7 82 6. Encapsulation . . . . . . . . . . . . . . . . . . . . . . . . 7 83 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 84 7.1. Tunnel Encapsulation Tunnel Type . . . . . . . . . . . . 7 85 7.2. Tunnel Encapsulation Sub-TLVs . . . . . . . . . . . . . . 8 86 8. Security Considerations . . . . . . . . . . . . . . . . . . . 8 87 9. Manageability Considerations . . . . . . . . . . . . . . . . 9 88 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 89 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 90 11.1. Normative References . . . . . . . . . . . . . . . . . . 10 91 11.2. Informative References . . . . . . . . . . . . . . . . . 10 92 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 94 1. Introduction 96 Data centers (DCs) are critical components of the infrastructure used 97 by network operators to provide services to their customers. DCs are 98 attached to the Internet or a backbone network by gateway routers 99 (GWs). One DC typically has more than one GW for various reasons 100 including commercial preferences, load balancing, and resiliency 101 against connection of device failure. 103 Segment Routing (SR) [RFC8402] is a popular protocol mechanism for 104 use within a DC, but also for steering traffic that flows between two 105 DC sites. In order for a source (ingress) DC that uses SR to load 106 balance the flows it sends to a destination (egress) DC, it needs to 107 know the complete set of entry nodes (i.e., GWs) for that egress DC 108 from the backbone network connecting the two DCs. Note that it is 109 assumed that the connected set of DCs and the backbone network 110 connecting them are part of the same SR BGP Link State (LS) instance 111 ([RFC7752] and [I-D.ietf-idr-bgpls-segment-routing-epe]) so that 112 traffic engineering using SR may be used for these flows. 114 SR may also be operated in other domains, such as access networks. 115 Those domains also need to be connected across backbone networks 116 through gateways. 118 Suppose that there are two gateways, GW1 and GW2 as shown in 119 Figure 1, for a given egress SR domain and that they each advertise a 120 route to prefix X which is located within the egress SR domain with 121 each setting itself as next hop. One might think that the GWs for X 122 could be inferred from the routes' next hop fields, but typically it 123 is not the case that both routes get distributed across the backbone: 124 rather only the best route, as selected by BGP, is distributed. This 125 precludes load balancing flows across both GWs. 127 ----------------- --------------------- 128 | Ingress | | Egress ------ | 129 | SR Domain | | SR Domain |Prefix| | 130 | | | | X | | 131 | | | ------ | 132 | -- | | --- --- | 133 | |GW| | | |GW1| |GW2| | 134 -------++-------- ----+-----------+-+-- 135 | \ | / | 136 | \ | / | 137 | -+------------- --------+--------+-- | 138 | ||PE| ----| |---- |PE| |PE| | | 139 | | -- |ASBR+------+ASBR| -- -- | | 140 | | ----| |---- | | 141 | | | | | | 142 | | ----| |---- | | 143 | | AS1 |ASBR+------+ASBR| AS2 | | 144 | | ----| |---- | | 145 | --------------- -------------------- | 146 --+-----------------------------------------------+-- 147 | |PE| |PE| | 148 | -- AS3 -- | 149 | | 150 ----------------------------------------------------- 152 Figure 1: Example Segment Routing Domain Interconnection 154 The obvious solution to this problem is to use the BGP feature that 155 allows the advertisement of multiple paths in BGP (known as Add- 156 Paths) [RFC7911] to ensure that all routes to X get advertised by 157 BGP. However, even if this is done, the identity of the GWs will be 158 lost as soon as the routes get distributed through an Autonomous 159 System Border Router (ASBR) that will set itself to be the next hop. 160 And if there are multiple Autonomous Systems (ASes) in the backbone, 161 not only will the next hop change several times, but the Add-Paths 162 technique will experience scaling issues. This all means that the 163 Add-Paths approach is limited to SR domains connected over a single 164 AS. 166 This document defines a solution that overcomes this limitation and 167 works equally well with a backbone constructed from one or more ASes. 168 The solution uses the Tunnel Encapsulation attribute 169 [I-D.ietf-idr-tunnel-encaps] as follows: 171 We define a new tunnel type, "SR Tunnel". When the GWs to a given 172 SR domain advertise a route to a prefix X within the SR domain, 173 they will each include a Tunnel Encapsulation attribute with 174 multiple tunnel instances each of type "SR Tunnel" (value 17), one 175 for each GW, and each containing a Remote Endpoint sub-TLV with 176 that GW's address. 178 In other words, each route advertised by a GW identifies all of the 179 GWs to the same SR domain (see Section 3 for a discussion of how GWs 180 discover each other). Therefore, even if only one of the routes is 181 distributed to other ASes, it will not matter how many times the next 182 hop changes, as the Tunnel Encapsulation attribute (and its remote 183 endpoint sub-TLVs) will remain unchanged. 185 To put this in the context of Figure 1, GW1 and GW2 discover each 186 other as gateways for the egress SR domain. Both GW1 and GW2 187 advertise themselves as having routes to prefix X. Furthermore, GW1 188 includes a Tunnel Encapsulation attribute with a tunnel instance of 189 type "SR tunnel" for itself and another for GW2. Similarly, GW2 190 includes a Tunnel Encapsulation for itself and another for GW1. The 191 gateway in the ingress SR domain can now see all possible paths to 192 the egress SR domain regardless of which route advertisement is 193 propagated to it, and it can choose one, or balance traffic flows as 194 it sees fit. 196 The protocol extensions defined in this document are put into the 197 broader context of SR domain interconnection by 198 [I-D.farrel-spring-sr-domain-interconnect]. That document shows how 199 other existing protocol elements may be combined with the extensions 200 defined in this document to provide a full system. 202 2. Requirements Language 204 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 205 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 206 "OPTIONAL" in this document are to be interpreted as described in BCP 207 14 [RFC2119] [RFC8174] when, and only when, they appear in all 208 capitals, as shown here. 210 3. SR Domain Gateway Auto-Discovery 212 To allow a given SR domain's GWs to auto-discover each other and to 213 coordinate their operations, the following procedures are 214 implemented: 216 o Each GW is configured with an identifier for the SR domain. That 217 identifier is common across all GWs to the domain (i.e., the same 218 identifier is used by all GWs to the same SR domain), and unique 219 across all SR domains that are connected (i.e., across all GWs to 220 all SR domains that are interconnected). 222 o A route target ([RFC4360]) is attached to each GW's auto-discovery 223 route and has its value set to the SR domain identifier. 225 o Each GW constructs an import filtering rule to import any route 226 that carries a route target with the same SR domain identifier 227 that the GW itself uses. This means that only these GWs will 228 import those routes, and that all GWs to the same SR domain will 229 import each other's routes and will learn (auto-discover) the 230 current set of active GWs for the SR domain. 232 The auto-discovery route that each GW advertises consists of the 233 following: 235 o An IPv4 or IPv6 NLRI containing one of the GW's loopback addresses 236 (that is, with an AFI/SAFI pair that is one of 1/1, 2/1, 1/4, or 237 2/4). 239 o A Tunnel Encapsulation attribute containing the GW's encapsulation 240 information, which at a minimum consists of an SR Tunnel TLV (type 241 TBD1 to be allocated by IANA) with a Remote Endpoint sub-TLV as 242 specified in [I-D.ietf-idr-tunnel-encaps]. 244 To avoid the side effect of applying the Tunnel Encapsulation 245 attribute to any packet that is addressed to the GW itself, the GW 246 SHOULD use a different loopback address for the two cases. 248 As described in Section 1, each GW will include a Tunnel 249 Encapsulation attribute for each GW that is active for the SR domain 250 (including itself), and will include these in every route advertised 251 externally to the SR domain by each GW. As the current set of active 252 GWs changes (due to the addition of a new GW or the failure/removal 253 of an existing GW) each externally advertised route will be re- 254 advertised with the set of SR tunnel instances reflecting the current 255 set of active GWs. 257 If a gateway becomes disconnected from the backbone network, or if 258 the SR domain operator decides to terminate the gateway's activity, 259 it withdraws the advertisements described above. This means that 260 remote gateways at other sites will stop seeing advertisements from 261 this gateway. It also means that other local gateways at this site 262 will "unlearn" the removed gateway and stop including a Tunnel 263 Encapsulation attribute for the removed gateway in their 264 advertisements. 266 4. Relationship to BGP Link State and Egress Peer Engineering 268 When a remote GW receives a route to a prefix X it can use the SR 269 tunnel instances within the contained Tunnel Encapsulation attribute 270 to identify the GWs through which X can be reached. It uses this 271 information to compute SR Traffic Engineering (SR TE) paths across 272 the backbone network looking at the information advertised to it in 273 SR BGP Link State (BGP-LS) [I-D.ietf-idr-bgp-ls-segment-routing-ext] 274 and correlated using the SR domain identity. SR Egress Peer 275 Engineering (EPE) [I-D.ietf-idr-bgpls-segment-routing-epe] can be 276 used to supplement the information advertised in BGP-LS. 278 5. Advertising an SR Domain Route Externally 280 When a packet destined for prefix X is sent on an SR TE path to a GW 281 for the SR domain containing X, it needs to carry the receiving GW's 282 label for X such that this label rises to the top of the stack before 283 the GW completes its processing of the packet. To achieve this we 284 place a Prefix SID sub-TLV [I-D.ietf-idr-tunnel-encaps] for X in each 285 SR tunnel instance in the Tunnel Encapsulation attribute in the 286 externally advertised route for X. 288 Alternatively, if the GWs for a given SR domain are configured to 289 allow remote GWs to perform SR TE through that SR domain for a prefix 290 X, then each GW computes an SR TE path through that SR domain to X 291 from each of the currently active GWs, and places each in an MPLS 292 label stack sub-TLV [I-D.ietf-idr-tunnel-encaps] in the SR tunnel 293 instance for that GW. 295 6. Encapsulation 297 If the GWs for a given SR domain are configured to allow remote GWs 298 to send them a packet in that SR domain's native encapsulation, then 299 each GW will also include multiple instances of a tunnel TLV for that 300 native encapsulation in externally advertised routes: one for each GW 301 and each containing a remote endpoint sub-TLV with that GW's address. 302 A remote GW may then encapsulate a packet according to the rules 303 defined via the sub-TLVs included in each of the tunnel TLV 304 instances. 306 7. IANA Considerations 308 7.1. Tunnel Encapsulation Tunnel Type 310 IANA maintains a registry called "Border Gateway Protocol (BGP) 311 Parameters" with a sub-registry called "BGP Tunnel Encapsulation 312 Attribute Tunnel Types." The registration policy for this registry 313 is First-Come First-Served [RFC8126]. 315 IANA has assigned the value 17 from this sub-registry for "SR 316 Tunnel". 318 7.2. Tunnel Encapsulation Sub-TLVs 320 IANA maintains a registry called "Border Gateway Protocol (BGP) 321 Parameters" with a sub-registry called "BGP Tunnel Encapsulation 322 Attribute Sub-TLVs." The registration policy for this registry is 323 Standards Action.[RFC8126]. 325 IANA is requested to assign a codepoint from this sub-registry for 326 "SR Tunnel TLV" (TBD1). The next available value may be used and 327 reference should be made to this document. 329 8. Security Considerations 331 From a protocol point of view, the mechanisms described in this 332 document can leverage the security mechanisms already defined for 333 BGP. Further discussion of security considerations for BGP may be 334 found in the BGP specification itself [RFC4271] and in the security 335 analysis for BGP [RFC4272]. The original discussion of the use of 336 the TCP MD5 signature option to protect BGP sessions is found in 337 [RFC5925], while [RFC6952] includes an analysis of BGP keying and 338 authentication issues. 340 The mechanisms described in this document involve sharing routing or 341 reachability information between domains: that may mean disclosing 342 information that is normally contained within a domain. So it needs 343 to be understood that normal security paradigms based on the 344 boundaries of domains are weakened. Discussion of these issues with 345 respect to VPNs can be found in [RFC4364], while [RFC7926] describes 346 many of the issues associated with the exchange of topology or TE 347 information between domains. 349 Particular exposures resulting from this work include: 351 o Gateways to a domain will know about all other gateways to the 352 same domain. This feature applies within a domain and so is not a 353 substantial exposure, but it does mean that if the BGP exchanges 354 within a domain can be snooped or if a gateway can be subverted 355 then an attacker may learn the full set of gateways to a domain. 356 This would facilitate more effective attacks on that domain. 358 o The existence of multiple gateways to a domain becomes more 359 visible across the backbone and even into remote domains. This 360 means that an attacker is able to prepare a more comprehensive 361 attack than exists when only the locally attached backbone network 362 (e.g., the AS that hosts the domain) can see all of the gateways 363 to a site. For example, a Denial of Service attack on a single GW 364 is mitigated by the existence of other GWs, but if the attacker 365 knows about all the gateways then the whole set can be attacked at 366 once. 368 o A node in a domain that does not have external BGP peering (i.e., 369 is not really a domain gateway and cannot speak BGP into the 370 backbone network) may be able to get itself advertised as a 371 gateway by letting other genuine gateways discover it (by speaking 372 BGP to them within the domain) and so may get those genuine 373 gateways to advertise it as a gateway into the backbone network. 374 This would allow the malicious node to attract traffic without 375 having to have secure BGP peerings with out-of-domain nodes. 377 o If it is possible to modify a BGP message within the backbone, it 378 may be possible to spoof the existence of a gateway. This could 379 cause traffic to be attracted to a specific node and might result 380 in black-holing of traffic. 382 All of the issues in the list above could cause disruption to domain 383 interconnection, but are not new protocol vulnerabilities so much as 384 new exposures of information that SHOULD be protected against using 385 existing protocol mechanisms. Furthermore, it is a general 386 observation that if these attacks are possible then it is highly 387 likely that far more significant attacks can be made on the routing 388 system. It should be noted that BGP peerings are not discovered, but 389 always arise from explicit configuration. 391 9. Manageability Considerations 393 The principal configuration item added by this solution is the 394 allocation of an SR domain identifier. The same identifier MUST be 395 assigned to every GW to the same domain, and each domain MUST have a 396 different identifier. This requires coordination, probably through a 397 central management agent. 399 It should be noted that BGP peerings are not discovered, but always 400 arise from explicit configuration. This is no different from any 401 other BGP operation. 403 10. Acknowledgements 405 Thanks to Bruno Rijsman and Stephane Litkowsji for review comments, 406 and to Robert Raszuk for useful discussions. 408 11. References 410 11.1. Normative References 412 [I-D.ietf-idr-bgpls-segment-routing-epe] 413 Previdi, S., Talaulikar, K., Filsfils, C., Patel, K., Ray, 414 S., and J. Dong, "BGP-LS extensions for Segment Routing 415 BGP Egress Peer Engineering", draft-ietf-idr-bgpls- 416 segment-routing-epe-19 (work in progress), May 2019. 418 [I-D.ietf-idr-tunnel-encaps] 419 Patel, K., Velde, G., and S. Ramachandra, "The BGP Tunnel 420 Encapsulation Attribute", draft-ietf-idr-tunnel-encaps-15 421 (work in progress), December 2019. 423 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 424 Requirement Levels", BCP 14, RFC 2119, 425 DOI 10.17487/RFC2119, March 1997, 426 . 428 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 429 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 430 DOI 10.17487/RFC4271, January 2006, 431 . 433 [RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended 434 Communities Attribute", RFC 4360, DOI 10.17487/RFC4360, 435 February 2006, . 437 [RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP 438 Authentication Option", RFC 5925, DOI 10.17487/RFC5925, 439 June 2010, . 441 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 442 S. Ray, "North-Bound Distribution of Link-State and 443 Traffic Engineering (TE) Information Using BGP", RFC 7752, 444 DOI 10.17487/RFC7752, March 2016, 445 . 447 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 448 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 449 May 2017, . 451 11.2. Informative References 453 [I-D.farrel-spring-sr-domain-interconnect] 454 Farrel, A. and J. Drake, "Interconnection of Segment 455 Routing Domains - Problem Statement and Solution 456 Landscape", draft-farrel-spring-sr-domain-interconnect-05 457 (work in progress), October 2018. 459 [I-D.ietf-idr-bgp-ls-segment-routing-ext] 460 Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H., 461 and M. Chen, "BGP Link-State extensions for Segment 462 Routing", draft-ietf-idr-bgp-ls-segment-routing-ext-16 463 (work in progress), June 2019. 465 [RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis", 466 RFC 4272, DOI 10.17487/RFC4272, January 2006, 467 . 469 [RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private 470 Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February 471 2006, . 473 [RFC6952] Jethanandani, M., Patel, K., and L. Zheng, "Analysis of 474 BGP, LDP, PCEP, and MSDP Issues According to the Keying 475 and Authentication for Routing Protocols (KARP) Design 476 Guide", RFC 6952, DOI 10.17487/RFC6952, May 2013, 477 . 479 [RFC7911] Walton, D., Retana, A., Chen, E., and J. Scudder, 480 "Advertisement of Multiple Paths in BGP", RFC 7911, 481 DOI 10.17487/RFC7911, July 2016, 482 . 484 [RFC7926] Farrel, A., Ed., Drake, J., Bitar, N., Swallow, G., 485 Ceccarelli, D., and X. Zhang, "Problem Statement and 486 Architecture for Information Exchange between 487 Interconnected Traffic-Engineered Networks", BCP 206, 488 RFC 7926, DOI 10.17487/RFC7926, July 2016, 489 . 491 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 492 Writing an IANA Considerations Section in RFCs", BCP 26, 493 RFC 8126, DOI 10.17487/RFC8126, June 2017, 494 . 496 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 497 Decraene, B., Litkowski, S., and R. Shakir, "Segment 498 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 499 July 2018, . 501 Authors' Addresses 503 Adrian Farrel 504 Old Dog Consulting 506 Email: adrian@olddog.co.uk 508 John Drake 509 Juniper Networks 511 Email: jdrake@juniper.net 513 Eric Rosen 514 Juniper Networks 516 Email: erosen52@gmail.com 518 Keyur Patel 519 Arrcus, Inc. 521 Email: keyur@arrcus.com 523 Luay Jalil 524 Verizon 526 Email: luay.jalil@verizon.com