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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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-19) exists of draft-ietf-idr-bgpls-segment-routing-epe-13 == Outdated reference: A later version (-22) exists of draft-ietf-idr-tunnel-encaps-06 ** Obsolete normative reference: RFC 7752 (Obsoleted by RFC 9552) == Outdated reference: A later version (-15) exists of draft-ietf-spring-segment-routing-12 Summary: 1 error (**), 0 flaws (~~), 4 warnings (==), 1 comment (--).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 J. Drake 3 Internet-Draft A. Farrel 4 Intended status: Standards Track E. Rosen 5 Expires: January 2, 2018 Juniper Networks 6 K. Patel 7 Arrcus, Inc. 8 L. Jalil 9 Verizon 10 July 1, 2017 12 Gateway Auto-Discovery and Route Advertisement for Segment Routing 13 Enabled Domain Interconnection 14 draft-drake-bess-datacenter-gateway-04 16 Abstract 18 Data centers have become critical components of the infrastructure 19 used by network operators to provide services to their customers. 20 Data centers are attached to the Internet or a backbone network by 21 gateway routers. One data center typically has more than one gateway 22 for commercial, load balancing, and resiliency reasons. 24 Segment routing is a popular protocol mechanism for operating within 25 a data center, but also for steering traffic that flows between two 26 data center sites. In order that one data center site may load 27 balance the traffic it sends to another data center site it needs to 28 know the complete set of gateway routers at the remote data center, 29 the points of connection from those gateways to the backbone network, 30 and the connectivity across the backbone network. 32 Segment routing may also be operated in other domains, such as access 33 networks. Those domains also need to be connected across backbone 34 networks through gateways. 36 This document defines a mechanism using the BGP Tunnel Encapsulation 37 attribute to allow each gateway router to advertise the routes to the 38 prefixes in the segment routing domains to which it provides access, 39 and also to advertise on behalf of each other gateway to the same 40 segment routing domain. 42 Requirements Language 44 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 45 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 46 document are to be interpreted as described in [RFC2119]. 48 Status of This Memo 50 This Internet-Draft is submitted in full conformance with the 51 provisions of BCP 78 and BCP 79. 53 Internet-Drafts are working documents of the Internet Engineering 54 Task Force (IETF). Note that other groups may also distribute 55 working documents as Internet-Drafts. The list of current Internet- 56 Drafts is at http://datatracker.ietf.org/drafts/current/. 58 Internet-Drafts are draft documents valid for a maximum of six months 59 and may be updated, replaced, or obsoleted by other documents at any 60 time. It is inappropriate to use Internet-Drafts as reference 61 material or to cite them other than as "work in progress." 63 This Internet-Draft will expire on January 2, 2018. 65 Copyright Notice 67 Copyright (c) 2017 IETF Trust and the persons identified as the 68 document authors. All rights reserved. 70 This document is subject to BCP 78 and the IETF Trust's Legal 71 Provisions Relating to IETF Documents 72 (http://trustee.ietf.org/license-info) in effect on the date of 73 publication of this document. Please review these documents 74 carefully, as they describe your rights and restrictions with respect 75 to this document. Code Components extracted from this document must 76 include Simplified BSD License text as described in Section 4.e of 77 the Trust Legal Provisions and are provided without warranty as 78 described in the Simplified BSD License. 80 Table of Contents 82 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 83 2. SR Domain Gateway Auto-Discovery . . . . . . . . . . . . . . 5 84 3. Relationship to BGP Link State and Egress Peer Engineering . 6 85 4. Advertising an SR Domain Route Externally . . . . . . . . . . 6 86 5. Encapsulation . . . . . . . . . . . . . . . . . . . . . . . . 7 87 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 88 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 89 8. Manageability Considerations . . . . . . . . . . . . . . . . 7 90 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 91 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 92 10.1. Normative References . . . . . . . . . . . . . . . . . . 8 93 10.2. Informative References . . . . . . . . . . . . . . . . . 8 94 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 96 1. Introduction 98 Data centers (DCs) have become critical components of the 99 infrastructure used by network operators to provide services to their 100 customers. DCs are attached to the Internet or a backbone network by 101 gateway routers (GWs). One DC typically has more than one GW for 102 various reasons including commercial preferences, load balancing, and 103 resiliency against connection of device failure. 105 Segment routing (SR) [I-D.ietf-spring-segment-routing] is a popular 106 protocol mechanism for operating within a DC, but also for steering 107 traffic that flows between two DC sites. In order for an ingress DC 108 that uses SR to load balance the flows it sends to an egress DC, it 109 needs to know the complete set of entry nodes (i.e., GWs) for that 110 egress DC from the backbone network connecting the two DCs. Note 111 that it is assumed that the connected set of DCs and the backbone 112 network connecting them are part of the same SR BGP Link State (LS) 113 instance ([RFC7752] and [I-D.ietf-idr-bgpls-segment-routing-epe]) so 114 that traffic engineering using SR may be used for these flows. 116 Segment routing may also be operated in other domains, such as access 117 networks. Those domains also need to be connected across backbone 118 networks through gateways. 120 Suppose that there are two gateways, GW1 and GW2 as shown in 121 Figure 1, for a given egress segment routing domain and that they 122 each advertise a route to prefix X which is located within the egress 123 segment routing domain with each setting itself as next hop. One 124 might think that the GWs for X could be inferred from the routes' 125 next hop fields, but typically it is not the case that both routes 126 get distributed across the backbone: rather only the best route, as 127 selected by BGP, is distributed. This precludes load balancing flows 128 across both GWs. 130 ----------------- --------------------- 131 | Ingress | | Egress ------ | 132 | SR Domain | | SR Domain |Prefix| | 133 | | | | X | | 134 | | | ------ | 135 | -- | | --- --- | 136 | |GW| | | |GW1| |GW2| | 137 -------++--------- ----+-----------+-+-- 138 | \ | / | 139 | \ | / | 140 | -+------------- --------+--------+-- | 141 | ||PE| ----| |---- |PE| |PE| | | 142 | | -- |ASBR+------+ASBR| -- -- | | 143 | | ----| |---- | | 144 | | | | | | 145 | | ----| |---- | | 146 | | AS1 |ASBR+------+ASBR| AS2 | | 147 | | ----| |---- | | 148 | --------------- -------------------- | 149 --+-----------------------------------------------+-- 150 | |PE| |PE| | 151 | -- AS3 -- | 152 | | 153 ----------------------------------------------------- 155 Figure 1: Example Segment Routing Domain Interconnection 157 The obvious solution to this problem is to use the BGP feature that 158 allows the advertisement of multiple paths in BGP (known as Add- 159 Paths) [RFC7911] to ensure that all routes to X get advertised by 160 BGP. However, even if this is done, the identity of the GWs will be 161 lost as soon as the routes get distributed through an Autonomous 162 System Border Router (ASBR) that will set itself to be the next hop. 163 And if there are multiple Autonomous Systems (ASes) in the backbone, 164 not only will the next hop change several times, but the Add-Paths 165 technique will experience scaling issues. This all means that this 166 approach is limited to SR domains connected over a single AS. 168 This document defines a solution that overcomes this limitation and 169 works equally well with a backbone constructed from one or more ASes. 170 This solution uses the Tunnel Encapsulation attribute 171 [I-D.ietf-idr-tunnel-encaps] as follows: 173 We define a new tunnel type, "SR tunnel". When the GWs to a given 174 SR domain advertise a route to a prefix X within the SR domain, 175 they will each include a Tunnel Encapsulation attribute with 176 multiple tunnel instances each of type "SR tunnel", one for each 177 GW, and each containing a Remote Endpoint sub-TLV with that GW's 178 address. 180 In other words, each route advertised by any GW identifies all of the 181 GWs to the same SR domain (see Section 2 for a discussion of how GWs 182 discover each other). Therefore, even if only one of the routes is 183 distributed to other ASes, it will not matter how many times the next 184 hop changes, as the Tunnel Encapsulation attribute (and its remote 185 endpoint sub-TLVs) will remain unchanged. 187 To put this in the context of Figure 1, GW1 and GW2 discover each 188 other as gateways for the egress SR domain. Both GW1 and GW2 189 advertise themselves as having routes to prefix X. Furthermore, GW1 190 includes a Tunnel Encapsulation attribute with a tunnel instance of 191 type "SR tunnel" for itself and another for GW2. Similarly, GW2 192 includes a Tunnel Encapsulation for itself and another for GW1. The 193 gateway in the ingress SR domain can now see all possible paths to 194 the egress SR domain regardless of which route advertisement is 195 propagated to it, and it can choose one or balance traffic flows as 196 it sees fit. 198 2. SR Domain Gateway Auto-Discovery 200 To allow a given SR domain's GWs to auto-discover each other and to 201 coordinate their operations, the following procedures are 202 implemented: 204 o Each GW is configured with an identifier for the SR domain that is 205 common across all GWs to the domain (i.e., across all GWs to all 206 SR domains that are interconnected) and unique across all SR 207 domains that are connected. 209 o A route target ([RFC4360]) is attached to each GW's auto-discovery 210 route and has its value set to the SR domain identifier. 212 o Each GW constructs an import filtering rule to import any route 213 that carries a route target with the same SR domain identifier 214 that the GW itself uses. This means that only these GWs will 215 import those routes and that all GWs to the same SR domain will 216 import each other's routes and will learn (auto-discover) the 217 current set of active GWs for the SR domain. 219 The auto-discovery route each GW advertises consists of the 220 following: 222 o An IPv4 or IPv6 NLRI containing one of the GW's loopback addresses 223 (that is, with AFI/SAFI that is one of 1/1, 2/1, 1/4, or 2/4). 225 o A Tunnel Encapsulation attribute containing the GW's encapsulation 226 information, which at a minimum consists of an SR tunnel TLV (type 227 to be allocated by IANA) with a Remote Endpoint sub-TLV as 228 specified in [I-D.ietf-idr-tunnel-encaps]. 230 To avoid the side effect of applying the Tunnel Encapsulation 231 attribute to any packet that is addressed to the GW itself, the GW 232 SHOULD use a different loopback address for the two cases. 234 As described in Section 1, each GW will include a Tunnel 235 Encapsulation attribute for each GW that is active for the SR domain 236 (including itself), and will include these in every route advertised 237 externally to the SR domain by each GW. As the current set of 238 active GWs changes (due to the addition of a new GW or the failure/ 239 removal of an existing GW) each externally advertised route will be 240 re-advertised with the set of SR tunnel instances reflecting the 241 current set of active GWs. 243 If a gateway becomes disconnected from the backbone network, or if 244 the SR domain operator decides to terminate the gateway's activity, 245 it withdraws the advertisements described above. This means that 246 remote gateways at other sites will stop seeing advertisements from 247 this gateway. It also means that other local gateways at this site 248 will "unlearn" the removed gateway and stop including a Tunnel 249 Encapsulation attribute for the removed gateway in their 250 advertisements. 252 3. Relationship to BGP Link State and Egress Peer Engineering 254 When a remote GW receives a route to a prefix X it can use the SR 255 tunnel instances within the contained Tunnel Encapsulation attribute 256 to identify the GWs through which X can be reached. It uses this 257 information to compute SR TE paths across the backbone network 258 looking at the information advertised to it in SR BGP Link State 259 (BGP-LS) [I-D.gredler-idr-bgp-ls-segment-routing-ext] and correlated 260 using the SR domain identity. SR Egress Peer Engineering (EPE) 261 [I-D.ietf-idr-bgpls-segment-routing-epe] can be used to supplement 262 the information advertised in the BGP-LS. 264 4. Advertising an SR Domain Route Externally 266 When a packet destined for prefix X is sent on an SR TE path to a GW 267 for the SR domain containing X, it needs to carry the receiving GW's 268 label for X such that this label rises to the top of the stack before 269 the GW completes its processing of the packet. To achieve this we 270 place a prefix-SID sub-TLV for X in each SR tunnel instance in the 271 Tunnel Encapsulation attribute in the externally advertised route for 272 X. 274 Alternatively, if the GWs for a given SR domain are configured to 275 allow remote GWs to perform SR TE through that SR domain for a prefix 276 X, then each GW computes an SR TE path through that SR domain to X 277 from each of the currently active GWs, and places each in an MPLS 278 label stack sub-TLV [I-D.ietf-idr-tunnel-encaps] in the SR tunnel 279 instance for that GW. 281 5. Encapsulation 283 If the GWs for a given SR domain are configured to allow remote GWs 284 to send them a packet in that SR domain's native encapsulation, then 285 each GW will also include multiple instances of a tunnel TLV for that 286 native encapsulation in externally advertised routes: one for each GW 287 and each containing a remote endpoint sub-TLV with that GW's address. 288 A remote GW may then encapsulate a packet according to the rules 289 defined via the sub-TLVs included in each of the tunnel TLV 290 instances. 292 6. IANA Considerations 294 IANA maintains a registry called "BGP parameters" with a sub-registry 295 called "BGP Tunnel Encapsulation Tunnel Types." The registration 296 policy for this registry is First-Come First-Served. 298 IANA is requested to assign a codepoint from this sub-registry for 299 "SR Tunnel". The next available value may be used and reference 300 should be made to this document. 302 [[Note: This text is likely to be replaced with a specific code point 303 value once FCFS allocation has been made.]] 305 7. Security Considerations 307 TBD 309 8. Manageability Considerations 311 TBD 313 9. Acknowledgements 315 Thanks to Bruno Rijsman for review comments, and to Robert Raszuk for 316 useful discussions. 318 10. References 320 10.1. Normative References 322 [I-D.ietf-idr-bgpls-segment-routing-epe] 323 Previdi, S., Filsfils, C., Patel, K., Ray, S., and J. 324 Dong, "BGP-LS extensions for Segment Routing BGP Egress 325 Peer Engineering", draft-ietf-idr-bgpls-segment-routing- 326 epe-13 (work in progress), June 2017. 328 [I-D.ietf-idr-tunnel-encaps] 329 Rosen, E., Patel, K., and G. Velde, "The BGP Tunnel 330 Encapsulation Attribute", draft-ietf-idr-tunnel-encaps-06 331 (work in progress), June 2017. 333 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 334 Requirement Levels", BCP 14, RFC 2119, 335 DOI 10.17487/RFC2119, March 1997, 336 . 338 [RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended 339 Communities Attribute", RFC 4360, DOI 10.17487/RFC4360, 340 February 2006, . 342 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 343 S. Ray, "North-Bound Distribution of Link-State and 344 Traffic Engineering (TE) Information Using BGP", RFC 7752, 345 DOI 10.17487/RFC7752, March 2016, 346 . 348 10.2. Informative References 350 [I-D.gredler-idr-bgp-ls-segment-routing-ext] 351 Previdi, S., Psenak, P., Filsfils, C., Gredler, H., Chen, 352 M., and j. jefftant@gmail.com, "BGP Link-State extensions 353 for Segment Routing", draft-gredler-idr-bgp-ls-segment- 354 routing-ext-04 (work in progress), October 2016. 356 [I-D.ietf-spring-segment-routing] 357 Filsfils, C., Previdi, S., Decraene, B., Litkowski, S., 358 and R. Shakir, "Segment Routing Architecture", draft-ietf- 359 spring-segment-routing-12 (work in progress), June 2017. 361 [RFC7911] Walton, D., Retana, A., Chen, E., and J. Scudder, 362 "Advertisement of Multiple Paths in BGP", RFC 7911, 363 DOI 10.17487/RFC7911, July 2016, 364 . 366 Authors' Addresses 368 John Drake 369 Juniper Networks 371 Email: jdrake@juniper.net 373 Adrian Farrel 374 Juniper Networks 376 Email: afarrel@juniper.net 378 Eric Rosen 379 Juniper Networks 381 Email: erosen@juniper.net 383 Keyur Patel 384 Arrcus, Inc. 386 Email: keyur@arrcus.com 388 Luay Jalil 389 Verizon 391 Email: luay.jalil@verizon.com