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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IDR S. Previdi, Ed. 3 Internet-Draft C. Filsfils 4 Intended status: Standards Track A. Lindem 5 Expires: July 20, 2018 Cisco Systems 6 A. Sreekantiah 8 H. Gredler 9 RtBrick Inc. 10 January 16, 2018 12 Segment Routing Prefix SID extensions for BGP 13 draft-ietf-idr-bgp-prefix-sid-10 15 Abstract 17 Segment Routing (SR) architecture allows a node to steer a packet 18 flow through any topological path and service chain by leveraging 19 source routing. The ingress node prepends an SR header to a packet 20 containing a set of segment identifiers (SID). Each SID represents a 21 topological or a service-based instruction. Per-flow state is 22 maintained only on the ingress node of the SR domain. 24 This document defines an optional, transitive BGP attribute for 25 announcing BGP Prefix Segment Identifiers (BGP Prefix-SID) 26 information. 28 Requirements Language 30 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 31 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 32 "OPTIONAL" in this document are to be interpreted as described in BCP 33 14 [RFC2119] [RFC8174] when, and only when, they appear in all 34 capitals, as shown here. 36 Status of This Memo 38 This Internet-Draft is submitted in full conformance with the 39 provisions of BCP 78 and BCP 79. 41 Internet-Drafts are working documents of the Internet Engineering 42 Task Force (IETF). Note that other groups may also distribute 43 working documents as Internet-Drafts. The list of current Internet- 44 Drafts is at http://datatracker.ietf.org/drafts/current/. 46 Internet-Drafts are draft documents valid for a maximum of six months 47 and may be updated, replaced, or obsoleted by other documents at any 48 time. It is inappropriate to use Internet-Drafts as reference 49 material or to cite them other than as "work in progress." 51 This Internet-Draft will expire on July 20, 2018. 53 Copyright Notice 55 Copyright (c) 2018 IETF Trust and the persons identified as the 56 document authors. All rights reserved. 58 This document is subject to BCP 78 and the IETF Trust's Legal 59 Provisions Relating to IETF Documents 60 (http://trustee.ietf.org/license-info) in effect on the date of 61 publication of this document. Please review these documents 62 carefully, as they describe your rights and restrictions with respect 63 to this document. Code Components extracted from this document must 64 include Simplified BSD License text as described in Section 4.e of 65 the Trust Legal Provisions and are provided without warranty as 66 described in the Simplified BSD License. 68 Table of Contents 70 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 71 2. BGP-Prefix-SID . . . . . . . . . . . . . . . . . . . . . . . 4 72 2.1. MPLS BGP Prefix SID . . . . . . . . . . . . . . . . . . . 4 73 2.2. IPv6 Prefix Segment . . . . . . . . . . . . . . . . . . . 5 74 3. BGP Prefix-SID Attribute . . . . . . . . . . . . . . . . . . 5 75 3.1. Label-Index TLV . . . . . . . . . . . . . . . . . . . . . 6 76 3.2. IPv6 SID . . . . . . . . . . . . . . . . . . . . . . . . 7 77 3.3. Originator SRGB TLV . . . . . . . . . . . . . . . . . . . 7 78 4. Receiving BGP Prefix-SID Attribute . . . . . . . . . . . . . 9 79 4.1. MPLS Dataplane: Labeled Unicast . . . . . . . . . . . . . 9 80 4.2. IPv6 Dataplane . . . . . . . . . . . . . . . . . . . . . 10 81 5. Advertising BGP Prefix-SID Attribute . . . . . . . . . . . . 10 82 5.1. MPLS Dataplane: Labeled Unicast . . . . . . . . . . . . . 11 83 5.2. IPv6 Dataplane . . . . . . . . . . . . . . . . . . . . . 11 84 6. Error Handling of BGP Prefix-SID Attribute . . . . . . . . . 11 85 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 86 8. Manageability Considerations . . . . . . . . . . . . . . . . 13 87 9. Security Considerations . . . . . . . . . . . . . . . . . . . 13 88 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 13 89 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14 90 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 91 12.1. Normative References . . . . . . . . . . . . . . . . . . 14 92 12.2. Informative References . . . . . . . . . . . . . . . . . 15 93 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 95 1. Introduction 97 Segment Routing (SR) architecture leverages the source routing 98 paradigm. A group of inter-connected nodes that use SR forms an SR 99 domain. A segment represents either a topological instruction such 100 as "go to prefix P following shortest path" or a service instruction 101 (e.g.: "pass through deep packet inspection"). Other types of 102 segments may be defined in the future. 104 A segment is identified through a Segment Identifier (SID). 105 Typically, the ingress node of the SR domain prepends an SR header 106 containing segments identifiers (SIDs) to an incoming packet. 108 As described in [I-D.ietf-spring-segment-routing], when SR is applied 109 to the MPLS dataplane ([I-D.ietf-spring-segment-routing-mpls]) the 110 SID consists of a label while when SR is applied to the IPv6 111 dataplane the SID consists of an IPv6 address. 113 A BGP-Prefix Segment (and its BGP Prefix-SID), is a BGP segment 114 attached to a BGP prefix. A BGP Prefix-SID is always a global SID 115 ([I-D.ietf-spring-segment-routing]) within the SR/BGP domain (i.e., 116 the set of Autonomous Systems under a common administration and 117 control and where SR is used) and identifies an instruction to 118 forward the packet over the ECMP-aware best-path computed by BGP to 119 the related prefix. The BGP Prefix-SID is the identifier of the BGP 120 prefix segment. In this document, we always refer to the BGP Segment 121 by the BGP Prefix-SID. 123 This document describes the BGP extension to signal the BGP Prefix- 124 SID. Specifically, this document defines a BGP attribute known as 125 the BGP Prefix-SID attribute and specifies the rules to originate, 126 receive, and handle error conditions for the attribute. 128 The BGP Prefix-SID attribute defined in this document can be attached 129 to prefixes from AFI/SAFI combinations: 131 Multiprotocol BGP labeled IPv4/IPv6 Unicast ([RFC8277]). 133 Multiprotocol BGP ([RFC4760]) unlabeled IPv6 Unicast. 135 [I-D.ietf-spring-segment-routing-msdc] describes example use cases 136 where the BGP Prefix-SID is used for the above AFI/SAFI combinations. 138 It should be noted that: 140 o A BGP Prefix-SID MAY be global between domains when the 141 interconnected domains agree on the SID allocation scheme. 142 Alternatively, when interconnecting domains, the ASBRs of each 143 domain will have to handle the advertisement of unique SIDs. The 144 mechanisms for such interconnection are outside the scope of the 145 protocol extensions defined in this document. 147 o A BGP Prefix-SID MAY be attached to a prefix. In addition, each 148 prefix will likely have a different AS_PATH attribute. This 149 implies that each prefix is advertised individually, reducing the 150 ability to pack BGP advertisements (when sharing common 151 attributes). 153 2. BGP-Prefix-SID 155 The BGP Prefix-SID attached to a BGP prefix P represents the 156 instruction "go to Prefix P" along its BGP best path (potentially 157 ECMP-enabled). 159 2.1. MPLS BGP Prefix SID 161 The BGP Prefix-SID is realized on the MPLS dataplane 162 ([I-D.ietf-spring-segment-routing-mpls]) in the following way: 164 The operator assigns a globally unique label index, L_I, to a 165 locally sourced prefix of a BGP speaker N which is advertised to 166 all other BGP speakers in the SR domain. 168 According to [I-D.ietf-spring-segment-routing], each BGP speaker 169 is configured with a label block called the Segment Routing Global 170 Block (SRGB). While [I-D.ietf-spring-segment-routing] recommends 171 to use the same SRGB across all the nodes within the SR domain, 172 the SRGB of a node is a local property and could be different on 173 different speakers. The drawbacks of the use case where BGP 174 speakers have different SRGBs are documented in 175 [I-D.ietf-spring-segment-routing] and 176 [I-D.ietf-spring-segment-routing-msdc]. 178 If traffic-engineering within the SR domain is required, each node 179 may also be required to advertise topological information and 180 Peering SIDs for each of its links and peers. This information is 181 required to perform the explicit path computation and to express 182 an explicit path as a list of SIDs. The advertisement of 183 topological information and Peer segments (Peer SIDs) is done 184 through [I-D.ietf-idr-bgpls-segment-routing-epe]. 186 If the BGP speakers are not all configured with the same SRGB, and 187 if traffic-engineering within the SR domain is required, each node 188 may be required to advertise its local SRGB in addition to the 189 topological information. 191 This documents assumes that BGP-LS is the preferred method for 192 collecting both peer segments (Peer SIDs) and SRGB information 193 through [RFC7752], [I-D.ietf-idr-bgpls-segment-routing-epe], and 194 [I-D.ietf-idr-bgp-ls-segment-routing-ext]. However, as an 195 optional alternative for the advertisement of the local SRGB 196 without the topology nor the peer SIDs, hence without 197 applicability for TE, the Originator SRGB TLV of the prefix-SID 198 attribute is specified in Section 3.3 of this document. 200 As defined in [I-D.ietf-spring-segment-routing], the label index 201 L_I is an offset into the SRGB. Each BGP speaker derives its 202 local MPLS label, L, by adding L_I to the start value of its own 203 SRGB, and programs L in its MPLS dataplane as its incoming/local 204 label for the prefix. It should be noted that while SRGBs and 205 SIDs are advertised using 32-bit values, the derived label is 206 advertised in the 20 right-most bits. See Section 4.1 for more 207 details. 209 The outgoing label for the prefix is found in the NLRI of the 210 Multiprotocol BGP labeled IPv4/IPv6 Unicast prefix advertisement. 211 The label index L_I is only used as a hint to derive the local/ 212 incoming label. 214 Section 3.1 of this document specifies the Label-Index TLV of the 215 BGP Prefix-SID attribute; this TLV can be used to advertise the 216 label index for a given prefix. 218 In order to advertise the label index of a given prefix P and, 219 optionally, the SRGB, an extension to BGP is needed: the BGP Prefix- 220 SID attribute. This extension is described in subsequent sections. 222 2.2. IPv6 Prefix Segment 224 When SR is used over an IPv6 dataplane, the BGP Prefix-SID consists 225 of an IPv6 address assigned to the BGP speaker. 227 3. BGP Prefix-SID Attribute 229 The BGP Prefix-SID attribute is an optional, transitive BGP path 230 attribute. The attribute type code 40 has been assigned by IANA (see 231 Section 7). 233 The BGP Prefix-SID attribute is defined here to be a set of elements 234 encoded as "Type/Length/Value" tuples (i.e., a set of TLVs). All BGP 235 Prefix-SID attribute TLVs will start with a 1-octet type and a 236 2-octet length. The following TLVs are defined in this document: 238 o Label-Index TLV 239 o IPv6 SID TLV 241 o Originator SRGB TLV 243 The Label-Index and Originator SRGB TLVs are used only when SR is 244 applied to the MPLS dataplane. 246 The IPv6 SID TLV is used only when SR is applied to the IPv6 247 dataplane. 249 For future extendibility, unknown TLVs are ignored and propagated 250 unmodified. 252 3.1. Label-Index TLV 254 The Label-Index TLV MUST be present in the BGP Prefix-SID attribute 255 attached to Labeled IPv4/IPv6 unicast prefixes ([RFC8277]). It will 256 be ignored when received for other BGP AFI/SAFI combinations. The 257 Label-Index TLV has the following format: 259 0 1 2 3 260 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 1 261 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 262 | Type | Length | RESERVED | 263 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 264 | Flags | Label Index | 265 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 266 | Label Index | 267 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 269 where: 271 o Type is 1. 273 o Length: is 7, the total length in octets of the value portion of 274 the TLV. 276 o RESERVED: 8-bit field. MUST be clear on transmission and MUST be 277 ignored on reception. 279 o Flags: 16 bits of flags. None are defined by this document. The 280 flag field MUST be clear on transmission and MUST be ignored on 281 reception. 283 o Label Index: 32-bit value representing the index value in the SRGB 284 space. 286 3.2. IPv6 SID 288 The IPv6 SID TLV MAY be present in the BGP Prefix-SID attribute 289 attached to MP-BGP unlabeled IPv6 unicast prefixes ([RFC4760]). It 290 will be ignored for other BGP AFI/SAFI combinations. The IPv6 SID 291 TLV has the following format: 293 0 1 2 3 294 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 1 295 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 296 | Type | Length | RESERVED | 297 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 298 | RESERVED | | 299 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 300 | | 301 | IPv6 SID (16 octets) | 302 | | 303 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 304 | | 305 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 307 where: 309 o Type is 2. 311 o Length: is 19, the total length in octets of the value portion of 312 the TLV. 314 o RESERVED: 24-bit field for future use. MUST be clear on 315 transmission and MUST be ignored on reception. 317 o IPv6 SID: 16 octets. 319 3.3. Originator SRGB TLV 321 The Originator SRGB TLV is an optional TLV and has the following 322 format: 324 0 1 2 3 325 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 1 326 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 327 | Type | Length | Flags | 328 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 329 | Flags | 330 +-+-+-+-+-+-+-+-+ 332 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 333 | SRGB 1 (6 octets) | 334 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 335 | | 336 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 338 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 339 | SRGB n (6 octets) | 340 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 341 | | 342 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 344 where: 346 o Type is 3. 348 o Length is the total length in octets of the value portion of the 349 TLV: 2 + multiple of 6. 351 o Flags: 16 bits of flags. None are defined in this document. 352 Flags MUST be clear on transmission and MUST be ignored on 353 reception. 355 o SRGB: 3 octets of base followed by 3 octets of range. Note that 356 the SRGB field MAY appear multiple times. If the SRGB field 357 appears multiple times, the SRGB consists of multiple ranges. 359 The Originator SRGB TLV contains the SRGB of the node originating the 360 prefix to which the BGP Prefix-SID is attached. The Originator SRGB 361 TLV MUST NOT be changed during the propagation of the BGP update. 363 The originator SRGB describes the SRGB of the node where the BGP 364 Prefix SID is attached. It is used to build segment routing policies 365 when different SRGBs are used in the fabric, for example 366 ([I-D.ietf-spring-segment-routing-msdc]). 368 The originator SRGB may only appear in a BGP Prefix-SID attribute 369 attached to Labeled IPv4/IPv6 unicast prefixes ([RFC8277]). It will 370 be ignored when received for other BGP AFI/SAFI combinations. 372 4. Receiving BGP Prefix-SID Attribute 374 A BGP speaker receiving a BGP Prefix-SID attribute from an EBGP 375 neighbor residing outside the boundaries of the SR domain, MUST 376 discard the attribute unless it is configured to accept the attribute 377 from the EBGP neighbor. A BGP speaker MAY log an error for further 378 analysis when discarding an attribute. 380 4.1. MPLS Dataplane: Labeled Unicast 382 A Multiprotocol BGP labeled IPv4/IPv6 Unicast ([RFC8277]) session 383 type is required. 385 A BGP speaker may be locally configured with an SRGB=[SRGB_Start, 386 SRGB_End]. The preferred method for deriving the SRGB is a matter of 387 local node configuration. 389 Given a label index L_I, we call L = L_I + SRGB_Start as the derived 390 label. A BGP Prefix-SID attribute is designated "unacceptable" for a 391 speaker M if the derived label value L lies outside the SRGB 392 configured on M. Otherwise the Label-Index TLV is designated 393 "acceptable" to speaker M. 395 The mechanisms through which a given label index value is assigned to 396 a given prefix are outside the scope of this document. The label- 397 index value associated with a prefix is locally configured at the BGP 398 node originating the prefix. 400 The BGP Prefix-SID attribute MUST contain the Label-Index TLV and MAY 401 contain the Originator SRGB TLV. A BGP Prefix-SID attribute received 402 without a Label-Index TLV MUST be considered as "unacceptable" by the 403 receiving speaker. 405 If multiple prefixes are received with the same label index value, 406 all these prefixes MUST have their BGP Prefix-SID attribute 407 considered as "unacceptable" by the receiving speaker. 409 When a BGP speaker receives a path from a neighbor with an acceptable 410 BGP Prefix-SID attribute, it MUST program the derived label as the 411 local label for the prefix in its MPLS dataplane. In case of an 412 error, a BGP speaker MUST follow to the error handling rules 413 specified in Section 6. A BGP speaker MAY log an error for further 414 analysis. 416 When a BGP speaker receives a path from a neighbor with an 417 unacceptable BGP Prefix-SID attribute or when a BGP speaker receives 418 a path from a neighbor with a BGP Prefix-SID attribute but is unable 419 to process it (it does not have the capability or local policy 420 disables the capability), it MUST treat the path as if it came 421 without a BGP Prefix-SID attribute. For the purposes of local label 422 allocation, a BGP speaker MUST assign a local (also called dynamic) 423 label (non-SRGB) for such a prefix as per classic Multiprotocol BGP 424 labeled IPv4/IPv6 Unicast ([RFC8277]) operation. A BGP speaker MAY 425 log an error for further analysis. 427 The outgoing label is always programmed as per classic Multiprotocol 428 BGP labeled IPv4/IPv6 Unicast ([RFC8277]) operation. 430 Specifically, a BGP speaker receiving a prefix with a BGP Prefix-SID 431 attribute and a label NLRI field of Implicit NULL from a neighbor 432 MUST adhere to standard behavior and program its MPLS dataplane to 433 pop the top label when forwarding traffic to the prefix. The label 434 NLRI defines the outbound label that MUST be used by the receiving 435 node. The label index gives the information to the receiving node on 436 which local/incoming label the BGP speaker SHOULD assign. 438 4.2. IPv6 Dataplane 440 When an SR IPv6 BGP speaker receives an IPv6 Unicast BGP Update with 441 a prefix having the BGP Prefix-SID attribute attached, it checks 442 whether the IPv6 SID TLV is present. If present and the chosen as 443 the best path, the prefix is installed into the Segment Routing IPv6 444 dataplane as described in [I-D.ietf-spring-segment-routing]. 446 The Label-Index and Originator SRGB TLVs MUST be ignored on 447 reception. For future extendibility, no TLVs are required for the 448 BGP IPv6 unicast address family. However, a BGP Prefix-SID attribute 449 corresponding to the BGP IPv6 address family without an IPv6 SID TLV 450 will be ignored. 452 5. Advertising BGP Prefix-SID Attribute 454 The BGP Prefix-SID attribute MAY be attached to labeled BGP prefixes 455 (IPv4/IPv6) [RFC8277] or to IPv6 unicast prefixes [RFC4760]. In 456 order to prevent distribution of the BGP Prefix-SID attribute beyond 457 its intended scope of applicability, attribute filtering SHOULD be 458 deployed. 460 A BGP speaker that advertises a path received from one of its 461 neighbors SHOULD advertise the BGP Prefix-SID received with the path 462 without modification, as long as the BGP Prefix-SID was acceptable. 463 If the path did not come with a BGP Prefix-SID attribute, the speaker 464 MAY attach a BGP Prefix-SID to the path if configured to do so. The 465 content of the TLVs present in the BGP Prefix-SID is determined by 466 the configuration. 468 5.1. MPLS Dataplane: Labeled Unicast 470 A BGP speaker that originates a prefix attaches the BGP Prefix-SID 471 attribute when it advertises the prefix to its neighbors via 472 Multiprotocol BGP labeled IPv4/IPv6 Unicast ([RFC8277]). The value 473 of the label index in the Label-Index TLV is determined by 474 configuration. 476 A BGP speaker that originates a BGP Prefix-SID attribute MAY 477 optionally announce the Originator SRGB TLV along with the mandatory 478 Label-Index TLV. The content of the Originator SRGB TLV is 479 determined by configuration. 481 Since the label index value must be unique within an SR domain, by 482 default an implementation SHOULD NOT advertise the BGP Prefix-SID 483 attribute outside an Autonomous System unless it is explicitly 484 configured to do so. 486 In all cases, the label field of the advertised NLRI ([RFC8277], 487 [RFC4364]) MUST be set to the local/incoming label programmed in the 488 MPLS dataplane for the given advertised prefix. If the prefix is 489 associated with one of the BGP speaker's interfaces, this is the 490 usual MPLS label (such as the Implicit or Explicit NULL label). 492 5.2. IPv6 Dataplane 494 A BGP speaker that originates an IPv6 prefix with the BGP Prefix-SID 495 attribute MAY include the IPv6 SID TLV. 497 6. Error Handling of BGP Prefix-SID Attribute 499 When a BGP Speaker receives a BGP Update message containing a 500 malformed or unacceptable BGP Prefix-SID attribute attached to a 501 Labeled IPv4/IPv6 unicast prefix [RFC8277], it MUST ignore the 502 received BGP Prefix-SID attributes and not advertise it to other BGP 503 peers. This is equivalent to the "Attribute discard" action 504 specified in [RFC7606]. When discarding an attribute, a BGP speaker 505 SHOULD log an error for further analysis. 507 When a BGP Speaker receives a BGP Update message containing a 508 malformed or unacceptable BGP Prefix-SID attribute attached to an 509 unlabeled IPv6 unicast prefix [RFC4760], it MUST treat the 510 advertisement as a withdrawal. This is equivalent to the "Treat-as- 511 withdraw" action specified in [RFC7606]. This action is required 512 since simply ignoring the BGP Prefix-SID attribute would modify the 513 installed path and the "Attribute discard" option is not applicable 514 in this case [RFC7606]. When withdrawing the prefix, a BGP speaker 515 SHOULD log an error for further analysis. 517 Consistent with [RFC7606], only the first occurrence of the BGP 518 Prefix-SID attribute will be considered and subsequent occurrences 519 will be discarded. Similarily, only the first occurrence of a BGP 520 Prefix-SID attribute TLV of a given TLV type will be considered 521 unless the specification of that TLV type allows for multiple 522 occurrences. 524 For future extendibility, unknown TLVs should be ignored and 525 propagated unmodified. 527 7. IANA Considerations 529 This document defines a BGP path attribute known as the BGP Prefix- 530 SID attribute. This document requests IANA to assign an attribute 531 code type (suggested value: 40) the BGP Prefix-SID attribute from the 532 BGP Path Attributes registry. 534 Currently, IANA temporarily assigned the following: 536 40 BGP Prefix-SID (TEMPORARY - registered 2015-09-30, expires 537 2016-09-30) [draft-ietf-idr-bgp-prefix-sid] 539 This document defines 3 TLVs for the BGP Prefix-SID attribute. These 540 TLVs need to be registered with IANA. We request IANA to create a 541 registry for BGP Prefix-SID Attribute TLVs as follows: 543 Under "Border Gateway Protocol (BGP) Parameters" registry, "BGP 544 Prefix-SID TLV Types" Reference: draft-ietf-idr-bgp-prefix-sid 545 Registration Procedure(s): Values 1-254 First Come, First Served, 546 Value 0 and 255 reserved 548 Value Type Reference 549 0 Reserved this document 550 1 Label-Index this document 551 2 IPv6 SID this document 552 3 Originator SRGB this document 553 4-254 Unassigned 554 255 Reserved this document 556 This document also creates a registry for the 16 bits of flags in the 557 Label-Index TLV. Initially, the registry will be empty. Flag bits 558 will be allocated First-Come, First Served consistent with the BGP- 559 SID TLV Types registry. 561 Finally, this document creates a registry for the 16 bits of flags in 562 the SRGB Originator TLV. Initially, the registry will be empty. 563 Flag bits will be allocated First-Come, First Served consistent with 564 the BGP-SID TLV Types registry. 566 8. Manageability Considerations 568 This document defines a BGP attribute to address use cases such as 569 the one described in [I-D.ietf-spring-segment-routing-msdc]. It is 570 assumed that advertisement of the BGP Prefix-SID attribute is 571 controlled by the operator in order to: 573 o Prevent undesired origination/advertisement of the BGP Prefix-SID 574 attribute. By default, a BGP Prefix-SID attribute SHOULD NOT be 575 attached to a prefix and advertised. Hence, BGP Prefix-SID 576 advertisement SHOULD require explicit enablement. 578 o Prevent any undesired propagation of the BGP Prefix-SID attribute. 579 By default, the BGP Prefix-SID is not advertised outside the 580 boundary of a single SR/administrative domain which may include 581 one or more ASes. The propagation to other ASes MUST be 582 explicitly configured. 584 The deployment model described in 585 [I-D.ietf-spring-segment-routing-msdc] assumes multiple Autonomous 586 Systems (ASes) under a common administrative domain. For this use 587 case, the BGP Prefix-SID advertisement is applicable to the inter-AS 588 context, i.e., EBGP, while it is confined to a single administrative 589 domain. 591 9. Security Considerations 593 This document introduces a BGP attribute (BGP Prefix-SID) which 594 inherits the security considerations expressed in: [RFC4271], 595 [RFC8277], and [I-D.ietf-spring-segment-routing]. 597 It should be noted that, as described in Section 8, this document 598 refers to a deployment model where all nodes are under the single 599 administrative domain. In this context, we assume that the operator 600 doesn't want to leak any information related to internal prefixes and 601 topology outside of the administrative domain. The internal 602 information includes the BGP Prefix-SID. In order to prevent such 603 leaking, the standard BGP mechanisms (filters) are applied at the 604 boundary of the SR/administrative domain. 606 10. Contributors 608 Keyur Patel 609 Arrcus, Inc. 610 US 612 Email: Keyur@arrcus.com 613 Saikat Ray 614 Unaffiliated 615 US 617 Email: raysaikat@gmail.com 619 11. Acknowledgements 621 The authors would like to thank Satya Mohanty for his contribution to 622 this document. 624 The authors would like to thank Alvaro Retana for substantive 625 comments as part of the Routing AD review. 627 The authors would like to thank Shyam Sethuram for comments and 628 discussion of TLV processing and validation. 630 12. References 632 12.1. Normative References 634 [I-D.ietf-spring-segment-routing] 635 Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B., 636 Litkowski, S., and R. Shakir, "Segment Routing 637 Architecture", draft-ietf-spring-segment-routing-14 (work 638 in progress), December 2017. 640 [I-D.ietf-spring-segment-routing-mpls] 641 Filsfils, C., Previdi, S., Bashandy, A., Decraene, B., 642 Litkowski, S., and R. Shakir, "Segment Routing with MPLS 643 data plane", draft-ietf-spring-segment-routing-mpls-11 644 (work in progress), October 2017. 646 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 647 Requirement Levels", BCP 14, RFC 2119, 648 DOI 10.17487/RFC2119, March 1997, . 651 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 652 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 653 DOI 10.17487/RFC4271, January 2006, . 656 [RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private 657 Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February 658 2006, . 660 [RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, 661 "Multiprotocol Extensions for BGP-4", RFC 4760, 662 DOI 10.17487/RFC4760, January 2007, . 665 [RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K. 666 Patel, "Revised Error Handling for BGP UPDATE Messages", 667 RFC 7606, DOI 10.17487/RFC7606, August 2015, 668 . 670 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 671 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 672 May 2017, . 674 [RFC8277] Rosen, E., "Using BGP to Bind MPLS Labels to Address 675 Prefixes", RFC 8277, DOI 10.17487/RFC8277, October 2017, 676 . 678 12.2. Informative References 680 [I-D.ietf-idr-bgp-ls-segment-routing-ext] 681 Previdi, S., Psenak, P., Filsfils, C., Gredler, H., and M. 682 Chen, "BGP Link-State extensions for Segment Routing", 683 draft-ietf-idr-bgp-ls-segment-routing-ext-03 (work in 684 progress), July 2017. 686 [I-D.ietf-idr-bgpls-segment-routing-epe] 687 Previdi, S., Filsfils, C., Patel, K., Ray, S., and J. 688 Dong, "BGP-LS extensions for Segment Routing BGP Egress 689 Peer Engineering", draft-ietf-idr-bgpls-segment-routing- 690 epe-14 (work in progress), December 2017. 692 [I-D.ietf-spring-segment-routing-msdc] 693 Filsfils, C., Previdi, S., Mitchell, J., Aries, E., and P. 694 Lapukhov, "BGP-Prefix Segment in large-scale data 695 centers", draft-ietf-spring-segment-routing-msdc-08 (work 696 in progress), December 2017. 698 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 699 S. Ray, "North-Bound Distribution of Link-State and 700 Traffic Engineering (TE) Information Using BGP", RFC 7752, 701 DOI 10.17487/RFC7752, March 2016, . 704 Authors' Addresses 706 Stefano Previdi (editor) 707 Cisco Systems 708 IT 710 Email: stefano@previdi.net 712 Clarence Filsfils 713 Cisco Systems 714 Brussels 715 Belgium 717 Email: cfilsfils@cisco.com 719 Acee Lindem 720 Cisco Systems 721 301 Midenhall Way 722 Cary, NC 27513 723 USA 725 Email: acee@cisco.com 727 Arjun Sreekantiah 729 Email: arjunhrs@gmail.com 731 Hannes Gredler 732 RtBrick Inc. 734 Email: hannes@rtbrick.com