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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IDR S. Previdi 3 Internet-Draft C. Filsfils 4 Intended status: Standards Track A. Lindem, Ed. 5 Expires: December 28, 2018 Cisco Systems 6 A. Sreekantiah 8 H. Gredler 9 RtBrick Inc. 10 June 26, 2018 12 Segment Routing Prefix SID extensions for BGP 13 draft-ietf-idr-bgp-prefix-sid-27 15 Abstract 17 Segment Routing (SR) leverages the source routing paradigm. A node 18 steers a packet through an ordered list of instructions, called 19 segments. A segment can represent any instruction, topological or 20 service-based. The ingress node prepends an SR header to a packet 21 containing a set of segment identifiers (SID). Each SID represents a 22 topological or a service-based instruction. Per-flow state is 23 maintained only on the ingress node of the SR domain. An SR domain 24 is defined as a single administrative domain for global SID 25 assignment. 27 This document defines an optional, transitive BGP attribute for 28 announcing BGP Prefix Segment Identifiers (BGP Prefix-SID) 29 information and the specification for SR-MPLS SIDs. 31 Requirements Language 33 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 34 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 35 "OPTIONAL" in this document are to be interpreted as described in BCP 36 14 [RFC2119] [RFC8174] when, and only when, they appear in all 37 capitals, as shown here. 39 Status of This Memo 41 This Internet-Draft is submitted in full conformance with the 42 provisions of BCP 78 and BCP 79. 44 Internet-Drafts are working documents of the Internet Engineering 45 Task Force (IETF). Note that other groups may also distribute 46 working documents as Internet-Drafts. The list of current Internet- 47 Drafts is at http://datatracker.ietf.org/drafts/current/. 49 Internet-Drafts are draft documents valid for a maximum of six months 50 and may be updated, replaced, or obsoleted by other documents at any 51 time. It is inappropriate to use Internet-Drafts as reference 52 material or to cite them other than as "work in progress." 54 This Internet-Draft will expire on December 28, 2018. 56 Copyright Notice 58 Copyright (c) 2018 IETF Trust and the persons identified as the 59 document authors. All rights reserved. 61 This document is subject to BCP 78 and the IETF Trust's Legal 62 Provisions Relating to IETF Documents 63 (http://trustee.ietf.org/license-info) in effect on the date of 64 publication of this document. Please review these documents 65 carefully, as they describe your rights and restrictions with respect 66 to this document. Code Components extracted from this document must 67 include Simplified BSD License text as described in Section 4.e of 68 the Trust Legal Provisions and are provided without warranty as 69 described in the Simplified BSD License. 71 Table of Contents 73 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 74 2. MPLS BGP Prefix SID . . . . . . . . . . . . . . . . . . . . . 4 75 3. BGP Prefix-SID Attribute . . . . . . . . . . . . . . . . . . 5 76 3.1. Label-Index TLV . . . . . . . . . . . . . . . . . . . . . 5 77 3.2. Originator SRGB TLV . . . . . . . . . . . . . . . . . . . 6 78 4. Receiving BGP Prefix-SID Attribute . . . . . . . . . . . . . 8 79 4.1. MPLS Dataplane: Labeled Unicast . . . . . . . . . . . . . 8 80 5. Advertising BGP Prefix-SID Attribute . . . . . . . . . . . . 10 81 5.1. MPLS Dataplane: Labeled Unicast . . . . . . . . . . . . . 10 82 6. Error Handling of BGP Prefix-SID Attribute . . . . . . . . . 10 83 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 84 8. Manageability Considerations . . . . . . . . . . . . . . . . 12 85 9. Security Considerations . . . . . . . . . . . . . . . . . . . 13 86 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 14 87 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14 88 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 89 12.1. Normative References . . . . . . . . . . . . . . . . . . 14 90 12.2. Informative References . . . . . . . . . . . . . . . . . 16 91 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 93 1. Introduction 95 The Segment Routing (SR) architecture leverages the source routing 96 paradigm. A segment represents either a topological instruction such 97 as "go to prefix P following shortest path" or a service instruction. 98 Other types of segments may be defined in the future. 100 A segment is identified through a Segment Identifier (SID). An SR 101 domain is defined as a single administrative domain for global SID 102 assignment. It may be comprised of a single Autonomous System (AS) 103 or multiple ASes under consolidated global SID administration. 104 Typically, the ingress node of the SR domain prepends an SR header 105 containing segments identifiers (SIDs) to an incoming packet. 107 As described in [I-D.ietf-spring-segment-routing], when SR is applied 108 to the MPLS dataplane ([I-D.ietf-spring-segment-routing-mpls]), the 109 SID consists of a label. 111 [I-D.ietf-spring-segment-routing] also describes how segment routing 112 can be applied to an IPv6 dataplane (SRv6) using an IPv6 routing 113 header containing a stack of SR SIDs encoded as IPv6 addresses 114 [I-D.ietf-6man-segment-routing-header]. The applicability and 115 support for Segment Routing over IPv6 is beyond the scope of this 116 document. 118 A BGP-Prefix Segment is a BGP prefix with a Prefix-SID attached. A 119 BGP Prefix-SID is always a global SID 120 ([I-D.ietf-spring-segment-routing]) within the SR domain and 121 identifies an instruction to forward the packet over the Equal-Cost 122 Multi-Path (ECMP) best-path computed by BGP to the related prefix. 123 The BGP Prefix-SID is the identifier of the BGP prefix segment. In 124 this document, we always refer to the BGP-Prefix segment by the BGP 125 Prefix-SID. 127 This document describes the BGP extension to signal the BGP Prefix- 128 SID. Specifically, this document defines a BGP attribute known as 129 the BGP Prefix-SID attribute and specifies the rules to originate, 130 receive, and handle error conditions for the attribute. 132 The BGP Prefix-SID attribute defined in this document can be attached 133 to prefixes from Multiprotocol BGP IPv4/IPv6 Labeled Unicast 134 ([RFC4760], [RFC8277]). Usage of the BGP Prefix-SID attribute for 135 other Address Family Identifier (AFI)/ Subsequent Address Family 136 Identifier (SAFI) combinations is not defined herein but may be 137 specified in future specifications. 139 [I-D.ietf-spring-segment-routing-msdc] describes example use cases 140 where the BGP Prefix-SID is used for the above AFI/SAFI combinations. 142 It should be noted that: 144 o A BGP Prefix-SID will be global across ASes when the 145 interconnected ASes are part of the same SR domain. 146 Alternatively, when interconnecting ASes, the ASBRs of each domain 147 will have to handle the advertisement of unique SIDs. The 148 mechanisms for such interconnection are outside the scope of the 149 protocol extensions defined in this document. 151 o A BGP Prefix-SID MAY be attached to a BGP prefix. This implies 152 that each prefix is advertised individually, reducing the ability 153 to pack BGP advertisements (when sharing common attributes). 155 2. MPLS BGP Prefix SID 157 The BGP Prefix-SID is realized on the MPLS dataplane 158 ([I-D.ietf-spring-segment-routing-mpls]) in the following way: 160 The operator assigns a globally unique label index, L_I, to a 161 locally originated prefix of a BGP speaker N which is advertised 162 to all other BGP speakers in the SR domain. 164 According to [I-D.ietf-spring-segment-routing], each BGP speaker 165 is configured with a label block called the Segment Routing Global 166 Block (SRGB). While [I-D.ietf-spring-segment-routing] recommends 167 using the same SRGB across all the nodes within the SR domain, the 168 SRGB of a node is a local property and could be different on 169 different speakers. The drawbacks of the use case where BGP 170 speakers have different SRGBs are documented in 171 [I-D.ietf-spring-segment-routing] and 172 [I-D.ietf-spring-segment-routing-msdc]. 174 If traffic-engineering within the SR domain is required, each node 175 may also be required to advertise topological information and 176 Peering SIDs for each of its links and peers. This information is 177 required to perform the explicit path computation and to express 178 an explicit path as a list of SIDs. The advertisement of 179 topological information and peer segments (Peer SIDs) is done 180 through [I-D.ietf-idr-bgpls-segment-routing-epe]. 182 If a prefix segment is to be included in an MPLS label stack, 183 e.g., for traffic engineering purposes, the knowledge of the SRGB 184 of the originator of the prefix is required in order to compute 185 the local label used by the originator. 187 This document assumes that BGP-LS is the preferred method for 188 collecting both peer segments (Peer SIDs) and SRGB information 189 through [RFC7752], [I-D.ietf-idr-bgpls-segment-routing-epe], and 191 [I-D.ietf-idr-bgp-ls-segment-routing-ext]. However, as an 192 optional alternative for the advertisement of the local SRGB 193 without the topology nor the peer SIDs, hence without 194 applicability for TE, the Originator SRGB TLV of the BGP Prefix- 195 SID attribute is specified in Section 3.2 of this document. 197 A BGP speaker will derive its local MPLS label L from the label 198 index L_I and its local SRGB as described in 199 [I-D.ietf-spring-segment-routing-mpls]. The BGP speaker then 200 programs the MPLS label L in its MPLS dataplane as its incoming/ 201 local label for the prefix. See Section 4.1 for more details. 203 The outgoing label for the prefix is found in the Network Layer 204 Reachability Information (NLRI) of the Multiprotocol BGP IPv4/IPv6 205 Labeled Unicast prefix advertisement as defined in [RFC8277]. The 206 label index L_I is only used as a hint to derive the local/ 207 incoming label. 209 Section 3.1 of this document specifies the Label-Index TLV of the 210 BGP Prefix-SID attribute; this TLV can be used to advertise the 211 label index for a given prefix. 213 3. BGP Prefix-SID Attribute 215 The BGP Prefix-SID attribute is an optional, transitive BGP path 216 attribute. The attribute type code 40 has been assigned by IANA (see 217 Section 7). 219 The BGP Prefix-SID attribute is defined here to be a set of elements 220 encoded as "Type/Length/Value" tuples (i.e., a set of TLVs). All BGP 221 Prefix-SID attribute TLVs will start with a 1-octet type and a 222 2-octet length. The following TLVs are defined in this document: 224 o Label-Index TLV 226 o Originator SRGB TLV 228 The Label-Index and Originator SRGB TLVs are used only when SR is 229 applied to the MPLS dataplane. 231 For future extensibility, unknown TLVs MUST be ignored and propagated 232 unmodified. 234 3.1. Label-Index TLV 236 The Label-Index TLV MUST be present in the BGP Prefix-SID attribute 237 attached to IPv4/IPv6 Labeled Unicast prefixes ([RFC8277]). It MUST 238 be ignored when received for other BGP AFI/SAFI combinations. The 239 Label-Index TLV has the following format: 241 0 1 2 3 242 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 1 243 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 244 | Type | Length | RESERVED | 245 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 246 | Flags | Label Index | 247 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 248 | Label Index | 249 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 251 where: 253 o Type is 1. 255 o Length: is 7, the total length in octets of the value portion of 256 the TLV. 258 o RESERVED: 8-bit field. MUST be clear on transmission and MUST be 259 ignored on reception. 261 o Flags: 16 bits of flags. None are defined by this document. The 262 flag field MUST be clear on transmission and MUST be ignored on 263 reception. 265 o Label Index: 32-bit value representing the index value in the SRGB 266 space. 268 3.2. Originator SRGB TLV 270 The Originator SRGB TLV is an optional TLV and has the following 271 format: 273 0 1 2 3 274 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 1 275 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 276 | Type | Length | Flags | 277 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 278 | Flags | 279 +-+-+-+-+-+-+-+-+ 281 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 282 | SRGB 1 (6 octets) | 283 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 284 | | 285 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 287 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 288 | SRGB n (6 octets) | 289 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 290 | | 291 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 293 where: 295 o Type is 3. 297 o Length is the total length in octets of the value portion of the 298 TLV: 2 + (non-zero multiple of 6). 300 o Flags: 16 bits of flags. None are defined in this document. 301 Flags MUST be clear on transmission and MUST be ignored on 302 reception. 304 o SRGB: 3 octets specifying the first label in the range followed by 305 3 octets specifying the number of labels in the range. Note that 306 the SRGB field MAY appear multiple times. If the SRGB field 307 appears multiple times, the SRGB consists of multiple ranges that 308 are concatenated. 310 The Originator SRGB TLV contains the SRGB of the node originating the 311 prefix to which the BGP Prefix-SID is attached. The Originator SRGB 312 TLV MUST NOT be changed during the propagation of the BGP update. It 313 is used to build segment routing policies when different SRGBs are 314 used in the fabric, for example 315 ([I-D.ietf-spring-segment-routing-msdc]). 317 Examples of how the receiving routers concatenate the ranges and 318 build their neighbor's Segment Routing Global Block (SRGB) are 319 included in [I-D.ietf-spring-segment-routing-mpls]). 321 The Originator SRGB TLV may only appear in a BGP Prefix-SID attribute 322 attached to IPv4/IPv6 Labeled Unicast prefixes ([RFC8277]). It MUST 323 be ignored when received for other BGP AFI/SAFI combinations. Since 324 the Label-Index TLV is required for IPv4/IPv6 prefix applicability, 325 the Originator SRGB TLV will be ignored if it is not specified 326 consistent with Section 6. 328 If a BGP speaker receives a node's SRGB as an attribute of the BGP-LS 329 Node NLRI and the BGP speaker also receives the same node's SRGB in a 330 BGP Prefix-SID attribute, then the received values should be the 331 same. If the values are different, the values advertised in the BGP- 332 LS NLRI SHOULD be preferred and an error should be logged. 334 4. Receiving BGP Prefix-SID Attribute 336 A BGP speaker receiving a BGP Prefix-SID attribute from an External 337 BGP (EBGP) neighbor residing outside the boundaries of the SR domain 338 MUST discard the attribute unless it is configured to accept the 339 attribute from the EBGP neighbor. A BGP speaker SHOULD log an error 340 for further analysis when discarding an attribute. 342 4.1. MPLS Dataplane: Labeled Unicast 344 A BGP session supporting the Multiprotocol BGP labeled IPv4 or IPv6 345 Unicast ([RFC8277]) AFI/SAFI is required. 347 When the BGP Prefix-SID attribute is attached to a BGP labeled IPv4 348 or IPv6 Unicast [RFC8277] AFI/SAFI, it MUST contain the Label-Index 349 TLV and MAY contain the Originator SRGB TLV. A BGP Prefix-SID 350 attribute received without a Label-Index TLV MUST be considered as 351 "invalid" by the receiving speaker. 353 The label index provides guidance to the receiving BGP speaker as to 354 the incoming label that SHOULD be allocated to the prefix. 356 A BGP speaker may be locally configured with an SRGB=[SRGB_Start, 357 SRGB_End]. The preferred method for deriving the SRGB is a matter of 358 local node configuration. 360 The mechanisms through which a given label index value is assigned to 361 a given prefix are outside the scope of this document. 363 Given a label index L_I, we refer to (L = L_I + SRGB_Start) as the 364 derived label. A BGP Prefix-SID attribute is designated 365 "conflicting" for a speaker M if the derived label value L lies 366 outside the SRGB configured on M. Otherwise the Label-Index TLV is 367 designated "acceptable" to speaker M. 369 If multiple different prefixes are received with the same label 370 index, all of the different prefixes MUST have their BGP Prefix-SID 371 attribute considered as "conflicting". 373 If multiple valid paths for the same prefix are received from 374 multiple BGP speakers or, in the case of [RFC7911], from the same BGP 375 speaker, and the BGP Prefix-SID attributes do not contain the same 376 label index, then the label index from the best path BGP Prefix-SID 377 attribute SHOULD be chosen with a notable exception being when 378 [RFC5004] is being used to dampen route changes. 380 When a BGP speaker receives a path from a neighbor with an 381 "acceptable" BGP Prefix-SID attribute and that path is selected as 382 the best path, it SHOULD program the derived label as the label for 383 the prefix in its local MPLS dataplane. 385 When a BGP speaker receives a path from a neighbor with an "invalid" 386 or "conflicting" BGP Prefix-SID attribute or when a BGP speaker 387 receives a path from a neighbor with a BGP Prefix-SID attribute but 388 is unable to process it (e.g., local policy disables the 389 functionality), it MUST ignore the BGP Prefix-SID attribute. For the 390 purposes of label allocation, a BGP speaker MUST assign a local (also 391 called dynamic) label (non-SRGB) for such a prefix as per classic 392 Multiprotocol BGP IPv4/IPv6 Labeled Unicast ([RFC8277]) operation. 394 In the case of an "invalid" BGP Prefix-SID attribute, a BGP speaker 395 MUST follow the error handling rules specified in Section 6. A BGP 396 speaker SHOULD log an error for further analysis. In the case of a 397 "conflicting" BGP Prefix-SID attribute, a BGP speaker SHOULD NOT 398 treat it as error and SHOULD propagate the attribute unchanged. A 399 BGP Speaker SHOULD log a warning for further analysis, i.e., in the 400 case the conflict is not due to a label index transition. 402 When a BGP Prefix-SID attribute changes and transitions from 403 "conflicting" to "acceptable", the BGP Prefix-SID attributes for 404 other prefixes may also transition to "acceptable" as well. 405 Implementations SHOULD assure all impacted prefixes revert to using 406 the label indices corresponding to these newly "acceptable" BGP 407 Prefix-SID attributes. 409 The outgoing label is always programmed as per classic Multiprotocol 410 BGP IPv4/IPv6 Labeled Unicast ([RFC8277]) operation. Specifically, a 411 BGP speaker receiving a prefix with a BGP Prefix-SID attribute and a 412 label NLRI field of Implicit NULL [RFC3032] from a neighbor MUST 413 adhere to standard behavior and program its MPLS dataplane to pop the 414 top label when forwarding traffic to the prefix. The label NLRI 415 defines the outbound label that MUST be used by the receiving node. 417 5. Advertising BGP Prefix-SID Attribute 419 The BGP Prefix-SID attribute MAY be attached to BGP IPv4/IPv6 Label 420 Unicast prefixes [RFC8277]. In order to prevent distribution of the 421 BGP Prefix-SID attribute beyond its intended scope of applicability, 422 attribute filtering SHOULD be deployed to remove the BGP Prefix-SID 423 attribute at the administrative boundary of the segment routing 424 domain. 426 A BGP speaker that advertises a path received from one of its 427 neighbors SHOULD advertise the BGP Prefix-SID received with the path 428 without modification, as long as the BGP Prefix-SID was acceptable. 429 If the path did not come with a BGP Prefix-SID attribute, the speaker 430 MAY attach a BGP Prefix-SID to the path if configured to do so. The 431 content of the TLVs present in the BGP Prefix-SID is determined by 432 the configuration. 434 5.1. MPLS Dataplane: Labeled Unicast 436 A BGP speaker that originates a prefix attaches the BGP Prefix-SID 437 attribute when it advertises the prefix to its neighbors via 438 Multiprotocol BGP IPv4/IPv6 Labeled Unicast ([RFC8277]). The value 439 of the label index in the Label-Index TLV is determined by 440 configuration. 442 A BGP speaker that originates a BGP Prefix-SID attribute MAY 443 optionally announce the Originator SRGB TLV along with the mandatory 444 Label-Index TLV. The content of the Originator SRGB TLV is 445 determined by configuration. 447 Since the label index value must be unique within an SR domain, by 448 default an implementation SHOULD NOT advertise the BGP Prefix-SID 449 attribute outside an Autonomous System unless it is explicitly 450 configured to do so. 452 In all cases, the label field of the advertised NLRI ([RFC8277], 453 [RFC4364]) MUST be set to the local/incoming label programmed in the 454 MPLS dataplane for the given advertised prefix. If the prefix is 455 associated with one of the BGP speaker's interfaces, this is the 456 usual MPLS label (such as the Implicit or Explicit NULL label 457 [RFC3032]). 459 6. Error Handling of BGP Prefix-SID Attribute 461 When a BGP Speaker receives a BGP Update message containing a 462 malformed or invalid BGP Prefix-SID attribute attached to a IPv4/IPv6 463 Labeled Unicast prefix [RFC8277], it MUST ignore the received BGP 464 Prefix-SID attributes and not advertise it to other BGP peers. In 465 this context, a malformed BGP Prefix-SID attribute is one that cannot 466 be parsed due to not meeting the minimum attribute length 467 requirement, contains a TLV length that doesn't conform to the length 468 constraints for the TLV, or a contains TLV length that would extend 469 beyond the end of the attribute (as defined by the attribute length). 470 This is equivalent to the "Attribute discard" action specified in 471 [RFC7606]. When discarding an attribute, a BGP speaker SHOULD log an 472 error for further analysis. 474 As per with [RFC7606], if the BGP Prefix-SID attribute appears more 475 than once in an UPDATE message, then all the occurrences of the 476 attribute other than the first one SHALL be discarded and the UPDATE 477 message will continue to be processed. Similarly, if a recognized 478 TLV appears more than once in an BGP Prefix-SID attribute while the 479 specification only allows for a single occurrence, then all the 480 occurrences of the TLV other than the first one SHALL be discarded 481 and the Prefix-SID attribute will continue to be processed. 483 For future extensibility, unknown TLVs MUST be ignored and propagated 484 unmodified. 486 7. IANA Considerations 488 This document defines a BGP path attribute known as the BGP Prefix- 489 SID attribute. This document requests IANA to assign an attribute 490 code type (suggested value: 40) to the BGP Prefix-SID attribute from 491 the BGP Path Attributes registry. 493 IANA temporarily assigned the following: 495 40 BGP Prefix-SID (TEMPORARY - registered 2015-09-30, expires 496 2018-09-30) [draft-ietf-idr-bgp-prefix-sid] 498 This document defines two TLVs for the BGP Prefix-SID attribute. 499 These TLVs need to be registered with IANA. We request IANA to 500 create a registry for BGP Prefix-SID Attribute TLVs as follows: 502 Under "Border Gateway Protocol (BGP) Parameters" registry, "BGP 503 Prefix-SID TLV Types" Reference: draft-ietf-idr-bgp-prefix-sid 504 Registration Procedure(s): Values 1-254 - Expert Review as defined in 505 [RFC8126], Value 0 and 255 reserved 506 Value Type Reference 507 0 Reserved this document 508 1 Label-Index this document 509 2 Deprecated this document 510 3 Originator SRGB this document 511 4-254 Unassigned 512 255 Reserved this document 514 The value 2 previously corresponded to the IPv6 SID TLV which was 515 specified in previous versions of this document. It was removed and 516 usage of the BGP Prefix-SID for Segment Routing over the IPv6 517 dataplane [I-D.ietf-spring-segment-routing] has been deferred to 518 future specifications. 520 This document also requests creation of the "BGP Prefix-SID Label- 521 Index TLV Flags" registry under the "Border Gateway Protocol (BGP) 522 Parameters" registry, Reference: draft-ietf-idr-bgp-prefix-sid. 523 Initially, this 16-bit flags registry will be empty. The 524 registration policy for flag bits will Expert Review [RFC8126] 525 consistent with the BGP Prefix-SID TLV Types registry. 527 Finally, this document requests creation of the "BGP Prefix-SID 528 Originator SRGB TLV Flags" registry under the "Border Gateway 529 Protocol (BGP) Parameters" registry, Reference: draft-ietf-idr-bgp- 530 prefix-sid. Initially, this 16-bit flags registry will be empty. 531 The registration policy for flag bits will Expert Review [RFC8126] 532 consistent with the BGP Prefix-SID TLV Types registry. 534 The designated experts must be good and faithful stewards of the 535 above registries, assuring that each request is legitimate and 536 corresponds to a viable use case. Given the limited number of bits 537 in the flags registries and the applicability to a single TLV, 538 additional scrutiny should be afforded to flag bit allocation 539 requests. In general, no single use case should require more than 540 one flag bit and, should the use case require more, alternate 541 encodings using new TLVs should be considered. 543 8. Manageability Considerations 545 This document defines a BGP attribute to address use cases such as 546 the one described in [I-D.ietf-spring-segment-routing-msdc]. It is 547 assumed that advertisement of the BGP Prefix-SID attribute is 548 controlled by the operator in order to: 550 o Prevent undesired origination/advertisement of the BGP Prefix-SID 551 attribute. By default, a BGP Prefix-SID attribute SHOULD NOT be 552 attached to a prefix and advertised. Hence, BGP Prefix-SID 553 advertisement SHOULD require explicit enablement. 555 o Prevent any undesired propagation of the BGP Prefix-SID attribute. 556 By default, the BGP Prefix-SID is not advertised outside the 557 boundary of a single SR/administrative domain which may include 558 one or more ASes. The propagation to other ASes MUST be 559 explicitly configured. 561 The deployment model described in 562 [I-D.ietf-spring-segment-routing-msdc] assumes multiple Autonomous 563 Systems (ASes) under a common administrative domain. For this use 564 case, the BGP Prefix-SID advertisement is applicable to the inter-AS 565 context, i.e., EBGP, while it is confined to a single administrative 566 domain. 568 9. Security Considerations 570 This document introduces a BGP attribute (BGP Prefix-SID) which 571 inherits the security considerations expressed in: [RFC4271], 572 [RFC8277], and [I-D.ietf-spring-segment-routing]. 574 When advertised using BGPsec as described in [RFC8205], the BGP 575 Prefix-SID attribute doesn't impose any unique security 576 considerations. It should be noted that the BGP Prefix-SID attribute 577 is not protected by the BGPsec signatures. 579 It should be noted that, as described in Section 8, this document 580 refers to a deployment model where all nodes are under the single 581 administrative domain. In this context, we assume that the operator 582 doesn't want to leak any information related to internal prefixes and 583 topology outside of the administrative domain. The internal 584 information includes the BGP Prefix-SID. In order to prevent such 585 leaking, the common BGP mechanisms (filters) are applied at the 586 boundary of the SR/administrative domain. Local BGP attribute 587 filtering policies and mechanisms are not standardized and, 588 consequently, beyond the scope of this document. 590 To prevent a Denial-of-Service (DoS) or Distributed-Denial-of-Service 591 (DDoS) attack due to excessive BGP updates with an invalid or 592 conflicting BGP Prefix-SID attribute, error log message rate-limiting 593 as well as suppression of duplicate error log messages SHOULD be 594 deployed. 596 Since BGP-LS is the preferred method for advertising SRGB 597 information, the BGP speaker SHOULD log an error if a BGP Prefix-SID 598 attribute is received with SRGB information different from that 599 received as an attribute of the same node's BGP-LS Node NLRI. 601 10. Contributors 603 Keyur Patel 604 Arrcus, Inc. 605 US 607 Email: Keyur@arrcus.com 609 Saikat Ray 610 Unaffiliated 611 US 613 Email: raysaikat@gmail.com 615 11. Acknowledgements 617 The authors would like to thank Satya Mohanty for his contribution to 618 this document. 620 The authors would like to thank Alvaro Retana for substantive 621 comments as part of the Routing AD review. 623 The authors would like to thank Bruno Decraene for substantive 624 comments and suggested text as part of the Routing Directorate 625 review. 627 The authors would like to thank Shyam Sethuram for comments and 628 discussion of TLV processing and validation. 630 The authors would like to thank Robert Raszuk for comments and 631 suggestions regarding the MPLS data plane behavior. 633 The authors would like to thank Krishna Deevi, Juan Alcaide, Howard 634 Yang, and Jakob Heitz for discussions on conflicting BGP Prefix-SID 635 label indices and BGP add paths. 637 The authors would like to thank Peter Yee, Tony Przygienda, Mirja 638 Kuehlewind, Alexey Melnikov, Eric Rescorla, Suresh Krishnan, Warren 639 Kumari, Ben Campbell Sue Hares, and Martin Vigoureux for IDR Working 640 Group last call, IETF Last Call, directorate, and IESG reviews. 642 12. References 644 12.1. Normative References 646 [I-D.ietf-spring-segment-routing] 647 Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B., 648 Litkowski, S., and R. Shakir, "Segment Routing 649 Architecture", draft-ietf-spring-segment-routing-15 (work 650 in progress), January 2018. 652 [I-D.ietf-spring-segment-routing-mpls] 653 Bashandy, A., Filsfils, C., Previdi, S., Decraene, B., 654 Litkowski, S., and R. Shakir, "Segment Routing with MPLS 655 data plane", draft-ietf-spring-segment-routing-mpls-14 656 (work in progress), June 2018. 658 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 659 Requirement Levels", BCP 14, RFC 2119, 660 DOI 10.17487/RFC2119, March 1997, . 663 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 664 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 665 DOI 10.17487/RFC4271, January 2006, . 668 [RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private 669 Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February 670 2006, . 672 [RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, 673 "Multiprotocol Extensions for BGP-4", RFC 4760, 674 DOI 10.17487/RFC4760, January 2007, . 677 [RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K. 678 Patel, "Revised Error Handling for BGP UPDATE Messages", 679 RFC 7606, DOI 10.17487/RFC7606, August 2015, 680 . 682 [RFC7911] Walton, D., Retana, A., Chen, E., and J. Scudder, 683 "Advertisement of Multiple Paths in BGP", RFC 7911, 684 DOI 10.17487/RFC7911, July 2016, . 687 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 688 Writing an IANA Considerations Section in RFCs", BCP 26, 689 RFC 8126, DOI 10.17487/RFC8126, June 2017, 690 . 692 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 693 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 694 May 2017, . 696 [RFC8205] Lepinski, M., Ed. and K. Sriram, Ed., "BGPsec Protocol 697 Specification", RFC 8205, DOI 10.17487/RFC8205, September 698 2017, . 700 [RFC8277] Rosen, E., "Using BGP to Bind MPLS Labels to Address 701 Prefixes", RFC 8277, DOI 10.17487/RFC8277, October 2017, 702 . 704 12.2. Informative References 706 [I-D.ietf-6man-segment-routing-header] 707 Previdi, S., Filsfils, C., Leddy, J., Matsushima, S., and 708 d. daniel.voyer@bell.ca, "IPv6 Segment Routing Header 709 (SRH)", draft-ietf-6man-segment-routing-header-13 (work in 710 progress), May 2018. 712 [I-D.ietf-idr-bgp-ls-segment-routing-ext] 713 Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H., 714 and M. Chen, "BGP Link-State extensions for Segment 715 Routing", draft-ietf-idr-bgp-ls-segment-routing-ext-08 716 (work in progress), May 2018. 718 [I-D.ietf-idr-bgpls-segment-routing-epe] 719 Previdi, S., Filsfils, C., Patel, K., Ray, S., and J. 720 Dong, "BGP-LS extensions for Segment Routing BGP Egress 721 Peer Engineering", draft-ietf-idr-bgpls-segment-routing- 722 epe-15 (work in progress), March 2018. 724 [I-D.ietf-spring-segment-routing-msdc] 725 Filsfils, C., Previdi, S., Dawra, G., Aries, E., and P. 726 Lapukhov, "BGP-Prefix Segment in large-scale data 727 centers", draft-ietf-spring-segment-routing-msdc-09 (work 728 in progress), May 2018. 730 [RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., 731 Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack 732 Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001, 733 . 735 [RFC5004] Chen, E. and S. Sangli, "Avoid BGP Best Path Transitions 736 from One External to Another", RFC 5004, 737 DOI 10.17487/RFC5004, September 2007, . 740 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 741 S. Ray, "North-Bound Distribution of Link-State and 742 Traffic Engineering (TE) Information Using BGP", RFC 7752, 743 DOI 10.17487/RFC7752, March 2016, . 746 Authors' Addresses 748 Stefano Previdi 749 Cisco Systems 750 IT 752 Email: stefano@previdi.net 754 Clarence Filsfils 755 Cisco Systems 756 Brussels 757 Belgium 759 Email: cfilsfils@cisco.com 761 Acee Lindem (editor) 762 Cisco Systems 763 301 Midenhall Way 764 Cary, NC 27513 765 USA 767 Email: acee@cisco.com 769 Arjun Sreekantiah 771 Email: arjunhrs@gmail.com 773 Hannes Gredler 774 RtBrick Inc. 776 Email: hannes@rtbrick.com