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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: August 11, 2018 Cisco Systems 6 A. Sreekantiah 8 H. Gredler 9 RtBrick Inc. 10 February 7, 2018 12 Segment Routing Prefix SID extensions for BGP 13 draft-ietf-idr-bgp-prefix-sid-14 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 August 11, 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 . . . . . . . . . . . . 11 82 5.1. MPLS Dataplane: Labeled Unicast . . . . . . . . . . . . . 11 83 5.2. IPv6 Dataplane . . . . . . . . . . . . . . . . . . . . . 12 84 6. Error Handling of BGP Prefix-SID Attribute . . . . . . . . . 12 85 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 86 8. Manageability Considerations . . . . . . . . . . . . . . . . 13 87 9. Security Considerations . . . . . . . . . . . . . . . . . . . 14 88 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 14 89 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14 90 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 15 91 12.1. Normative References . . . . . . . . . . . . . . . . . . 15 92 12.2. Informative References . . . . . . . . . . . . . . . . . 16 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 Usage of the BGP Prefix-SID attribute for other AFI/SAFI combinations 136 is not defined herein but may be specified in future specifications. 138 [I-D.ietf-spring-segment-routing-msdc] describes example use cases 139 where the BGP Prefix-SID is used for the above AFI/SAFI combinations. 141 It should be noted that: 143 o A BGP Prefix-SID MAY be global between domains when the 144 interconnected domains agree on the SID allocation scheme. 145 Alternatively, when interconnecting domains, the ASBRs of each 146 domain will have to handle the advertisement of unique SIDs. The 147 mechanisms for such interconnection are outside the scope of the 148 protocol extensions defined in this document. 150 o A BGP Prefix-SID MAY be attached to a prefix. In addition, each 151 prefix will likely have a different AS_PATH attribute. This 152 implies that each prefix is advertised individually, reducing the 153 ability to pack BGP advertisements (when sharing common 154 attributes). 156 2. BGP-Prefix-SID 158 The BGP Prefix-SID advertised for BGP prefix P indicates that the 159 segment routed path should be used (as described below) if the BGP 160 best path selects the corresponding Network Layer Reachability 161 Information (NLRI). 163 2.1. MPLS BGP Prefix SID 165 The BGP Prefix-SID is realized on the MPLS dataplane 166 ([I-D.ietf-spring-segment-routing-mpls]) in the following way: 168 The operator assigns a globally unique label index, L_I, to a 169 locally sourced prefix of a BGP speaker N which is advertised to 170 all other BGP speakers in the SR domain. 172 According to [I-D.ietf-spring-segment-routing], each BGP speaker 173 is configured with a label block called the Segment Routing Global 174 Block (SRGB). While [I-D.ietf-spring-segment-routing] recommends 175 using the same SRGB across all the nodes within the SR domain, the 176 SRGB of a node is a local property and could be different on 177 different speakers. The drawbacks of the use case where BGP 178 speakers have different SRGBs are documented in 179 [I-D.ietf-spring-segment-routing] and 180 [I-D.ietf-spring-segment-routing-msdc]. 182 If traffic-engineering within the SR domain is required, each node 183 may also be required to advertise topological information and 184 Peering SIDs for each of its links and peers. This information is 185 required to perform the explicit path computation and to express 186 an explicit path as a list of SIDs. The advertisement of 187 topological information and peer segments (Peer SIDs) is done 188 through [I-D.ietf-idr-bgpls-segment-routing-epe]. 190 If the BGP speakers are not all configured with the same SRGB, and 191 if traffic-engineering within the SR domain is required, each node 192 may be required to advertise its local SRGB in addition to the 193 topological information. 195 This documents assumes that BGP-LS is the preferred method for 196 collecting both peer segments (Peer SIDs) and SRGB information 197 through [RFC7752], [I-D.ietf-idr-bgpls-segment-routing-epe], and 198 [I-D.ietf-idr-bgp-ls-segment-routing-ext]. However, as an 199 optional alternative for the advertisement of the local SRGB 200 without the topology nor the peer SIDs, hence without 201 applicability for TE, the Originator SRGB TLV of the prefix-SID 202 attribute is specified in Section 3.3 of this document. 204 As defined in [I-D.ietf-spring-segment-routing], the label index 205 L_I is an offset into the SRGB. Each BGP speaker derives its 206 local MPLS label, L, by adding L_I to the start value of its own 207 SRGB, and programs L in its MPLS dataplane as its incoming/local 208 label for the prefix. It should be noted that while SRGBs and 209 SIDs are advertised using 32-bit values, the derived label is 210 advertised in the 20 right-most bits. See Section 4.1 for more 211 details. 213 The outgoing label for the prefix is found in the NLRI of the 214 Multiprotocol BGP labeled IPv4/IPv6 Unicast prefix advertisement 215 as defined in [RFC8277]. The label index L_I is only used as a 216 hint to derive the local/incoming label. 218 Section 3.1 of this document specifies the Label-Index TLV of the 219 BGP Prefix-SID attribute; this TLV can be used to advertise the 220 label index for a given prefix. 222 In order to advertise the label index of a given prefix P and, 223 optionally, the SRGB, an extension to BGP is needed: the BGP Prefix- 224 SID attribute. This extension is described in subsequent sections. 226 2.2. IPv6 Prefix Segment 228 When SR is used over an IPv6 dataplane, the BGP Prefix-SID consists 229 of an IPv6 address assigned to the BGP speaker. 231 3. BGP Prefix-SID Attribute 233 The BGP Prefix-SID attribute is an optional, transitive BGP path 234 attribute. The attribute type code 40 has been assigned by IANA (see 235 Section 7). 237 The BGP Prefix-SID attribute is defined here to be a set of elements 238 encoded as "Type/Length/Value" tuples (i.e., a set of TLVs). All BGP 239 Prefix-SID attribute TLVs will start with a 1-octet type and a 240 2-octet length. The following TLVs are defined in this document: 242 o Label-Index TLV 244 o IPv6 SID TLV 246 o Originator SRGB TLV 248 The Label-Index and Originator SRGB TLVs are used only when SR is 249 applied to the MPLS dataplane. 251 The IPv6 SID TLV is used only when SR is applied to the IPv6 252 dataplane. 254 For future extensibility, unknown TLVs MUST be ignored and propagated 255 unmodified. 257 3.1. Label-Index TLV 259 The Label-Index TLV MUST be present in the BGP Prefix-SID attribute 260 attached to Labeled IPv4/IPv6 unicast prefixes ([RFC8277]). It MUST 261 be ignored when received for other BGP AFI/SAFI combinations. The 262 Label-Index TLV has the following format: 264 0 1 2 3 265 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 1 266 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 267 | Type | Length | RESERVED | 268 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 269 | Flags | Label Index | 270 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 271 | Label Index | 272 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 274 where: 276 o Type is 1. 278 o Length: is 7, the total length in octets of the value portion of 279 the TLV. 281 o RESERVED: 8-bit field. MUST be clear on transmission and MUST be 282 ignored on reception. 284 o Flags: 16 bits of flags. None are defined by this document. The 285 flag field MUST be clear on transmission and MUST be ignored on 286 reception. 288 o Label Index: 32-bit value representing the index value in the SRGB 289 space. 291 3.2. IPv6 SID 293 The IPv6 SID TLV MAY be present in the BGP Prefix-SID attribute 294 attached to MP-BGP unlabeled IPv6 unicast prefixes ([RFC4760]). It 295 MUST be ignored for other BGP AFI/SAFI combinations. The IPv6 SID 296 TLV has the following format: 298 0 1 2 3 299 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 1 300 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 301 | Type | Length | RESERVED | 302 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 303 | RESERVED | | 304 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 305 | | 306 | IPv6 SID (16 octets) | 307 | | 308 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 309 | | 310 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 312 where: 314 o Type is 2. 316 o Length: is 19, the total length in octets of the value portion of 317 the TLV. 319 o RESERVED: 24-bit field for future use. MUST be clear on 320 transmission and MUST be ignored on reception. 322 o IPv6 SID: 16 octets. 324 3.3. Originator SRGB TLV 326 The Originator SRGB TLV is an optional TLV and has the following 327 format: 329 0 1 2 3 330 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 1 331 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 332 | Type | Length | Flags | 333 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 334 | Flags | 335 +-+-+-+-+-+-+-+-+ 337 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 338 | SRGB 1 (6 octets) | 339 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 340 | | 341 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 343 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 344 | SRGB n (6 octets) | 345 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 346 | | 347 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 349 where: 351 o Type is 3. 353 o Length is the total length in octets of the value portion of the 354 TLV: 2 + (multiple of 6). 356 o Flags: 16 bits of flags. None are defined in this document. 357 Flags MUST be clear on transmission and MUST be ignored on 358 reception. 360 o SRGB: 3 octets of base followed by 3 octets of range. Note that 361 the SRGB field MAY appear multiple times. If the SRGB field 362 appears multiple times, the SRGB consists of multiple ranges that 363 are concatenated. 365 The Originator SRGB TLV contains the SRGB of the node originating the 366 prefix to which the BGP Prefix-SID is attached. The Originator SRGB 367 TLV MUST NOT be changed during the propagation of the BGP update. 369 The originator SRGB describes the SRGB of the node where the BGP 370 Prefix SID is attached. It is used to build segment routing policies 371 when different SRGBs are used in the fabric, for example 372 ([I-D.ietf-spring-segment-routing-msdc]). 374 The receiving routers concatenate the ranges and build the Segment 375 Routing Global Block (SRGB) as follows: 377 SRGB = [100, 199] 378 [1000, 1099] 379 [500, 599] 381 The indexes span multiple ranges: 383 index=0 means label 100 384 ... 385 index 99 means label 199 386 index 100 means label 1000 387 index 199 means label 1099 388 ... 389 index 200 means label 500 390 ... 392 The originator SRGB may only appear in a BGP Prefix-SID attribute 393 attached to Labeled IPv4/IPv6 unicast prefixes ([RFC8277]). It MUST 394 be ignored when received for other BGP AFI/SAFI combinations. Since 395 the Label-Index TLV is required for IPv4/IPv6 prefix applicability, 396 the originator SRGB will be ignored if it is not specified consistent 397 with Section 6. 399 4. Receiving BGP Prefix-SID Attribute 401 A BGP speaker receiving a BGP Prefix-SID attribute from an EBGP 402 neighbor residing outside the boundaries of the SR domain MUST 403 discard the attribute unless it is configured to accept the attribute 404 from the EBGP neighbor. A BGP speaker SHOULD log an error for 405 further analysis when discarding an attribute. 407 4.1. MPLS Dataplane: Labeled Unicast 409 A Multiprotocol BGP labeled IPv4/IPv6 Unicast ([RFC8277]) session 410 type is required. 412 A BGP speaker may be locally configured with an SRGB=[SRGB_Start, 413 SRGB_End]. The preferred method for deriving the SRGB is a matter of 414 local node configuration. 416 Given a label index L_I, we refer to (L = L_I + SRGB_Start) as the 417 derived label. A BGP Prefix-SID attribute is designated 418 "unacceptable" for a speaker M if the derived label value L lies 419 outside the SRGB configured on M. Otherwise the Label-Index TLV is 420 designated "acceptable" to speaker M. 422 The mechanisms through which a given label index value is assigned to 423 a given prefix are outside the scope of this document. 425 The BGP Prefix-SID attribute MUST contain the Label-Index TLV and MAY 426 contain the Originator SRGB TLV. A BGP Prefix-SID attribute received 427 without a Label-Index TLV MUST be considered as "unacceptable" by the 428 receiving speaker. 430 If multiple prefixes are received with the same label index value, 431 all these prefixes MUST have their BGP Prefix-SID attribute 432 considered as "unacceptable" by the receiving speaker. 434 When a BGP speaker receives a path from a neighbor with an acceptable 435 BGP Prefix-SID attribute and that path is selected as the best path, 436 it SHOULD program the derived label as the local label for the prefix 437 in its MPLS dataplane. In case of an error, a BGP speaker MUST 438 follow to the error handling rules specified in Section 6. A BGP 439 speaker SHOULD log an error for further analysis. 441 When a BGP speaker receives a path from a neighbor with an 442 unacceptable BGP Prefix-SID attribute or when a BGP speaker receives 443 a path from a neighbor with a BGP Prefix-SID attribute but is unable 444 to process it (it does not have the capability or local policy 445 disables the capability), it MUST treat the path as if it came 446 without a BGP Prefix-SID attribute. For the purposes of local label 447 allocation, a BGP speaker MUST assign a local (also called dynamic) 448 label (non-SRGB) for such a prefix as per classic Multiprotocol BGP 449 labeled IPv4/IPv6 Unicast ([RFC8277]) operation. A BGP speaker 450 SHOULD log an error for further analysis. 452 The outgoing label is always programmed as per classic Multiprotocol 453 BGP labeled IPv4/IPv6 Unicast ([RFC8277]) operation. Specifically, a 454 BGP speaker receiving a prefix with a BGP Prefix-SID attribute and a 455 label NLRI field of Implicit NULL from a neighbor MUST adhere to 456 standard behavior and program its MPLS dataplane to pop the top label 457 when forwarding traffic to the prefix. The label NLRI defines the 458 outbound label that MUST be used by the receiving node. 460 The label index provides the receiving BGP speaker with guidance as 461 to the incoming label that SHOULD be assigned by that BGP speaker. 463 4.2. IPv6 Dataplane 465 When an SR IPv6 BGP speaker receives an IPv6 Unicast BGP Update with 466 a prefix having the BGP Prefix-SID attribute attached, it checks 467 whether the IPv6 SID TLV is present. If present and chosen as the 468 best path, the prefix is installed into the Segment Routing IPv6 469 dataplane as described in [I-D.ietf-spring-segment-routing]. 471 The Label-Index and Originator SRGB TLVs MUST be ignored on 472 reception. For future extensibility, no TLVs are required for the 473 BGP IPv6 unicast address family. However, a BGP Prefix-SID attribute 474 corresponding to the BGP IPv6 address family without an IPv6 SID TLV 475 SHOULD be ignored. 477 5. Advertising BGP Prefix-SID Attribute 479 The BGP Prefix-SID attribute MAY be attached to labeled BGP prefixes 480 (IPv4/IPv6) [RFC8277] or to IPv6 unicast prefixes [RFC4760]. In 481 order to prevent distribution of the BGP Prefix-SID attribute beyond 482 its intended scope of applicability, attribute filtering SHOULD be 483 deployed to remove the BGP Prefix-SID attribute at the adminstrative 484 boundary of the segment routing domain. 486 A BGP speaker that advertises a path received from one of its 487 neighbors SHOULD advertise the BGP Prefix-SID received with the path 488 without modification, as long as the BGP Prefix-SID was acceptable. 489 If the path did not come with a BGP Prefix-SID attribute, the speaker 490 MAY attach a BGP Prefix-SID to the path if configured to do so. The 491 content of the TLVs present in the BGP Prefix-SID is determined by 492 the configuration. 494 5.1. MPLS Dataplane: Labeled Unicast 496 A BGP speaker that originates a prefix attaches the BGP Prefix-SID 497 attribute when it advertises the prefix to its neighbors via 498 Multiprotocol BGP labeled IPv4/IPv6 Unicast ([RFC8277]). The value 499 of the label index in the Label-Index TLV is determined by 500 configuration. 502 A BGP speaker that originates a BGP Prefix-SID attribute MAY 503 optionally announce the Originator SRGB TLV along with the mandatory 504 Label-Index TLV. The content of the Originator SRGB TLV is 505 determined by configuration. 507 Since the label index value must be unique within an SR domain, by 508 default an implementation SHOULD NOT advertise the BGP Prefix-SID 509 attribute outside an Autonomous System unless it is explicitly 510 configured to do so. 512 In all cases, the label field of the advertised NLRI ([RFC8277], 513 [RFC4364]) MUST be set to the local/incoming label programmed in the 514 MPLS dataplane for the given advertised prefix. If the prefix is 515 associated with one of the BGP speaker's interfaces, this is the 516 usual MPLS label (such as the Implicit or Explicit NULL label). 518 5.2. IPv6 Dataplane 520 A BGP speaker that originates an IPv6 prefix with the BGP Prefix-SID 521 attribute SHOULD include the IPv6 SID TLV. 523 6. Error Handling of BGP Prefix-SID Attribute 525 When a BGP Speaker receives a BGP Update message containing a 526 malformed or unacceptable BGP Prefix-SID attribute attached to a 527 Labeled IPv4/IPv6 unicast prefix [RFC8277], it MUST ignore the 528 received BGP Prefix-SID attributes and not advertise it to other BGP 529 peers. This is equivalent to the "Attribute discard" action 530 specified in [RFC7606]. When discarding an attribute, a BGP speaker 531 SHOULD log an error for further analysis. 533 When a BGP Speaker receives a BGP Update message containing a 534 malformed or unacceptable BGP Prefix-SID attribute attached to an 535 unlabeled IPv6 unicast prefix [RFC4760], it MUST treat the 536 advertisement as a withdrawal. This is equivalent to the "Treat-as- 537 withdraw" action specified in [RFC7606]. This action is required 538 since simply ignoring the BGP Prefix-SID attribute would modify the 539 installed path and the "Attribute discard" option is not applicable 540 in this case [RFC7606]. When withdrawing the prefix, a BGP speaker 541 SHOULD log an error for further analysis. 543 Consistent with [RFC7606], only the first occurrence of the BGP 544 Prefix-SID attribute will be considered and subsequent occurrences 545 will be discarded. Similarly, only the first occurrence of a BGP 546 Prefix-SID attribute TLV of a given TLV type will be considered 547 unless the specification of that TLV type allows for multiple 548 occurrences. 550 For future extensibility, unknown TLVs MUST be ignored and propagated 551 unmodified. 553 7. IANA Considerations 555 This document defines a BGP path attribute known as the BGP Prefix- 556 SID attribute. This document requests IANA to assign an attribute 557 code type (suggested value: 40) to the BGP Prefix-SID attribute from 558 the BGP Path Attributes registry. 560 Currently, IANA temporarily assigned the following: 562 40 BGP Prefix-SID (TEMPORARY - registered 2015-09-30, expires 563 2016-09-30) [draft-ietf-idr-bgp-prefix-sid] 565 This document defines 3 TLVs for the BGP Prefix-SID attribute. These 566 TLVs need to be registered with IANA. We request IANA to create a 567 registry for BGP Prefix-SID Attribute TLVs as follows: 569 Under "Border Gateway Protocol (BGP) Parameters" registry, "BGP 570 Prefix-SID TLV Types" Reference: draft-ietf-idr-bgp-prefix-sid 571 Registration Procedure(s): Values 1-254 First Come First Served 572 (FCFS), Value 0 and 255 reserved 574 Value Type Reference 575 0 Reserved this document 576 1 Label-Index this document 577 2 IPv6 SID this document 578 3 Originator SRGB this document 579 4-254 Unassigned 580 255 Reserved this document 582 This document also creates a registry for the 16 bits of flags in the 583 Label-Index TLV. Initially, the registry will be empty. Flag bits 584 will be allocated First Come First Served (FCFS) consistent with the 585 BGP-SID TLV Types registry. 587 Finally, this document creates a registry for the 16 bits of flags in 588 the SRGB Originator TLV. Initially, the registry will be empty. 589 Flag bits will be allocated First Come First Served (FCFS) consistent 590 with the BGP-SID TLV Types registry. 592 8. Manageability Considerations 594 This document defines a BGP attribute to address use cases such as 595 the one described in [I-D.ietf-spring-segment-routing-msdc]. It is 596 assumed that advertisement of the BGP Prefix-SID attribute is 597 controlled by the operator in order to: 599 o Prevent undesired origination/advertisement of the BGP Prefix-SID 600 attribute. By default, a BGP Prefix-SID attribute SHOULD NOT be 601 attached to a prefix and advertised. Hence, BGP Prefix-SID 602 advertisement SHOULD require explicit enablement. 604 o Prevent any undesired propagation of the BGP Prefix-SID attribute. 605 By default, the BGP Prefix-SID is not advertised outside the 606 boundary of a single SR/administrative domain which may include 607 one or more ASes. The propagation to other ASes MUST be 608 explicitly configured. 610 The deployment model described in 611 [I-D.ietf-spring-segment-routing-msdc] assumes multiple Autonomous 612 Systems (ASes) under a common administrative domain. For this use 613 case, the BGP Prefix-SID advertisement is applicable to the inter-AS 614 context, i.e., EBGP, while it is confined to a single administrative 615 domain. 617 9. Security Considerations 619 This document introduces a BGP attribute (BGP Prefix-SID) which 620 inherits the security considerations expressed in: [RFC4271], 621 [RFC8277], and [I-D.ietf-spring-segment-routing]. 623 When advertised using BGPsec as described in [RFC8205], the BGP 624 Prefix-SID attribute doesn't impose any unique security 625 considerations. 627 It should be noted that, as described in Section 8, this document 628 refers to a deployment model where all nodes are under the single 629 administrative domain. In this context, we assume that the operator 630 doesn't want to leak any information related to internal prefixes and 631 topology outside of the administrative domain. The internal 632 information includes the BGP Prefix-SID. In order to prevent such 633 leaking, the standard BGP mechanisms (filters) are applied at the 634 boundary of the SR/administrative domain. 636 To prevent a Denial-of-Service (DoS) or Distributed-Denial-of-Service 637 (DDoS) attack due to excessive BGP updates with an unacceptable BGP 638 Prefix-SID attribute, message rate-limiting as well as suppression of 639 duplicate messages SHOULD be deployed. 641 10. Contributors 643 Keyur Patel 644 Arrcus, Inc. 645 US 647 Email: Keyur@arrcus.com 649 Saikat Ray 650 Unaffiliated 651 US 653 Email: raysaikat@gmail.com 655 11. Acknowledgements 657 The authors would like to thank Satya Mohanty for his contribution to 658 this document. 660 The authors would like to thank Alvaro Retana for substantive 661 comments as part of the Routing AD review. 663 The authors would like to thank Shyam Sethuram for comments and 664 discussion of TLV processing and validation. 666 The authors would like to thank Peter Yee, Tony Przygienda, Mirja 667 Kuehlewind, Alexey Melnikov, Eric Rescorla, Suresh Krishnan, and 668 Warren Kumari for IETF Last Call directorate and IESG reviews. 670 12. References 672 12.1. Normative References 674 [I-D.ietf-spring-segment-routing] 675 Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B., 676 Litkowski, S., and R. Shakir, "Segment Routing 677 Architecture", draft-ietf-spring-segment-routing-15 (work 678 in progress), January 2018. 680 [I-D.ietf-spring-segment-routing-mpls] 681 Filsfils, C., Previdi, S., Bashandy, A., Decraene, B., 682 Litkowski, S., and R. Shakir, "Segment Routing with MPLS 683 data plane", draft-ietf-spring-segment-routing-mpls-11 684 (work in progress), October 2017. 686 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 687 Requirement Levels", BCP 14, RFC 2119, 688 DOI 10.17487/RFC2119, March 1997, . 691 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 692 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 693 DOI 10.17487/RFC4271, January 2006, . 696 [RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private 697 Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February 698 2006, . 700 [RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, 701 "Multiprotocol Extensions for BGP-4", RFC 4760, 702 DOI 10.17487/RFC4760, January 2007, . 705 [RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K. 706 Patel, "Revised Error Handling for BGP UPDATE Messages", 707 RFC 7606, DOI 10.17487/RFC7606, August 2015, 708 . 710 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 711 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 712 May 2017, . 714 [RFC8205] Lepinski, M., Ed. and K. Sriram, Ed., "BGPsec Protocol 715 Specification", RFC 8205, DOI 10.17487/RFC8205, September 716 2017, . 718 [RFC8277] Rosen, E., "Using BGP to Bind MPLS Labels to Address 719 Prefixes", RFC 8277, DOI 10.17487/RFC8277, October 2017, 720 . 722 12.2. Informative References 724 [I-D.ietf-idr-bgp-ls-segment-routing-ext] 725 Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H., 726 and M. Chen, "BGP Link-State extensions for Segment 727 Routing", draft-ietf-idr-bgp-ls-segment-routing-ext-04 728 (work in progress), January 2018. 730 [I-D.ietf-idr-bgpls-segment-routing-epe] 731 Previdi, S., Filsfils, C., Patel, K., Ray, S., and J. 732 Dong, "BGP-LS extensions for Segment Routing BGP Egress 733 Peer Engineering", draft-ietf-idr-bgpls-segment-routing- 734 epe-14 (work in progress), December 2017. 736 [I-D.ietf-spring-segment-routing-msdc] 737 Filsfils, C., Previdi, S., Mitchell, J., Aries, E., and P. 738 Lapukhov, "BGP-Prefix Segment in large-scale data 739 centers", draft-ietf-spring-segment-routing-msdc-08 (work 740 in progress), December 2017. 742 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and 743 S. Ray, "North-Bound Distribution of Link-State and 744 Traffic Engineering (TE) Information Using BGP", RFC 7752, 745 DOI 10.17487/RFC7752, March 2016, . 748 Authors' Addresses 749 Stefano Previdi (editor) 750 Cisco Systems 751 IT 753 Email: stefano@previdi.net 755 Clarence Filsfils 756 Cisco Systems 757 Brussels 758 Belgium 760 Email: cfilsfils@cisco.com 762 Acee Lindem 763 Cisco Systems 764 301 Midenhall Way 765 Cary, NC 27513 766 USA 768 Email: acee@cisco.com 770 Arjun Sreekantiah 772 Email: arjunhrs@gmail.com 774 Hannes Gredler 775 RtBrick Inc. 777 Email: hannes@rtbrick.com