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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-25) exists of draft-ietf-isis-segment-routing-extensions-19 == Outdated reference: A later version (-27) exists of draft-ietf-ospf-segment-routing-extensions-25 == Outdated reference: A later version (-22) exists of draft-ietf-spring-segment-routing-mpls-14 ** Obsolete normative reference: RFC 6347 (Obsoleted by RFC 9147) == Outdated reference: A later version (-26) exists of draft-ietf-6man-segment-routing-header-14 Summary: 1 error (**), 0 flaws (~~), 5 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group X. Xu 3 Internet-Draft Alibaba 4 Intended status: Standards Track S. Bryant 5 Expires: February 2, 2019 Huawei 6 A. Farrel 7 Juniper 8 S. Hassan 9 Cisco 10 W. Henderickx 11 Nokia 12 Z. Li 13 Huawei 14 August 01, 2018 16 SR-MPLS over IP 17 draft-ietf-mpls-sr-over-ip-00 19 Abstract 21 MPLS Segment Routing (SR-MPLS in short) is an MPLS data plane-based 22 source routing paradigm in which the sender of a packet is allowed to 23 partially or completely specify the route the packet takes through 24 the network by imposing stacked MPLS labels on the packet. SR-MPLS 25 could be leveraged to realize a source routing mechanism across MPLS, 26 IPv4, and IPv6 data planes by using an MPLS label stack as a source 27 routing instruction set while preserving backward compatibility with 28 SR-MPLS. 30 This document describes how SR-MPLS capable routers and IP-only 31 routers can seamlessly co-exist and interoperate through the use of 32 SR-MPLS label stacks and IP encapsulation/tunneling such as MPLS-in- 33 UDP as defined in RFC 7510. 35 Status of This Memo 37 This Internet-Draft is submitted in full conformance with the 38 provisions of BCP 78 and BCP 79. 40 Internet-Drafts are working documents of the Internet Engineering 41 Task Force (IETF). Note that other groups may also distribute 42 working documents as Internet-Drafts. The list of current Internet- 43 Drafts is at https://datatracker.ietf.org/drafts/current/. 45 Internet-Drafts are draft documents valid for a maximum of six months 46 and may be updated, replaced, or obsoleted by other documents at any 47 time. It is inappropriate to use Internet-Drafts as reference 48 material or to cite them other than as "work in progress." 49 This Internet-Draft will expire on February 2, 2019. 51 Copyright Notice 53 Copyright (c) 2018 IETF Trust and the persons identified as the 54 document authors. All rights reserved. 56 This document is subject to BCP 78 and the IETF Trust's Legal 57 Provisions Relating to IETF Documents 58 (https://trustee.ietf.org/license-info) in effect on the date of 59 publication of this document. Please review these documents 60 carefully, as they describe your rights and restrictions with respect 61 to this document. Code Components extracted from this document must 62 include Simplified BSD License text as described in Section 4.e of 63 the Trust Legal Provisions and are provided without warranty as 64 described in the Simplified BSD License. 66 Table of Contents 68 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 69 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 70 3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 3 71 4. Procedures of SR-MPLS over IP . . . . . . . . . . . . . . . . 5 72 4.1. Forwarding Entry Construction . . . . . . . . . . . . . . 5 73 4.2. Packet Forwarding Procedures . . . . . . . . . . . . . . 7 74 4.2.1. Packet Forwarding with Penultimate Hop Popping . . . 8 75 4.2.2. Packet Forwarding without Penultimate Hop Popping . . 9 76 4.2.3. Additional Forwarding Procedures . . . . . . . . . . 10 77 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 78 6. Security Considerations . . . . . . . . . . . . . . . . . . . 12 79 7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 12 80 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13 81 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 82 9.1. Normative References . . . . . . . . . . . . . . . . . . 13 83 9.2. Informative References . . . . . . . . . . . . . . . . . 15 84 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15 86 1. Introduction 88 MPLS Segment Routing (SR-MPLS in short) 89 [I-D.ietf-spring-segment-routing-mpls] is an MPLS data plane-based 90 source routing paradigm in which the sender of a packet is allowed to 91 partially or completely specify the route the packet takes through 92 the network by imposing stacked MPLS labels on the packet. SR-MPLS 93 could be leveraged to realize a source routing mechanism across MPLS, 94 IPv4, and IPv6 data planes by using an MPLS label stack as a source 95 routing instruction set while preserving backward compatibility with 96 SR-MPLS. More specifically, the source routing instruction set 97 information contained in a source routed packet could be uniformly 98 encoded as an MPLS label stack no matter whether the underlay is 99 IPv4, IPv6, or MPLS. 101 This document describes how SR-MPLS capable routers and IP-only 102 routers can seamlessly co-exist and interoperate through the use of 103 SR-MPLS label stacks and IP encapsulation/tunneling such as MPLS-in- 104 UDP [RFC7510]. 106 Although the source routing instructions are encoded as MPLS labels, 107 this is a hardware convenience rather than an indication that the 108 whole MPLS protocol stack needs to be deployed. In particular, the 109 MPLS control protocols are not used in this or any other form of SR- 110 MPLS. 112 Section 3 describes various use cases for the tunneling SR-MPLS over 113 IP. Section 4 describes a typical application scenario and how the 114 packet forwarding happens. 116 2. Terminology 118 This memo makes use of the terms defined in [RFC3031] and 119 [I-D.ietf-spring-segment-routing-mpls]. 121 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 122 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 123 "OPTIONAL" in this document are to be interpreted as described in BCP 124 14 [RFC2119] [RFC8174] when, and only when, they appear in all 125 capitals, as shown here. 127 3. Use Cases 129 Tunneling SR-MPLS using IPv4 and/or IPv6 tunnels is useful at least 130 in the following use cases: 132 o Incremental deployment of the SR-MPLS technology may be 133 facilitated by tunneling SR-MPLS packets across parts of a network 134 that are not SR-MPLS enabled using an IP tunneling mechanism such 135 as MPLS-in-UDP [RFC7510]. The tunnel destination address is the 136 address of the next SR-MPLS-capable node along the path (i.e., the 137 egress of the active node segment). This is shown in Figure 1. 139 ________________________ 140 _______ ( ) _______ 141 ( ) ( IP Network ) ( ) 142 ( SR-MPLS ) ( ) ( SR-MPLS ) 143 ( Network ) ( ) ( Network ) 144 ( -------- -------- ) 145 ( | Border | SR-in-UDP Tunnel | Border | ) 146 ( | Router |========================| Router | ) 147 ( | R1 | | R2 | ) 148 ( -------- -------- ) 149 ( ) ( ) ( ) 150 ( ) ( ) ( ) 151 (_______) ( ) (_______) 152 (________________________) 154 Figure 1: SR-MPLS in UDP to Tunnel Between SR-MPLS Sites 156 o If encoding of entropy is desired, IP tunneling mechanisms that 157 allow encoding of entropy, such as MPLS-in-UDP encapsulation 158 [RFC7510] where the source port of the UDP header is used as an 159 entropy field, may be used to maximize the utilization of ECMP 160 and/or UCMP, specially when it is difficult to make use of entropy 161 label mechanism. Refer to [I-D.ietf-mpls-spring-entropy-label]) 162 for more discussion about using entropy label in SR-MPLS. 164 o Tunneling MPLS into IP provides a technology that enables SR in an 165 IPv4 and/or IPv6 network where the routers do not support SRv6 166 capabilities [I-D.ietf-6man-segment-routing-header] and where MPLS 167 forwarding is not an option. This is shown in Figure Figure 2. 169 __________________________________ 170 __( IP Network )__ 171 __( )__ 172 ( -- -- -- ) 173 -------- -- -- |SR| -- |SR| -- |SR| -- -------- 174 | Ingress| |IR| |IR| | | |IR| | | |IR| | | |IR| | Egress | 175 --->| Router |===========| |======| |======| |======| Router |---> 176 | SR | | | | | | | | | | | | | | | | | | SR | 177 -------- -- -- | | -- | | -- | | -- -------- 178 (__ -- -- -- __) 179 (__ __) 180 (__________________________________) 182 Key: 183 IR : IP-only Router 184 SR : SR-MPLS-capable Router 185 == : SR-MPLS in UDP Tunnel 187 Figure 2: SR-MPLS Enabled Within an IP Network 189 4. Procedures of SR-MPLS over IP 191 This section describes the construction of forwarding information 192 base (FIB) entries and the forwarding behavior that allow the 193 deployment of SR-MPLS when some routers in the network are IP only 194 (i.e., do not support SR-MPLS). Note that the examples described in 195 Section 4.1 and Section 4.2 assume that OSPF or ISIS is enabled: in 196 fact, other mechanisms of discovery and advertisement could be used 197 including other routing protocols (such as BGP) or a central 198 controller. 200 4.1. Forwarding Entry Construction 202 This sub-section describes the how to construct the forwarding 203 information base (FIB) entry on an SR-MPLS-capable router when some 204 or all of the next-hops along the shortest path towards a prefix-SID 205 are IP-only routers. 207 Consider router A that receives a labeled packet with top label L(E) 208 that corresponds to the prefix-SID SID(E) of prefix P(E) advertised 209 by router E. Suppose the ith next-hop router (termed NHi) along the 210 shortest path from router A toward SID(E) is not SR-MPLS capable 211 while both routers A and E are SR-MPLS capable. The following 212 processing steps apply: 214 o Router E is SR-MPLS capable so it advertises the SR-Capabilities 215 sub-TLV including the SRGB as described in 216 [I-D.ietf-ospf-segment-routing-extensions] and 217 [I-D.ietf-isis-segment-routing-extensions]. 219 o Router E advertises the prefix-SID SID(E) of prefix P(E) so MUST 220 also advertise the encapsulation endpoint and the tunnel type of 221 any tunnel used to reach E. It does this using the mechanisms 222 described in [I-D.ietf-isis-encapsulation-cap] or 223 [I-D.ietf-ospf-encapsulation-cap]. 225 o If A and E are in different IGP areas/levels, then: 227 * The OSPF Tunnel Encapsulation TLV 228 [I-D.ietf-ospf-encapsulation-cap] or the ISIS Tunnel 229 Encapsulation sub-TLV [I-D.ietf-isis-encapsulation-cap] is 230 flooded domain-wide. 232 * The OSPF SID/label range TLV 233 [I-D.ietf-ospf-segment-routing-extensions] or the ISIS SR- 234 Capabilities Sub-TLV [I-D.ietf-isis-segment-routing-extensions] 235 is advertised domain-wide. This way router A knows the 236 characteristics of the router that originated the advertisement 237 of SID(E) (i.e., router E). 239 * When router E advertises the prefix P(E): 241 + If router E is running ISIS it uses the extended 242 reachability TLV (TLVs 135, 235, 236, 237) and associates 243 the IPv4/IPv6 or IPv4/IPv6 source router ID sub-TLV(s) 244 [RFC7794]. 246 + If router E is running OSPF it uses the OSPFv2 Extended 247 Prefix Opaque LSA [RFC7684] and sets the flooding scope to 248 AS-wide. 250 * If router E is running ISIS and advertises the ISIS 251 capabilities TLV (TLV 242) [RFC7981], it MUST set the "router- 252 ID" field to a valid value or include an IPV6 TE router-ID sub- 253 TLV (TLV 12), or do both. The "S" bit (flooding scope) of the 254 ISIS capabilities TLV (TLV 242) MUST be set to "1" . 256 o Router A programs the FIB entry for prefix P(E) corresponding to 257 the SID(E) as follows: 259 * If the NP flag in OSPF or the P flag in ISIS is clear: 261 pop the top label 263 * If the NP flag in OSPF or the P flag in ISIS is set: 265 swap the top label to a value equal to SID(E) plus the lower 266 bound of the SRGB of E 268 * Encapsulate the packet according to the encapsulation 269 advertised in [I-D.ietf-isis-encapsulation-cap] or 270 [I-D.ietf-ospf-encapsulation-cap] 272 * Send the packet towards the next hop NHi. 274 4.2. Packet Forwarding Procedures 276 [RFC7510] specifies an IP-based encapsulation for MPLS, i.e., MPLS- 277 in-UDP, which is applicable in some circumstances where IP-based 278 encapsulation for MPLS is required and further fine-grained load 279 balancing of MPLS packets over IP networks over Equal-Cost Multipath 280 (ECMP) and/or Link Aggregation Groups (LAGs) is required as well. 281 This section provides details about the forwarding procedure when 282 when UDP encapsulation is adopted for SR-MPLS over IP. 284 Nodes that are SR-MPLS capable can process SR-MPLS packets. Not all 285 of the nodes in an SR-MPLS domain are SR-MPLS capable. Some nodes 286 may be "legacy routers" that cannot handle SR-MPLS packets but can 287 forward IP packets. An SR-MPLS-capable node may advertise its 288 capabilities using the IGP as described in Section 4. There are six 289 types of node in an SR-MPLS domain: 291 o Domain ingress nodes that receive packets and encapsulate them for 292 transmission across the domain. Those packets may be any payload 293 protocol including native IP packets or packets that are already 294 MPLS encapsulated. 296 o Legacy transit nodes that are IP routers but that are not SR-MPLS 297 capable (i.e., are not able to perform segment routing). 299 o Transit nodes that are SR-MPLS capable but that are not identified 300 by a SID in the SID stack. 302 o Transit nodes that are SR-MPLS capable and need to perform SR-MPLS 303 routing because they are identified by a SID in the SID stack. 305 o The penultimate SR-MPLS capable node on the path that processes 306 the last SID on the stack on behalf of the domain egress node. 308 o The domain egress node that forwards the payload packet for 309 ultimate delivery. 311 4.2.1. Packet Forwarding with Penultimate Hop Popping 313 The description in this section assumes that the label associated 314 with each prefix-SID is advertised by the owner of the prefix-SID is 315 a Penultimate Hop Popping (PHP) label. That is, the NP flag in OSPF 316 or the P flag in ISIS associated with the prefix SID is not set. 318 +-----+ +-----+ +-----+ +-----+ +-----+ 319 | A +-------+ B +-------+ C +--------+ D +--------+ H | 320 +-----+ +--+--+ +--+--+ +--+--+ +-----+ 321 | | | 322 | | | 323 +--+--+ +--+--+ +--+--+ 324 | E +-------+ F +--------+ G | 325 +-----+ +-----+ +-----+ 327 +--------+ 328 |IP(A->E)| 329 +--------+ +--------+ +--------+ 330 | UDP | |IP(E->G)| |IP(G->H)| 331 +--------+ +--------+ +--------+ 332 | L(G) | | UDP | | UDP | 333 +--------+ +--------+ +--------+ 334 | L(H) | | L(H) | |Exp Null| 335 +--------+ +--------+ +--------+ 336 | Packet | ---> | Packet | ---> | Packet | 337 +--------+ +--------+ +--------+ 339 Figure 3: Packet Forwarding Example with PHP 341 In the example shown in Figure 3, assume that routers A, E, G and H 342 are SR-MPLS-capable while the remaining routers (B, C, D and F) are 343 only capable of forwarding IP packets. Routers A, E, G, and H 344 advertise their Segment Routing related information via IS-IS or 345 OSPF. 347 Now assume that router A (the Domain ingress) wants to send a packet 348 to router H (the Domain egress) via the explicit path {E->G->H}. 349 Router A will impose an MPLS label stack on the packet that 350 corresponds to that explicit path. Since the next hop toward router 351 E is only IP-capable (B is a legacy transit node), router A replaces 352 the top label (that indicated router E) with a UDP-based tunnel for 353 MPLS (i.e., MPLS-over-UDP [RFC7510]) to router E and then sends the 354 packet. In other words, router A pops the top label and then 355 encapsulates the MPLS packet in a UDP tunnel to router E. 357 When the IP-encapsulated MPLS packet arrives at router E (which is an 358 SR-MPLS-capable transit node), router E strips the IP-based tunnel 359 header and then process the decapsulated MPLS packet. The top label 360 indicates that the packet must be forwarded toward router G. Since 361 the next hop toward router G is only IP-capable, router E replaces 362 the current top label with an MPLS-over-UDP tunnel toward router G 363 and sends it out. That is, router E pops the top label and then 364 encapsulates the MPLS packet in a UDP tunnel to router G. 366 When the packet arrives at router G, router G will strip the IP-based 367 tunnel header and then process the decapsulated MPLS packet. The top 368 label indicates that the packet must be forwarded toward router H. 369 Since the next hop toward router H is only IP-capable (D is a legacy 370 transit router), router G would replace the current top label with an 371 MPLS-over-UDP tunnel toward router H and send it out. However, since 372 router G reaches the bottom of the label stack (G is the penultimate 373 SR-MPLS capable node on the path) this would leave the original 374 packet that router A wanted to send to router H encapsulated in UDP 375 as if it was MPLS (i.e., with a UDP header and destination port 376 indicating MPLS) even though the original packet could have been any 377 protocol. That is, the final SR-MPLS has been popped exposing the 378 payload packet. 380 To handle this, when a router (here it is router G) pops the final 381 SR-MPLS label, it inserts an explicit null label [RFC3032] before 382 encapsulating the packet in an MPLS-over-UDP tunnel toward router H 383 and sending it out. That is, router G pops the top label, discovers 384 it has reached the bottom of stack, pushes an explicit null label, 385 and then encapsulates the MPLS packet in a UDP tunnel to router H. 387 4.2.2. Packet Forwarding without Penultimate Hop Popping 389 Figure 4 demonstrates the packet walk in the case where the label 390 associated with each prefix-SID advertised by the owner of the 391 prefix-SID is not a Penultimate Hop Popping (PHP) label (i.e., the 392 the NP flag in OSPF or the P flag in ISIS associated with the prefix 393 SID is set). Apart from the PHP function the roles of the routers is 394 unchanged from Section 4.2.1. 396 +-----+ +-----+ +-----+ +-----+ +-----+ 397 | A +-------+ B +-------+ C +--------+ D +--------+ H | 398 +-----+ +--+--+ +--+--+ +--+--+ +-----+ 399 | | | 400 | | | 401 +--+--+ +--+--+ +--+--+ 402 | E +-------+ F +--------+ G | 403 +-----+ +-----+ +-----+ 405 +--------+ 406 |IP(A->E)| 407 +--------+ +--------+ 408 | UDP | |IP(E->G)| 409 +--------+ +--------+ +--------+ 410 | L(E) | | UDP | |IP(G->H)| 411 +--------+ +--------+ +--------+ 412 | L(G) | | L(G) | | UDP | 413 +--------+ +--------+ +--------+ 414 | L(H) | | L(H) | | L(H) | 415 +--------+ +--------+ +--------+ 416 | Packet | ---> | Packet | ---> | Packet | 417 +--------+ +--------+ +--------+ 419 Figure 4: Packet Forwarding Example without PHP 421 As can be seen from the figure, the SR-MPLS label for each segment is 422 left in place until the end of the segment where it is popped and the 423 next instruction is processed. 425 4.2.3. Additional Forwarding Procedures 427 Non-MPLS Interfaces: Although the description in the previous two 428 sections is based on the use of prefix-SIDs, tunneling SR-MPLS 429 packets is useful when the top label of a received SR-MPLS packet 430 indicates an adjacency-SID and the corresponding adjacent node to 431 that adjacency-SID is not capable of MPLS forwarding but can still 432 process SR-MPLS packets. In this scenario the top label would be 433 replaced by an IP tunnel toward that adjacent node and then 434 forwarded over the corresponding link indicated by the adjacency- 435 SID. 437 When to use IP-based Tunnel: The description in the previous two 438 sections is based on the assumption that MPLS-over-UDP tunnel is 439 used when the nexthop towards the next segment is not MPLS- 440 enabled. However, even in the case where the nexthop towards the 441 next segment is MPLS-capable, an MPLS-over-UDP tunnel towards the 442 next segment could still be used instead due to local policies. 443 For instance, in the example as described in Figure 4, assume F is 444 now an SR-MPLS-capable transit node while all the other 445 assumptions keep unchanged, since F is not identified by a SID in 446 the stack and an MPLS-over-UDP tunnel is preferred to an MPLS LSP 447 according to local policies, router E would replace the current 448 top label with an MPLS-over-UDP tunnel toward router G and send it 449 out. 451 IP Header Fields: When encapsulating an MPLS packet in UDP, the 452 resulting packet is further encapsulated in IP for transmission. 453 IPv4 or IPv6 may be used according to the capabilities of the 454 network. The address fields are set as described in Section 3. 455 The other IP header fields (such as DSCP code point, or IPv6 Flow 456 Label) on each UDP-encapsulated segment can be set according to 457 the operator's policy: they may be copied from the header of the 458 incoming packet; they may be promoted from the header of the 459 payload packet; they may be set according to instructions 460 programmed to be associated with the SID; or they may be 461 configured dependent on the outgoing interface and payload. 463 Entropy and ECMP: When encapsulating an MPLS packet with an IP 464 tunnel header that is capable of encoding entropy (such as 465 [RFC7510]), the corresponding entropy field (the source port in 466 case UDP tunnel) MAY be filled with an entropy value that is 467 generated by the encapsulator to uniquely identify a flow. 468 However, what constitutes a flow is locally determined by the 469 encapsulator. For instance, if the MPLS label stack contains at 470 least one entropy label and the encapsulator is capable of reading 471 that entropy label, the entropy label value could be directly 472 copied to the source port of the UDP header. Otherwise, the 473 encapsulator may have to perform a hash on the whole label stack 474 or the five-tuple of the SR-MPLS payload if the payload is 475 determined as an IP packet. To avoid re-performing the hash or 476 hunting for the entropy label each time the packet is encapsulated 477 in a UDP tunnel it MAY be desirable that the entropy value 478 contained in the incoming packet (i.e., the UDP source port value) 479 is retained when stripping the UDP header and is re-used as the 480 entropy value of the outgoing packet. 482 5. IANA Considerations 484 This document makes no requests for IANA action. 486 6. Security Considerations 488 The security consideration of [RFC8354] and [RFC7510] apply. DTLS 489 [RFC6347] SHOULD be used where security is needed on an MPLS-SR-over- 490 UDP segment. 492 It is difficult for an attacker to pass a raw MPLS encoded packet 493 into a network and operators have considerable experience at 494 excluding such packets at the network boundaries. 496 It is easy for an ingress node to detect any attempt to smuggle an IP 497 packet into the network since it would see that the UDP destination 498 port was set to MPLS. SR packets not having a destination address 499 terminating in the network would be transparently carried and would 500 pose no security risk to the network under consideration. 502 Where control plane techniques are used (as described in 503 Authors' Addresses it is important that these protocols are 504 adequately secured for the environment in which they are run. 506 7. Contributors 508 Ahmed Bashandy 509 Individual 510 Email: abashandy.ietf@gmail.com 512 Clarence Filsfils 513 Cisco 514 Email: cfilsfil@cisco.com 516 John Drake 517 Juniper 518 Email: jdrake@juniper.net 520 Shaowen Ma 521 Juniper 522 Email: mashao@juniper.net 524 Mach Chen 525 Huawei 526 Email: mach.chen@huawei.com 528 Hamid Assarpour 529 Broadcom 530 Email:hamid.assarpour@broadcom.com 532 Robert Raszuk 533 Bloomberg LP 534 Email: robert@raszuk.net 536 Uma Chunduri 537 Huawei 538 Email: uma.chunduri@gmail.com 540 Luis M. Contreras 541 Telefonica I+D 542 Email: luismiguel.contrerasmurillo@telefonica.com 544 Luay Jalil 545 Verizon 546 Email: luay.jalil@verizon.com 548 Gunter Van De Velde 549 Nokia 550 Email: gunter.van_de_velde@nokia.com 552 Tal Mizrahi 553 Marvell 554 Email: talmi@marvell.com 556 Jeff Tantsura 557 Individual 558 Email: jefftant@gmail.com 560 8. Acknowledgements 562 Thanks to Joel Halpern, Bruno Decraene, Loa Andersson, Ron Bonica, 563 Eric Rosen, Jim Guichard, and Gunter Van De Velde for their 564 insightful comments on this draft. 566 9. References 568 9.1. Normative References 570 [I-D.ietf-isis-encapsulation-cap] 571 Xu, X., Decraene, B., Raszuk, R., Chunduri, U., Contreras, 572 L., and L. Jalil, "Advertising Tunnelling Capability in 573 IS-IS", draft-ietf-isis-encapsulation-cap-01 (work in 574 progress), April 2017. 576 [I-D.ietf-isis-segment-routing-extensions] 577 Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A., 578 Gredler, H., Litkowski, S., Decraene, B., and J. Tantsura, 579 "IS-IS Extensions for Segment Routing", draft-ietf-isis- 580 segment-routing-extensions-19 (work in progress), July 581 2018. 583 [I-D.ietf-ospf-encapsulation-cap] 584 Xu, X., Decraene, B., Raszuk, R., Contreras, L., and L. 585 Jalil, "The Tunnel Encapsulations OSPF Router 586 Information", draft-ietf-ospf-encapsulation-cap-09 (work 587 in progress), October 2017. 589 [I-D.ietf-ospf-segment-routing-extensions] 590 Psenak, P., Previdi, S., Filsfils, C., Gredler, H., 591 Shakir, R., Henderickx, W., and J. Tantsura, "OSPF 592 Extensions for Segment Routing", draft-ietf-ospf-segment- 593 routing-extensions-25 (work in progress), April 2018. 595 [I-D.ietf-spring-segment-routing-mpls] 596 Bashandy, A., Filsfils, C., Previdi, S., Decraene, B., 597 Litkowski, S., and R. Shakir, "Segment Routing with MPLS 598 data plane", draft-ietf-spring-segment-routing-mpls-14 599 (work in progress), June 2018. 601 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 602 Requirement Levels", BCP 14, RFC 2119, 603 DOI 10.17487/RFC2119, March 1997, 604 . 606 [RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol 607 Label Switching Architecture", RFC 3031, 608 DOI 10.17487/RFC3031, January 2001, 609 . 611 [RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., 612 Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack 613 Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001, 614 . 616 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 617 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 618 January 2012, . 620 [RFC7510] Xu, X., Sheth, N., Yong, L., Callon, R., and D. Black, 621 "Encapsulating MPLS in UDP", RFC 7510, 622 DOI 10.17487/RFC7510, April 2015, 623 . 625 [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., 626 Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute 627 Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 628 2015, . 630 [RFC7794] Ginsberg, L., Ed., Decraene, B., Previdi, S., Xu, X., and 631 U. Chunduri, "IS-IS Prefix Attributes for Extended IPv4 632 and IPv6 Reachability", RFC 7794, DOI 10.17487/RFC7794, 633 March 2016, . 635 [RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions 636 for Advertising Router Information", RFC 7981, 637 DOI 10.17487/RFC7981, October 2016, 638 . 640 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 641 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 642 May 2017, . 644 9.2. Informative References 646 [I-D.ietf-6man-segment-routing-header] 647 Filsfils, C., Previdi, S., Leddy, J., Matsushima, S., and 648 d. daniel.voyer@bell.ca, "IPv6 Segment Routing Header 649 (SRH)", draft-ietf-6man-segment-routing-header-14 (work in 650 progress), June 2018. 652 [I-D.ietf-mpls-spring-entropy-label] 653 Kini, S., Kompella, K., Sivabalan, S., Litkowski, S., 654 Shakir, R., and J. Tantsura, "Entropy label for SPRING 655 tunnels", draft-ietf-mpls-spring-entropy-label-12 (work in 656 progress), July 2018. 658 [RFC8354] Brzozowski, J., Leddy, J., Filsfils, C., Maglione, R., 659 Ed., and M. Townsley, "Use Cases for IPv6 Source Packet 660 Routing in Networking (SPRING)", RFC 8354, 661 DOI 10.17487/RFC8354, March 2018, 662 . 664 Authors' Addresses 666 Xiaohu Xu 667 Alibaba 669 Email: xiaohu.xxh@alibaba-inc.com 670 Stewart Bryant 671 Huawei 673 Email: stewart.bryant@gmail.com 675 Adrian Farrel 676 Juniper 678 Email: afarrel@juniper.net 680 Syed Hassan 681 Cisco 683 Email: shassan@cisco.com 685 Wim Henderickx 686 Nokia 688 Email: wim.henderickx@nokia.com 690 Zhenbin Li 691 Huawei 693 Email: lizhenbin@huawei.com