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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 MPLS Working Group Rajiv Asati 2 Internet Draft Carlos Pignataro 3 Updates: 5036, 6720 (if approved) Kamran Raza 4 Intended status: Standards Track Cisco 5 Expires: July 2015 6 Vishwas Manral 7 Hewlett-Packard, Inc 9 Rajiv Papneja 10 Huawei 12 January 11, 2015 14 Updates to LDP for IPv6 15 draft-ietf-mpls-ldp-ipv6-15 17 Status of this Memo 19 This Internet-Draft is submitted in full conformance with the 20 provisions of BCP 78 and BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF). Note that other groups may also distribute 24 working documents as Internet-Drafts. The list of current Internet- 25 Drafts is at http://datatracker.ietf.org/drafts/current/. 27 Internet-Drafts are draft documents valid for a maximum of six 28 months and may be updated, replaced, or obsoleted by other documents 29 at any time. It is inappropriate to use Internet-Drafts as 30 reference material or to cite them other than as "work in progress." 32 This Internet-Draft will expire on July 11, 2015. 34 Copyright Notice 36 Copyright (c) 2015 IETF Trust and the persons identified as the 37 document authors. All rights reserved. 39 This document is subject to BCP 78 and the IETF Trust's Legal 40 Provisions Relating to IETF Documents 41 (http://trustee.ietf.org/license-info) in effect on the date of 42 publication of this document. Please review these documents 43 carefully, as they describe your rights and restrictions with 44 respect to this document. Code Components extracted from this 45 document must include Simplified BSD License text as described in 46 Section 4.e of the Trust Legal Provisions and are provided without 47 warranty as described in the Simplified BSD License. 49 This document may contain material from IETF Documents or IETF 50 Contributions published or made publicly available before November 51 10, 2008. The person(s) controlling the copyright in some of this 52 material may not have granted the IETF Trust the right to allow 53 modifications of such material outside the IETF Standards Process. 54 Without obtaining an adequate license from the person(s) controlling 55 the copyright in such materials, this document may not be modified 56 outside the IETF Standards Process, and derivative works of it may 57 not be created outside the IETF Standards Process, except to format 58 it for publication as an RFC or to translate it into languages other 59 than English. 61 Abstract 63 The Label Distribution Protocol (LDP) specification defines 64 procedures to exchange label bindings over either IPv4, or IPv6 or 65 both networks. This document corrects and clarifies the LDP behavior 66 when IPv6 network is used (with or without IPv4). This document 67 updates RFC 5036 and RFC 6720. 69 Table of Contents 71 1. Introduction...................................................3 72 1.1. Topology Scenarios for Dual-stack Environment.............4 73 1.2. Single-hop vs. Multi-hop LDP Peering......................5 74 2. Specification Language.........................................6 75 3. LSP Mapping....................................................7 76 4. LDP Identifiers................................................7 77 5. Neighbor Discovery.............................................8 78 5.1. Basic Discovery Mechanism.................................8 79 5.1.1. Maintaining Hello Adjacencies........................9 80 5.2. Extended Discovery Mechanism..............................9 81 6. LDP Session Establishment and Maintenance......................9 82 6.1. Transport connection establishment.......................10 83 6.1.1. Determining Transport connection Roles..............11 84 6.2. LDP Sessions Maintenance.................................14 85 7. Address Distribution..........................................15 86 8. Label Distribution............................................16 87 9. LDP Identifiers and Duplicate Next Hop Addresses..............17 88 10. LDP TTL Security.............................................18 89 11. IANA Considerations..........................................18 90 12. Security Considerations......................................18 91 13. Acknowledgments..............................................19 92 14. Additional Contributors......................................19 93 15. References...................................................21 94 15.1. Normative References....................................21 95 15.2. Informative References..................................21 96 Appendix A.......................................................23 97 A.1. LDPv6 and LDPv4 Interoperability Safety Net..............23 98 A.2. Accommodating Non-RFC5036 compliant implementations......23 99 A.3. Why prohibit IPv4-mapped IPv6 addresses in LDP...........24 100 A.4. Why 32-bit value even for IPv6 LDP Router ID.............24 101 Author's Addresses...............................................25 103 1. Introduction 105 The LDP [RFC5036] specification defines procedures and messages for 106 exchanging FEC-label bindings over either IPv4 or IPv6 or both (e.g. 107 Dual-stack) networks. 109 However, RFC5036 specification has the following deficiency (or 110 lacks details) in regards to IPv6 usage (with or without IPv4): 112 1) LSP Mapping: No rule for mapping a particular packet to a 113 particular LSP that has an Address Prefix FEC element containing 114 IPv6 address of the egress router 116 2) LDP Identifier: No details specific to IPv6 usage 118 3) LDP Discovery: No details for using a particular IPv6 destination 119 (multicast) address or the source address 121 4) LDP Session establishment: No rule for handling both IPv4 and 122 IPv6 transport address optional objects in a Hello message, and 123 subsequently two IPv4 and IPv6 transport connections 125 5) LDP Address Distribution: No rule for advertising IPv4 or/and 126 IPv6 Address bindings over an LDP session 128 6) LDP Label Distribution: No rule for advertising IPv4 or/and IPv6 129 FEC-label bindings over an LDP session, and for handling the co- 130 existence of IPv4 and IPv6 FEC Elements in the same FEC TLV 132 7) Next Hop Address Resolution: No rule for accommodating the usage 133 of duplicate link-local IPv6 addresses 135 8) LDP TTL Security: No rule for built-in Generalized TTL Security 136 Mechanism (GTSM) in LDP with IPv6 (this is a deficiency in 137 RFC6720) 139 This document addresses the above deficiencies by specifying the 140 desired behavior/rules/details for using LDP in IPv6 enabled 141 networks (IPv6-only or Dual-stack networks). 143 Note that this document updates RFC5036 and RFC6720. 145 1.1. Topology Scenarios for Dual-stack Environment 147 Two LSRs may involve basic and/or extended LDP discovery in IPv6 148 and/or IPv4 address-families in various topology scenarios. 150 This document addresses the following 3 topology scenarios in which 151 the LSRs may be connected via one or more Dual-stack LDP enabled 152 interfaces (figure 1), or one or more Single-stack LDP enabled 153 interfaces (figure 2 and figure 3): 155 R1------------------R2 156 IPv4+IPv6 158 Figure 1 LSRs connected via a Dual-stack Interface 160 IPv4 161 R1=================R2 162 IPv6 164 Figure 2 LSRs connected via two Single-stack Interfaces 165 R1------------------R2---------------R3 166 IPv4 IPv6 168 Figure 3 LSRs connected via a Single-stack Interface 170 Note that the topology scenario illustrated in figure 1 also covers 171 the case of a Single-stack LDP enabled interface (IPv4, say) being 172 converted to a Dual-stacked LDP enabled interface (by enabling IPv6 173 routing as well as IPv6 LDP), even though the LDPoIPv4 session may 174 already be established between the LSRs. 176 Note that the topology scenario illustrated in figure 2 also covers 177 the case of two routers getting connected via an additional Single- 178 stack LDP enabled interface (IPv6 routing and IPv6 LDP), even though 179 the LDPoIPv4 session may already be established between the LSRs 180 over the existing interface(s). 182 This document also addresses the scenario in which the LSRs do the 183 extended discovery in IPv6 and/or IPv4 address-families: 185 IPv4 186 R1-------------------R2 187 IPv6 189 Figure 4 LSRs involving IPv4 and IPv6 address-families 191 1.2. Single-hop vs. Multi-hop LDP Peering 193 LDP TTL Security mechanism specified by this document applies only 194 to single-hop LDP peering sessions, but not to multi-hop LDP peering 195 sessions, in line with Section 5.5 of [RFC5082] that describes 196 Generalized TTL Security Mechanism (GTSM). 198 As a consequence, any LDP feature that relies on multi-hop LDP 199 peering session would not work with GTSM and will warrant 200 (statically or dynamically) disabling GTSM. Please see section 10. 202 2. Specification Language 204 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 205 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 206 document are to be interpreted as described in [RFC2119]. 208 Abbreviations: 210 LDP - Label Distribution Protocol 212 LDPoIPv4 - LDP over IPv4 transport connection 214 LDPoIPv6 - LDP over IPv6 transport connection 216 FEC - Forwarding Equivalence Class 218 TLV - Type Length Value 220 LSR - Label Switching Router 222 LSP - Label Switched Path 224 LSPv4 - IPv4-signaled Label Switched Path [RFC4798] 226 LSPv6 - IPv6-signaled Label Switched Path [RFC4798] 228 AFI - Address Family Identifier 230 LDP Id - LDP Identifier 232 Single-stack LDP - LDP supporting just one address family (for 233 discovery, session setup, address/label binding 234 exchange etc.) 236 Dual-stack LDP - LDP supporting two address families (for 237 discovery, session setup, address/label binding 238 exchange etc.) 240 Dual-stack LSR - LSR supporting Dual-stack LDP for a peer 242 Single-stack LSR - LSR supporting Single-stack LDP for a peer 244 Note that an LSR can be a Dual-stack and Single-stack LSR at the 245 same time for different peers. This document loosely uses the term 246 address family to mean IP address family. 248 3. LSP Mapping 250 Section 2.1 of [RFC5036] specifies the procedure for mapping a 251 particular packet to a particular LSP using three rules. Quoting the 252 3rd rule from RFC5036: 254 "If it is known that a packet must traverse a particular egress 255 router, and there is an LSP that has an Address Prefix FEC element 256 that is a /32 address of that router, then the packet is mapped to 257 that LSP." 259 This rule is correct for IPv4, but not for IPv6, since an IPv6 260 router may even have a /64 or /96 or /128 (or whatever prefix 261 length) address. Hence, it is reasonable to say IPv4 or IPv6 address 262 instead of /32 or /128 addresses as shown below in the updated rule: 264 "If it is known that a packet must traverse a particular egress 265 router, and there is an LSP that has an Address Prefix FEC element 266 that is an IPv4 or IPv6 address of that router, then the packet is 267 mapped to that LSP." 269 4. LDP Identifiers 271 In line with section 2.2.2 of [RFC5036], this document specifies the 272 usage of 32-bit (unsigned non-zero integer) LSR Id on an IPv6 273 enabled LSR (with or without Dual-stacking). 275 This document also qualifies the first sentence of last paragraph of 276 Section 2.5.2 of [RFC5036] to be per address family and therefore 277 updates that sentence to the following: 279 "For a given address family, an LSR MUST advertise the same 280 transport address in all Hellos that advertise the same label 281 space." 283 This rightly enables the per-platform label space to be shared 284 between IPv4 and IPv6. 286 In summary, this document mandates the usage of a common LDP 287 identifier (same LSR Id aka LDP Router Id as well as a common Label 288 space id) for both IPv4 and IPv6 address families. 290 5. Neighbor Discovery 292 If Dual-stack LDP is enabled (e.g. LDP enabled in both IPv6 and IPv4 293 address families) on an interface or for a targeted neighbor, then 294 the LSR MUST transmit both IPv6 and IPv4 LDP (Link or targeted) 295 Hellos and include the same LDP Identifier (assuming per-platform 296 label space usage) in them. 298 If Single-stack LDP is enabled (e.g. LDP enabled in either IPv6 or 299 IPv4 address family), then the LSR MUST transmit either IPv6 or IPv4 300 LDP (Link or targeted) Hellos respectively. 302 5.1. Basic Discovery Mechanism 304 Section 2.4.1 of [RFC5036] defines the Basic Discovery mechanism for 305 directly connected LSRs. Following this mechanism, LSRs periodically 306 send LDP Link Hellos destined to "all routers on this subnet" group 307 multicast IP address. 309 Interesting enough, per the IPv6 addressing architecture [RFC4291], 310 IPv6 has three "all routers on this subnet" multicast addresses: 312 FF01:0:0:0:0:0:0:2 = Interface-local scope 314 FF02:0:0:0:0:0:0:2 = Link-local scope 316 FF05:0:0:0:0:0:0:2 = Site-local scope 318 [RFC5036] does not specify which particular IPv6 'all routers on 319 this subnet' group multicast IP address should be used by LDP Link 320 Hellos. 322 This document specifies the usage of link-local scope e.g. 323 FF02:0:0:0:0:0:0:2 as the destination multicast IP address in IPv6 324 LDP Link Hellos. An LDP Link Hello packet received on any of the 325 other destination addresses MUST be dropped. Additionally, the link- 326 local IPv6 address MUST be used as the source IP address in IPv6 LDP 327 Link Hellos. 329 Also, the LDP Link Hello packets MUST have their IPv6 Hop Limit set 330 to 255, be checked for the same upon receipt (before any LDP 331 specific processing) and be handled as specified in Generalized TTL 332 Security Mechanism (GTSM) section 3 of [RFC5082]. The built-in 333 inclusion of GTSM automatically protects IPv6 LDP from off-link 334 attacks. 336 More importantly, if an interface is a Dual-stack LDP interface 337 (e.g. LDP enabled in both IPv6 and IPv4 address families), then the 338 LSR MUST periodically transmit both IPv6 and IPv4 LDP Link Hellos 339 (using the same LDP Identifier per section 4) on that interface and 340 be able to receive them. This facilitates discovery of IPv6-only, 341 IPv4-only and Dual-stack peers on the interface's subnet and ensures 342 successful subsequent peering using the appropriate (address family) 343 transport on a multi-access or broadcast interface. 345 An implementation MUST transmit IPv6 LDP link Hellos before IPv4 LDP 346 Link Hellos on a Dual-stack interface, particularly during the 347 interface coming into service or configuration time. 349 5.1.1. Maintaining Hello Adjacencies 351 In case of Dual-stack LDP enabled interface, the LSR SHOULD maintain 352 link Hello adjacencies for both IPv4 and IPv6 address families. This 353 document, however, allows an LSR to maintain Rx-side Link Hello 354 adjacency only for the address family that has been used for the 355 establishment of the LDP session (whether LDPoIPv4 or LDPoIPv6 356 session). 358 5.2. Extended Discovery Mechanism 360 The extended discovery mechanism (defined in section 2.4.2 of 361 [RFC5036]), in which the targeted LDP Hellos are sent to a unicast 362 IPv6 address destination, requires only one IPv6 specific 363 consideration: the link-local IPv6 addresses MUST NOT be used as the 364 targeted LDP hello packet's source or destination addresses. 366 6. LDP Session Establishment and Maintenance 368 Section 2.5.1 of [RFC5036] defines a two-step process for LDP 369 session establishment, once the neighbor discovery has completed 370 (i.e. LDP Hellos have been exchanged): 372 1. Transport connection establishment 373 2. Session initialization 375 The forthcoming sub-section 6.1 discusses the LDP consideration for 376 IPv6 and/or Dual-stacking in the context of session establishment, 377 whereas sub-section 6.2 discusses the LDP consideration for IPv6 378 and/or Dual-stacking in the context of session maintenance. 380 6.1. Transport connection establishment 382 Section 2.5.2 of [RFC5036] specifies the use of an optional 383 transport address object (TLV) in LDP Hello message to convey the 384 transport (IP) address, however, it does not specify the behavior of 385 LDP if both IPv4 and IPv6 transport address objects (TLV) are sent 386 in a Hello message or separate Hello messages. More importantly, it 387 does not specify whether both IPv4 and IPv6 transport connections 388 should be allowed, if both IPv4 and IPv6 Hello adjacencies were 389 present prior to the session establishment. 391 This document specifies that: 393 1. An LSR MUST NOT send a Hello message containing both IPv4 and 394 IPv6 transport address optional objects. In other words, there 395 MUST be at most one optional Transport Address object in a 396 Hello message. An LSR MUST include only the transport address 397 whose address family is the same as that of the IP packet 398 carrying the Hello message. 400 2. An LSR SHOULD accept the Hello message that contains both IPv4 401 and IPv6 transport address optional objects, but MUST use only 402 the transport address whose address family is the same as that 403 of the IP packet carrying the Hello message. An LSR SHOULD 404 accept only the first transport object for a given address 405 family in the received Hello message, and ignore the rest, if 406 the LSR receives more than one transport object for a given 407 address family. 409 3. An LSR MUST send separate Hello messages (each containing 410 either IPv4 or IPv6 transport address optional object) for each 411 IP address family, if Dual-stack LDP was enabled. 413 4. An LSR MUST use a global unicast IPv6 address in IPv6 transport 414 address optional object of outgoing targeted Hellos, and check 415 for the same in incoming targeted hellos (i.e. MUST discard the 416 targeted hello, if it failed the check). 418 5. An LSR MUST prefer using a global unicast IPv6 address in IPv6 419 transport address optional object of outgoing Link Hellos, if 420 it had to choose between global unicast IPv6 address and 421 unique-local or link-local IPv6 address. 423 6. A Single-stack LSR MUST establish LDPoIPv4 or LDPoIPv6 session 424 with a remote LSR as per the enabled address-family. 426 7. A Dual-stack LSR MUST NOT initiate (or accept the request for) 427 a TCP connection for a new LDP session with a remote LSR, if 428 they already have an LDPoIPv4 or LDPoIPv6 session (for the same 429 LDP Identifier) established. 431 This means that only one transport connection is established 432 regardless of IPv6 or/and IPv4 Hello adjacencies presence 433 between two LSRs. 435 8. A Dual-stack LSR MUST prefer establishing LDPoIPv6 session with 436 a remote LSR by following the 'transport connection role' 437 determination logic in section 6.1.1. 439 6.1.1. Determining Transport connection Roles 441 Section 2.5.2 of [RFC5036] specifies the rules for determining 442 active/passive roles in setting up TCP connection. These rules are 443 clear for a Single-stack LDP, but not for a Dual-stack LDP, in which 444 an LSR may assume different roles for different address families, 445 causing LDP session to not get established. 447 To ensure deterministic transport connection (active/passive) role 448 in case of Dual-stack LDP, this document specifies that the Dual- 449 stack LSR convey its transport connection preference in every LDP 450 Hello message. This preference is encoded in a new TLV, named Dual- 451 stack capability TLV, as defined below: 453 0 1 2 3 454 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 9 0 1 455 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 456 |1|0| Dual-stack capability | Length | 457 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 458 |TR | Reserved | MBZ | 459 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 461 Figure 5 Dual-stack capability TLV 463 Where: 465 U and F bits: 1 and 0 (as specified by RFC5036) 467 Dual-stack capability: TLV code point (to be assigned by IANA). 469 TR, Transport Connection Preference. 471 This document defines the following 2 values: 473 0100: LDPoIPv4 connection 475 0110: LDPoIPv6 connection (default) 477 Reserved 479 This field is reserved. It MUST be set to zero on 480 transmission and ignored on receipt. 482 A Dual-stack LSR (i.e. LSR supporting Dual-stack LDP for a peer) 483 MUST include "Dual-stack capability" TLV in all of its LDP Hellos, 484 and MUST set the "TR" field to announce its preference for either 485 LDPoIPv4 or LDPoIPv6 transport connection for that peer. The default 486 preference is LDPoIPv6. 488 A Dual-stack LSR MUST always check for the presence of "Dual-stack 489 capability" TLV in the received hello messages, and take appropriate 490 actions as follows: 492 1. If "Dual-stack capability" TLV is present and remote preference 493 does not match with the local preference (or does not get 494 recognized), then the LSR MUST discard the hello message and 495 log an error. 497 If LDP session was already in place, then LSR MUST send a fatal 498 Notification message with status code [Transport Connection 499 mismatch, IANA allocation TBD] and reset the session. 501 2. If "Dual-stack capability" TLV is present, and remote 502 preference matches with the local preference, then: 504 a) If TR=0100 (LDPoIPv4), then determine the active/passive 505 roles for TCP connection using IPv4 transport address as 506 defined in section 2.5.2 of RFC 5036. 508 b) If TR=0110 (LDPoIPv6), then determine the active/passive 509 roles for TCP connection by using IPv6 transport address 510 as defined in section 2.5.2 of RFC 5036. 512 3. If "Dual-stack capability" TLV is NOT present, and 514 a) Only IPv4 hellos are received, then the neighbor is deemed 515 as a legacy IPv4-only LSR (supporting Single-stack LDP), 516 hence, an LDPoIPv4 session SHOULD be established (similar 517 to that of 2a above). 519 However, if IPv6 hellos are also received at any time from 520 that neighbor, then the neighbor is deemed as a non- 521 compliant Dual-stack LSR (similar to that of 3c below), 522 resulting in any established LDPoIPv4 session being reset 523 and a fatal Notification message being sent (with status 524 code of 'Dual-Stack Non-Compliance', IANA allocation TBD). 526 b) Only IPv6 hellos are received, then the neighbor is deemed 527 as an IPv6-only LSR (supporting Single-stack LDP) and 528 LDPoIPv6 session SHOULD be established (similar to that of 529 2b above). 531 However, if IPv4 hellos are also received at any time from 532 that neighbor, then the neighbor is deemed as a non- 533 compliant Dual-stack LSR (similar to that of 3c below), 534 resulting in any established LDPoIPv6 session being reset 535 and a fatal Notification message being sent (with status 536 code of 'Dual-Stack Non-Compliance', IANA allocation TBD). 538 c) Both IPv4 and IPv6 hellos are received, then the neighbor 539 is deemed as a non-compliant Dual-stack neighbor, and is 540 not allowed to have any LDP session. A Notification 541 message should be sent (with status code of 'Dual-Stack 542 Non-Compliance', IANA allocation TBD). 544 A Dual-stack LSR MUST convey the same transport connection 545 preference ("TR" field value) in all (link and targeted) Hellos that 546 advertise the same label space to the same peer and/or on same 547 interface. This ensures that two LSRs linked by multiple Hello 548 adjacencies using the same label spaces play the same connection 549 establishment role for each adjacency. 551 A Dual-stack LSR MUST follow section 2.5.5 of RFC5036 and check for 552 matching Hello messages from the peer (either all Hellos also 553 include the Dual-stack capability (with same TR value) or none do). 555 A Single-stack LSR do not need to use the Dual-stack capability in 556 hello messages and SHOULD ignore this capability, if received. 558 An implementation may provide an option to favor one AFI (IPv4, say) 559 over another AFI (IPv6, say) for the TCP transport connection, so as 560 to use the favored IP version for the LDP session, and force 561 deterministic active/passive roles. 563 Note - An alternative to this new Capability TLV could be a new Flag 564 value in LDP Hello message, however, it will get used even in a 565 Single-stack IPv6 LDP networks and linger on forever, even though 566 Dual-stack will not. Hence, this alternative is discarded. 568 6.2. LDP Sessions Maintenance 570 This document specifies that two LSRs maintain a single LDP session 571 regardless of number of Link or Targeted Hello adjacencies between 572 them, as described in section 6.1. This is independent of whether: 574 - they are connected via a Dual-stack LDP enabled interface(s) or 575 via two (or more) Single-stack LDP enabled interfaces; 576 - a Single-stack LDP enabled interface is converted to a Dual-stack 577 LDP enabled interface (e.g. figure 1) on either LSR; 578 - an additional Single-stack or Dual-stack LDP enabled interface is 579 added or removed between two LSRs (e.g. figure 2). 581 The procedures defined in section 6.1 SHOULD result in setting up 582 the LDP session in preferred AFI only after the loss of an existing 583 LDP session (because of link failure, node failure, reboot etc.). 585 If the last hello adjacency for a given address family goes down 586 (e.g. due to Dual-stack LDP enabled interfaces being converted into 587 a Single-stack LDP enabled interfaces on one LSR etc.), and that 588 address family is the same as the one used in the transport 589 connection, then the transport connection (LDP session) MUST be 590 reset. Otherwise, the LDP session MUST stay intact. 592 If the LDP session is torn down for whatever reason (LDP disabled 593 for the corresponding transport, hello adjacency expiry, preference 594 mismatch etc.), then the LSRs SHOULD initiate establishing a new LDP 595 session as per the procedures described in section 6.1 of this 596 document. 598 7. Binding Distribution 600 LSRs by definition can be enabled for Dual-stack LDP globally and/or 601 per peer so as to exchange the address and label bindings for both 602 IPv4 and IPv6 address-families, independent of LDPoIPv4 or LDPoIPV6 603 session between them. 605 However, there might be some legacy LSRs that are fully RFC 5036 606 compliant for IPv4, but non-compliant for IPv6 (say, section 3.5.5.1 607 of RFC 5036), causing them to reset the session upon receiving IPv6 608 address bindings or IPv6 FEC (Prefix) label bindings from a peer 609 compliant with this document. This is somewhat undesirable, as 610 clarified further Appendix A.1 and A.2. 612 To help maintain backward compatibility (i.e. accommodate IPv4-only 613 LDP implementations that may not be compliant with RFC 5036 section 614 3.5.5.1 ), this specification requires that an LSR MUST NOT send 615 any IPv6 bindings to a peer if peer has been determined as a legacy 616 LSR. 618 The 'Dual-stack capability' TLV, which is defined in section 6.1.1, 619 is also used to determine if a peer is a legacy (IPv4-only Single- 620 stack) LSR or not. 622 7.1. Address Distribution 624 An LSR MUST NOT advertise (via ADDRESS message) any IPv4-mapped IPv6 625 addresses (defined in section 2.5.5.2 of [RFC4291]), and ignore such 626 addresses, if ever received. Please see Appendix A.3. 628 If an LSR is enabled with Single-stack LDP for any peer, then it 629 MUST advertise (via ADDRESS message) its local IP addresses as per 630 the enabled address family to that peer, and process received 631 Address messages containing IP addresses as per the enabled address 632 family from that peer. 634 If an LSR is enabled with Dual-stack LDP for a peer and 636 1. Is NOT able to find the Dual-stack capability TLV in the 637 incoming IPv4 LDP hello messages from that peer, then the LSR 638 MUST NOT advertise its local IPv6 Addresses to the peer. 640 2. Is able to find the Dual-stack capability in the incoming IPv4 641 (or IPv6) LDP Hello messages from that peer, then it MUST 642 advertise (via ADDRESS message) its local IPv4 and IPv6 643 addresses to that peer. 645 3. Is NOT able to find the Dual-stack capability in the incoming 646 IPv6 LDP Hello messages, then it MUST advertise (via ADDRESS 647 message) only its local IPv6 addresses to that peer. 649 This last point helps to maintain forward compatibility (no 650 need to require this TLV in case of IPv6 Single-stack LDP). 652 7.2. Label Distribution 654 An LSR MUST NOT allocate and MUST NOT advertise FEC-Label bindings 655 for link-local or IPv4-mapped IPv6 addresses (defined in section 656 2.5.5.2 of [RFC4291]), and ignore such bindings, if ever received. 657 Please see Appendix A.3. 659 If an LSR is enabled with Single-stack LDP for any peer, then it 660 MUST advertise (via Label Mapping message) FEC-Label bindings for 661 the enabled address family to that peer, and process received FEC- 662 Label bindings for the enabled address family from that peer. 664 If an LSR is enabled with Dual-stack LDP for a peer and 666 1. Is NOT able to find the Dual-stack capability TLV in the 667 incoming IPv4 LDP hello messages from that peer, then the LSR 668 MUST NOT advertise IPv6 FEC-label bindings to the peer (even if 669 IP capability negotiation for IPv6 address family was done). 671 2. Is able to find the Dual-stack capability in the incoming IPv4 672 (or IPv6) LDP Hello messages from that peer, then it MUST 673 advertise FEC-Label bindings for both IPv4 and IPv6 address 674 families to that peer. 676 3. Is NOT able to find the Dual-stack capability in the incoming 677 IPv6 LDP Hello messages, then it MUST advertise FEC-Label 678 bindings for IPv6 address families to that peer. 680 This last point helps to maintain forward compatibility (no 681 need to require this TLV for IPv6 Single-stack LDP). 683 An LSR MAY further constrain the advertisement of FEC-label bindings 684 for a particular address family by negotiating the IP Capability for 685 a given address family, as specified in [IPPWCap] document. This 686 allows an LSR pair to neither advertise nor receive the undesired 687 FEC-label bindings on a per address family basis to a peer. 689 If an LSR is configured to change an interface or peer from Single- 690 stack LDP to Dual-stack LDP, then an LSR SHOULD use Typed Wildcard 691 FEC procedures [RFC5918] to request the label bindings for the 692 enabled address family. This helps to relearn the label bindings 693 that may have been discarded before without resetting the session. 695 8. LDP Identifiers and Duplicate Next Hop Addresses 697 RFC5036 section 2.7 specifies the logic for mapping the IP routing 698 next-hop (of a given FEC) to an LDP peer so as to find the correct 699 label entry for that FEC. The logic involves using the IP routing 700 next-hop address as an index into the (peer Address) database (which 701 is populated by the Address message containing mapping between each 702 peer's local addresses and its LDP Identifier) to determine the LDP 703 peer. 705 However, this logic is insufficient to deal with duplicate IPv6 706 (link-local) next-hop addresses used by two or more peers. The 707 reason is that all interior IPv6 routing protocols (can) use link- 708 local IPv6 addresses as the IP routing next-hops, and 'IPv6 709 Addressing Architecture [RFC4291]' allows a link-local IPv6 address 710 to be used on more than one links. 712 Hence, this logic is extended by this specification to use not only 713 the IP routing next-hop address, but also the IP routing next-hop 714 interface to uniquely determine the LDP peer(s). The next-hop 715 address-based LDP peer mapping is to be done through LDP peer 716 address database (populated by Address messages received from the 717 LDP peers), whereas next-hop interface-based LDP peer mapping is to 718 be done through LDP hello adjacency/interface database (populated by 719 hello messages received from the LDP peers). 721 This extension solves the problem of two or more peers using the 722 same link-local IPv6 address (in other words, duplicate peer 723 addresses) as the IP routing next-hops. 725 Lastly, for better scale and optimization, an LSR may advertise only 726 the link-local IPv6 addresses in the Address message, assuming that 727 the peer uses only the link-local IPv6 addresses as static and/or 728 dynamic IP routing next-hops. 730 9. LDP TTL Security 732 This document recommends enabling Generalized TTL Security Mechanism 733 (GTSM) for LDP, as specified in [RFC6720], for the LDP/TCP transport 734 connection over IPv6 (i.e. LDPoIPv6). The GTSM inclusion is intended 735 to automatically protect IPv6 LDP peering session from off-link 736 attacks. 738 [RFC6720] allows for the implementation to statically 739 (configuration) and/or dynamically override the default behavior 740 (enable/disable GTSM) on a per-peer basis. Suffice to say that such 741 an option could be set on either LSR (since GTSM negotiation would 742 ultimately disable GTSM between LSR and its peer(s)). 744 LDP Link Hello packets MUST have their IPv6 Hop Limit set to 255, 745 and be checked for the same upon receipt before any further 746 processing, as per section 3 of [RFC5082]. 748 10. IANA Considerations 750 This document defines a new optional parameter for the LDP Hello 751 Message and two new status codes for the LDP Notification Message. 753 The 'Dual-Stack capability' parameter requires a code point from the 754 TLV Type Name Space. IANA is requested to allocated a code point 755 from the IETF Consensus range 0x0700-0x07ff for the 'Dual-Stack 756 capability' TLV. 758 The 'Transport Connection Mismatch' status code requires a code 759 point from the Status Code Name Space. IANA is requested to allocate 760 a code point from the IETF Consensus range and mark the E bit column 761 with a '1'. 763 The 'Dual-Stack Non-Compliance' status code requires a code point 764 from the Status Code Name Space. IANA is requested to allocate a 765 code point from the IETF Consensus range and mark the E bit column 766 with a '1'. 768 11. Security Considerations 770 The extensions defined in this document only clarify the behavior of 771 LDP, they do not define any new protocol procedures. Hence, this 772 document does not add any new security issues to LDP. 774 While the security issues relevant for the [RFC5036] are relevant 775 for this document as well, this document reduces the chances of off- 776 link attacks when using IPv6 transport connection by including the 777 use of GTSM procedures [RFC5082]. Please see section 9 for LDP TTL 778 Security details. 780 Moreover, this document allows the use of IPsec [RFC4301] for IPv6 781 protection, hence, LDP can benefit from the additional security as 782 specified in [RFC7321] as well as [RFC5920]. 784 12. Acknowledgments 786 We acknowledge the authors of [RFC5036], since some text in this 787 document is borrowed from [RFC5036]. 789 Thanks to Bob Thomas for providing critical feedback to improve this 790 document early on. 792 Many thanks to Eric Rosen, Lizhong Jin, Bin Mo, Mach Chen, Shane 793 Amante, Pranjal Dutta, Mustapha Aissaoui, Matthew Bocci, Mark Tinka, 794 Tom Petch, Kishore Tiruveedhula, Manoj Dutta, Vividh Siddha, Qin Wu, 795 Simon Perreault, Brian E Carpenter, Santosh Esale, Danial Johari and 796 Loa Andersson for thoroughly reviewing this document, and providing 797 insightful comments and multiple improvements. 799 This document was prepared using 2-Word-v2.0.template.dot. 801 13. Additional Contributors 803 The following individuals contributed to this document: 805 Kamran Raza 806 Cisco Systems, Inc. 807 2000 Innovation Drive 808 Kanata, ON K2K-3E8, Canada 809 Email: skraza@cisco.com 810 Nagendra Kumar 811 Cisco Systems, Inc. 812 SEZ Unit, Cessna Business Park, 813 Bangalore, KT, India 814 Email: naikumar@cisco.com 816 Andre Pelletier 817 Cisco Systems, Inc. 818 2000 Innovation Drive 819 Kanata, ON K2K-3E8, Canada 820 Email: apelleti@cisco.com 822 14. References 824 14.1. Normative References 826 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 827 Requirement Levels", BCP 14, RFC 2119, March 1997. 829 [RFC4291] Hinden, R. and S. Deering, "Internet Protocol Version 6 830 (IPv6) Addressing Architecture", RFC 4291, February 2006. 832 [RFC5036] Andersson, L., Minei, I., and Thomas, B., "LDP 833 Specification", RFC 5036, October 2007. 835 [RFC5082] Pignataro, C., Gill, V., Heasley, J., Meyer, D., and 836 Savola, P., "The Generalized TTL Security Mechanism 837 (GTSM)", RFC 5082, October 2007. 839 [RFC5918] Asati, R., Minei, I., and Thomas, B., "Label Distribution 840 Protocol (LDP) 'Typed Wildcard Forward Equivalence Class 841 (FEC)", RFC 5918, October 2010. 843 14.2. Informative References 845 [RFC4301] Kent, S. and K. Seo, "Security Architecture and Internet 846 Protocol", RFC 4301, December 2005. 848 [RFC7321] Manral, V., "Cryptographic Algorithm Implementation 849 Requirements for Encapsulating Security Payload (ESP) and 850 Authentication Header (AH)", RFC 7321, April 2007. 852 [RFC5920] Fang, L., "Security Framework for MPLS and GMPLS 853 Networks", RFC 5920, July 2010. 855 [RFC4798] De Clercq, et al., "Connecting IPv6 Islands over IPv4 MPLS 856 Using IPv6 Provider Edge Routers (6PE)", RFC 4798, 857 February 2007. 859 [IPPWCap] Raza, K., "LDP IP and PW Capability", draft-ietf-mpls-ldp- 860 ip-pw-capability, October 2014. 862 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 863 for IPv6", RFC 5340, July 2008. 865 [RFC6286] E. Chen, and J. Yuan, "Autonomous-System-Wide Unique BGP 866 Identifier for BGP-4", RFC 6286, June 2011. 868 [RFC6720] R. Asati, and C. Pignataro, "The Generalized TTL Security 869 Mechanism (GTSM) for the Label Distribution Protocol 870 (LDP)", RFC 6720, August 2012. 872 [RFC4038] M-K. Shin, Y-G. Hong, J. Hagino, P. Savola, and E. M. 873 Castro, "Application Aspects of IPv6 Transition", RFC 874 4038, March 2005. 876 Appendix A. 878 A.1. LDPv6 and LDPv4 Interoperability Safety Net 880 It is not safe to assume that RFC5036 compliant implementations have 881 supported handling IPv6 address family (IPv6 FEC label) in Label 882 Mapping message all along. 884 If a router upgraded with this specification advertised both IPv4 885 and IPv6 FECs in the same label mapping message, then an IPv4-only 886 peer (not knowing how to process such a message) may abort 887 processing the entire label mapping message (thereby discarding even 888 the IPv4 label FECs), as per the section 3.4.1.1 of RFC5036. 890 This would result in LDPv6 to be somewhat undeployable in existing 891 production networks. 893 The change proposed in section 8 of this document provides a good 894 safety net and makes LDPv6 incrementally deployable without making 895 any such assumption on the routers' support for IPv6 FEC processing 896 in current production networks. 898 A.2. Accommodating Non-RFC5036-compliant implementations 900 It is not safe to assume that implementations have been RFC5036 901 compliant in gracefully handling IPv6 address family (IPv6 Address 902 List TLV) in Address message all along. 904 If a router upgraded with this specification advertised IPv6 905 addresses (with or without IPv4 addresses) in Address message, then 906 an IPv4-only peer (not knowing how to process such a message) may 907 not follow section 3.5.5.1 of RFC5036, and tear down the LDP 908 session. 910 This would result in LDPv6 to be somewhat undeployable in existing 911 production networks. 913 The change proposed in section 7 of this document provides a good 914 safety net and makes LDPv6 incrementally deployable without making 915 any such assumption on the routers' support for IPv6 FEC processing 916 in current production networks. 918 A.3. Why prohibit IPv4-mapped IPv6 addresses in LDP 920 Per discussion with 6MAN and V6OPS working groups, the overwhelming 921 consensus was to not promote IPv4-mapped IPv6 addresses appear in 922 the routing table, as well as in LDP (address and label) databases. 924 Also, [RFC4038] section 4.2 suggests that IPv4-mapped IPv6 addressed 925 packets should never appear on the wire. 927 A.4. Why 32-bit value even for IPv6 LDP Router ID 929 The first four octets of the LDP identifier, the 32-bit LSR Id (e.g. 930 (i.e. LDP Router Id), identify the LSR and is a globally unique 931 value within the MPLS network. This is regardless of the address 932 family used for the LDP session. 934 Please note that 32-bit LSR Id value would not map to any IPv4- 935 address in an IPv6 only LSR (i.e., single stack), nor would there be 936 an expectation of it being IP routable, nor DNS-resolvable. In IPv4 937 deployments, the LSR Id is typically derived from an IPv4 address, 938 generally assigned to a loopback interface. In IPv6 only 939 deployments, this 32-bit LSR Id must be derived by some other means 940 that guarantees global uniqueness within the MPLS network, similar 941 to that of BGP Identifier [RFC6286] and OSPF router ID [RFC5340]. 943 This document reserves 0.0.0.0 as the LSR Id, and prohibits its 944 usage with IPv6, in line with OSPF router Id in OSPF version 3 945 [RFC5340]. 947 Author's Addresses 949 Vishwas Manral 950 Hewlet-Packard, Inc. 951 19111 Pruneridge Ave., Cupertino, CA, 95014 952 Phone: 408-447-1497 953 Email: vishwas.manral@hp.com 955 Rajiv Papneja 956 Huawei Technologies 957 2330 Central Expressway 958 Santa Clara, CA 95050 959 Phone: +1 571 926 8593 960 EMail: rajiv.papneja@huawei.com 962 Rajiv Asati 963 Cisco Systems, Inc. 964 7025 Kit Creek Road 965 Research Triangle Park, NC 27709-4987 966 Email: rajiva@cisco.com 968 Carlos Pignataro 969 Cisco Systems, Inc. 970 7200 Kit Creek Road 971 Research Triangle Park, NC 27709-4987 972 Email: cpignata@cisco.com