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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: August 2015 6 Vishwas Manral 7 Hewlett-Packard, Inc 9 Rajiv Papneja 10 Huawei 12 February 26, 2015 14 Updates to LDP for IPv6 15 draft-ietf-mpls-ldp-ipv6-17 17 Abstract 19 The Label Distribution Protocol (LDP) specification defines 20 procedures to exchange label bindings over either IPv4, or IPv6 or 21 both networks. This document corrects and clarifies the LDP behavior 22 when IPv6 network is used (with or without IPv4). This document 23 updates RFC 5036 and RFC 6720. 25 Status of this Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at http://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six 36 months and may be updated, replaced, or obsoleted by other documents 37 at any time. It is inappropriate to use Internet-Drafts as 38 reference material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on August 26, 2015. 42 Copyright Notice 43 Copyright (c) 2015 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents 48 (http://trustee.ietf.org/license-info) in effect on the date of 49 publication of this document. Please review these documents 50 carefully, as they describe your rights and restrictions with 51 respect to this document. Code Components extracted from this 52 document must include Simplified BSD License text as described in 53 Section 4.e of the Trust Legal Provisions and are provided without 54 warranty as described in the Simplified BSD License. 56 This document may contain material from IETF Documents or IETF 57 Contributions published or made publicly available before November 58 10, 2008. The person(s) controlling the copyright in some of this 59 material may not have granted the IETF Trust the right to allow 60 modifications of such material outside the IETF Standards Process. 61 Without obtaining an adequate license from the person(s) controlling 62 the copyright in such materials, this document may not be modified 63 outside the IETF Standards Process, and derivative works of it may 64 not be created outside the IETF Standards Process, except to format 65 it for publication as an RFC or to translate it into languages other 66 than English. 68 Table of Contents 70 1. Introduction...................................................3 71 1.1. Topology Scenarios for Dual-stack Environment.............4 72 1.2. Single-hop vs. Multi-hop LDP Peering......................5 73 2. Specification Language.........................................6 74 3. LSP Mapping....................................................7 75 4. LDP Identifiers................................................7 76 5. Neighbor Discovery.............................................8 77 5.1. Basic Discovery Mechanism.................................8 78 5.1.1. Maintaining Hello Adjacencies........................9 79 5.2. Extended Discovery Mechanism..............................9 80 6. LDP Session Establishment and Maintenance......................9 81 6.1. Transport connection establishment.......................10 82 6.1.1. Determining Transport connection Roles..............11 83 6.2. LDP Sessions Maintenance.................................14 84 7. Binding Distribution..........................................15 85 7.1. Address Distribution.....................................15 86 7.2. Label Distribution.......................................16 88 8. LDP Identifiers and Duplicate Next Hop Addresses..............17 89 9. LDP TTL Security..............................................18 90 10. IANA Considerations..........................................18 91 11. Security Considerations......................................18 92 12. Acknowledgments..............................................19 93 13. Additional Contributors......................................19 94 14. References...................................................21 95 14.1. Normative References....................................21 96 14.2. Informative References..................................21 97 Appendix A.......................................................23 98 A.1. LDPv6 and LDPv4 Interoperability Safety Net..............23 99 A.2. Accommodating Non-RFC5036-compliant implementations......23 100 A.3. Why prohibit IPv4-mapped IPv6 addresses in LDP...........24 101 A.4. Why 32-bit value even for IPv6 LDP Router ID.............24 102 Author's Addresses...............................................25 104 1. Introduction 106 The LDP [RFC5036] specification defines procedures and messages for 107 exchanging FEC-label bindings over either IPv4 or IPv6 or both (e.g. 108 Dual-stack) networks. 110 However, RFC5036 specification has the following deficiency (or 111 lacks details) in regards to IPv6 usage (with or without IPv4): 113 1) LSP Mapping: No rule for mapping a particular packet to a 114 particular LSP that has an Address Prefix FEC element containing 115 IPv6 address of the egress router 117 2) LDP Identifier: No details specific to IPv6 usage 119 3) LDP Discovery: No details for using a particular IPv6 destination 120 (multicast) address or the source address 122 4) LDP Session establishment: No rule for handling both IPv4 and 123 IPv6 transport address optional objects in a Hello message, and 124 subsequently two IPv4 and IPv6 transport connections 126 5) LDP Address Distribution: No rule for advertising IPv4 or/and 127 IPv6 Address bindings over an LDP session 129 6) LDP Label Distribution: No rule for advertising IPv4 or/and IPv6 130 FEC-label bindings over an LDP session, and for handling the co- 131 existence of IPv4 and IPv6 FEC Elements in the same FEC TLV 133 7) Next Hop Address Resolution: No rule for accommodating the usage 134 of duplicate link-local IPv6 addresses 136 8) LDP TTL Security: No rule for built-in Generalized TTL Security 137 Mechanism (GTSM) in LDP with IPv6 (this is a deficiency in 138 RFC6720) 140 This document addresses the above deficiencies by specifying the 141 desired behavior/rules/details for using LDP in IPv6 enabled 142 networks (IPv6-only or Dual-stack networks). This document closes 143 the IPv6 MPLS gap discussed in Sections 3.2.1, 3.2.2, and 3.3.1.1 of 144 [RFC7439]. 146 Note that this document updates RFC5036 and RFC6720. 148 1.1. Topology Scenarios for Dual-stack Environment 150 Two LSRs may involve basic and/or extended LDP discovery in IPv6 151 and/or IPv4 address-families in various topology scenarios. 153 This document addresses the following 3 topology scenarios in which 154 the LSRs may be connected via one or more Dual-stack LDP enabled 155 interfaces (figure 1), or one or more Single-stack LDP enabled 156 interfaces (figure 2 and figure 3): 158 R1------------------R2 159 IPv4+IPv6 161 Figure 1 LSRs connected via a Dual-stack Interface 163 IPv4 164 R1=================R2 165 IPv6 167 Figure 2 LSRs connected via two Single-stack Interfaces 168 R1------------------R2---------------R3 169 IPv4 IPv6 171 Figure 3 LSRs connected via a Single-stack Interface 173 Note that the topology scenario illustrated in figure 1 also covers 174 the case of a Single-stack LDP enabled interface (IPv4, say) being 175 converted to a Dual-stacked LDP enabled interface (by enabling IPv6 176 routing as well as IPv6 LDP), even though the LDPoIPv4 session may 177 already be established between the LSRs. 179 Note that the topology scenario illustrated in figure 2 also covers 180 the case of two routers getting connected via an additional Single- 181 stack LDP enabled interface (IPv6 routing and IPv6 LDP), even though 182 the LDPoIPv4 session may already be established between the LSRs 183 over the existing interface(s). 185 This document also addresses the scenario in which the LSRs do the 186 extended discovery in IPv6 and/or IPv4 address-families: 188 IPv4 189 R1-------------------R2 190 IPv6 192 Figure 4 LSRs involving IPv4 and IPv6 address-families 194 1.2. Single-hop vs. Multi-hop LDP Peering 196 LDP TTL Security mechanism specified by this document applies only 197 to single-hop LDP peering sessions, but not to multi-hop LDP peering 198 sessions, in line with Section 5.5 of [RFC5082] that describes 199 Generalized TTL Security Mechanism (GTSM). 201 As a consequence, any LDP feature that relies on multi-hop LDP 202 peering session would not work with GTSM and will warrant 203 (statically or dynamically) disabling GTSM. Please see section 10. 205 2. Specification Language 207 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 208 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 209 document are to be interpreted as described in [RFC2119]. 211 Abbreviations: 213 LDP - Label Distribution Protocol 215 LDPoIPv4 - LDP over IPv4 transport connection 217 LDPoIPv6 - LDP over IPv6 transport connection 219 FEC - Forwarding Equivalence Class 221 TLV - Type Length Value 223 LSR - Label Switching Router 225 LSP - Label Switched Path 227 LSPv4 - IPv4-signaled Label Switched Path [RFC4798] 229 LSPv6 - IPv6-signaled Label Switched Path [RFC4798] 231 AFI - Address Family Identifier 233 LDP Id - LDP Identifier 235 Single-stack LDP - LDP supporting just one address family (for 236 discovery, session setup, address/label binding 237 exchange etc.) 239 Dual-stack LDP - LDP supporting two address families (for 240 discovery, session setup, address/label binding 241 exchange etc.) 243 Dual-stack LSR - LSR supporting Dual-stack LDP for a peer 245 Single-stack LSR - LSR supporting Single-stack LDP for a peer 247 Note that an LSR can be a Dual-stack and Single-stack LSR at the 248 same time for different peers. This document loosely uses the term 249 address family to mean IP address family. 251 3. LSP Mapping 253 Section 2.1 of [RFC5036] specifies the procedure for mapping a 254 particular packet to a particular LSP using three rules. Quoting the 255 3rd rule from RFC5036: 257 "If it is known that a packet must traverse a particular egress 258 router, and there is an LSP that has an Address Prefix FEC element 259 that is a /32 address of that router, then the packet is mapped to 260 that LSP." 262 This rule is correct for IPv4, but not for IPv6, since an IPv6 263 router may even have a /64 or /96 or /128 (or whatever prefix 264 length) address. Hence, that rule is updated to use IPv4 or IPv6 265 address instead of /32 or /128 addresses as shown below: 267 "If it is known that a packet must traverse a particular egress 268 router, and there is an LSP that has an Address Prefix FEC element 269 that is an IPv4 or IPv6 address of that router, then the packet is 270 mapped to that LSP." 272 4. LDP Identifiers 274 In line with section 2.2.2 of [RFC5036], this document specifies the 275 usage of 32-bit (unsigned non-zero integer) LSR Id on an IPv6 276 enabled LSR (with or without Dual-stacking). 278 This document also qualifies the first sentence of last paragraph of 279 Section 2.5.2 of [RFC5036] to be per address family and therefore 280 updates that sentence to the following: 282 "For a given address family, an LSR MUST advertise the same 283 transport address in all Hellos that advertise the same label 284 space." 286 This rightly enables the per-platform label space to be shared 287 between IPv4 and IPv6. 289 In summary, this document mandates the usage of a common LDP 290 identifier (same LSR Id aka LDP Router Id as well as a common Label 291 space id) for both IPv4 and IPv6 address families. 293 5. Neighbor Discovery 295 If Dual-stack LDP is enabled (e.g. LDP enabled in both IPv6 and IPv4 296 address families) on an interface or for a targeted neighbor, then 297 the LSR MUST transmit both IPv6 and IPv4 LDP (Link or targeted) 298 Hellos and include the same LDP Identifier (assuming per-platform 299 label space usage) in them. 301 If Single-stack LDP is enabled (e.g. LDP enabled in either IPv6 or 302 IPv4 address family), then the LSR MUST transmit either IPv6 or IPv4 303 LDP (Link or targeted) Hellos respectively. 305 5.1. Basic Discovery Mechanism 307 Section 2.4.1 of [RFC5036] defines the Basic Discovery mechanism for 308 directly connected LSRs. Following this mechanism, LSRs periodically 309 send LDP Link Hellos destined to "all routers on this subnet" group 310 multicast IP address. 312 Interesting enough, per the IPv6 addressing architecture [RFC4291], 313 IPv6 has three "all routers on this subnet" multicast addresses: 315 FF01:0:0:0:0:0:0:2 = Interface-local scope 317 FF02:0:0:0:0:0:0:2 = Link-local scope 319 FF05:0:0:0:0:0:0:2 = Site-local scope 321 [RFC5036] does not specify which particular IPv6 'all routers on 322 this subnet' group multicast IP address should be used by LDP Link 323 Hellos. 325 This document specifies the usage of link-local scope e.g. 326 FF02:0:0:0:0:0:0:2 as the destination multicast IP address in IPv6 327 LDP Link Hellos. An LDP Link Hello packet received on any of the 328 other destination addresses MUST be dropped. Additionally, the link- 329 local IPv6 address MUST be used as the source IP address in IPv6 LDP 330 Link Hellos. 332 Also, the LDP Link Hello packets MUST have their IPv6 Hop Limit set 333 to 255, be checked for the same upon receipt (before any LDP 334 specific processing) and be handled as specified in Generalized TTL 335 Security Mechanism (GTSM) section 3 of [RFC5082]. The built-in 336 inclusion of GTSM automatically protects IPv6 LDP from off-link 337 attacks. 339 More importantly, if an interface is a Dual-stack LDP interface 340 (e.g. LDP enabled in both IPv6 and IPv4 address families), then the 341 LSR MUST periodically transmit both IPv6 and IPv4 LDP Link Hellos 342 (using the same LDP Identifier per section 4) on that interface and 343 be able to receive them. This facilitates discovery of IPv6-only, 344 IPv4-only and Dual-stack peers on the interface's subnet and ensures 345 successful subsequent peering using the appropriate (address family) 346 transport on a multi-access or broadcast interface. 348 5.1.1. Maintaining Hello Adjacencies 350 In case of Dual-stack LDP enabled interface, the LSR SHOULD maintain 351 link Hello adjacencies for both IPv4 and IPv6 address families. This 352 document, however, allows an LSR to maintain Rx-side Link Hello 353 adjacency only for the address family that has been used for the 354 establishment of the LDP session (whether LDPoIPv4 or LDPoIPv6 355 session). 357 5.2. Extended Discovery Mechanism 359 The extended discovery mechanism (defined in section 2.4.2 of 360 [RFC5036]), in which the targeted LDP Hellos are sent to a unicast 361 IPv6 address destination, requires only one IPv6 specific 362 consideration: the link-local IPv6 addresses MUST NOT be used as the 363 targeted LDP hello packet's source or destination addresses. 365 6. LDP Session Establishment and Maintenance 367 Section 2.5.1 of [RFC5036] defines a two-step process for LDP 368 session establishment, once the neighbor discovery has completed 369 (i.e. LDP Hellos have been exchanged): 371 1. Transport connection establishment 372 2. Session initialization 374 The forthcoming sub-section 6.1 discusses the LDP consideration for 375 IPv6 and/or Dual-stacking in the context of session establishment, 376 whereas sub-section 6.2 discusses the LDP consideration for IPv6 377 and/or Dual-stacking in the context of session maintenance. 379 6.1. Transport connection establishment 381 Section 2.5.2 of [RFC5036] specifies the use of an optional 382 transport address object (TLV) in LDP Hello message to convey the 383 transport (IP) address, however, it does not specify the behavior of 384 LDP if both IPv4 and IPv6 transport address objects (TLV) are sent 385 in a Hello message or separate Hello messages. More importantly, it 386 does not specify whether both IPv4 and IPv6 transport connections 387 should be allowed, if both IPv4 and IPv6 Hello adjacencies were 388 present prior to the session establishment. 390 This document specifies that: 392 1. An LSR MUST NOT send a Hello message containing both IPv4 and 393 IPv6 transport address optional objects. In other words, there 394 MUST be at most one optional Transport Address object in a 395 Hello message. An LSR MUST include only the transport address 396 whose address family is the same as that of the IP packet 397 carrying the Hello message. 399 2. An LSR SHOULD accept the Hello message that contains both IPv4 400 and IPv6 transport address optional objects, but MUST use only 401 the transport address whose address family is the same as that 402 of the IP packet carrying the Hello message. An LSR SHOULD 403 accept only the first transport object for a given address 404 family in the received Hello message, and ignore the rest, if 405 the LSR receives more than one transport object for a given 406 address family. 408 3. An LSR MUST send separate Hello messages (each containing 409 either IPv4 or IPv6 transport address optional object) for each 410 IP address family, if Dual-stack LDP is enabled (for an 411 interface or neighbor). 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 either LDPoIPv4 or LDPoIPv6 424 session 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 SHOULD prefer establishing an LDPoIPv6 session 436 (instead of LDPoIPv4 session) with a remote Dual-stack LSR by 437 following the 'transport connection role' determination logic 438 in section 6.1.1. 440 Additionally, to ensure the above preference in case of Dual- 441 stack LDP being enabled on an interface, it would be desirable 442 that IPv6 LDP Link Hellos are transmitted before IPv4 LDP Link 443 Hellos, particularly when an interface is coming into service 444 or being reconfigured. 446 6.1.1. Determining Transport connection Roles 448 Section 2.5.2 of [RFC5036] specifies the rules for determining 449 active/passive roles in setting up TCP connection. These rules are 450 clear for a Single-stack LDP, but not for a Dual-stack LDP, in which 451 an LSR may assume different roles for different address families, 452 causing LDP session to not get established. 454 To ensure deterministic transport connection (active/passive) role 455 in case of Dual-stack LDP, this document specifies that the Dual- 456 stack LSR conveys its transport connection preference in every LDP 457 Hello message. This preference is encoded in a new TLV, named Dual- 458 stack capability TLV, as defined below: 460 0 1 2 3 461 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 1 462 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 463 |1|0| Dual-stack capability | Length | 464 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 465 |TR | Reserved | MBZ | 466 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 468 Figure 5 Dual-stack capability TLV 470 Where: 472 U and F bits: 1 and 0 (as specified by RFC5036) 474 Dual-stack capability: TLV code point (to be assigned by IANA). 476 TR, Transport Connection Preference. 478 This document defines the following 2 values: 480 0100: LDPoIPv4 connection 482 0110: LDPoIPv6 connection (default) 484 Reserved 486 This field is reserved. It MUST be set to zero on 487 transmission and ignored on receipt. 489 A Dual-stack LSR (i.e. LSR supporting Dual-stack LDP for a peer) 490 MUST include "Dual-stack capability" TLV in all of its LDP Hellos, 491 and MUST set the "TR" field to announce its preference for either 492 LDPoIPv4 or LDPoIPv6 transport connection for that peer. The default 493 preference is LDPoIPv6. 495 A Dual-stack LSR MUST always check for the presence of "Dual-stack 496 capability" TLV in the received hello messages, and take appropriate 497 actions as follows: 499 1. If "Dual-stack capability" TLV is present and remote preference 500 does not match with the local preference (or does not get 501 recognized), then the LSR MUST discard the hello message and 502 log an error. 504 If LDP session was already in place, then LSR MUST send a fatal 505 Notification message with status code [Transport Connection 506 mismatch, IANA allocation TBD] and reset the session. 508 2. If "Dual-stack capability" TLV is present, and remote 509 preference matches with the local preference, then: 511 a) If TR=0100 (LDPoIPv4), then determine the active/passive 512 roles for TCP connection using IPv4 transport address as 513 defined in section 2.5.2 of RFC 5036. 515 b) If TR=0110 (LDPoIPv6), then determine the active/passive 516 roles for TCP connection by using IPv6 transport address 517 as defined in section 2.5.2 of RFC 5036. 519 3. If "Dual-stack capability" TLV is NOT present, and 521 a) Only IPv4 hellos are received, then the neighbor is deemed 522 as a legacy IPv4-only LSR (supporting Single-stack LDP), 523 hence, an LDPoIPv4 session SHOULD be established (similar 524 to that of 2a above). 526 However, if IPv6 hellos are also received at any time 527 during the life of session from that neighbor, then the 528 neighbor is deemed as a non-compliant Dual-stack LSR 529 (similar to that of 3c below), resulting in any 530 established LDPoIPv4 session being reset and a fatal 531 Notification message being sent (with status code of 532 'Dual-Stack Non-Compliance', IANA allocation TBD). 534 b) Only IPv6 hellos are received, then the neighbor is deemed 535 as an IPv6-only LSR (supporting Single-stack LDP) and 536 LDPoIPv6 session SHOULD be established (similar to that of 537 2b above). 539 However, if IPv4 hellos are also received at any time 540 during the life of session from that neighbor, then the 541 neighbor is deemed as a non-compliant Dual-stack LSR 542 (similar to that of 3c below), resulting in any 543 established LDPoIPv6 session being reset and a fatal 544 Notification message being sent (with status code of 545 'Dual-Stack Non-Compliance', IANA allocation TBD). 547 c) Both IPv4 and IPv6 hellos are received, then the neighbor 548 is deemed as a non-compliant Dual-stack neighbor, and is 549 not allowed to have any LDP session. A Notification 550 message should be sent (with status code of 'Dual-Stack 551 Non-Compliance', IANA allocation TBD). 553 A Dual-stack LSR MUST convey the same transport connection 554 preference ("TR" field value) in all (link and targeted) Hellos that 555 advertise the same label space to the same peer and/or on same 556 interface. This ensures that two LSRs linked by multiple Hello 557 adjacencies using the same label spaces play the same connection 558 establishment role for each adjacency. 560 A Dual-stack LSR MUST follow section 2.5.5 of RFC5036 and check for 561 matching Hello messages from the peer (either all Hellos also 562 include the Dual-stack capability (with same TR value) or none do). 564 A Single-stack LSR do not need to use the Dual-stack capability in 565 hello messages and SHOULD ignore this capability, if received. 567 An implementation may provide an option to favor one AFI (IPv4, say) 568 over another AFI (IPv6, say) for the TCP transport connection, so as 569 to use the favored IP version for the LDP session, and force 570 deterministic active/passive roles. 572 Note - An alternative to this new Capability TLV could be a new Flag 573 value in LDP Hello message, however, it will get used even in a 574 Single-stack IPv6 LDP networks and linger on forever, even though 575 Dual-stack will not. Hence, this alternative is discarded. 577 6.2. LDP Sessions Maintenance 579 This document specifies that two LSRs maintain a single LDP session 580 regardless of number of Link or Targeted Hello adjacencies between 581 them, as described in section 6.1. This is independent of whether: 583 - they are connected via a Dual-stack LDP enabled interface(s) or 584 via two (or more) Single-stack LDP enabled interfaces; 585 - a Single-stack LDP enabled interface is converted to a Dual-stack 586 LDP enabled interface (e.g. figure 1) on either LSR; 587 - an additional Single-stack or Dual-stack LDP enabled interface is 588 added or removed between two LSRs (e.g. figure 2). 590 If the last hello adjacency for a given address family goes down 591 (e.g. due to Dual-stack LDP enabled interfaces being converted into 592 a Single-stack LDP enabled interfaces on one LSR etc.), and that 593 address family is the same as the one used in the transport 594 connection, then the transport connection (LDP session) MUST be 595 reset. Otherwise, the LDP session MUST stay intact. 597 If the LDP session is torn down for whatever reason (LDP disabled 598 for the corresponding transport, hello adjacency expiry, preference 599 mismatch etc.), then the LSRs SHOULD initiate establishing a new LDP 600 session as per the procedures described in section 6.1 of this 601 document. 603 7. Binding Distribution 605 LSRs by definition can be enabled for Dual-stack LDP globally and/or 606 per peer so as to exchange the address and label bindings for both 607 IPv4 and IPv6 address-families, independent of LDPoIPv4 or LDPoIPV6 608 session between them. 610 However, there might be some legacy LSRs that are fully RFC 5036 611 compliant for IPv4, but non-compliant for IPv6 (say, section 3.5.5.1 612 of RFC 5036), causing them to reset the session upon receiving IPv6 613 address bindings or IPv6 FEC (Prefix) label bindings from a peer 614 compliant with this document. This is somewhat undesirable, as 615 clarified further Appendix A.1 and A.2. 617 To help maintain backward compatibility (i.e. accommodate IPv4-only 618 LDP implementations that may not be compliant with RFC 5036 section 619 3.5.5.1), this specification requires that an LSR MUST NOT send any 620 IPv6 bindings to a peer if peer has been determined as a legacy LSR. 622 The 'Dual-stack capability' TLV, which is defined in section 6.1.1, 623 is also used to determine if a peer is a legacy (IPv4-only Single- 624 stack) LSR or not. 626 7.1. Address Distribution 628 An LSR MUST NOT advertise (via ADDRESS message) any IPv4-mapped IPv6 629 addresses (defined in section 2.5.5.2 of [RFC4291]), and ignore such 630 addresses, if ever received. Please see Appendix A.3. 632 If an LSR is enabled with Single-stack LDP for any peer, then it 633 MUST advertise (via ADDRESS message) its local IP addresses as per 634 the enabled address family to that peer, and process received 635 Address messages containing IP addresses as per the enabled address 636 family from that peer. 638 If an LSR is enabled with Dual-stack LDP for a peer and 640 1. Is NOT able to find the Dual-stack capability TLV in the 641 incoming IPv4 LDP hello messages from that peer, then the LSR 642 MUST NOT advertise its local IPv6 Addresses to the peer. 644 2. Is able to find the Dual-stack capability in the incoming IPv4 645 (or IPv6) LDP Hello messages from that peer, then it MUST 646 advertise (via ADDRESS message) its local IPv4 and IPv6 647 addresses to that peer. 649 3. Is NOT able to find the Dual-stack capability in the incoming 650 IPv6 LDP Hello messages, then it MUST advertise (via ADDRESS 651 message) only its local IPv6 addresses to that peer. 653 This last point helps to maintain forward compatibility (no 654 need to require this TLV in case of IPv6 Single-stack LDP). 656 7.2. Label Distribution 658 An LSR MUST NOT allocate and MUST NOT advertise FEC-Label bindings 659 for link-local or IPv4-mapped IPv6 addresses (defined in section 660 2.5.5.2 of [RFC4291]), and ignore such bindings, if ever received. 661 Please see Appendix A.3. 663 If an LSR is enabled with Single-stack LDP for any peer, then it 664 MUST advertise (via Label Mapping message) FEC-Label bindings for 665 the enabled address family to that peer, and process received FEC- 666 Label bindings for the enabled address family from that peer. 668 If an LSR is enabled with Dual-stack LDP for a peer and 670 1. Is NOT able to find the Dual-stack capability TLV in the 671 incoming IPv4 LDP hello messages from that peer, then the LSR 672 MUST NOT advertise IPv6 FEC-label bindings to the peer (even if 673 IP capability negotiation for IPv6 address family was done). 675 2. Is able to find the Dual-stack capability in the incoming IPv4 676 (or IPv6) LDP Hello messages from that peer, then it MUST 677 advertise FEC-Label bindings for both IPv4 and IPv6 address 678 families to that peer. 680 3. Is NOT able to find the Dual-stack capability in the incoming 681 IPv6 LDP Hello messages, then it MUST advertise FEC-Label 682 bindings for IPv6 address families to that peer. 684 This last point helps to maintain forward compatibility (no 685 need to require this TLV for IPv6 Single-stack LDP). 687 An LSR MAY further constrain the advertisement of FEC-label bindings 688 for a particular address family by negotiating the IP Capability for 689 a given address family, as specified in [IPPWCap] document. This 690 allows an LSR pair to neither advertise nor receive the undesired 691 FEC-label bindings on a per address family basis to a peer. 693 If an LSR is configured to change an interface or peer from Single- 694 stack LDP to Dual-stack LDP, then an LSR SHOULD use Typed Wildcard 695 FEC procedures [RFC5918] to request the label bindings for the 696 enabled address family. This helps to relearn the label bindings 697 that may have been discarded before without resetting the session. 699 8. LDP Identifiers and Duplicate Next Hop Addresses 701 RFC5036 section 2.7 specifies the logic for mapping the IP routing 702 next-hop (of a given FEC) to an LDP peer so as to find the correct 703 label entry for that FEC. The logic involves using the IP routing 704 next-hop address as an index into the (peer Address) database (which 705 is populated by the Address message containing mapping between each 706 peer's local addresses and its LDP Identifier) to determine the LDP 707 peer. 709 However, this logic is insufficient to deal with duplicate IPv6 710 (link-local) next-hop addresses used by two or more peers. The 711 reason is that all interior IPv6 routing protocols (can) use link- 712 local IPv6 addresses as the IP routing next-hops, and 'IPv6 713 Addressing Architecture [RFC4291]' allows a link-local IPv6 address 714 to be used on more than one links. 716 Hence, this logic is extended by this specification to use not only 717 the IP routing next-hop address, but also the IP routing next-hop 718 interface to uniquely determine the LDP peer(s). The next-hop 719 address-based LDP peer mapping is to be done through LDP peer 720 address database (populated by Address messages received from the 721 LDP peers), whereas next-hop interface-based LDP peer mapping is to 722 be done through LDP hello adjacency/interface database (populated by 723 hello messages received from the LDP peers). 725 This extension solves the problem of two or more peers using the 726 same link-local IPv6 address (in other words, duplicate peer 727 addresses) as the IP routing next-hops. 729 Lastly, for better scale and optimization, an LSR may advertise only 730 the link-local IPv6 addresses in the Address message, assuming that 731 the peer uses only the link-local IPv6 addresses as static and/or 732 dynamic IP routing next-hops. 734 9. LDP TTL Security 736 This document recommends enabling Generalized TTL Security Mechanism 737 (GTSM) for LDP, as specified in [RFC6720], for the LDP/TCP transport 738 connection over IPv6 (i.e. LDPoIPv6). The GTSM inclusion is intended 739 to automatically protect IPv6 LDP peering session from off-link 740 attacks. 742 [RFC6720] allows for the implementation to statically 743 (configuration) and/or dynamically override the default behavior 744 (enable/disable GTSM) on a per-peer basis. Such a configuration an 745 option could be set on either LSR (since GTSM negotiation would 746 ultimately disable GTSM between LSR and its peer(s)). 748 LDP Link Hello packets MUST have their IPv6 Hop Limit set to 255, 749 and be checked for the same upon receipt before any further 750 processing, as per section 3 of [RFC5082]. 752 10. IANA Considerations 754 This document defines a new optional parameter for the LDP Hello 755 Message and two new status codes for the LDP Notification Message. 757 The 'Dual-Stack capability' parameter requires a code point from the 758 TLV Type Name Space. IANA is requested to allocated a code point 759 from the IETF Consensus range 0x0700-0x07ff for the 'Dual-Stack 760 capability' TLV. 762 The 'Transport Connection Mismatch' status code requires a code 763 point from the Status Code Name Space. IANA is requested to allocate 764 a code point from the IETF Consensus range and mark the E bit column 765 with a '1'. 767 The 'Dual-Stack Non-Compliance' status code requires a code point 768 from the Status Code Name Space. IANA is requested to allocate a 769 code point from the IETF Consensus range and mark the E bit column 770 with a '1'. 772 11. Security Considerations 774 The extensions defined in this document only clarify the behavior of 775 LDP, they do not define any new protocol procedures. Hence, this 776 document does not add any new security issues to LDP. 778 While the security issues relevant for the [RFC5036] are relevant 779 for this document as well, this document reduces the chances of off- 780 link attacks when using IPv6 transport connection by including the 781 use of GTSM procedures [RFC5082]. Please see section 9 for LDP TTL 782 Security details. 784 Moreover, this document allows the use of IPsec [RFC4301] for IPv6 785 protection, hence, LDP can benefit from the additional security as 786 specified in [RFC7321] as well as [RFC5920]. 788 12. Acknowledgments 790 We acknowledge the authors of [RFC5036], since some text in this 791 document is borrowed from [RFC5036]. 793 Thanks to Bob Thomas for providing critical feedback to improve this 794 document early on. 796 Many thanks to Eric Rosen, Lizhong Jin, Bin Mo, Mach Chen, Shane 797 Amante, Pranjal Dutta, Mustapha Aissaoui, Matthew Bocci, Mark Tinka, 798 Tom Petch, Kishore Tiruveedhula, Manoj Dutta, Vividh Siddha, Qin Wu, 799 Simon Perreault, Brian E Carpenter, Santosh Esale, Danial Johari and 800 Loa Andersson for thoroughly reviewing this document, and providing 801 insightful comments and multiple improvements. 803 This document was prepared using 2-Word-v2.0.template.dot. 805 13. Additional Contributors 807 The following individuals contributed to this document: 809 Kamran Raza 810 Cisco Systems, Inc. 811 2000 Innovation Drive 812 Kanata, ON K2K-3E8, Canada 813 Email: skraza@cisco.com 814 Nagendra Kumar 815 Cisco Systems, Inc. 816 SEZ Unit, Cessna Business Park, 817 Bangalore, KT, India 818 Email: naikumar@cisco.com 820 Andre Pelletier 821 Cisco Systems, Inc. 822 2000 Innovation Drive 823 Kanata, ON K2K-3E8, Canada 824 Email: apelleti@cisco.com 826 14. References 828 14.1. Normative References 830 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 831 Requirement Levels", BCP 14, RFC 2119, March 1997. 833 [RFC4291] Hinden, R. and S. Deering, "Internet Protocol Version 6 834 (IPv6) Addressing Architecture", RFC 4291, February 2006. 836 [RFC5036] Andersson, L., Minei, I., and Thomas, B., "LDP 837 Specification", RFC 5036, October 2007. 839 [RFC5082] Pignataro, C., Gill, V., Heasley, J., Meyer, D., and 840 Savola, P., "The Generalized TTL Security Mechanism 841 (GTSM)", RFC 5082, October 2007. 843 [RFC5918] Asati, R., Minei, I., and Thomas, B., "Label Distribution 844 Protocol (LDP) 'Typed Wildcard Forward Equivalence Class 845 (FEC)", RFC 5918, October 2010. 847 14.2. Informative References 849 [RFC4301] Kent, S. and K. Seo, "Security Architecture and Internet 850 Protocol", RFC 4301, December 2005. 852 [RFC7321] Manral, V., "Cryptographic Algorithm Implementation 853 Requirements for Encapsulating Security Payload (ESP) and 854 Authentication Header (AH)", RFC 7321, April 2007. 856 [RFC5920] Fang, L., "Security Framework for MPLS and GMPLS 857 Networks", RFC 5920, July 2010. 859 [RFC4798] De Clercq, et al., "Connecting IPv6 Islands over IPv4 MPLS 860 Using IPv6 Provider Edge Routers (6PE)", RFC 4798, 861 February 2007. 863 [IPPWCap] Raza, K., "LDP IP and PW Capability", draft-ietf-mpls-ldp- 864 ip-pw-capability, October 2014. 866 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 867 for IPv6", RFC 5340, July 2008. 869 [RFC6286] E. Chen, and J. Yuan, "Autonomous-System-Wide Unique BGP 870 Identifier for BGP-4", RFC 6286, June 2011. 872 [RFC6720] R. Asati, and C. Pignataro, "The Generalized TTL Security 873 Mechanism (GTSM) for the Label Distribution Protocol 874 (LDP)", RFC 6720, August 2012. 876 [RFC4038] M-K. Shin, Y-G. Hong, J. Hagino, P. Savola, and E. M. 877 Castro, "Application Aspects of IPv6 Transition", RFC 878 4038, March 2005. 880 [RFC7439] W. George, and C. Pignataro, "Gap Analysis for Operating 881 IPv6-Only MPLS Networks", RFC 7439, January 2015. 883 Appendix A. 885 A.1. LDPv6 and LDPv4 Interoperability Safety Net 887 It is not safe to assume that RFC5036 compliant implementations have 888 supported handling IPv6 address family (IPv6 FEC label) in Label 889 Mapping message all along. 891 If a router upgraded with this specification advertised both IPv4 892 and IPv6 FECs in the same label mapping message, then an IPv4-only 893 peer (not knowing how to process such a message) may abort 894 processing the entire label mapping message (thereby discarding even 895 the IPv4 label FECs), as per the section 3.4.1.1 of RFC5036. 897 This would result in LDPv6 to be somewhat undeployable in existing 898 production networks. 900 The change proposed in section 7 of this document provides a good 901 safety net and makes LDPv6 incrementally deployable without making 902 any such assumption on the routers' support for IPv6 FEC processing 903 in current production networks. 905 A.2. Accommodating Non-RFC5036-compliant implementations 907 It is not safe to assume that implementations have been RFC5036 908 compliant in gracefully handling IPv6 address family (IPv6 Address 909 List TLV) in Address message all along. 911 If a router upgraded with this specification advertised IPv6 912 addresses (with or without IPv4 addresses) in Address message, then 913 an IPv4-only peer (not knowing how to process such a message) may 914 not follow section 3.5.5.1 of RFC5036, and tear down the LDP 915 session. 917 This would result in LDPv6 to be somewhat undeployable in existing 918 production networks. 920 The changes proposed in section 6 and 7 of this document provides a 921 good safety net and makes LDPv6 incrementally deployable without 922 making any such assumption on the routers' support for IPv6 FEC 923 processing in current production networks. 925 A.3. Why prohibit IPv4-mapped IPv6 addresses in LDP 927 Per discussion with 6MAN and V6OPS working groups, the overwhelming 928 consensus was to not promote IPv4-mapped IPv6 addresses appear in 929 the routing table, as well as in LDP (address and label) databases. 931 Also, [RFC4038] section 4.2 suggests that IPv4-mapped IPv6 addressed 932 packets should never appear on the wire. 934 A.4. Why 32-bit value even for IPv6 LDP Router ID 936 The first four octets of the LDP identifier, the 32-bit LSR Id (e.g. 937 (i.e. LDP Router Id), identify the LSR and is a globally unique 938 value within the MPLS network. This is regardless of the address 939 family used for the LDP session. 941 Please note that 32-bit LSR Id value would not map to any IPv4- 942 address in an IPv6 only LSR (i.e., single stack), nor would there be 943 an expectation of it being IP routable, nor DNS-resolvable. In IPv4 944 deployments, the LSR Id is typically derived from an IPv4 address, 945 generally assigned to a loopback interface. In IPv6 only 946 deployments, this 32-bit LSR Id must be derived by some other means 947 that guarantees global uniqueness within the MPLS network, similar 948 to that of BGP Identifier [RFC6286] and OSPF router ID [RFC5340]. 950 This document reserves 0.0.0.0 as the LSR Id, and prohibits its 951 usage with IPv6, in line with OSPF router Id in OSPF version 3 952 [RFC5340]. 954 Author's Addresses 956 Rajiv Asati 957 Cisco Systems, Inc. 958 7025 Kit Creek Road 959 Research Triangle Park, NC 27709-4987 960 Email: rajiva@cisco.com 962 Vishwas Manral 963 Hewlet-Packard, Inc. 964 19111 Pruneridge Ave., Cupertino, CA, 95014 965 Phone: 408-447-1497 966 Email: vishwas@ionosnetworks.com 968 Kamran Raza 969 Cisco Systems, Inc., 970 2000 Innovation Drive, 971 Ottawa, ON K2K-3E8, Canada. 972 E-mail: skraza@cisco.com 974 Rajiv Papneja 975 Huawei Technologies 976 2330 Central Expressway 977 Santa Clara, CA 95050 978 Phone: +1 571 926 8593 979 EMail: rajiv.papneja@huawei.com 981 Carlos Pignataro 982 Cisco Systems, Inc. 983 7200 Kit Creek Road 984 Research Triangle Park, NC 27709-4987 985 Email: cpignata@cisco.com