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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 11, 2015 14 Updates to LDP for IPv6 15 draft-ietf-mpls-ldp-ipv6-16 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 11, 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..........................................14 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..............................................17 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 was enabled. 412 An LSR MUST transmit IPv6 LDP link Hellos before IPv4 LDP Link 413 Hellos, if Dual-stack LDP was enabled on an interface, 414 particularly during the interface coming into service or 415 configuration time. 417 4. An LSR MUST use a global unicast IPv6 address in IPv6 transport 418 address optional object of outgoing targeted Hellos, and check 419 for the same in incoming targeted hellos (i.e. MUST discard the 420 targeted hello, if it failed the check). 422 5. An LSR MUST prefer using a global unicast IPv6 address in IPv6 423 transport address optional object of outgoing Link Hellos, if 424 it had to choose between global unicast IPv6 address and 425 unique-local or link-local IPv6 address. 427 6. A Single-stack LSR MUST establish LDPoIPv4 or LDPoIPv6 session 428 with a remote LSR as per the enabled address-family. 430 7. A Dual-stack LSR MUST NOT initiate (or accept the request for) 431 a TCP connection for a new LDP session with a remote LSR, if 432 they already have an LDPoIPv4 or LDPoIPv6 session (for the same 433 LDP Identifier) established. 435 This means that only one transport connection is established 436 regardless of IPv6 or/and IPv4 Hello adjacencies presence 437 between two LSRs. 439 8. A Dual-stack LSR MUST prefer establishing LDPoIPv6 session with 440 a remote LSR by following the 'transport connection role' 441 determination logic in section 6.1.1. 443 6.1.1. Determining Transport connection Roles 445 Section 2.5.2 of [RFC5036] specifies the rules for determining 446 active/passive roles in setting up TCP connection. These rules are 447 clear for a Single-stack LDP, but not for a Dual-stack LDP, in which 448 an LSR may assume different roles for different address families, 449 causing LDP session to not get established. 451 To ensure deterministic transport connection (active/passive) role 452 in case of Dual-stack LDP, this document specifies that the Dual- 453 stack LSR conveys its transport connection preference in every LDP 454 Hello message. This preference is encoded in a new TLV, named Dual- 455 stack capability TLV, as defined below: 457 0 1 2 3 458 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 1 459 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 460 |1|0| Dual-stack capability | Length | 461 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 462 |TR | Reserved | MBZ | 463 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 465 Figure 5 Dual-stack capability TLV 467 Where: 469 U and F bits: 1 and 0 (as specified by RFC5036) 471 Dual-stack capability: TLV code point (to be assigned by IANA). 473 TR, Transport Connection Preference. 475 This document defines the following 2 values: 477 0100: LDPoIPv4 connection 479 0110: LDPoIPv6 connection (default) 481 Reserved 483 This field is reserved. It MUST be set to zero on 484 transmission and ignored on receipt. 486 A Dual-stack LSR (i.e. LSR supporting Dual-stack LDP for a peer) 487 MUST include "Dual-stack capability" TLV in all of its LDP Hellos, 488 and MUST set the "TR" field to announce its preference for either 489 LDPoIPv4 or LDPoIPv6 transport connection for that peer. The default 490 preference is LDPoIPv6. 492 A Dual-stack LSR MUST always check for the presence of "Dual-stack 493 capability" TLV in the received hello messages, and take appropriate 494 actions as follows: 496 1. If "Dual-stack capability" TLV is present and remote preference 497 does not match with the local preference (or does not get 498 recognized), then the LSR MUST discard the hello message and 499 log an error. 501 If LDP session was already in place, then LSR MUST send a fatal 502 Notification message with status code [Transport Connection 503 mismatch, IANA allocation TBD] and reset the session. 505 2. If "Dual-stack capability" TLV is present, and remote 506 preference matches with the local preference, then: 508 a) If TR=0100 (LDPoIPv4), then determine the active/passive 509 roles for TCP connection using IPv4 transport address as 510 defined in section 2.5.2 of RFC 5036. 512 b) If TR=0110 (LDPoIPv6), then determine the active/passive 513 roles for TCP connection by using IPv6 transport address 514 as defined in section 2.5.2 of RFC 5036. 516 3. If "Dual-stack capability" TLV is NOT present, and 518 a) Only IPv4 hellos are received, then the neighbor is deemed 519 as a legacy IPv4-only LSR (supporting Single-stack LDP), 520 hence, an LDPoIPv4 session SHOULD be established (similar 521 to that of 2a above). 523 However, if IPv6 hellos are also received at any time 524 during the life of session from that neighbor, then the 525 neighbor is deemed as a non-compliant Dual-stack LSR 526 (similar to that of 3c below), resulting in any 527 established LDPoIPv4 session being reset and a fatal 528 Notification message being sent (with status code of 529 'Dual-Stack Non-Compliance', IANA allocation TBD). 531 b) Only IPv6 hellos are received, then the neighbor is deemed 532 as an IPv6-only LSR (supporting Single-stack LDP) and 533 LDPoIPv6 session SHOULD be established (similar to that of 534 2b above). 536 However, if IPv4 hellos are also received at any time 537 during the life of session from that neighbor, then the 538 neighbor is deemed as a non-compliant Dual-stack LSR 539 (similar to that of 3c below), resulting in any 540 established LDPoIPv6 session being reset and a fatal 541 Notification message being sent (with status code of 542 'Dual-Stack Non-Compliance', IANA allocation TBD). 544 c) Both IPv4 and IPv6 hellos are received, then the neighbor 545 is deemed as a non-compliant Dual-stack neighbor, and is 546 not allowed to have any LDP session. A Notification 547 message should be sent (with status code of 'Dual-Stack 548 Non-Compliance', IANA allocation TBD). 550 A Dual-stack LSR MUST convey the same transport connection 551 preference ("TR" field value) in all (link and targeted) Hellos that 552 advertise the same label space to the same peer and/or on same 553 interface. This ensures that two LSRs linked by multiple Hello 554 adjacencies using the same label spaces play the same connection 555 establishment role for each adjacency. 557 A Dual-stack LSR MUST follow section 2.5.5 of RFC5036 and check for 558 matching Hello messages from the peer (either all Hellos also 559 include the Dual-stack capability (with same TR value) or none do). 561 A Single-stack LSR do not need to use the Dual-stack capability in 562 hello messages and SHOULD ignore this capability, if received. 564 An implementation may provide an option to favor one AFI (IPv4, say) 565 over another AFI (IPv6, say) for the TCP transport connection, so as 566 to use the favored IP version for the LDP session, and force 567 deterministic active/passive roles. 569 Note - An alternative to this new Capability TLV could be a new Flag 570 value in LDP Hello message, however, it will get used even in a 571 Single-stack IPv6 LDP networks and linger on forever, even though 572 Dual-stack will not. Hence, this alternative is discarded. 574 6.2. LDP Sessions Maintenance 576 This document specifies that two LSRs maintain a single LDP session 577 regardless of number of Link or Targeted Hello adjacencies between 578 them, as described in section 6.1. This is independent of whether: 580 - they are connected via a Dual-stack LDP enabled interface(s) or 581 via two (or more) Single-stack LDP enabled interfaces; 582 - a Single-stack LDP enabled interface is converted to a Dual-stack 583 LDP enabled interface (e.g. figure 1) on either LSR; 584 - an additional Single-stack or Dual-stack LDP enabled interface is 585 added or removed between two LSRs (e.g. figure 2). 587 If the last hello adjacency for a given address family goes down 588 (e.g. due to Dual-stack LDP enabled interfaces being converted into 589 a Single-stack LDP enabled interfaces on one LSR etc.), and that 590 address family is the same as the one used in the transport 591 connection, then the transport connection (LDP session) MUST be 592 reset. Otherwise, the LDP session MUST stay intact. 594 If the LDP session is torn down for whatever reason (LDP disabled 595 for the corresponding transport, hello adjacency expiry, preference 596 mismatch etc.), then the LSRs SHOULD initiate establishing a new LDP 597 session as per the procedures described in section 6.1 of this 598 document. 600 7. Binding Distribution 602 LSRs by definition can be enabled for Dual-stack LDP globally and/or 603 per peer so as to exchange the address and label bindings for both 604 IPv4 and IPv6 address-families, independent of LDPoIPv4 or LDPoIPV6 605 session between them. 607 However, there might be some legacy LSRs that are fully RFC 5036 608 compliant for IPv4, but non-compliant for IPv6 (say, section 3.5.5.1 609 of RFC 5036), causing them to reset the session upon receiving IPv6 610 address bindings or IPv6 FEC (Prefix) label bindings from a peer 611 compliant with this document. This is somewhat undesirable, as 612 clarified further Appendix A.1 and A.2. 614 To help maintain backward compatibility (i.e. accommodate IPv4-only 615 LDP implementations that may not be compliant with RFC 5036 section 616 3.5.5.1), this specification requires that an LSR MUST NOT send any 617 IPv6 bindings to a peer if peer has been determined as a legacy LSR. 619 The 'Dual-stack capability' TLV, which is defined in section 6.1.1, 620 is also used to determine if a peer is a legacy (IPv4-only Single- 621 stack) LSR or not. 623 7.1. Address Distribution 625 An LSR MUST NOT advertise (via ADDRESS message) any IPv4-mapped IPv6 626 addresses (defined in section 2.5.5.2 of [RFC4291]), and ignore such 627 addresses, if ever received. Please see Appendix A.3. 629 If an LSR is enabled with Single-stack LDP for any peer, then it 630 MUST advertise (via ADDRESS message) its local IP addresses as per 631 the enabled address family to that peer, and process received 632 Address messages containing IP addresses as per the enabled address 633 family from that peer. 635 If an LSR is enabled with Dual-stack LDP for a peer and 637 1. Is NOT able to find the Dual-stack capability TLV in the 638 incoming IPv4 LDP hello messages from that peer, then the LSR 639 MUST NOT advertise its local IPv6 Addresses to the peer. 641 2. Is able to find the Dual-stack capability in the incoming IPv4 642 (or IPv6) LDP Hello messages from that peer, then it MUST 643 advertise (via ADDRESS message) its local IPv4 and IPv6 644 addresses to that peer. 646 3. Is NOT able to find the Dual-stack capability in the incoming 647 IPv6 LDP Hello messages, then it MUST advertise (via ADDRESS 648 message) only its local IPv6 addresses to that peer. 650 This last point helps to maintain forward compatibility (no 651 need to require this TLV in case of IPv6 Single-stack LDP). 653 7.2. Label Distribution 655 An LSR MUST NOT allocate and MUST NOT advertise FEC-Label bindings 656 for link-local or IPv4-mapped IPv6 addresses (defined in section 657 2.5.5.2 of [RFC4291]), and ignore such bindings, if ever received. 658 Please see Appendix A.3. 660 If an LSR is enabled with Single-stack LDP for any peer, then it 661 MUST advertise (via Label Mapping message) FEC-Label bindings for 662 the enabled address family to that peer, and process received FEC- 663 Label bindings for the enabled address family from that peer. 665 If an LSR is enabled with Dual-stack LDP for a peer and 667 1. Is NOT able to find the Dual-stack capability TLV in the 668 incoming IPv4 LDP hello messages from that peer, then the LSR 669 MUST NOT advertise IPv6 FEC-label bindings to the peer (even if 670 IP capability negotiation for IPv6 address family was done). 672 2. Is able to find the Dual-stack capability in the incoming IPv4 673 (or IPv6) LDP Hello messages from that peer, then it MUST 674 advertise FEC-Label bindings for both IPv4 and IPv6 address 675 families to that peer. 677 3. Is NOT able to find the Dual-stack capability in the incoming 678 IPv6 LDP Hello messages, then it MUST advertise FEC-Label 679 bindings for IPv6 address families to that peer. 681 This last point helps to maintain forward compatibility (no 682 need to require this TLV for IPv6 Single-stack LDP). 684 An LSR MAY further constrain the advertisement of FEC-label bindings 685 for a particular address family by negotiating the IP Capability for 686 a given address family, as specified in [IPPWCap] document. This 687 allows an LSR pair to neither advertise nor receive the undesired 688 FEC-label bindings on a per address family basis to a peer. 690 If an LSR is configured to change an interface or peer from Single- 691 stack LDP to Dual-stack LDP, then an LSR SHOULD use Typed Wildcard 692 FEC procedures [RFC5918] to request the label bindings for the 693 enabled address family. This helps to relearn the label bindings 694 that may have been discarded before without resetting the session. 696 8. LDP Identifiers and Duplicate Next Hop Addresses 698 RFC5036 section 2.7 specifies the logic for mapping the IP routing 699 next-hop (of a given FEC) to an LDP peer so as to find the correct 700 label entry for that FEC. The logic involves using the IP routing 701 next-hop address as an index into the (peer Address) database (which 702 is populated by the Address message containing mapping between each 703 peer's local addresses and its LDP Identifier) to determine the LDP 704 peer. 706 However, this logic is insufficient to deal with duplicate IPv6 707 (link-local) next-hop addresses used by two or more peers. The 708 reason is that all interior IPv6 routing protocols (can) use link- 709 local IPv6 addresses as the IP routing next-hops, and 'IPv6 710 Addressing Architecture [RFC4291]' allows a link-local IPv6 address 711 to be used on more than one links. 713 Hence, this logic is extended by this specification to use not only 714 the IP routing next-hop address, but also the IP routing next-hop 715 interface to uniquely determine the LDP peer(s). The next-hop 716 address-based LDP peer mapping is to be done through LDP peer 717 address database (populated by Address messages received from the 718 LDP peers), whereas next-hop interface-based LDP peer mapping is to 719 be done through LDP hello adjacency/interface database (populated by 720 hello messages received from the LDP peers). 722 This extension solves the problem of two or more peers using the 723 same link-local IPv6 address (in other words, duplicate peer 724 addresses) as the IP routing next-hops. 726 Lastly, for better scale and optimization, an LSR may advertise only 727 the link-local IPv6 addresses in the Address message, assuming that 728 the peer uses only the link-local IPv6 addresses as static and/or 729 dynamic IP routing next-hops. 731 9. LDP TTL Security 733 This document recommends enabling Generalized TTL Security Mechanism 734 (GTSM) for LDP, as specified in [RFC6720], for the LDP/TCP transport 735 connection over IPv6 (i.e. LDPoIPv6). The GTSM inclusion is intended 736 to automatically protect IPv6 LDP peering session from off-link 737 attacks. 739 [RFC6720] allows for the implementation to statically 740 (configuration) and/or dynamically override the default behavior 741 (enable/disable GTSM) on a per-peer basis. Such a configuration an 742 option could be set on either LSR (since GTSM negotiation would 743 ultimately disable GTSM between LSR and its peer(s)). 745 LDP Link Hello packets MUST have their IPv6 Hop Limit set to 255, 746 and be checked for the same upon receipt before any further 747 processing, as per section 3 of [RFC5082]. 749 10. IANA Considerations 751 This document defines a new optional parameter for the LDP Hello 752 Message and two new status codes for the LDP Notification Message. 754 The 'Dual-Stack capability' parameter requires a code point from the 755 TLV Type Name Space. IANA is requested to allocated a code point 756 from the IETF Consensus range 0x0700-0x07ff for the 'Dual-Stack 757 capability' TLV. 759 The 'Transport Connection Mismatch' status code requires a code 760 point from the Status Code Name Space. IANA is requested to allocate 761 a code point from the IETF Consensus range and mark the E bit column 762 with a '1'. 764 The 'Dual-Stack Non-Compliance' status code requires a code point 765 from the Status Code Name Space. IANA is requested to allocate a 766 code point from the IETF Consensus range and mark the E bit column 767 with a '1'. 769 11. Security Considerations 771 The extensions defined in this document only clarify the behavior of 772 LDP, they do not define any new protocol procedures. Hence, this 773 document does not add any new security issues to LDP. 775 While the security issues relevant for the [RFC5036] are relevant 776 for this document as well, this document reduces the chances of off- 777 link attacks when using IPv6 transport connection by including the 778 use of GTSM procedures [RFC5082]. Please see section 9 for LDP TTL 779 Security details. 781 Moreover, this document allows the use of IPsec [RFC4301] for IPv6 782 protection, hence, LDP can benefit from the additional security as 783 specified in [RFC7321] as well as [RFC5920]. 785 12. Acknowledgments 787 We acknowledge the authors of [RFC5036], since some text in this 788 document is borrowed from [RFC5036]. 790 Thanks to Bob Thomas for providing critical feedback to improve this 791 document early on. 793 Many thanks to Eric Rosen, Lizhong Jin, Bin Mo, Mach Chen, Shane 794 Amante, Pranjal Dutta, Mustapha Aissaoui, Matthew Bocci, Mark Tinka, 795 Tom Petch, Kishore Tiruveedhula, Manoj Dutta, Vividh Siddha, Qin Wu, 796 Simon Perreault, Brian E Carpenter, Santosh Esale, Danial Johari and 797 Loa Andersson for thoroughly reviewing this document, and providing 798 insightful comments and multiple improvements. 800 This document was prepared using 2-Word-v2.0.template.dot. 802 13. Additional Contributors 804 The following individuals contributed to this document: 806 Kamran Raza 807 Cisco Systems, Inc. 808 2000 Innovation Drive 809 Kanata, ON K2K-3E8, Canada 810 Email: skraza@cisco.com 812 Nagendra Kumar 813 Cisco Systems, Inc. 814 SEZ Unit, Cessna Business Park, 815 Bangalore, KT, India 816 Email: naikumar@cisco.com 817 Andre Pelletier 818 Cisco Systems, Inc. 819 2000 Innovation Drive 820 Kanata, ON K2K-3E8, Canada 821 Email: apelleti@cisco.com 823 14. References 825 14.1. Normative References 827 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 828 Requirement Levels", BCP 14, RFC 2119, March 1997. 830 [RFC4291] Hinden, R. and S. Deering, "Internet Protocol Version 6 831 (IPv6) Addressing Architecture", RFC 4291, February 2006. 833 [RFC5036] Andersson, L., Minei, I., and Thomas, B., "LDP 834 Specification", RFC 5036, October 2007. 836 [RFC5082] Pignataro, C., Gill, V., Heasley, J., Meyer, D., and 837 Savola, P., "The Generalized TTL Security Mechanism 838 (GTSM)", RFC 5082, October 2007. 840 [RFC5918] Asati, R., Minei, I., and Thomas, B., "Label Distribution 841 Protocol (LDP) 'Typed Wildcard Forward Equivalence Class 842 (FEC)", RFC 5918, October 2010. 844 14.2. Informative References 846 [RFC4301] Kent, S. and K. Seo, "Security Architecture and Internet 847 Protocol", RFC 4301, December 2005. 849 [RFC7321] Manral, V., "Cryptographic Algorithm Implementation 850 Requirements for Encapsulating Security Payload (ESP) and 851 Authentication Header (AH)", RFC 7321, April 2007. 853 [RFC5920] Fang, L., "Security Framework for MPLS and GMPLS 854 Networks", RFC 5920, July 2010. 856 [RFC4798] De Clercq, et al., "Connecting IPv6 Islands over IPv4 MPLS 857 Using IPv6 Provider Edge Routers (6PE)", RFC 4798, 858 February 2007. 860 [IPPWCap] Raza, K., "LDP IP and PW Capability", draft-ietf-mpls-ldp- 861 ip-pw-capability, October 2014. 863 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 864 for IPv6", RFC 5340, July 2008. 866 [RFC6286] E. Chen, and J. Yuan, "Autonomous-System-Wide Unique BGP 867 Identifier for BGP-4", RFC 6286, June 2011. 869 [RFC6720] R. Asati, and C. Pignataro, "The Generalized TTL Security 870 Mechanism (GTSM) for the Label Distribution Protocol 871 (LDP)", RFC 6720, August 2012. 873 [RFC4038] M-K. Shin, Y-G. Hong, J. Hagino, P. Savola, and E. M. 874 Castro, "Application Aspects of IPv6 Transition", RFC 875 4038, March 2005. 877 [RFC7439] W. George, and C. Pignataro, "Gap Analysis for Operating 878 IPv6-Only MPLS Networks", RFC 7439, January 2015. 880 Appendix A. 882 A.1. LDPv6 and LDPv4 Interoperability Safety Net 884 It is not safe to assume that RFC5036 compliant implementations have 885 supported handling IPv6 address family (IPv6 FEC label) in Label 886 Mapping message all along. 888 If a router upgraded with this specification advertised both IPv4 889 and IPv6 FECs in the same label mapping message, then an IPv4-only 890 peer (not knowing how to process such a message) may abort 891 processing the entire label mapping message (thereby discarding even 892 the IPv4 label FECs), as per the section 3.4.1.1 of RFC5036. 894 This would result in LDPv6 to be somewhat undeployable in existing 895 production networks. 897 The change proposed in section 7 of this document provides a good 898 safety net and makes LDPv6 incrementally deployable without making 899 any such assumption on the routers' support for IPv6 FEC processing 900 in current production networks. 902 A.2. Accommodating Non-RFC5036-compliant implementations 904 It is not safe to assume that implementations have been RFC5036 905 compliant in gracefully handling IPv6 address family (IPv6 Address 906 List TLV) in Address message all along. 908 If a router upgraded with this specification advertised IPv6 909 addresses (with or without IPv4 addresses) in Address message, then 910 an IPv4-only peer (not knowing how to process such a message) may 911 not follow section 3.5.5.1 of RFC5036, and tear down the LDP 912 session. 914 This would result in LDPv6 to be somewhat undeployable in existing 915 production networks. 917 The changes proposed in section 6 and 7 of this document provides a 918 good safety net and makes LDPv6 incrementally deployable without 919 making any such assumption on the routers' support for IPv6 FEC 920 processing in current production networks. 922 A.3. Why prohibit IPv4-mapped IPv6 addresses in LDP 924 Per discussion with 6MAN and V6OPS working groups, the overwhelming 925 consensus was to not promote IPv4-mapped IPv6 addresses appear in 926 the routing table, as well as in LDP (address and label) databases. 928 Also, [RFC4038] section 4.2 suggests that IPv4-mapped IPv6 addressed 929 packets should never appear on the wire. 931 A.4. Why 32-bit value even for IPv6 LDP Router ID 933 The first four octets of the LDP identifier, the 32-bit LSR Id (e.g. 934 (i.e. LDP Router Id), identify the LSR and is a globally unique 935 value within the MPLS network. This is regardless of the address 936 family used for the LDP session. 938 Please note that 32-bit LSR Id value would not map to any IPv4- 939 address in an IPv6 only LSR (i.e., single stack), nor would there be 940 an expectation of it being IP routable, nor DNS-resolvable. In IPv4 941 deployments, the LSR Id is typically derived from an IPv4 address, 942 generally assigned to a loopback interface. In IPv6 only 943 deployments, this 32-bit LSR Id must be derived by some other means 944 that guarantees global uniqueness within the MPLS network, similar 945 to that of BGP Identifier [RFC6286] and OSPF router ID [RFC5340]. 947 This document reserves 0.0.0.0 as the LSR Id, and prohibits its 948 usage with IPv6, in line with OSPF router Id in OSPF version 3 949 [RFC5340]. 951 Author's Addresses 953 Vishwas Manral 954 Hewlet-Packard, Inc. 955 19111 Pruneridge Ave., Cupertino, CA, 95014 956 Phone: 408-447-1497 957 Email: vishwas.manral@hp.com 959 Rajiv Papneja 960 Huawei Technologies 961 2330 Central Expressway 962 Santa Clara, CA 95050 963 Phone: +1 571 926 8593 964 EMail: rajiv.papneja@huawei.com 966 Rajiv Asati 967 Cisco Systems, Inc. 968 7025 Kit Creek Road 969 Research Triangle Park, NC 27709-4987 970 Email: rajiva@cisco.com 972 Carlos Pignataro 973 Cisco Systems, Inc. 974 7200 Kit Creek Road 975 Research Triangle Park, NC 27709-4987 976 Email: cpignata@cisco.com