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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 MPLS Working Group Kamran Raza 3 Internet Draft Sami Boutros 4 Intended Status: Standards Track 5 Expires: July 17, 2015 Cisco Systems, Inc. 7 January 18, 2015 9 Controlling State Advertisements Of Non-negotiated LDP Applications 11 draft-ietf-mpls-ldp-ip-pw-capability-09.txt 13 Status of this Memo 15 This Internet-Draft is submitted to IETF in full conformance with the 16 provisions of BCP 78 and BCP 79. 18 Internet-Drafts are working documents of the Internet Engineering Task 19 Force (IETF), its areas, and its working groups. Note that other 20 groups may also distribute working documents as Internet-Drafts. 22 Internet-Drafts are draft documents valid for a maximum of six months 23 and may be updated, replaced, or obsoleted by other documents at any 24 time. It is inappropriate to use Internet-Drafts as reference 25 material or to cite them other than as "work in progress." 27 The list of current Internet-Drafts can be accessed at 28 http://www.ietf.org/1id-abstracts.html 30 The list of Internet-Draft Shadow Directories can be accessed at 31 http://www.ietf.org/shadow.html 33 Copyright Notice 35 Copyright (c) 2015 IETF Trust and the persons identified as the 36 document authors. All rights reserved. 38 This document is subject to BCP 78 and the IETF Trust's Legal 39 Provisions Relating to IETF Documents 40 (http://trustee.ietf.org/license-info) in effect on the date of 41 publication of this document. Please review these documents carefully, 42 as they describe your rights and restrictions with respect to this 43 document. Code Components extracted from this document must include 44 Simplified BSD License text as described in Section 4.e of the Trust 45 Legal Provisions and are provided without warranty as described in the 46 Simplified BSD License. 48 Abstract 50 There is no capability negotiation done for Label Distribution 51 Protocol (LDP) applications that setup Label Switched Paths (LSPs) for 52 IP prefixes or that signal Point-to-point (P2P) Pseudowires (PWs) for 53 Layer 2 Virtual Private Networks (L2VPNs). When an LDP session comes 54 up, an LDP speaker may unnecessarily advertise its local state for 55 such LDP applications even when the peer session is established for 56 some other applications like Multipoint LDP (mLDP) or Inter-Chassis 57 Communication Protocol (ICCP). This document defines a solution by 58 which an LDP speaker announces to its peer its disinterest in such 59 non-negotiated applications, thus disabling the unnecessary 60 advertisement of corresponding application state, which would have 61 otherwise be advertised over the established LDP session. 63 Table of Contents 65 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 66 2. Conventions used in this document . . . . . . . . . . . . . . . 4 67 3. Non-negotiated LDP applications . . . . . . . . . . . . . . . . 4 68 3.1. Non-interesting State . . . . . . . . . . . . . . . . . . . 4 69 3.1.1. Prefix-LSPs . . . . . . . . . . . . . . . . . . . . . 5 70 3.1.2. P2P-PWs . . . . . . . . . . . . . . . . . . . . . . . 5 71 4. Controlling State Advertisement . . . . . . . . . . . . . . . . 5 72 4.1. State Advertisement Control Capability . . . . . . . . . . 5 73 4.2. Capabilities Procedures . . . . . . . . . . . . . . . . . . 8 74 4.2.1. State Control Capability in an Initialization message . 8 75 4.2.2. State Control capability in a Capability message . . . 9 76 5. Applicability Statement . . . . . . . . . . . . . . . . . . . . 9 77 6. Operational Examples . . . . . . . . . . . . . . . . . . . . . 11 78 6.1. Disabling Prefix-LSPs and P2P-PWs on an ICCP session . . . 11 79 6.2. Disabling Prefix-LSPs on a L2VPN/PW T-LDP session . . . . . 11 80 6.3. Disabling Prefix-LSPs dynamically on an estab. LDP session 11 81 6.4. Disabling Prefix-LSPs on an mLDP-only session . . . . . . . 12 82 6.5. Disabling IPv4 or IPv6 Prefix-LSPs on a dual-stack LSR . . 12 83 7. Security Considerations . . . . . . . . . . . . . . . . . . . . 13 84 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 13 85 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 86 9.1. Normative References . . . . . . . . . . . . . . . . . . . 13 87 9.2. Informative References . . . . . . . . . . . . . . . . . . 13 88 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14 89 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14 91 1. Introduction 93 LDP Capabilities specification [RFC5561] introduced a mechanism to 94 negotiate LDP capabilities for a given feature between peer Label 95 Switching Routers (LSRs). The capability mechanism insures that no 96 unnecessary state is exchanged between peer LSRs unless the 97 corresponding feature capability is successfully negotiated between 98 the peers. 100 Newly defined LDP features and applications, such as Typed Wildcard 101 Forwarding Equivalence Class (FEC) [RFC5918], Inter-Chassis 102 Communication Protocol [RFC7275], mLDP [RFC6388], and L2VPN Point-to- 103 multipoint (P2MP) PW [P2MP-PW] make use of LDP capabilities framework 104 for their feature negotiation. However, the earlier LDP application to 105 establish LSPs for IP unicast prefixes, and application to signal 106 L2VPN P2P PW [RFC4447] [RFC4762] allowed LDP speakers to exchange 107 application state without any capability negotiation, thus causing 108 unnecessary state advertisement when a given application is not 109 enabled on one of the LDP speakers participating in a given session. 110 For example, when bringing up and using an LDP peer session with a 111 remote Provider Edge (PE) LSR for purely ICCP signaling reasons, an 112 LDP speaker may unnecessarily advertise labels for IP (unicast) 113 prefixes to this ICCP related LDP peer. 115 Another example of unnecessary state advertisement can be cited when 116 LDP is to be deployed in an IP dual-stack environment. For instance, 117 an LSR that is locally enabled to setup LSPs for both IPv4 and IPv6 118 prefixes may advertise (address and label) bindings for both IPv4 and 119 IPv6 address families towards an LDP peer that is interested in IPv4 120 bindings only. In this case, the advertisement of IPv6 bindings to the 121 peer is unnecessary, as well as wasteful, from the point of view of 122 LSR memory/CPU and network resource consumption. 124 To avoid this unnecessary state advertisement and exchange, currently 125 an operator is typically required to configure and define filtering 126 policies on the LSR, which introduces unnecessary operational overhead 127 and complexity for such deployments. 129 This document defines an LDP Capabilities [RFC5561] based solution by 130 which an LDP speaker may announce to its peer(s) its disinterest (or 131 non-support) for state to setup IP Prefix LSPs and/or to signal L2VPN 132 P2P PW at the time of session establishment. This capability helps in 133 avoiding unnecessary state advertisement for such feature 134 applications. This document also states the mechanics to dynamically 135 disable or enable the state advertisement for such applications during 136 the session lifetime. The non-interesting state of an application 137 depends on the type of application and is described later in section 138 3.1. 140 2. Conventions used in this document 142 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 143 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 144 document are to be interpreted as described in RFC-2119 [RFC2119]. 146 The term "IP" in this document refers to both IPv4 and IPv6 unicast 147 address families. 149 3. Non-negotiated LDP applications 151 For the applications that existed prior to the definition of LDP 152 Capabilities framework [RFC5561], an LDP speaker typically advertises, 153 without waiting for any capabilities exchange and negotiation, its 154 corresponding application state to its peers after the session 155 establishment. These early LDP applications include: 157 o IPv4/IPv6 Prefix LSPs Setup 158 o L2VPN P2P FEC128 and FEC129 PWs signaling 160 This document onward uses following shorthand terms for these earlier 161 LDP applications: 163 o "Prefix-LSPs": Refers to an application that sets up LDP LSPs 164 corresponding to IP routes/prefixes by advertising label 165 bindings for Prefix FEC (as defined in RFC-5036). 167 o "P2P-PWs": Refers to an application that signals FEC 128 and/or 168 FEC 129 L2VPN P2P Pseudowires using LDP (as defined in RFC-4447). 170 To disable unnecessary state exchange for such LDP applications over 171 an established LDP session, a new capability is being introduced in 172 this document. This new capability controls the advertisement of 173 application state and enables an LDP speaker to notify its peer its 174 disinterest in the state of one or more of these "Non-negotiated" LDP 175 applications at the time of session establishment. Upon receipt of 176 such capability, the receiving LDP speaker, if supporting the 177 capability, disables the advertisement of the state related to the 178 application towards the sender of the capability. This new capability 179 can also be sent later in a Capability message to either disable a 180 previously enabled application's state advertisement or to enable a 181 previously disabled application's state advertisement. 183 3.1. Non-interesting State 185 A non-interesting state of a non-negotiated LDP application: 186 - is the application state which is of a no interest to an LSR and 187 need not be advertised to the LSR; 189 - need not be advertised in any of the LDP protocol messages; 190 - is dependent on application type and specified accordingly. 192 3.1.1 Prefix-LSPs 194 For Prefix-LSPs application type, the non-interesting state refers to 195 any state related to IP Prefix FEC (such as FEC label bindings, LDP 196 Status). This document, however, does not classify IP address 197 bindings (advertised via ADDRESS message) as a non-interesting state 198 and allows the advertisement of IP Address bindings. The reason for 199 this allowance is that an LSR typically uses peer IP address(es) to 200 map an IP routing nexthop/address to an LDP peer for their 201 functionality. For example, mLDP [RFC6388] uses peer's IP address(es) 202 to determine its upstream LSR to reach Root node as well as to select 203 forwarding interface towards its downstream LSR. Hence in an mLDP- 204 only network, while it is desirable to disable advertisement of label 205 bindings for IP (unicast) Prefixes, disabling advertisement of IP 206 address bindings will break mLDP functionality. Similarly, other LDP 207 applications may also depend on learnt peer IP address and hence this 208 document does not put IP address binding into a non-interesting state 209 category to facilitate such LDP applications. 211 3.1.2 P2P-PWs 213 For P2P-PWs application type, the non-interesting state refers to any 214 state related to P2P PW FEC128/FEC129 (such as FEC label bindings, 215 MAC [address] withdrawal, and LDP PW Status). From now onward in this 216 document, the term "state" will mean to refer to the "non-interesting 217 state" for an application, as defined in this section. 219 4. Controlling State Advertisement 221 To control advertisement of non-interesting state related to non- 222 negotiated LDP applications defined in section 3, a new capability 223 TLV is defined as follows. 225 4.1. State Advertisement Control Capability 227 The "State Advertisement Control Capability" is a new Capability 228 Parameter TLV defined in accordance with section 3 of LDP 229 Capabilities specification [RFC5561]. The format of this new TLV is 230 as follows: 232 0 1 2 3 233 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 234 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 235 |U|F|State Adv. Ctrl. Cap (IANA)| Length | 236 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 237 |S| Reserved | | 238 +-+-+-+-+-+-+-+-+ 239 | | 240 ~ State Advertisement Control Element(s) ~ 241 | | 242 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 244 Figure 1: Format of an "State Advertisement Control Capability" TLV 246 The value of the U-bit for the TLV MUST be set to 1 so that a 247 receiver MUST silently ignore this TLV if unknown to it, and continue 248 processing the rest of the message. Whereas, The value of F-bit MUST 249 be set to 0. Once advertised, this capability cannot be withdrawn; 250 thus S-bit MUST be set to 1 in an Initialization and Capability 251 message. 253 The capability data associated with this State Advertisement Control 254 (SAC) Capability TLV is one or more State Advertisement Control 255 Elements, where each element indicates enabling/disabling of 256 advertisement of non-interesting state for a given application. The 257 format of a SAC Element is defined as follows: 259 0 1 2 3 4 5 6 7 260 +-+-+-+-+-+-+-+-+ 261 |D| App |Unused | 262 +-+-+-+-+-+-+-+-+ 264 Figure 2: Format of "State Advertisement Control Element" 266 Where: 267 D bit: Controls the advertisement of the state specified in "App" 268 field: 269 1: Disable state advertisement 270 0: Enable state advertisement 271 When sent in an Initialization message, D bit MUST be set 272 to 1. 274 App: Defines the legacy application type whose state advertisement 275 is to be controlled. The value of this field is defined as 276 follows: 278 1: IPv4 Prefix-LSPs (LSPs for IPv4 prefixes) 279 2: IPv6 Prefix-LSPs (LSPs for IPv6 prefixes) 280 3: FEC128 P2P-PW (L2VPN PWid FEC signaling) 281 4: FEC129 P2P-PW (L2VPN Generalized PWid FEC signaling) 283 Any other value in this field MUST be treated as an error. 285 Unused: MBZ on transmit and ignored on receipt. 287 The "Length" field of SAC Capability TLV (in octets) is computed as 288 following: 289 Length (in octets) = 1 + number of SAC elements 290 For example, if there are two SAC elements present, then the Length 291 field is set to 3 octets. A receiver of this capability TLV can 292 deduce the number of elements present in the TLV by using the Length 293 field. 295 From now onward, this document uses the term "element" to refer to a 296 SAC Element. 298 As described earlier, SAC Capability TLV MAY be included by an LDP 299 speaker in an Initialization message to signal to its peer LSR that 300 state exchange for one or more application(s) need to be disabled on 301 the given peer session. This TLV can also be sent later in a 302 Capability message to selectively enable or disable these 303 applications. If there are more than one elements present in a SAC 304 Capability TLV, the elements MUST belong to distinct app types and 305 the an app type MUST NOT appear more than once. If a receiver 306 receives such a malformed TLV, it SHOULD discard this TLV and 307 continue processing rest of the message. If an LSR receives a message 308 with a SAC capability TLV containing an element with "App" field set 309 to a value other than defined above, the receiver MUST ignore and 310 discard the element and continue processing the rest of the TLV. 312 To control more than one application state, a sender LSR can either 313 send a single capability TLV in a message with multiple elements 314 present, or can send separate messages with capability TLV specifying 315 one or more elements. A receiving LSR, however, MUST treat each 316 incoming capability TLV with an element corresponding to a given 317 application type as an update to its existing policy for the given 318 type. 320 To understand capability updates from an example, let us consider 2 321 LSRs, S (LDP speaker) and P (LDP peer), both of which support all the 322 non-negotiated applications listed earlier. By default, these LSR 323 will advertise state for these applications, as configured, to their 324 peer as soon as an LDP session is established. Now assume that P 325 receives from S a SAC capability in an Initialization message with 326 "IPv6 Prefix-LSPs" and "FEC129 P2P-PW" applications disabled. This 327 updates P's outbound policy towards S to advertise state related to 328 only IPv4 Prefix-LSPs and FEC128 P2P-PW applications. Later, P 329 receives another capability update from S via a Capability message 330 with "IPv6 Prefix-LSPs" enabled and "FEC128 P2P-PWs" disabled. This 331 results in P's outbound policy towards S to advertise both IPv4 and 332 IPv6 Prefix-LSPs application state, and disable both FEC128 and 333 FEC129 P2P-PWs signaling. Finally, P receives another update from S 334 via a Capability message that specifies to disable all four non- 335 negotiated applications state, resulting in P outbound policy towards 336 S to block/disable state for all these applications, and only 337 advertise state for any other application, as applicable. 339 4.2. Capabilities Procedures 341 The SAC capability conveys the desire of an LSR to disable the 342 receipt of unwanted/unnecessary state from its LDP peer. This 343 capability is unilateral and unidirectional in nature, and a 344 receiving LSR is not required to send a similar capability TLV in an 345 Initialization or Capability message towards the sender of this 346 capability. This unilateral behavior conforms to the procedures 347 defined in the Section 6 of LDP Capabilities [RFC5561]. 349 After this capability is successfully negotiated (i.e. sent by an LSR 350 and received/understood by its peer), then the receiving LSR MUST NOT 351 advertise any state related to the disabled applications towards the 352 capability sending LSR until and unless these application states are 353 explicitly enabled again via a capability update. Upon receipt of a 354 capability update to disable an enabled application [state] during 355 the lifetime of a session, the receiving LSR MUST also withdraw from 356 the peer any previously advertised state corresponding to the 357 disabled application. 359 If a receiving LDP speaker does not understand the SAC capability 360 TLV, then it MUST respond to the sender with "Unsupported TLV" 361 notification as described in LDP Capabilities [RFC5561]. If a 362 receiving LDP speaker does not understand or does not support an 363 application specified in an application control element, it SHOULD 364 silently ignore/skip such an element and continue processing rest of 365 the TLV. 367 4.2.1. State Control Capability in an Initialization message 369 LDP Capabilities [RFC5561] framework dictates that the S-bit of 370 capability parameter in an Initialization message MUST be set to 1 371 and SHOULD be ignored on receipt. 373 An LDP speaker determines (e.g. via some local configuration or 374 default policy) if it needs to disable Prefix-LSPs and/or P2P-PWs 375 applications with a peer LSR. If there is a need to disable, then the 376 SAC TLV needs to be included in the Initialization message with 377 respective SAC elements included with their D bit set to 1. 379 An LDP speaker that supports the SAC capability MUST interpret the 380 capability TLV in a received Initialization message such that it 381 disables the advertisement of the application state towards the 382 capability sending LSR for Prefix-LSPs and/or P2P-PWs applications if 383 their SAC element's D bit is set to 1. 385 4.2.2. State Control capability in a Capability message 387 If the LDP peer supports "Dynamic Announcement Capability" [RFC5561], 388 then an LDP speaker may send SAC capability in a Capability message 389 towards the peer. Once advertised, these capabilities cannot be 390 withdrawn and hence the S-bit of the TLV MUST be set to 1 when sent 391 in a Capability message. 393 An LDP speaker may decide to send this TLV towards an LDP peer if one 394 or more of its Prefix-LSPs and/or P2P-PWs applications get disabled, 395 or if previously disabled application gets enabled again. In this 396 case, the LDP speaker constructs the TLV with appropriate SAC 397 element(s) and sends the corresponding capability TLV in a Capability 398 message. 400 Upon receipt of this TLV in a Capability message, the receiving LDP 401 speaker reacts in the same manner as it reacts upon the receipt of 402 this TLV in an Initialization message. Additionally, the peer 403 withdraws/advertises the application state from/to the capability 404 sending LDP speaker according to the capability update. 406 5. Applicability Statement 408 The procedures defined in this document may result in disabling 409 announcement of label bindings for IP Prefixes and/or P2P PW FECs, 410 and hence should be used with caution and discretion. This document 411 recommends that this new SAC capability and its procedures SHOULD be 412 enabled on an LSR only via a configuration knob. This knob could 413 either be a global LDP knob or be implemented per LDP neighbor. 414 Hence, it is recommended that an operator SHOULD enable this 415 capability and its associated procedures on an LSR towards a neighbor 416 only if it is known that such bindings advertisement and exchange 417 with the neighbor is unnecessary and wasteful. 419 Following table summarizes a non-exhaustive list of typical LDP 420 session types on which this new SAC capability and its procedures are 421 expected to be applied to disable advertisement of non-interesting 422 state: 424 +===============================+================================+ 425 | Session Type(s) | Non-interesting State | 426 +===============================+================================+ 427 | P2P-PW FEC128-only | IP Prefix LSPs + P2P-PW FEC129 | 428 |-------------------------------|--------------------------------| 429 | P2P-PW only (FEC128/129) | IP Prefix LSPs | 430 |-------------------------------|--------------------------------| 431 | IPv4-only on a Dual-Stack LSR | IPv6 Prefix LSPs + P2P-PW | 432 |-------------------------------|--------------------------------| 433 | IPv6-only on a Dual-Stack LSR | IPv4 Prefix LSPs + P2P-PW | 434 |-------------------------------|--------------------------------| 435 | mLDP-only | IP Prefix LSPs + P2P-PW | 436 |-------------------------------|--------------------------------| 437 | ICCP-only | IP Prefix LSPs + P2P-PW | 438 +-------------------------------+--------------------------------+ 440 It is to be noted that if an application state needs changing after 441 session initialization (e.g. to enable previously disabled 442 application or to disable previously enabled application), the 443 procedures defined in this document expect LSR peers to support LDP 444 "Dynamic Announcement" Capability to announce the change in SAC 445 capability via LDP Capability message. However, if any of the peering 446 LSR does not support this capability, the alternate option is to 447 force reset the LDP session to advertise the new SAC capability 448 accordingly during the following session initialization. 450 Following are some more important points that an operator need to 451 consider regarding the applicability of this new capability and 452 associated procedures defined in this document: 454 - An operator SHOULD disable Prefix-LSPs state on any Targeted LDP 455 (T-LDP) session that is established for ICCP-only and/or PW-only 456 purposes. 458 - An operator MUST NOT disable Prefix-LSPs state on any T-LDP session 459 that is established for remote LFA FRR [RLFA] reasons. 461 - In a remote LFA FRR [RLFA] enabled network, it is RECOMMENDED to 462 not disable Prefix-LSPs state on a T-LDP session even if the 463 current session type is PW-only and/or ICCP-only. This is 464 recommended because any remote/T-LDP neighbor could potentially be 465 picked as a remote LFA PQ node. 467 - This capability SHOULD be enabled for Prefix-LSPs in the 468 scenarios when it is desirable to disable (or enable) 469 advertisement of "all" the prefix label bindings. For scenarios 470 when a "subset" of bindings need to be filtered, the existing 471 filtering procedures pertaining to label binding announcement 472 should be used. 474 - It is allowed to use label advertisement filtering policies in 475 conjunction with the procedures defined in this document for 476 Prefix-LSPs. In such cases, the label bindings will be announced 477 as per the label filtering policy for the given neighbor when 478 Prefix-LSP application is enabled. 480 6. Operational Examples 482 6.1. Disabling Prefix-LSPs and P2P-PWs on an ICCP session 484 Consider two PE routers, LSR1 and LSR2, which understand/support SAC 485 capability TLV, and have an established LDP session to exchange ICCP 486 state related to dual-homed devices connected to these LSRs. Let us 487 assume that both LSRs are provisioned not to exchange any state for 488 Prefix-LSPs (IPv4/IPv6) and P2P-PWs (FEC128/129) application. 490 To indicate their disinterest in these applications, the LSRs will 491 include a SAC capability TLV (with 4 SAC elements corresponding to 492 these 4 applications with D bit set to 1 for each one) in the 493 Initialization message. Upon receipt of this TLV in Initialization 494 message, the receiving LSR will disable the advertisement of 495 IPv4/IPv6 label bindings, as well as P2P PW FEC128/129 signaling, 496 towards its peer after session establishment. 498 6.2. Disabling Prefix-LSPs on a L2VPN/PW T-LDP session 500 Now, consider LSR1 and LSR2 have an established T-LDP session for 501 P2P-PWs application to exchange label bindings for FEC 128/129. Given 502 that there is no need to exchange IP label bindings amongst the PE 503 LSRs over a PW T-LDP session in most typical deployments, let us 504 assume that LSRs are provisioned to disable IPv4/IPv6 Prefix-LSPs 505 application state on the given PW session. 507 To indicate their disinterest in Prefix-LSPs application over a PW T- 508 LDP session, the LSRs will follow/apply the same procedures as 509 described in previous section. As a result, only P2P-PWs related 510 state will be exchanged between these LSRs over this T-LDP session. 512 6.3. Disabling Prefix-LSPs dynamically on an established LDP session 514 Assume that LSRs from previous sections were initially provisioned to 515 exchange both Prefix-LSPs and P2P-PWs state over the session between 516 them, and also support "Dynamic Announcement" Capability [RFC5561]. 517 Now, assume that LSR1 is dynamically provisioned to disable 518 (IPv4/IPv6) Prefix-LSPs over T-LDP session with LSR2. In this case, 519 LSR1 will send SAC capability TLV in a Capability message towards 520 LSR2 with application control elements defined for IPv4 and IPv6 521 Prefix-LSPs with D bit set to 1. Upon receipt of this TLV, LSR2 will 522 disable Prefix-LSPs application state(s) towards LSR1 and withdraw 523 all previously advertised application state from LSR1. To withdraw 524 label bindings from its peer, LSR2 MAY use a single Prefix FEC Typed 525 Wildcard Label Withdraw message [RFC5918] if the peer supports Typed 526 Wildcard FEC capability. 528 This dynamic disability of Prefix-LSPs application does not impact 529 L2VPN P2P-PWs application on the given session, and both LSRs should 530 continue to exchange PW Signaling application related state. 532 6.4. Disabling Prefix-LSPs on an mLDP-only session 534 Now assume that LSR1 and LSR2 have formed an LDP session to exchange 535 mLDP state only. In typical deployments, LSR1 and LSR2 also exchange 536 bindings for IP (unicast) prefixes upon mLDP session, which is 537 unnecessary and wasteful for an mLDP-only LSR. 539 Using the procedures defined earlier, an LSR can indicate its 540 disinterest in Prefix-LSPs application state to its peer upon session 541 establishment time or dynamically later via LDP capabilities update. 543 Reference to section 3.1, the peer disables the advertisement of any 544 state related to IP Prefix FECs, but still advertises IP address 545 bindings that are required for the correct operation of mLDP. 547 6.5. Disabling IPv4 or IPv6 Prefix-LSPs on a dual-stack LSR 549 In IP dual-stack scenarios, LSR2 may advertise unnecessary state 550 (e.g. IPv6 prefix label bindings) towards peer LSR1 corresponding to 551 IPv6 Prefix-LSPs application once a session is established mainly for 552 exchanging state for IPv4. The similar scenario also applies when 553 advertising IPv4 Prefix-LSPs state on a session meant for IPv6. The 554 SAC capability and its procedures defined in this document can help 555 to avoid such unnecessary state advertisement. 557 Consider IP dual-stack environment where LSR2 is enabled for Prefix- 558 LSPs application for both IPv4 and IPv6, but LSR1 is enabled for (or 559 interested in) only IPv4 Prefix-LSPs. To avoid receiving unwanted 560 state advertisement for IPv6 Prefix-LSPs application from LSR2, LSR1 561 can send SAC capability with element for IPv6 Prefix-LSPs with D bit 562 set to 1 in the Initialization message towards LSR2 at the time of 563 session establishment. Upon receipt of this capability, LSR2 will 564 disable all IPv6 label binding advertisement towards LSR1. If IPv6 565 Prefix-LSPs application is later enabled on LSR1, LSR1 can update the 566 capability by sending SAC capability in a Capability message towards 567 LSR2 to enable this application dynamically. 569 7. Security Considerations 571 The proposal introduced in this document does not introduce any new 572 security considerations beyond that already apply to the base LDP 573 specification [RFC5036] and [RFC5920]. 575 8. IANA Considerations 577 This document defines a new LDP capability parameter TLV. IANA is 578 requested to assign the lowest available value after 0x0500 from "TLV 579 Type Name Space" in the "Label Distribution Protocol (LDP) 580 Parameters" registry as the new code point for the new LDP capability 581 TLV code point. 583 +-----+---------------------+---------------+-----------------------+ 584 |Value| Description | Reference |Notes/Registration Date| 585 +-----+---------------------+---------------+-----------------------+ 586 | TBA | State Advertisement | This document | | 587 | | Control Capability | | | 588 +-----+---------------------+---------------+-----------------------+ 590 9. References 592 9.1 Normative References 594 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 595 Requirement Levels", BCP 14, RFC 2119, March 1997, 596 . 598 [RFC5036] Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed., 599 "LDP Specification", RFC 5036, October 2007, 600 . 602 [RFC5561] Thomas, B., Raza, K., Aggarwal, S., Aggarwal, R., and JL. 603 Le Roux, "LDP Capabilities", RFC 5561, July 2009, 604 . 606 9.2 Informative References 608 [RFC4447] Martini, L., Ed., Rosen, E., El-Aawar, N., Smith, T., and 609 G. Heron, "Pseudowire Setup and Maintenance Using the 610 Label Distribution Protocol (LDP)", RFC 4447, April 2006, 611 . 613 [RFC4762] Lasserre, M., Ed., and V. Kompella, Ed., "Virtual Private 614 LAN Service (VPLS) Using Label Distribution Protocol (LDP) 615 Signaling", RFC 4762, January 2007, . 618 [RFC5918] Asati, R., Minei, I., and B. Thomas, "Label Distribution 619 Protocol (LDP) 'Typed Wildcard' Forward Equivalence Class 620 (FEC)", RFC 5918, August 2010, . 623 [RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS 624 Networks", RFC 5920, July 2010, . 627 [RFC6388] Wijnands, IJ., Ed., Minei, I., Ed., Kompella, K., and B. 628 Thomas, "Label Distribution Protocol Extensions for Point- 629 to-Multipoint and Multipoint-to-Multipoint Label Switched 630 Paths", RFC 6388, November 2011, . 633 [RFC7275] Martini, L., Salam, S., Sajassi, A., Bocci, M., 634 Matsushima, S., and T. Nadeau, "Inter-Chassis 635 Communication Protocol for Layer 2 Virtual Private Network 636 (L2VPN) Provider Edge (PE) Redundancy", RFC 7275, June 637 2014, . 639 [P2MP-PW] Martini, L. et. al, "Signaling Root-Initiated Point-to- 640 Multipoint Pseudowires using LDP", draft-ietf-pwe3-p2mp- 641 pw-04.txt, Work in Progress, March 2012. 643 [RLFA] Bryant, S., Filsfils, C., Previdi, S., Shand, M., So, N., 644 "Remote LFA FRR", draft-ietf-rtgwg-remote-lfa-10, Work in 645 Progress, January 2015. 647 10. Acknowledgments 649 The authors would like to thank Eric Rosen and Alexander Vainshtein 650 for their review and valuable comments. We also acknowledge Karthik 651 Subramanian and IJsbrand Wijnands for bringing up mLDP use case. 653 Authors' Addresses 655 Kamran Raza 656 Cisco Systems, Inc., 657 2000 Innovation Drive, 658 Ottawa, ON K2K-3E8, Canada. 659 E-mail: skraza@cisco.com 661 Sami Boutros 662 Cisco Systems, Inc. 663 3750 Cisco Way, 664 San Jose, CA 95134, USA. 665 E-mail: sboutros@cisco.com