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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 MPLS Working Group Kamran Raza 2 Internet Draft Sami Boutros 3 Updates: 5036, 4447 (if approved) Luca Martini 4 Intended status: Standards Track Cisco Systems, Inc. 5 Expires: February 7, 2013 6 Nicolai Leymann 7 Deutsche Telekom 9 August 8, 2012 11 Applicability of LDP Label Advertisement Mode 13 draft-ietf-mpls-ldp-applicability-label-adv-00.txt 15 Abstract 17 An LDP speaker negotiates the label advertisement mode with its LDP 18 peer at the time of session establishment. Although different 19 applications sharing the same LDP session may need different modes 20 of label distribution and advertisement, there is only one type of 21 label advertisement mode that is negotiated and used per LDP 22 session. This document clarifies the use and the applicability of 23 session's negotiated label advertisement mode, and categorizes LDP 24 applications into two broad categories of negotiated mode-bound and 25 mode-independent applications. The document also suggests an update 26 to RFC 5036 and RFC 4447 to remove any ambiquity and conflict in the 27 area of using correct label advertisement mode for a given 28 application. 30 Status of this Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF), its areas, and its working groups. Note that 37 other groups may also distribute working documents as Internet- 38 Drafts. 40 Internet-Drafts are draft documents valid for a maximum of six 41 months and may be updated, replaced, or obsoleted by other documents 42 at any time. It is inappropriate to use Internet-Drafts as 43 reference material or to cite them other than as "work in progress." 45 The list of current Internet-Drafts can be accessed at 46 http://www.ietf.org/ietf/1id-abstracts.txt 47 The list of Internet-Draft Shadow Directories can be accessed at 48 http://www.ietf.org/shadow.html 50 This Internet-Draft will expire on February 7, 2013. 52 Copyright Notice 54 Copyright (c) 2012 IETF Trust and the persons identified as the 55 document authors. All rights reserved. 57 This document is subject to BCP 78 and the IETF Trust's Legal 58 Provisions Relating to IETF Documents 59 (http://trustee.ietf.org/license-info) in effect on the date of 60 publication of this document. Please review these documents 61 carefully, as they describe your rights and restrictions with 62 respect to this document. Code Components extracted from this 63 document must include Simplified BSD License text as described in 64 Section 4.e of the Trust Legal Provisions and are provided without 65 warranty as described in the Simplified BSD License. 67 Table of Contents 69 1. Introduction 3 70 2. Conventions used in this document 3 71 3. Label Advertisement Mode Applicability 4 72 3.1. Label Advertisement Mode Negotiation 4 73 3.2. Mode-based Categorization of LDP Applications 4 74 3.2.1. Session mode-bound Applications 5 75 3.2.2. Session mode-independent Applications 5 76 3.3. Unacceptable label advertisement mode 6 77 4. Clarification on Mode Applicability 6 78 4.1. Update to RFC-5036 7 79 4.2. Update to RFC-4447 7 80 5. Security Considerations 7 81 6. IANA Considerations 7 82 7. References 7 83 7.1. Normative References 7 84 7.2. Informative References 8 85 8. Acknowledgments 8 87 1. Introduction 89 The MPLS architecture [RFC3031] defines two modes of label 90 advertisement for an LSR: 92 1. Downstream-on-Demand 94 2. Unsolicited Downstream 96 The "Downstream-on-Demand" mode requires an LSR to explicitly 97 request the label binding for FECs from its peer, whereas 98 "Unsolicited Downstream" mode allows an LSR to distribute the label 99 binding for FECs to LSR peers that have not explicitly requested 100 them. The MPLS architecture also specifies that on any given label 101 distribution adjacency, the upstream LSR and the downstream LSR must 102 agree to use a single label advertisement mode. 104 Label Distribution Protocol (LDP) [RFC5036] allows label 105 advertisement mode negotiation at time of session establishment 106 (section 3.5.3 [RFC5036]). To comply with MPLS architecture, LDP 107 specification also dictates that only single label advertisement 108 mode is agreed and used for a given LDP session between two LSRs. 110 With the advent of new LDP applications, such as L2VPN [RFC4447], 111 mLDP [RFC6388], ICCP [ICCP], there are situations when an LDP 112 session is shared across more than one application to exchange label 113 bindings for different types of FEC. Although different applications 114 sharing the same LDP session may need a different type of label 115 advertisement mode negotiated, there is only one type of label 116 advertisement mode that is negotiated and agreed at the time of 117 establishment of LDP session. 119 This document clarifies the use and the applicability of label 120 advertisement mode of a session for each application using the 121 session. It also categorizes LDP applications into two broad 122 categories of mode-bound and mode-independent applications. 124 The document also suggests an update to RFC-5036 and RFC-4447 to 125 remove any ambiguity and conflict in the area of using correct label 126 advertisement mode for a given LDP application. 128 2. Conventions used in this document 130 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 131 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 132 document are to be interpreted as described in RFC-2119 [RFC2119]. 134 The unqualified term "mode" used in document refers to "label 135 advertisement mode". 137 Please also note that LDP specification [RFC5036] uses the term 138 "Downstream Unsolicited" to refer to "Unsolicited Downstream". The 139 LDP specification also uses the terms "label distribution mode" and 140 "label advertisement mode" interchangeably. Like LDP specification 141 document, this document also uses these terms interchangeably. 143 3. Label Advertisement Mode Applicability 145 3.1. Label Advertisement Mode Negotiation 147 Label advertisement mode is negotiated between LSR peers at the time 148 of session establishment. The label advertisement mode is specified 149 in LDP Initialization message's "Common Session Parameter" TLV by 150 setting A-bit (Label Advertisement Discipline bit) to 1 or 0 for 151 Downstream-on-Demand or Downstream-Unsolicited modes respectively. 152 The negotiation of the A-bit is specified in section 3.5.3 of 153 [RFC5036] as follows: 155 "If one LSR proposes Downstream Unsolicited and the other proposes 156 Downstream on Demand, the rules for resolving this difference is: 158 - If the session is for a label-controlled ATM link or a 159 label- controlled Frame Relay link, then Downstream on Demand 160 MUST be used. 162 - Otherwise, Downstream Unsolicited MUST be used." 164 Once label advertisement mode has been negotiated and agreed, both 165 LSR peers must use the same mode for label binding exchange. 167 3.2. Mode-based Categorization of LDP Applications 169 The earlier applications, defined and identified at the time of 170 standardization of LDP base specification RFC-3036, using LDP to 171 exchange their FEC bindings were: 173 . Dynamic Label Switching for IP Prefixes 175 . Label-controlled ATM/FR 177 Since then, several new applications have emerged that use LDP to 178 signal their FEC bindings and/or application data. These include: 180 . L2VPN P2P PW ([RFC4447]) 181 . L2VPN P2MP PW ([P2MP-PW]) 183 . mLDP ([RFC6388]) 185 . ICCP ([ICCP]) 187 We divide the LDP applications into two broad categories from label 188 advertisement mode usage point of view: 190 1. Session mode-bound Applications 192 2. Session mode-independent Applications 194 3.2.1. Session mode-bound Applications 196 We define a "session mode-bound application" to be an application 197 which uses the negotiated label advertisement mode. This means that 198 the FEC-label binding exchange for such an LDP applications MUST use 199 the label advertisement mode negotiated for the LDP session. 201 The early LDP applications "Dynamic Label Switching for IP Prefixes" 202 and "Label-controlled ATM/FR" are included into this category. 204 3.2.2. Session mode-independent Applications 206 We define a "session mode-independent application" to be an 207 application which does not care about the negotiated label 208 advertisement mode. This means that the FEC-label binding, or any 209 other application data, exchange for such an LDP application does 210 not care about, nor tied to the "negotiated" label advertisement 211 mode of the session; rather, the information exchange is driven by 212 the application need and procedures as described by its 213 specification document. For example, [RFC6388] specifies procedures 214 to advertise P2MP FEC label binding in an unsolicited manner, 215 irrespective of the negotiated label advertisement mode of the 216 session. 218 The applications, PW (P2P and P2MP), MLDP, and ICCP, are included 219 into this category of LDP applications. 221 3.2.2.1. Upstream Label Assignment 223 As opposed to downstream assigned label advertisement defined by 224 [RFC3031], [RFC6389] specification defines new mode of label 225 advertisement where label advertisement and distribution occurs for 226 upstream assigned labels. 228 As stated earlier in this document, LDP base specification RFC-5036 229 only allows specifying Downstream-Unsolicited or Downstream-on-Demand 230 mode. This means that any LDP application that requires upstream 231 assigned label advertisement also falls under the category of Session 232 mode-independent application. 234 3.3. Unacceptable label advertisement mode 236 The procedures related to unacceptable label advertisement mode, as 237 defined in RFC-5036 section 3.5.3, continue to apply for any "mode- 238 bound" FEC/application. For a "mode-independent" FEC/application, 239 mode negotiation does not apply and hence both LSRs MUST operate in 240 the mode specified for the given application by the respective 241 specification. 243 If a session is jointly shared amongst mode-bound and mode- 244 independent FEC/applications, session will not be established if the 245 label advertisement mode is unacceptable (between the LSRs) for a 246 given mode-bound FEC/application type. This is inline with RFC-5036 247 section 3.5.3 specification for unacceptable mode. 249 4. Clarification on Mode Applicability 251 To remove any ambiguity and conflict amongst different 252 specifications with regards to the use of LDP session's label 253 advertisement mode, we propose an update to LDP base specification 254 RFC-5036 to clarify the applicability of session's negotiated mode. 256 Furthermore, RFC-4447 specifies LDP extensions and procedures to 257 exchange label bindings for P2P PW FECs [RFC4447], and dictates the 258 use of Downstream-Unsolicited mode for an LDP session related to 259 L2VPN PW. This mode dictation creates a direct conflict in 260 situations when a PW LDP session is shared with an LDP application 261 with Downstream-on-Demand mode (such as Label switching Application 262 for IP prefixes). To remove such a conflict, we also propose an 263 update to a section of RFC-4447. 265 4.1. Update to RFC-5036 267 The section 3.5.3 of [RFC5036] is updated to add following two 268 statements under the description of "A, Label Advertisement 269 Discipline": 271 - The negotiated label advertisement discipline only applies to FEC 272 label binding advertisement of "Address Prefix" FECs; 274 - Any new document specifying a new FEC MUST state the 275 applicability of the negotiated label advertisement discipline for 276 that FEC. 278 4.2. Update to RFC-4447 280 The section 3 of [RFC4447] states: 282 "LDP MUST be used in its downstream unsolicited mode." 284 Since PW application falls under session mode-independent 285 application category, the above statement in [RFC4447] should be 286 read to mean as follows: 288 "LDP MUST exchange PW FEC label bindings in downstream unsolicited 289 manner, independent of the negotiated label advertisement mode of 290 the LDP session". 292 5. Security Considerations 294 This document specification only clarifies the applicability of LDP 295 session's label advertisement mode, and hence does not add any LDP 296 security mechanics and considerations to those already defined in 297 LDP specification [RFC5036]. 299 6. IANA Considerations 301 None. 303 7. References 305 7.1. Normative References 307 [RFC5036] L. Andersson, I. Minei, and B. Thomas, "LDP 308 Specification", RFC 5036, September 2007. 310 [RFC4447] L. Martini, Editor, E. Rosen, El-Aawar, T. Smith, G. 311 Heron, "Pseudowire Setup and Maintenance using the Label 312 Distribution Protocol", RFC 4447, April 2006. 314 [RFC3031] E. Rosen, A. Viswanathan, and R. Callon, "Multiprotocol 315 Label Switching Architecture", RFC 3031, January 2001. 317 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 318 Requirement Levels", BCP 14, RFC2119, March 1997. 320 7.2. Informative References 322 [P2MP-PW] S. Boutros, L. Martini, S. Sivabalan, G. Del Vecchio, 323 Kamite, L. Jin, "Signaling Root-Initiated P2MP PWs using 324 LDP", draft-ietf-pwe3-p2mp-pw-04.txt, Work in Progress, 325 March 2012. 327 [RFC6388] I. Minei, I. Wijnand, K. Kompella, B., "LDP Extensions for 328 P2MP and MP2MP LSPs", RFC 6388, November 2011. 330 [ICCP] L. Martini, S. Salam, A. Sajassi, and S. Matsushima, 331 "Inter-Chassis Communication Protocol for L2VPN PE 332 Redundancy", draft-ietf-pwe3-iccp-08.txt, Work in 333 Progress, June 2012. 335 [RFC6389] R. Aggarwal, and J.L. Le Roux, "MPLS Upstream Label 336 Assignment for LDP", RFC 6389, November 2011. 338 8. Acknowledgments 340 We acknowledge the authors of [RFC5036] and [RFC4447] since some of 341 the text in this document is borrowed from their specification. We 342 also acknowledge Eric Rosen and Rajiv Asati for their review and 343 input. 345 This document was prepared using 2-Word-v2.0.template.dot. 347 Authors' Addresses 349 Kamran Raza 350 Cisco Systems, Inc. 351 2000 Innovation Drive, 352 Ottawa, ON K2K-3E8, Canada. 353 E-mail: skraza@cisco.com 354 Sami Boutros 355 Cisco Systems, Inc. 356 3750 Cisco Way, 357 San Jose, CA 95134, USA. 358 E-mail: sboutros@cisco.com 360 Luca Martini 361 Cisco Systems, Inc. 362 9155 East Nichols Avenue, Suite 400, 363 Englewood, CO 80112, USA. 364 E-mail: lmartini@cisco.com 366 Nicolai Leymann 367 Deutsche Telekom, 368 Winterfeldtstrasse 21-27, 369 10781 Berlin, Germany. 370 E-mail: N.Leymann@telekom.de