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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group Rajiv Asati 3 Internet Draft Cisco Systems, Inc. 4 Expiration Date: May 2008 5 Pradosh Mohapatra 6 Cisco Systems, Inc. 8 Bob Thomas 9 Cisco Systems, Inc. 11 Emily Chen 12 Huawei Technologies Co., Ltd. 14 November 2007 16 LDP End-of-LIB 18 draft-asati-mpls-ldp-end-of-lib-01.txt 20 Status of this Memo 22 By submitting this Internet-Draft, each author represents that any 23 applicable patent or other IPR claims of which he or she is aware 24 have been or will be disclosed, and any of which he or she becomes 25 aware will be disclosed, in accordance with Section 6 of BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF), its areas, and its working groups. Note that 29 other groups may also distribute working documents as Internet- 30 Drafts. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 The list of current Internet-Drafts can be accessed at 38 http://www.ietf.org/ietf/1id-abstracts.txt 40 The list of Internet-Draft Shadow Directories can be accessed at 41 http://www.ietf.org/shadow.html. 43 Copyright Notice 45 Copyright (C) The IETF TRUST (2007). 47 Abstract 49 There are situations following LDP session establishment where it 50 would be useful for an LDP speaker to know when its peer has 51 advertised all of its labels. These include session establishment 52 when LDP-IGP sync is in use and session re-establishment following 53 loss of an LDP session when LDP graceful restart is in use. The LDP 54 specification provides no mechanism for an LDP speaker to notify a 55 peer when it has completed its initial label advertisements to that 56 peer. This document specifies means for an LDP speaker to signal 57 completion of its initial label advertisements following session 58 establishment. 60 Table of Contents 62 1 Introduction ....................................... 3 63 2 Specification Language ............................. 3 64 3 Unrecognized Notification Capability ............... 3 65 4 Signaling Completion of Label Advertisement ........ 4 66 5 Usage Guidelines ................................... 5 67 5.1 IGP-Sync ........................................... 5 68 5.2 LDP Graceful Restart ............................... 6 69 5.3 Wildcard Label Request ............................. 6 70 5.4 Missing Expected End-of-LIB Notifications .......... 7 71 6 IANA Considerations ................................ 7 72 7 Security Considerations ............................ 7 73 8 References ......................................... 7 74 9 Author Information ................................. 8 75 10 Intellectual Property Statement .................... 9 76 11 Full Copyright Statement ........................... 9 78 1. Introduction 80 There are situations following LDP session establishment where it 81 would be useful for an LDP speaker to know when its peer has 82 advertised all of its labels. For example, when an LDP speaker is 83 using LDP-IGP synchronization procedures [LDPSynch] it would be 84 useful for the speaker to know when its peer has completed 85 advertisement of its IP label bindings.. Similarly, after an LDP 86 session is re-established when LDP Graceful Restart [RFC3478] is in 87 effect it would be helpful for each peer to signal the other after it 88 has advertised all its label bindings 90 The LDP specification [RFC5036] provides no mechanism for an LDP 91 speaker to notify a peer when it has completed its initial label 92 advertisements to that peer. 94 This document specifies use of a Notification message with the "End- 95 of-LIB" Status Code for an LDP speaker to signal completion of its 96 label advertisements following session establishment. 98 RFC5036 implicitly assumes that new Status Codes will be defined over 99 the course of time. However, it does not explicitly define the 100 behavior of an LDP speaker which does not understand the Status Code 101 in a Notification message. To avoid backward compatibility issues 102 this document specifies use of the LDP capability mechanism [LDPCap] 103 at session establishment time for informing a peer that an LDP 104 speaker is capable of handling Notification messages that carry 105 unrecognized Status Codes. 107 2. Specification Language 109 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 110 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 111 document are to be interpreted as described in [RFC2119]. 113 3. Unrecognized Notification Capability 115 An LDP speaker MAY include a Capability Parameter [LDPCap] in an 116 Initialization message to inform a peer that it ignores Notification 117 Messages that carry a Status TLV with a non-fatal Status Code unknown 118 to it. 120 The Capability Parameter for the Unrecognized Notification capability 121 is a TLV with the following format: 123 0 1 2 3 124 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 1 125 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 126 |U|F| Unrecog Notif (IANA) | Length | 127 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 128 |S| Reserved | 129 +-+-+-+-+-+-+-+-+ 131 where: 133 U and F bits: As specified by RFC5036. 135 Unrecog Notif: TLV code point to be assigned by IANA. 137 S-bit: Must be 1 (indicates that capability is being advertised). 139 Upon receiving a Notification with an unrecognized Status Code an LDP 140 speaker MAY generate a console or system log message for trouble 141 shooting purposes. 143 4. Signaling Completion of Label Advertisement 145 An LDP speaker MAY signal completion of its label advertisements to a 146 peer by means of a Notification message if its peer had advertised 147 the Unrecognized Notification capability during session 148 establishment. 150 Such a Notification message MUST carry: 152 - A Status TLV with TLV E- and F-bits set to zero that carries an 153 "End-of-LIB" Status Code. End-of-LIB is a new Status Code. 155 - A FEC TLV with the Typed Wildcard FEC Element [TypedWC] that 156 identifies the FEC type for which initial label advertisements 157 have been completed. In terms of Section 3.5.1 of RFC5036 this 158 TLV is an "Optional Parameter" of the Notification message. 160 An LDP speaker MUST NOT send a Notification which carries a Status 161 TLV with the End-of-LIB Status Code unless its peer had advertised 162 the Unrecognized Notification capability during session 163 establishment. 165 5. Usage Guidelines 167 The FEC's known to an LDP speaker and the labels the speaker has 168 bound to those FEC's may change over the course of time. This makes 169 determining when an LDP speaker has advertised "all" of its label 170 bindings for a given FEC type an issue. Ultimately, this 171 determination is a judgement call the LDP speaker makes. The 172 following guidelines may be useful. 174 An LDP speaker is assumed to "know" a set of FEC's. Depending on a 175 variety of criteria, such as: 177 - The label distribution control mode in use (Independent or 178 Ordered); 180 - The set of FEC's to which the speaker has bound local labels; 182 - Configuration settings which may constrain which label bindings 183 the speaker may advertise to peers; 185 the speaker can determine the set of bindings for a given FEC type 186 that it is permitted to advertise to a given peer. 188 IGP-Sync, LDP Graceful Restart, and the response to a Wildcard Label 189 Request [TypedWC] are situations that would benefit from End-of-LIB 190 Notification. In these situations after an LDP speaker completes its 191 label binding advertisements to a peer it should send the peer an 192 End-of-LIB Notification. The following considers each of these 193 situations in turn. 195 5.1. IGP-Sync 197 LDP-IGP Sync is a mechanism directly connected LDP speakers may use 198 to delay using the link connecting them for IP traffic until the 199 labels required to support IP over MPLS traffic on the link have been 200 learned. 202 Without an End-of-LIB Notification the speaker must rely on some 203 heuristic to determine when it has received all of its peer's label 204 bindings. The heuristic chosen could cause LDP to signal the IGP too 205 soon in which case the likelihood that traffic will be dropped 206 increases, or too late in which case traffic is kept on sub-optimal 207 paths longer than necessary. 209 Following session establishment with a directly connected peer that 210 has advertised the Unrecognized Notification capability an LDP 211 speaker using LDP-IGP Sync may send the peer an End-of-LIB 212 Notification after it completes advertisement of its IP label 213 bindings to the peer. The LDP speaker may use an End-of-LIB 214 Notification from a directly connected peer to determine when the 215 peer has completed its label advertisements for IP prefixes. After 216 the speaker has exchanged End-of-LIB Notifications with the peer the 217 speaker should consider LDP to be fully operational for the link to 218 the peer and should signal the IGP to start advertising the link with 219 normal cost. 221 5.2. LDP Graceful Restart 223 LDP Graceful Restart helps reduce the loss of MPLS traffic caused by 224 the restart of a router's LDP component. It defines procedures that 225 allow routers capable of preserving MPLS forwarding state across the 226 restart to continue forwarding MPLS traffic for a pre-agreed upon 227 period using forwarding state installed prior to the restart. 229 During that period the restarting router and its peers consider the 230 preserved forwarding state to be usable but stale until it is 231 refreshed by receipt of new label advertisements following re- 232 establishment of new LDP sessions. When the period elapses any 233 remaining stale forwarding state is removed by the router. 235 Receipt of the End-of-LIB Notification from a peer in an LDP Graceful 236 Restart scenario enables an LDP speaker to stop using stale 237 forwarding information learned from that peer and to recover the 238 resources it requires without having to wait until the timeout 239 occurs. 241 5.3. Wildcard Label Request 243 When an LDP speaker receives a Label Request message for a Typed 244 Wildcard FEC from a peer it determines the set of bindings it is 245 permitted to advertise the peer for the FEC type specified by the 246 request. Assuming the peer had advertised the Unrecognized 247 Notification capability at session initialization time, the speaker 248 should send the peer an End-of-LIB Notification for the FEC type when 249 it completes advertisement of the permitted bindings. 251 As in the previous applications, receipt of the Notification 252 eliminates uncertainty as to when the peer has completed its 253 advertisements. 255 5.4. Missing Expected End-of-LIB Notifications 257 There is no guarantee that an LDP speaker will receive End-of-LIB 258 Notifications from a peer in a situation where it may be used. 260 Therefore, in situations where the End-of-LIB Notification may be 261 used an implementation SHOULD NOT depend on the receipt of the 262 notification. 264 To deal with the possibility of missing notifications an LDP speaker 265 may time out receipt of an expected End-of-LIB Notification, and if 266 the timeout occurs may behave as if it had received the notification. 268 6. IANA Considerations 270 This draft introduces a new LDP Status Code and a new LDP Capability 271 both of which require IANA assignment. 273 7. Security Considerations 275 No security considerations beyond those that apply to the base LDP 276 specification and described in [RFC5036] apply to signaling the End- 277 of-LIB condition as described in this document. 279 8. References 281 Normative References 283 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 284 Requirement Levels", BCP 14, RFC2119, March 1997. 286 [RFC5036] Andersson, L., Ed., Minei, I., Ed., and Thomas, B., Ed., 287 "LDP Specification", RFC 5036, October 2007. 289 [LDPCap] Thomas, B., Aggarwal, S., Aggarwal, R., Le Roux, J.L., 290 "LDP Capabilities", draft-ietf-mpls-ldp-capabilities-00, Work in 291 Progress, May 2007. 293 [TypedWC] Thomas, B., Minei, I., "LDP Typed Wildcard FEC", draft- 294 ietf-mpls-ldp-typed-wildcard-01, Work in Progress, May 2007. 296 Informative References 298 [LDPSynch] Jork, M., Atlas, A., Fang, L., "LDP IGP 299 Synchronization", draft-ietf-mpls-igp-sync-00,, Work in Progress, 300 September 2007. 302 [RFC3478] Leelanivas, M., Rekhter, Y., Aggarwal, R., "Graceful 303 Restart Mechanism for Label Distribution Protocol", February 2003. 305 9. Author Information 307 Rajiv Asati 308 Cisco Systems, Inc. 309 Mail Stop RTP6P/2/1 310 7025-6 Kit Creek Road PO Box 14987 311 Research Triangle Park , NORTH CAROLINA 27709-4987 312 Email: rajiva@cisco.com 314 Pradosh Mohapatra 315 Cisco Systems, Inc. 316 Mail Stop SJC15/3/3 317 3750 Cisco Way 318 San Jose , CALIFORNIA 95134 319 Email: pmohapat@cisco.com 321 Bob Thomas 322 Cisco Systems, Inc. 323 1414 Massachusetts Ave. 324 Boxborough MA 01719 325 Email: rhthomas@cisco.com 327 Emily Chen 328 Huawei Technologies Co., Ltd. 329 NO.5 Streat, Shangdi Information 330 Haidian 331 Beijing 332 China 333 Email: chenying220@huawei.com 335 10. Intellectual Property Statement 337 The IETF takes no position regarding the validity or scope of any 338 Intellectual Property Rights or other rights that might be claimed to 339 pertain to the implementation or use of the technology described in 340 this document or the extent to which any license under such rights 341 might or might not be available; nor does it represent that it has 342 made any independent effort to identify any such rights. 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Full Copyright Statement 361 Copyright (C) The IETF Trust (2007). 363 This document is subject to the rights, licenses and restrictions 364 contained in BCP 78, and except as set forth therein, the authors 365 retain all their rights. 367 This document and the information contained herein are provided on an 368 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 369 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST 370 AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, 371 EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT 372 THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY 373 IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR 374 PURPOSE.