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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 3272 (Obsoleted by RFC 9522) ** Downref: Normative reference to an Informational RFC: RFC 3469 ** Downref: Normative reference to an Informational RFC: RFC 3564 ** Downref: Normative reference to an Informational RFC: RFC 3985 ** Obsolete normative reference: RFC 4379 (Obsoleted by RFC 8029) Summary: 6 errors (**), 0 flaws (~~), 2 warnings (==), 9 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group L. Andersson 3 Internet-Draft Acreo AB 4 Updates: RFC 3032, RFC 3270, RFC R. Asati 5 5129, RFC 3272, RFC 3443, RFC Cisco Systems 6 3469, RFC 3564, RFC 3985, RFC December 5, 2008 7 4182, RFC 4364, RFC 4379, RFC 8 4448, RFC 4761 (if approved) 9 Intended status: Standards Track 10 Expires: June 8, 2009 12 Multi-Protocol Label Switching (MPLS) label stack entry: "EXP" field 13 renamed to "Traffic Class" field 14 draft-ietf-mpls-cosfield-def-08.txt 16 Status of this Memo 18 By submitting this Internet-Draft, each author represents that any 19 applicable patent or other IPR claims of which he or she is aware 20 have been or will be disclosed, and any of which he or she becomes 21 aware will be disclosed, in accordance with Section 6 of BCP 79. 23 Internet-Drafts are working documents of the Internet Engineering 24 Task Force (IETF), its areas, and its working groups. Note that 25 other groups may also distribute working documents as Internet- 26 Drafts. 28 Internet-Drafts are draft documents valid for a maximum of six months 29 and may be updated, replaced, or obsoleted by other documents at any 30 time. It is inappropriate to use Internet-Drafts as reference 31 material or to cite them other than as "work in progress." 33 The list of current Internet-Drafts can be accessed at 34 http://www.ietf.org/ietf/1id-abstracts.txt. 36 The list of Internet-Draft Shadow Directories can be accessed at 37 http://www.ietf.org/shadow.html. 39 This Internet-Draft will expire on June 8, 2009. 41 Abstract 43 The early Multiprotocol Label Switching (MPLS) documents defined the 44 form of the MPLS Label Stack entry. This includes a three bit field 45 called the "EXP field". The exact use of this field was not defined 46 by these documents, except to state that it was to be "reserved for 47 experimental use". 49 Although the intended use of the EXP field was as a "Class of 50 Service" (CoS) field, it was not named the CoS field by these early 51 documents because the use of such a CoS field was not considered to 52 be sufficiently defined. Today a number of standards documents 53 define its usage as a CoS field. . 55 To avoid misunderstanding about how this field may be used, it has 56 become increasingly necessary to rename this field. This document 57 changes the name of the field to the "Traffic Class field" ("TC 58 field".) In doing so it also updates documents that define the 59 current use of the EXP this field. 61 Table of Contents 63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 64 2. Details of change . . . . . . . . . . . . . . . . . . . . . . 6 65 2.1. RFC 3032 . . . . . . . . . . . . . . . . . . . . . . . . . 6 66 2.2. RFC 3270 . . . . . . . . . . . . . . . . . . . . . . . . . 7 67 2.3. RFC 5129 . . . . . . . . . . . . . . . . . . . . . . . . . 9 68 2.4. The Scope of this Change . . . . . . . . . . . . . . . . . 9 69 3. Use of the TC field . . . . . . . . . . . . . . . . . . . . . 11 70 4. IANA considerations . . . . . . . . . . . . . . . . . . . . . 12 71 5. Security considerations . . . . . . . . . . . . . . . . . . . 13 72 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14 73 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15 74 7.1. Normative References . . . . . . . . . . . . . . . . . . . 15 75 7.2. Informative references . . . . . . . . . . . . . . . . . . 16 76 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17 77 Intellectual Property and Copyright Statements . . . . . . . . . . 18 79 1. Introduction 81 The format of a MPLS label stack entry is defined by RFC 3032 82 [RFC3032], include a three bit field called the "EXP field". The 83 exact use of this field is not defined by RFC 3032 leaves, except to 84 state that it is to be "reserved for experimental use". 86 The EXP field, from the start, was intended to carry "Class of 87 Service" (CoS) information. The field was actually called the "Class 88 of Service field" in the early versions of the working group document 89 that was published as RFC 3032. However at the time that RFC 3032 90 was published the exact usage of this "Class of Service" field was 91 not agreed and the field was designated as "Experimental use"; hence 92 the name has since then been the "EXP Field". 94 The designation "for Experimental use" has led other Standards 95 Development Organizations (SDO) and implementors to the assume that 96 it possible to use the field for other purposes. This document 97 changes the name of the field to clearly indicate its use as a 98 traffic classification field. 100 At first we discussed to use the original "CoS field" as the name for 101 the field, but it has been pointed that this name does not cover the 102 following changes with respect to its usage, since RFC 3032 was 103 published. 105 1. The use of the EXP field was first defined in RFC 3270 [RFC3270] 106 where a method to define a variant of DiffServ Label Switched 107 Paths (LSP) called EXP-Inferred-PSC LSP (E-LSPs) was specified. 108 The PSC is a two stage acroynym that is expanded as Per Hop 109 Behavior (PHB) and PHB Scheduling Class (PSC). 111 2. The use of the EXP field as defined in RFC 3270 has been further 112 extended in RFC 5129 [RFC5129], where methods for explicit 113 congestion marking in MPLS are defined. 115 This document, hence, uses the name "Traffic Class Field (TC Field)", 116 which better covers the potential use. The MPLS TC field relates to 117 an MPLS encapsulated packet the same way as the IPv6 TC field relates 118 to an IPv6 encapsulted packet or the IPv4 Precedence field relates to 119 an IPv4 encapsulated packet. 121 The definitions of how the EXP field is used are perfectly clear in 122 RFC 3270 and RFC 5129. However, these RFCs do not explicitly state 123 they update RFC 3032, and this fact was not captured in the RFC 124 repository until after the work on this document were started. This 125 document updates RFC 3032, RFC 3270 and RFC 5129 to clarify the 126 intended usage of the TC field. Section 2 explains the changes. 128 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 129 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 130 document are to be interpreted as described in RFC 2119 [RFC2119]. 132 2. Details of change 134 The three RFCs are now updated according to the following. 136 2.1. RFC 3032 138 RFC 3032 states on page 4: 140 3. Experimental Use 142 This three-bit field is reserved for experimental use. 144 This paragraph is now changed to: 146 3. Traffic Class (TC) field 148 This three-bit field is used to carry Traffic Class information 149 and the change of the name is applicable to all places it occurs 150 in IETF RFCs and other IETF documents. 152 RFC 3270 and RFC 5129 updates the definition of the TC field and 153 describes how to use the field. 155 In Figure 1 on page 3 in RFC3032 the format of a label stack entry is 156 specified as: 158 0 1 2 3 159 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 1 160 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Label 161 | Label | Exp |S| TTL | Stack 162 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Entry 164 Label: Label Value, 20 bits 165 Exp: Experimental Use, 3 bits 166 S: Bottom of Stack, 1 bit 167 TTL: Time to Live, 8 bits 169 Figure 1 171 Figure 1 in RFC 3032 is now changed to match the change of name of 172 the TC field to: 174 0 1 2 3 175 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 1 176 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Label 177 | Label | TC |S| TTL | Stack 178 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Entry 180 Label: Label Value, 20 bits 181 CoS: Traffic Class field, 3 bits 182 S: Bottom of Stack, 1 bit 183 TTL: Time to Live, 8 bits 185 Figure 1 (new) 187 Note: The designation of the picture above as "Figure 1 new" is 188 introduced as a way to distinguish the figures in this draft. It 189 will still be "Figure 1." in RFC 3032. 191 2.2. RFC 3270 193 RFC 3270 says on page 6: 195 1.2 EXP-Inferred-PSC LSPs (E-LSP) 197 A single LSP can be used to support one or more OAs. Such LSPs 198 can support up to eight BAs of a given FEC, regardless of how many 199 OAs these BAs span. With such LSPs, the EXP field of the MPLS 200 Shim Header is used by the LSR to determine the PHB to be applied 201 to the packet. This includes both the PSC and the drop 202 preference. 204 We refer to such LSPs as "EXP-inferred-PSC LSPs" (E-LSP), since 205 the PSC of a packet transported on this LSP depends on the EXP 206 field value for that packet. 208 The mapping from the EXP field to the PHB (i.e., to PSC and drop 209 precedence) for a given such LSP, is either explicitly signaled at 210 label set-up or relies on a pre-configured mapping. 212 Detailed operations of E-LSPs are specified in section 3 below. 214 RFC 3270 is now updated like this: 216 a. A new paragraph is added at the end of section 1 "Introduction": 218 The EXP field has been renamed to the TC field, and thus all 219 references in RFC 3270 to EXP field SHOULD be taken to refer 220 to the TC field. 222 b. A new term is added to section 1.1 "Terminology": 224 TC Traffic Class (replaces the term EXP) 226 c. In section 1.1 "Terminology" the acronym E-LSP is now understood 227 to mean : 229 E-LSP Explicitly TC-encoded-PSC LSP 231 Section 1.2 on page 5 in RFC 3270 is now changed to: 233 1.2 Explicitly TC-encoded-PSC LSPs (E-LSP) 235 The EXP field has been renamed to the TC field, and thus all 236 references in RFC 3270 to EXP field SHOULD be taken to refer to 237 the TC field. However, we retain the acronym E-LSP (Explicitly 238 TC-encoded-PSC LSP) as the acronym is in widespread use. 240 A single LSP can be used to support one or more OAs. Such LSPs 241 can support up to eight BAs of a given FEC, regardless of how many 242 OAs these BAs span. With such LSPs, the TC field of the MPLS Shim 243 Header is used by the LSR to determine the PHB to be applied to 244 the packet. This includes both the PSC and the drop preference. 246 We refer to such LSPs as "Explicitly TC-encoded-PSC LSP" (E-LSP), 247 since the PSC of a packet transported on this LSP depends on the 248 TC field (previously called the EXP field) value for that packet. 250 The mapping from the TC field to the PHB (i.e., to PSC and drop 251 precedence) for a given such LSP, is either explicitly signaled at 252 label set-up or relies on a pre-configured mapping. 254 This is an update to RFC 3032 [RFC3032] in line with the original 255 intent of how this field in the MPLS Shim Header should be used 256 (as TC field). The RFC 3270 has itself been updated by RFC 5129 257 [RFC5129]. 259 Detailed operations of E-LSPs are specified in section 3 of 260 RFC3270. 262 2.3. RFC 5129 264 RFC 5129 is now updated like this: 266 A new paragraph is added at the end of section 1.1 "Background": 268 The EXP field has been renamed to the TC field, and thus all 269 references in RFC 5129 to EXP field SHOULD be taken to refer to 270 the TC field. 272 Section 2 (bullet 3) on page 6 of RFC 5129 says: 274 o A third possible approach was suggested by [Shayman]. In this 275 scheme, interior LSRs assume that the endpoints are ECN-capable, 276 but this assumption is checked when the final label is popped. If 277 an interior LSR has marked ECN in the EXP field of the shim 278 header, but the IP header says the endpoints are not ECN-capable, 279 the edge router (or penultimate router, if using penultimate hop 280 popping) drops the packet. We recommend this scheme, which we 281 call `per-domain ECT checking', and define it more precisely in 282 the following section. Its chief drawback is that it can cause 283 packets to be forwarded after encountering congestion only to be 284 dropped at the egress of the MPLS domain. The rationale for this 285 decision is given in Section 8.1. 287 Section 2 (bullet 3) of RFC 5129 is now updated changed to: 289 o A third possible approach was suggested by [Shayman]. In this 290 scheme, interior LSRs assume that the endpoints are ECN-capable, 291 but this assumption is checked when the final label is popped. If 292 an interior LSR has marked ECN in the TC field of the shim header, 293 but the IP header says the endpoints are not TC-capable, the edge 294 router (or penultimate router, if using penultimate hop popping) 295 drops the packet. We recommend this scheme, which we call `per- 296 domain ECT checking', and define it more precisely in the 297 following section. Its chief drawback is that it can cause 298 packets to be forwarded after encountering congestion only to be 299 dropped at the egress of the MPLS domain. The rationale for this 300 decision is given in Section 8.1. This scheme is an update to RFC 301 3032 [RFC3032] and RFC 3270 [RFC3270]. 303 2.4. The Scope of this Change 305 There are several places in the RFCs that has explicitly updated by 306 this document that reference the "Exp field", sometimes they refer to 307 the field as "Exp bits", "EXP bits" and "EXP". In all those 308 instances the references SHOULD be taken to reference the TC field. 310 There are also other RFCs, e.g. RFC 3272 [RFC3272], RFC 3443 311 [RFC3443], RFC 3469 [RFC3469], RFC 3564 [RFC3564], RFC 3985 312 [RFC3985], RFC 4182 [RFC4182], RFC 4364 [RFC4364], RFC 4379 313 [RFC4379], RFC 4448 [RFC4448] and RFC 4761 [RFC4761] that references 314 the "Exp field", sometimes they refer to the field as "Exp bits", 315 "EXP bits" and "EXP". For all RFCs, including but not limited to 316 those mentioned in this paragraph, such references SHOULD be taken to 317 reference the TC field. 319 3. Use of the TC field 321 Due to the limited number of bits in the TC field, their use for QoS 322 and ECN functions is intended to be flexible. These funtions may 323 rewrite all or some of the bits in the TC field. 325 Current implementations look at the TC field with and without label 326 context and the TC field may be copied to the label stack entries 327 that are pushed onto the label stack. This is done to avoid that 328 label stack entries that are pushed on to an existing label stack 329 have different TF fields from the rest of the label stack entries. 331 4. IANA considerations 333 There are no requests for IANA allocation of code points in this 334 document. 336 5. Security considerations 338 This document only changes the name of one field in the MPLS Shim 339 Header and thus does not introduce any new security considerations. 341 6. Acknowledgments 343 The author would like to thank Stewart Bryant, Bruce Davie, George 344 Swallow, and Francois Le Faucheur for their input to and review of 345 the current document. 347 The author also like to thanks George Swallow, Khatri Paresh and Phil 348 Bedard for their help with grammar and spelling, and a special thanks 349 to Adrian Farrel for a careful review and help trawling the RFC-sea 350 for RFCs that references the EXP field. 352 7. References 354 7.1. Normative References 356 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 357 Requirement Levels", BCP 14, RFC 2119, March 1997. 359 [RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., 360 Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack 361 Encoding", RFC 3032, January 2001. 363 [RFC3270] Le Faucheur, F., Wu, L., Davie, B., Davari, S., Vaananen, 364 P., Krishnan, R., Cheval, P., and J. Heinanen, "Multi- 365 Protocol Label Switching (MPLS) Support of Differentiated 366 Services", RFC 3270, May 2002. 368 [RFC3272] Awduche, D., Chiu, A., Elwalid, A., Widjaja, I., and X. 369 Xiao, "Overview and Principles of Internet Traffic 370 Engineering", RFC 3272, May 2002. 372 [RFC3443] Agarwal, P. and B. Akyol, "Time To Live (TTL) Processing 373 in Multi-Protocol Label Switching (MPLS) Networks", 374 RFC 3443, January 2003. 376 [RFC3469] Sharma, V. and F. Hellstrand, "Framework for Multi- 377 Protocol Label Switching (MPLS)-based Recovery", RFC 3469, 378 February 2003. 380 [RFC3564] Le Faucheur, F. and W. Lai, "Requirements for Support of 381 Differentiated Services-aware MPLS Traffic Engineering", 382 RFC 3564, July 2003. 384 [RFC3985] Bryant, S. and P. Pate, "Pseudo Wire Emulation Edge-to- 385 Edge (PWE3) Architecture", RFC 3985, March 2005. 387 [RFC4182] Rosen, E., "Removing a Restriction on the use of MPLS 388 Explicit NULL", RFC 4182, September 2005. 390 [RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private 391 Networks (VPNs)", RFC 4364, February 2006. 393 [RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol 394 Label Switched (MPLS) Data Plane Failures", RFC 4379, 395 February 2006. 397 [RFC4448] Martini, L., Rosen, E., El-Aawar, N., and G. Heron, 398 "Encapsulation Methods for Transport of Ethernet over MPLS 399 Networks", RFC 4448, April 2006. 401 [RFC4761] Kompella, K. and Y. Rekhter, "Virtual Private LAN Service 402 (VPLS) Using BGP for Auto-Discovery and Signaling", 403 RFC 4761, January 2007. 405 [RFC5129] Davie, B., Briscoe, B., and J. Tay, "Explicit Congestion 406 Marking in MPLS", RFC 5129, January 2008. 408 7.2. Informative references 410 [Shayman] Shayman, M. and R. Jaeger, University of Michigan, "Using 411 ECN to Signal Congestion Within an MPLS Domain", Work in 412 Progress, November 2000.", . 415 Authors' Addresses 417 Loa Andersson 418 Acreo AB 420 Email: loa@pi.nu 422 Rajiva Asati 423 Cisco Systems 425 Email: rajiva@cisco.com 427 Full Copyright Statement 429 Copyright (C) The IETF Trust (2008). 431 This document is subject to the rights, licenses and restrictions 432 contained in BCP 78, and except as set forth therein, the authors 433 retain all their rights. 435 This document and the information contained herein are provided on an 436 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 437 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 438 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 439 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 440 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 441 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 443 Intellectual Property 445 The IETF takes no position regarding the validity or scope of any 446 Intellectual Property Rights or other rights that might be claimed to 447 pertain to the implementation or use of the technology described in 448 this document or the extent to which any license under such rights 449 might or might not be available; nor does it represent that it has 450 made any independent effort to identify any such rights. 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