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Andersson 3 Internet-Draft Acreo AB 4 Intended status: Standards Track June 4, 2008 5 Expires: December 6, 2008 7 "EXP field" renamed to "CoS Field" 8 draft-ietf-mpls-cosfield-def-01.txt 10 Status of this Memo 12 By submitting this Internet-Draft, each author represents that any 13 applicable patent or other IPR claims of which he or she is aware 14 have been or will be disclosed, and any of which he or she becomes 15 aware will be disclosed, in accordance with Section 6 of BCP 79. 17 Internet-Drafts are working documents of the Internet Engineering 18 Task Force (IETF), its areas, and its working groups. Note that 19 other groups may also distribute working documents as Internet- 20 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/ietf/1id-abstracts.txt. 30 The list of Internet-Draft Shadow Directories can be accessed at 31 http://www.ietf.org/shadow.html. 33 This Internet-Draft will expire on December 6, 2008. 35 Abstract 37 The early MPLS documents defined the MPLS format, this definition 38 includes three bit field called "EXP field". The documentats leaves 39 the exact description of how the EXP field should be used undefined, 40 it is said said to be for "experimental use". 42 The EXP field has from the start been intended to be used for "Class 43 of Service". At the time the documents were published the use of 44 such a CoS field were considered not to be defined well enough and 45 the field were left for "Experimental use". 47 To avoid misunderstanding about how this field may be used this 48 document re-introduces the name "CoS field" for this field. In doing 49 so it also updates documents that defines and uses this field. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 54 2. Details of change . . . . . . . . . . . . . . . . . . . . . . 4 55 2.1. RFC 3032 . . . . . . . . . . . . . . . . . . . . . . . . . 4 56 2.2. RFC 3270 . . . . . . . . . . . . . . . . . . . . . . . . . 4 57 2.3. RFC 5129 . . . . . . . . . . . . . . . . . . . . . . . . . 5 58 3. Use of the CoS field . . . . . . . . . . . . . . . . . . . . . 7 59 4. IANA considerations . . . . . . . . . . . . . . . . . . . . . 8 60 5. Security considerations . . . . . . . . . . . . . . . . . . . 9 61 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 62 6.1. Normative References . . . . . . . . . . . . . . . . . . . 10 63 6.2. Informative references . . . . . . . . . . . . . . . . . . 10 64 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 11 65 Intellectual Property and Copyright Statements . . . . . . . . . . 12 67 1. Introduction 69 The format of the MPLS label is defined in RFC 3032 [RFC3032], that 70 definition includes three bit field called "EXP field". RFC 3032 71 leaves the exact description of how the EXP field should be used 72 undefined, it is said to be for "experimental use". 74 The EXP field has from the start been intended to be used for "Class 75 of Service", the field were actually called "Class of Service field" 76 in the early versions of the working group document that was publshed 77 as RFC 3032. However at the time that RFC 3032 were published the 78 "Class of Service" were considered not to be defined well enough and 79 the field were left for "Experimental use". 81 Since the "for Experimental use" terminology has lead other Standards 82 Development Organizations (SDO) and implementors to the assume that 83 it possible to use the field for other purposes that Class of Service 84 we now changes the name of the field to clearly indicate its use. 86 The use of the EXP field was first defined in RFC 3270 [RFC3270] 87 where a method to define a variant of DiffServ LSPs called EXP- 88 Inferred-PSC LSP (E-LSPs). 90 The use of the EXP field as defined in RFC 3270 has been further 91 extended in RFC 5129 [RFC5129], where methods for explicit congestion 92 marking in MPLS is defined. 94 The defintions of how the EXP field are used are perfectly clear in 95 RFC 3270 and RFC 5129. However it is never explicitly stated that 96 these RFCs updates RFC 3032, and it is not captured in the RFC 97 respository. This document changes RFC 3032, RFC 3270 and RFC 5129 98 to capture these updates. 100 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 101 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 102 document are to be interpreted as described in RFC 2119 [RFC2119]. 104 2. Details of change 106 The three RFCs are now updated according to the following. 108 2.1. RFC 3032 110 The RFC 3032 state on page 3: 112 3. Experimental Use 114 This three-bit field is reserved for experimental use. 116 This paragraph is now changed to: 118 3. Class of Service (CoS) field 120 This three-bit field is used to carry Class of Service information 121 and the change of the name is applicable to all places it occurs 122 in IETF RFCs and other IETF documents. 124 The definition of how to use the CoS field has been updated by RFC 125 3270 and RFC 5129. 127 2.2. RFC 3270 129 RFC 3270 says on page 6: 131 1.2 EXP-Inferred-PSC LSPs (E-LSP) 133 A single LSP can be used to support one or more OAs. Such LSPs 134 can support up to eight BAs of a given FEC, regardless of how many 135 OAs these BAs span. With such LSPs, the EXP field of the MPLS 136 Shim Header is used by the LSR to determine the PHB to be applied 137 to the packet. This includes both the PSC and the drop 138 preference. 140 We refer to such LSPs as "EXP-inferred-PSC LSPs" (E-LSP), since 141 the PSC of a packet transported on this LSP depends on the EXP 142 field value for that packet. 144 The mapping from the EXP field to the PHB (i.e., to PSC and drop 145 precedence) for a given such LSP, is either explicitly signaled at 146 label set-up or relies on a pre-configured mapping. 148 Detailed operations of E-LSPs are specified in section 3 below. 150 Section 1.2 on page 5 in RFC 3270 is now changed to: 152 1.2 EXP-Inferred-PSC LSPs (E-LSP) 154 The EXP field have been renamed to the CoS field, and thus all 155 references in RFC 3270 to EXP field SHOULD be taken to refer to 156 the CoS field. However, we retain the term E-LSP (EXP-Inferred- 157 PSC LSP) as it is in widespread use. 159 A single LSP can be used to support one or more OAs. Such LSPs 160 can support up to eight BAs of a given FEC, regardless of how many 161 OAs these BAs span. With such LSPs, the CoS field of the MPLS 162 Shim Header is used by the LSR to determine the PHB to be applied 163 to the packet. This includes both the PSC and the drop 164 preference. 166 We refer to such LSPs as "EXP-inferred-PSC LSPs" (E-LSP), since 167 the PSC of a packet transported on this LSP depends on the CoS 168 field (previously called the EXP field) value for that packet. 170 The mapping from the CoS field to the PHB (i.e., to PSC and drop 171 precedence) for a given such LSP, is either explicitly signaled at 172 label set-up or relies on a pre-configured mapping. 174 This is an update to RFC 3032 [RFC3032] in line with the original 175 intent of how this field in the MPLS Shim Header should be used 176 (as CoS field). The RFC 3270 has itself been updated by RFC 5129 177 [RFC5129]. 179 Detailed operations of E-LSPs are specified in section 3 of 180 RFC3270. 182 2.3. RFC 5129 184 Section 2 (bullet 3) on page 6 of RFC 5129 says: 186 o A third possible approach was suggested by [Shayman]. In this 187 scheme, interior LSRs assume that the endpoints are ECN-capable, 188 but this assumption is checked when the final label is popped. If 189 an interior LSR has marked ECN in the EXP field of the shim 190 header, but the IP header says the endpoints are not ECN-capable, 191 the edge router (or penultimate router, if using penultimate hop 192 popping) drops the packet. We recommend this scheme, which we 193 call `per-domain ECT checking', and define it more precisely in 194 the following section. Its chief drawback is that it can cause 195 packets to be forwarded after encountering congestion only to be 196 dropped at the egress of the MPLS domain. The rationale for this 197 decision is given in Section 8.1. 199 RFC 5219 is now updated like this: 201 A new paragraph is added at the end of section 1.1 "Background": 203 The EXP field have been renamed to the CoS field, and thus all 204 references in RFC 5219 to EXP field SHOULD be taken to refer to 205 the CoS field. 207 Section 2 (bullet 3) on page 6 ofis now changed to: 209 o A third possible approach was suggested by [Shayman]. In this 210 scheme, interior LSRs assume that the endpoints are ECN-capable, 211 but this assumption is checked when the final label is popped. If 212 an interior LSR has marked ECN in the CoS field of the shim 213 header, but the IP header says the endpoints are not CoS-capable, 214 the edge router (or penultimate router, if using penultimate hop 215 popping) drops the packet. We recommend this scheme, which we 216 call `per-domain ECT checking', and define it more precisely in 217 the following section. Its chief drawback is that it can cause 218 packets to be forwarded after encountering congestion only to be 219 dropped at the egress of the MPLS domain. The rationale for this 220 decision is given in Section 8.1. This scheme is an update to RFC 221 3032 [RFC3032] and RFC 3270 [RFC3270]. 223 3. Use of the CoS field 225 Due to the limited number of bits the particular use of the bits is 226 intended to be flexible - including the defininition of various QoS 227 and ECN functions. 229 Current implementations look at the CoS field with and without label 230 context and the CoS field may be copied to the labels that are pushed 231 onto the laabel stack. This is to avoid that the pushed labels has a 232 different CoS field. 234 CoS and ECN funtions may rewrite all or some of the bits. 236 4. IANA considerations 238 There are no request for IANA allocation of code points in this 239 document. 241 5. Security considerations 243 This document only changes the name of one field in the MPLS Shim 244 Header and thus do not introduce any new security considerations. 246 6. References 248 6.1. Normative References 250 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 251 Requirement Levels", BCP 14, RFC 2119, March 1997. 253 [RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., 254 Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack 255 Encoding", RFC 3032, January 2001. 257 [RFC3270] Le Faucheur, F., Wu, L., Davie, B., Davari, S., Vaananen, 258 P., Krishnan, R., Cheval, P., and J. Heinanen, "Multi- 259 Protocol Label Switching (MPLS) Support of Differentiated 260 Services", RFC 3270, May 2002. 262 [RFC5129] Davie, B., Briscoe, B., and J. Tay, "Explicit Congestion 263 Marking in MPLS", RFC 5129, January 2008. 265 6.2. Informative references 267 [Shayman] Shayman, M. and R. Jaeger, University of Michigan, "Using 268 ECN to Signal Congestion Within an MPLS Domain", Work in 269 Progress, November 2000.", . 272 Author's Address 274 Loa Andersson 275 Acreo AB 277 Email: loa@pi.nu 279 Full Copyright Statement 281 Copyright (C) The IETF Trust (2008). 283 This document is subject to the rights, licenses and restrictions 284 contained in BCP 78, and except as set forth therein, the authors 285 retain all their rights. 287 This document and the information contained herein are provided on an 288 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 289 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 290 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 291 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 292 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 293 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 295 Intellectual Property 297 The IETF takes no position regarding the validity or scope of any 298 Intellectual Property Rights or other rights that might be claimed to 299 pertain to the implementation or use of the technology described in 300 this document or the extent to which any license under such rights 301 might or might not be available; nor does it represent that it has 302 made any independent effort to identify any such rights. 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