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Andersson 3 Internet-Draft Acreo AB 4 Intended status: Standards Track May 19, 2008 5 Expires: November 20, 2008 7 "EXP field" renamed to "CoS Field" 8 draft-ietf-mpls-cosfield-def-00.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 November 20, 2008. 35 Abstract 37 - 39 Table of Contents 41 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 42 2. Details of change . . . . . . . . . . . . . . . . . . . . . . 4 43 2.1. RFC 3032 . . . . . . . . . . . . . . . . . . . . . . . . . 4 44 2.2. RFC 3270 . . . . . . . . . . . . . . . . . . . . . . . . . 4 45 2.3. RFC 5129 . . . . . . . . . . . . . . . . . . . . . . . . . 5 46 3. Use of the CoS field . . . . . . . . . . . . . . . . . . . . . 7 47 4. IANA considerations . . . . . . . . . . . . . . . . . . . . . 8 48 5. Security considerations . . . . . . . . . . . . . . . . . . . 9 49 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 50 6.1. Normative References . . . . . . . . . . . . . . . . . . . 10 51 6.2. Informative references . . . . . . . . . . . . . . . . . . 10 52 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 11 53 Intellectual Property and Copyright Statements . . . . . . . . . . 12 55 1. Introduction 57 The format of the MPLS label is defined in RFC 3032 [RFC3032], that 58 definition includes three bit field called "EXP field". RFC 3032 59 leaves the exact description of how the EXP field should be used 60 undefined, they are said to be for "experimental use". 62 The EXP field has from the start been intended to be used for "Class 63 of Service", the field were actually called "Class of Service field" 64 in the early versions of the working group document that was publshed 65 as RFC 3032. However at the time that RFC 3032 were published the 66 "Class of Service" were considered not to be defined well enough and 67 the field were left for "Experimental use". 69 The use of the EXP field was first defined in RFC 3270 [RFC3270] 70 where a method to define a variant of DiffServ LSPs called EXP- 71 Inferred-PSC LSP (E-LSPs). 73 The use of the EXP field as defined in RFC 3270 has been further 74 extended in RFC 5129 [RFC5129], where methods for explicit congestion 75 marking in MPLS is defined. 77 The defintions of how the EXP field are used are perfectly clear in 78 RFC 3270 and RFC 5129. However it is never explicitly stated that 79 these RFCs updates RFC 3032, and it is not captured in the RFC 80 respository. This document changes RFC 3032, RFC 3270 and RFC 5129 81 to capture these updates. 83 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 84 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 85 document are to be interpreted as described in RFC 2119 [RFC2119]. 87 2. Details of change 89 The three RFCs are now updated according to the following. 91 2.1. RFC 3032 93 The RFC 3032 state on page 3: 95 3. Experimental Use 97 This three-bit field is reserved for experimental use. 99 This paragraph is now changed to: 101 3. Class of Service (CoS) field 103 This three-bit field is used to carry Class of Service information 104 and the change of the name is applicable to all places it occurs 105 in IETF RFCs and other IETF documents. 107 The definition of how to use the CoS field has been updated by RFC 108 3270 and RFC 5129. 110 2.2. RFC 3270 112 RFC 3270 says on page 6: 114 1.2 EXP-Inferred-PSC LSPs (E-LSP) 116 A single LSP can be used to support one or more OAs. Such LSPs 117 can support up to eight BAs of a given FEC, regardless of how many 118 OAs these BAs span. With such LSPs, the EXP field of the MPLS 119 Shim Header is used by the LSR to determine the PHB to be applied 120 to the packet. This includes both the PSC and the drop 121 preference. 123 We refer to such LSPs as "EXP-inferred-PSC LSPs" (E-LSP), since 124 the PSC of a packet transported on this LSP depends on the EXP 125 field value for that packet. 127 The mapping from the EXP field to the PHB (i.e., to PSC and drop 128 precedence) for a given such LSP, is either explicitly signaled at 129 label set-up or relies on a pre-configured mapping. 131 Detailed operations of E-LSPs are specified in section 3 below. 133 Section 1.2 on page 5 in RFC 3270 is now changed to: 135 1.2 EXP-Inferred-PSC LSPs (E-LSP) 137 The EXP field have been renamed to the CoS field, and thus all 138 references in RFC 3270 to EXP field SHOULD be taken to refer to 139 the CoS field. However, we retain the term E-LSP (EXP-Inferred- 140 PSC LSP) as it is in widespread use. 142 A single LSP can be used to support one or more OAs. Such LSPs 143 can support up to eight BAs of a given FEC, regardless of how many 144 OAs these BAs span. With such LSPs, the CoS field of the MPLS 145 Shim Header is used by the LSR to determine the PHB to be applied 146 to the packet. This includes both the PSC and the drop 147 preference. 149 We refer to such LSPs as "EXP-inferred-PSC LSPs" (E-LSP), since 150 the PSC of a packet transported on this LSP depends on the CoS 151 field (previously called the EXP field) value for that packet. 153 The mapping from the CoS field to the PHB (i.e., to PSC and drop 154 precedence) for a given such LSP, is either explicitly signaled at 155 label set-up or relies on a pre-configured mapping. 157 This is an update to RFC 3032 [RFC3032] in line with the original 158 intent of how this field in the MPLS Shim Header should be used 159 (as CoS field). The RFC 3270 has itself been updated by RFC 5129 160 [RFC5129]. 162 Detailed operations of E-LSPs are specified in section 3 of 163 RFC3270. 165 2.3. RFC 5129 167 Section 2 (bullet 3) on page 6 of RFC 5129 says: 169 o A third possible approach was suggested by [Shayman]. In this 170 scheme, interior LSRs assume that the endpoints are ECN-capable, 171 but this assumption is checked when the final label is popped. If 172 an interior LSR has marked ECN in the EXP field of the shim 173 header, but the IP header says the endpoints are not ECN-capable, 174 the edge router (or penultimate router, if using penultimate hop 175 popping) drops the packet. We recommend this scheme, which we 176 call `per-domain ECT checking', and define it more precisely in 177 the following section. Its chief drawback is that it can cause 178 packets to be forwarded after encountering congestion only to be 179 dropped at the egress of the MPLS domain. The rationale for this 180 decision is given in Section 8.1. 182 RFC 5219 is now updated like this: 184 A new paragraph is added at the end of section 1.1 "Background": 186 The EXP field have been renamed to the CoS field, and thus all 187 references in RFC 5219 to EXP field SHOULD be taken to refer to 188 the CoS field. 190 Section 2 (bullet 3) on page 6 ofis now changed to: 192 o A third possible approach was suggested by [Shayman]. In this 193 scheme, interior LSRs assume that the endpoints are ECN-capable, 194 but this assumption is checked when the final label is popped. If 195 an interior LSR has marked ECN in the CoS field of the shim 196 header, but the IP header says the endpoints are not CoS-capable, 197 the edge router (or penultimate router, if using penultimate hop 198 popping) drops the packet. We recommend this scheme, which we 199 call `per-domain ECT checking', and define it more precisely in 200 the following section. Its chief drawback is that it can cause 201 packets to be forwarded after encountering congestion only to be 202 dropped at the egress of the MPLS domain. The rationale for this 203 decision is given in Section 8.1. This scheme is an update to RFC 204 3032 [RFC3032] and RFC 3270 [RFC3270]. 206 3. Use of the CoS field 208 Due to the limited number of bits the particular use of the bits is 209 intended to be flexible - including the defininition of various QoS 210 and ECN functions. 212 Current implementations look at the CoS field with and without label 213 context and the CoS field may be copied to the labels that are pushed 214 onto the laabel stack. This is to avoid that the pushed labels has a 215 different CoS field. 217 CoS and ECN funtions may rewrite all or some of the bits. 219 4. IANA considerations 221 TBD 223 5. Security considerations 225 This document only changes the name of one field in the MPLS Shim 226 Header and thus do not introduce any new security considerations. 228 6. References 230 6.1. Normative References 232 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 233 Requirement Levels", BCP 14, RFC 2119, March 1997. 235 [RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., 236 Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack 237 Encoding", RFC 3032, January 2001. 239 [RFC3270] Le Faucheur, F., Wu, L., Davie, B., Davari, S., Vaananen, 240 P., Krishnan, R., Cheval, P., and J. Heinanen, "Multi- 241 Protocol Label Switching (MPLS) Support of Differentiated 242 Services", RFC 3270, May 2002. 244 [RFC5129] Davie, B., Briscoe, B., and J. Tay, "Explicit Congestion 245 Marking in MPLS", RFC 5129, January 2008. 247 6.2. Informative references 249 [Shayman] Shayman, M. and R. Jaeger, University of Michigan, "Using 250 ECN to Signal Congestion Within an MPLS Domain", Work in 251 Progress, November 2000.", . 254 Author's Address 256 Loa Andersson 257 Acreo AB 259 Email: loa@pi.nu 261 Full Copyright Statement 263 Copyright (C) The IETF Trust (2008). 265 This document is subject to the rights, licenses and restrictions 266 contained in BCP 78, and except as set forth therein, the authors 267 retain all their rights. 269 This document and the information contained herein are provided on an 270 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 271 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 272 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 273 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 274 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 275 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 277 Intellectual Property 279 The IETF takes no position regarding the validity or scope of any 280 Intellectual Property Rights or other rights that might be claimed to 281 pertain to the implementation or use of the technology described in 282 this document or the extent to which any license under such rights 283 might or might not be available; nor does it represent that it has 284 made any independent effort to identify any such rights. 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