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(See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (March 10, 2008) is 5891 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) No issues found here. Summary: 1 error (**), 0 flaws (~~), 2 warnings (==), 7 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 Intended status: Standards Track March 10, 2008 5 Expires: September 11, 2008 7 MPLS EXP-bits definition 8 draft-andersson-mpls-expbits-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 September 11, 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 bits . . . . . . . . . . . . . . . . . . . . . 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 bits called "EXP bits". RFC 3032 leaves 59 the exact description of how the EXP bits should be used undefined, 60 they are said to be for "experimental use". 62 The EXP bits has from the start be intended to be used for "Class of 63 Service", the bits were actually called "Class of Service bits" in 64 the early versions of the working group document that was publshed as 65 RFC 3032.C 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 bit were left for "Experimental use". 69 The use of the EXP bits was first defined in RFC 3270 [RFC3270] where 70 a method to define a variant of DiffServ LSPs called EXP-Inferred-PSC 71 LSP (E-LSPs). 73 The use of the EXP bits 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 bits 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) bits 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 bits has been update 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 bits have been renamed to the CoS bits, and thus all 138 references in RFC 3270 to EXP bits should be taken to refer to the 139 CoS bits. However, we retain the term E-LSP (EXP-Inferred-PSC 140 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 bits of the MPLS Shim 145 Header is used by the LSR to determine the PHB to be applied to 146 the packet. This includes both the PSC and the drop preference. 148 We refer to such LSPs as "EXP-inferred-PSC LSPs" (E-LSP), since 149 the PSC of a packet transported on this LSP depends on the CoS 150 bits (previously called the EXP bits) value for that packet. 152 The mapping from the CoS bits to the PHB (i.e., to PSC and drop 153 precedence) for a given such LSP, is either explicitly signaled at 154 label set-up or relies on a pre-configured mapping. 156 This is an update to RFC 3032 [RFC3032] in line with the original 157 intent of how this field in the MPLS Shim Header should be used 158 (as CoS bits). The RFC 3270 has itself been updated by RFC 5129 159 [RFC5129]. 161 Detailed operations of E-LSPs are specified in section 3 of 162 RFC3270. 164 2.3. RFC 5129 166 Section 2 (bullet 3) on page 6 of RFC 5129 says: 168 o A third possible approach was suggested by [Shayman]. In this 169 scheme, interior LSRs assume that the endpoints are ECN-capable, 170 but this assumption is checked when the final label is popped. If 171 an interior LSR has marked ECN in the EXP field of the shim 172 header, but the IP header says the endpoints are not ECN-capable, 173 the edge router (or penultimate router, if using penultimate hop 174 popping) drops the packet. We recommend this scheme, which we 175 call `per-domain ECT checking', and define it more precisely in 176 the following section. Its chief drawback is that it can cause 177 packets to be forwarded after encountering congestion only to be 178 dropped at the egress of the MPLS domain. The rationale for this 179 decision is given in Section 8.1. 181 RFC 5219 is now updated like this: 183 A new paragraph is added at the end of section 1.1 "Background": 185 The EXP bits have been renamed to the CoS bits, and thus all 186 references in RFC 5219 to EXP bits should be taken to refer to the 187 CoS bits. 189 Section 2 (bullet 3) on page 6 ofis now changed to: 191 o A third possible approach was suggested by [Shayman]. In this 192 scheme, interior LSRs assume that the endpoints are ECN-capable, 193 but this assumption is checked when the final label is popped. If 194 an interior LSR has marked ECN in the CoS field of the shim 195 header, but the IP header says the endpoints are not CoS-capable, 196 the edge router (or penultimate router, if using penultimate hop 197 popping) drops the packet. We recommend this scheme, which we 198 call `per-domain ECT checking', and define it more precisely in 199 the following section. Its chief drawback is that it can cause 200 packets to be forwarded after encountering congestion only to be 201 dropped at the egress of the MPLS domain. The rationale for this 202 decision is given in Section 8.1. This scheme is an update to RFC 203 3032 [RFC3032] and RFC 3270 [RFC3270]. 205 3. Use of the CoS bits 207 Due to the limited number of bits the particular use of the bits is 208 intended to be flexible - including the defininition of various QoS 209 and ECN functions. 211 Current implementations look at the CoS bits with and without label 212 context and the CoS bits may be copied to the labels that are pushed 213 onto the laabel stack. This is to avoid that the pushed labels have 214 a different set of CoS bits. 216 CoS and ECN funtions may rewrite all or some of the bits. 218 4. IANA considerations 220 TBD 222 5. Security considerations 224 This document only changes the name of one field in the MPLS Shim 225 Header and thus do not introduce any new security considerations. 227 6. References 229 6.1. Normative References 231 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 232 Requirement Levels", BCP 14, RFC 2119, March 1997. 234 [RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., 235 Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack 236 Encoding", RFC 3032, January 2001. 238 [RFC3270] Le Faucheur, F., Wu, L., Davie, B., Davari, S., Vaananen, 239 P., Krishnan, R., Cheval, P., and J. Heinanen, "Multi- 240 Protocol Label Switching (MPLS) Support of Differentiated 241 Services", RFC 3270, May 2002. 243 [RFC5129] Davie, B., Briscoe, B., and J. Tay, "Explicit Congestion 244 Marking in MPLS", RFC 5129, January 2008. 246 6.2. Informative references 248 [Shayman] Shayman, M. and R. Jaeger, University of Michigan, "Using 249 ECN to Signal Congestion Within an MPLS Domain", Work in 250 Progress, November 2000.", . 253 Author's Address 255 Loa Andersson 256 Acreo AB 258 Email: loa@pi.se 260 Full Copyright Statement 262 Copyright (C) The IETF Trust (2008). 264 This document is subject to the rights, licenses and restrictions 265 contained in BCP 78, and except as set forth therein, the authors 266 retain all their rights. 268 This document and the information contained herein are provided on an 269 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 270 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 271 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 272 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 273 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 274 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 276 Intellectual Property 278 The IETF takes no position regarding the validity or scope of any 279 Intellectual Property Rights or other rights that might be claimed to 280 pertain to the implementation or use of the technology described in 281 this document or the extent to which any license under such rights 282 might or might not be available; nor does it represent that it has 283 made any independent effort to identify any such rights. 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