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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) == Unused Reference: 'RFC3031' is defined on line 306, but no explicit reference was found in the text == Unused Reference: 'RFC3032' is defined on line 309, but no explicit reference was found in the text == Unused Reference: 'RFC4023' is defined on line 311, but no explicit reference was found in the text Summary: 2 errors (**), 0 flaws (~~), 5 warnings (==), 9 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group Toerless Eckert 3 Internet Draft Eric C. Rosen (editor) 4 Expiration Date: August 2007 Cisco Systems, Inc. 5 Updates RFCs 3032 and 4023 6 Rahul Aggarwal 7 Yakov Rekhter 8 Juniper Networks, Inc. 10 February 2007 12 MPLS Multicast Encapsulations 14 draft-ietf-mpls-multicast-encaps-03.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 other 25 groups may also distribute working documents as Internet-Drafts. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 The list of current Internet-Drafts can be accessed at 33 http://www.ietf.org/ietf/1id-abstracts.txt. 35 The list of Internet-Draft Shadow Directories can be accessed at 36 http://www.ietf.org/shadow.html. 38 Abstract 40 RFC 3032 established two data link layer codepoints for MPLS: one to 41 indicate that the data link layer frame is carrying an MPLS unicast 42 packet, and the other to indicate that the data link layer frame is 43 carrying an MPLS multicast packet. This specification updates 44 RFC3032 by redefining the meaning of these two codepoints. The 45 former "multicast codepoint" is now to be used only on multiaccess 46 media, and it is to mean "the top label of the following label stack 47 is an upstream-assigned label". The former "unicast codepoint" is to 48 be used in all other cases. Whether the data link layer payload is a 49 unicast MPLS packet or a multicast MPLS packet is now to be 50 determined by looking up the top label, rather than by the codepoint. 52 RFC3032 does not specify the destination address to be placed in the 53 "MAC DA" field of an ethernet frame which carries an MPLS multicast 54 packet. This document provides that specification. 56 This document updates RFC 3032 and RFC 4023. 58 Contents 60 1 Introduction ......................................... 2 61 2 Upstream-Assigned vs. Downstream-Assigned ............ 3 62 3 Ethernet Codepoints .................................. 5 63 4 PPP Protocol Field ................................... 6 64 5 GRE Protocol Type .................................... 6 65 6 IP Protocol Number ................................... 6 66 7 Ethernet MAC DA for Multicast MPLS ................... 7 67 8 IANA Considerations .................................. 7 68 9 Security Considerations .............................. 7 69 10 Normative References ................................. 7 70 11 Informative References ............................... 8 71 12 Authors' Addresses ................................... 8 72 13 Full Copyright Statement ............................. 8 73 14 Intellectual Property ................................ 9 75 1. Introduction 77 RFC 3031 defines the "Next Hop Label Forwarding Entry" (NHLFE). The 78 NHLFE for a particular label maps the label into a next hop (among 79 other things). When an MPLS packet is received, its top label is 80 mapped to an NHLFE, and the packet is sent to the next hop specified 81 by the NHLFE. 83 We define a particular MPLS label to be a "multicast label" in a 84 particular context if the NHLFE to which it is mapped in that context 85 specifies a set of next hops, with the semantics that the packet is 86 to be replicated, and a copy of the packet sent to each of the 87 specified next hops. Note that this definition accommodates the case 88 where the set of next hops contains a single member. What makes a 89 label a multicast label in a particular context is the semantics 90 attached to the set, i.e., the intention to replicate the packet and 91 transmit to all members of the set if the set has more than one 92 member. 94 RFC 3032 established two data link layer codepoints for MPLS: one to 95 indicate that the data link layer frame is carrying an MPLS unicast 96 packet, and the other to indicate that the data link layer frame is 97 carrying an MPLS multicast packet. The term "multicast packet" is 98 not precisely defined in RFC 3032, though one may presume that the 99 "multicast" codepoint is intended to identify the packet's top label 100 as a multicast label. However, the multicast codepoint has never 101 been deployed, and further development of the procedures for MPLS 102 multicast have shown that, while there is a need for two codepoints, 103 the use of the two codepoints is not properly captured by RFC3032. 105 In particular, there is no need for the codepoint to indicate whether 106 the top MPLS label is a multicast label. When the receiver of an 107 MPLS packet looks up the top label, the NHLFE will specify whether 108 the label is a multicast label or not. 110 This document updates RFC 3032 and RFC 4023 by re-specifying the use 111 of the codepoints. 113 While RFC 3032 allows an MPLS packet to be carried in an ethernet 114 multicast frame, it fails to specify how the Medium Access Layer 115 Destination Address (MAC DA) field is to be set in that case. This 116 document provides that specification. 118 2. Upstream-Assigned vs. Downstream-Assigned 120 According to RFC 3031, if two MPLS Label Switching Routers (LSRs) are 121 adjacent in a label switched path (LSP), with respect to that LSP, 122 one of them may be called the "upstream" LSR and the other the 123 "downstream" LSR. Call these Ru and Rd respectively. Before Ru can 124 send an MPLS packet to Rd with label L at the top of the label stack, 125 Ru and Rd must agree on the Forwarding Equivalence Class (FEC) which 126 is bound to L. A particular binding of L to FEC F is called a 127 "downstream-assigned" binding if the binding is first made by Rd and 128 then advertised to Ru. If the binding is first made by Ru and then 129 advertised to Rd, it is called an "upstream-assigned" binding. 131 If Ru and RD are LSP adjacencies, then they transmit a MPLS packet to 132 each other through one of the following mechanisms: 134 1. by putting the MPLS packet in a data link layer frame and 135 transmitting the frame 137 2. by transmitting the MPLS packet through an MPLS tunnel, i.e., 138 by pushing an additional label (or labels) onto the label 139 stack, and then invoking mechanism 1, 141 3. by transmitting the MPLS packet through an IP-based tunnel 142 (e.g., via RFC 4023), and then invoking mechanisms 1 and/or 2. 144 In short, an MPLS packet is transmitted either through a data link or 145 through an MPLS tunnel or through an IP tunnel. In any of those 146 cases, when the packet emerges through the tunnel, the downstream LSR 147 must know whether the label that now appears at the top of the label 148 stack has an upstream-assigned label binding or a downstream-assigned 149 label binding. For convenience, we will speak of a label with an 150 upstream-assigned label binding as an "upstream-assigned label". 152 Unicast labels MUST be downstream-assigned. 154 Under certain conditions, specified below, multicast labels MAY be 155 upstream-assigned. The ability to use upstream-assigned labels is an 156 OPTIONAL feature. Upstream-assigned labels MUST NOT be used unless 157 it is known that the downstream LSR supports them. How this is known 158 is outside the scope of this document. 160 We discuss three different types of data link or tunnel: 162 - Point-to-Point. A point-to-point data link or tunnel associates 163 two systems, such that transmissions on that link or tunnel made 164 by the one are received by the other, and only by the other. 166 When an MPLS packet is transmitted on a point-to-point data link 167 or tunnel, its top label (before applying the data link or tunnel 168 encapsulation) MUST be a downstream-assigned label. 170 - Point-to-Multipoint. A point-to-multipoint link or tunnel 171 associates n systems, such that only one of them can transmit 172 onto the link or tunnel, and the transmissions may be received by 173 the other n-1 systems. 175 The top labels (before applying the data link or tunnel 176 encapsulation) of all MPLS packets which are transmitted on a 177 particular point-to-multipoint data link or tunnel MUST be of the 178 same type; either all upstream-assigned or all downstream- 179 assigned. This means that all the receivers on the MPLS or IP 180 tunnel must know a priori whether upstream-assigned or 181 downstream-assigned labels are being used in the tunnel. How 182 this is known is outside the scope of this document. 184 - Multipoint-to-Multipoint. A multipoint-to-multipoint link or 185 tunnel associates n systems, such that any of them can transmit 186 on the link or tunnel, and the transmissions may be received by 187 the other n-1 systems. 189 If MPLS packets are transmitted on a particular multipoint-to- 190 multipoint link or tunnel, one of the following scenarios 191 applies: 193 1. It is known (by methods outside the scope of this document) 194 that the top label of every MPLS packet on the link or 195 tunnel is downstream-assigned 197 2. It is known (by methods outside the scope of this document) 198 that the top label of every MPLS packet on the link or 199 tunnel is upstream-assigned 201 3. Some MPLS packets on the link may have upstream-assigned 202 top labels while some may have downstream-assigned top 203 labels 205 If (and only if) the third scenario applies, the data link or 206 tunnel encapsulation MUST provide a codepoint which specifies 207 whether the top label of the encapsulated MPLS packet is 208 upstream-assigned or downstream-assigned. If a particular type 209 of data link or tunnel does not provide such a codepoint, then 210 the third scenario MUST NOT be used. 212 The remainder of this document specifies procedures for setting the 213 data link layer codepoints and address fields. 215 3. Ethernet Codepoints 217 Ethernet is an example of a multipoint-to-multipoint data link. 219 Ethertype 0x8847 is used whenever a unicast ethernet frame carries an 220 MPLS packet. 222 Ethertype 0x8847 is also used whenever a multicast ethernet frame 223 carries an MPLS packet, EXCEPT for the case where the top label of 224 the MPLS packet has been upstream-assigned. 226 Ethertype 0x8848, formerly known as the "MPLS multicast codepoint", 227 is to be used only when an MPLS packet whose top label is upstream- 228 assigned is carried in a multicast ethernet frame. 230 4. PPP Protocol Field 232 PPP is an example of a point-to-point data link. When a PPP frame is 233 carrying an MPLS packet, the PPP Protocol field is always set to 234 0x0281. 236 5. GRE Protocol Type 238 RFC 4023 is modified as described below. 240 If the IP destination address of the GRE encapsulation is a unicast 241 IP address, then the ethertype value 0x8847 MUST be used in all cases 242 for the MPLS-in-GRE encapsulation. 244 If the IP destination address of the GRE encapsulation is a multicast 245 IP address, then: 247 - the ethertype value 0x8847 MUST be used when the top label of the 248 encapsulated MPLS packet is downstream-assigned, 250 - the ethertype value 0x8848 MUST be used when the top label of the 251 encapsulated MPLS packet is upstream-assigned. 253 Through procedures which are outside the scope of this specification, 254 it may be known that if the destination address of a GRE packet is a 255 multicast IP address, then the top label of the GRE payload is 256 upstream-assigned. In such a case, the occurrence of the 8847 257 codepoint in a GRE packet with a multicast destination IP address 258 MUST be considered an error, and the packet MUST be discarded. 260 6. IP Protocol Number 262 RFC 4023 is modified as follows: the IPv4 Protocol Number field or 263 the IPv6 Next Header field is always set to 137, whether or not the 264 encapsulated MPLS packet is an MPLS multicast packet. 266 If the IP destination address of the IP encapsulation is an IP 267 multicast address, the IP tunnel may be considered to be a point-to- 268 multipoint tunnel or a multipoint-to-multipoint tunnel. In either 269 case, either all encapsulated MPLS packets in the particular tunnel 270 have a downstream-assigned label at the top of the stack, or all 271 encapsulated MPLS packets in that tunnel have an upstream-assigned 272 label at the top of the stack. The means by which this is determined 273 for a particular tunnel is outside the scope of this specification. 275 7. Ethernet MAC DA for Multicast MPLS 277 When a multicast MPLS packet is carried in a multicast ethernet 278 frame, the Destination MAC Address shall be set to the value 01-00- 279 5e-8a-bc-de, where abcde is the twenty-bit (5-nibble) value of the 280 topmost MPLS label of the MPLS packet. 282 8. IANA Considerations 284 IANA already owns the set of ethernet multicast addresses in the 285 range 01-00-5e-00-00-00 to 01-00-5e-ff-ff-ff. Addresses in the range 286 01-00-5e-00-00-00 to 01-00-5e-7f-ff-ff are reserved for use when an 287 ethernet multicast frame carries an IP multicast packet. IANA shall 288 reserve ethernet addresses in the range 01-00-5e-80-00-00 to 01-00- 289 5e-8f-ff-ff for use when an ethernet multicast frame carries an MPLS 290 multicast packet. 292 9. Security Considerations 294 The security considerations of RFC 3032 and RFC 4023 apply. 296 Malicious changing of the codepoint may result in loss or misrouting 297 of packets. However, altering the codepoint without also altering the 298 label does not result in a predictable effect. 300 Malicious alteration of the MAC DA on an ethernet can result in 301 packets being received by a third party, rather than by the intended 302 recipient. 304 10. Normative References 306 [RFC3031] "Multiprotocol Label Switching Architecture", Rosen, 307 Viswanathan, Callon, January 2001 309 [RFC3032] "MPLS Label Stack Encoding", Rosen, et. al., January 2001 311 [RFC4023] "Encapsulating MPLS in IP or GRE", Worster, Rekhter, Rosen, 312 March 2005 314 11. Informative References 316 12. Authors' Addresses 318 Toerless Eckert 319 Cisco Systems, Inc. 320 170 Tasman Drive 321 San Jose, CA, 95134 322 Email: eckert@cisco.com 324 Eric C. Rosen 325 Cisco Systems, Inc. 326 1414 Massachusetts Avenue 327 Boxborough, MA 01719 328 Email: erosen@cisco.com 330 Rahul Aggarwal 331 Juniper Networks 332 1194 North Mathilda Ave. 333 Sunnyvale, CA 94089 334 Email: rahul@juniper.net 336 Yakov Rekhter 337 Juniper Networks 338 1194 North Mathilda Ave. 339 Sunnyvale, CA 94089 340 Email: yakov@juniper.net 342 13. Full Copyright Statement 344 Copyright (C) The IETF Trust (2007). 346 This document is subject to the rights, licenses and restrictions 347 contained in BCP 78, and except as set forth therein, the authors 348 retain all their rights. 350 This document and the information contained herein are provided on an 351 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 352 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 353 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 354 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 355 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 356 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 358 14. 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