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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 2006 Cisco Systems, Inc. 5 Updates RFCs 3032 and 4023 6 Rahul Aggarwal 7 Yakov Rekhter 8 Juniper Networks, Inc. 10 February 2006 12 MPLS Multicast Encapsulations 14 draft-ietf-mpls-multicast-encaps-00.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 a set of MPLS packets are transmitted on a multipoint-to- 190 multipoint link, their top labels (before applying the data link 191 or tunnel encapsulation) MAY be of different types, i.e., there 192 may be a mixture of upstream-assigned and downstream-assigned top 193 labels. 195 However, if upstream-assigned labels are to be used, the data 196 link or tunnel encapsulation MUST provide a codepoint which 197 specifies whether the top label of the encapsulated MPLS packet 198 is upstream-assigned or downstream-assigned. If a particular 199 type of data link or tunnel does not provide such a codepoint, 200 then upstream-assigned labels MUST NOT be used. 202 The remainder of this document specifies procedures for setting the 203 data link layer codepoints and address fields. 205 3. Ethernet Codepoints 207 Ethernet is an example of a multipoint-to-multipoint data link. 209 Ethertype 0x8847 is used whenever a unicast ethernet frame carries an 210 MPLS packet. 212 Ethertype 0x8847 is also used whenever a multicast ethernet frame 213 carries an MPLS packet, EXCEPT for the case where the top label of 214 the MPLS packet has been upstream-assigned. 216 Ethertype 0x8848, formerly known as the "MPLS multicast codepoint", 217 is to be used only when an MPLS packet whose top label is upstream- 218 assigned is carried in a multicast ethernet frame. 220 4. PPP Protocol Field 222 PPP is an example of a point-to-point data link. When a PPP frame is 223 carrying an MPLS packet, the PPP Protocol field is always set to 224 0x0281. 226 5. GRE Protocol Type 228 RFC 4023 is modified as described below. 230 If the IP destination address of the GRE encapsulation is a unicast 231 IP address, then the ethertype value 0x8847 MUST be used in all cases 232 for the MPLS-in-GRE encapsulation. 234 If the IP destination address of the GRE encapsulation is a multicast 235 IP address, then: 237 - if both upstream-assigned and downstream-assigned labels may 238 appear as the top label of the encapsulated MPLS packets, then 239 the ethertype value 0x8847 MUST be used when the aforesaid label 240 is downstream-assigned, and the ethertype value 0x8848 MUST be 241 used when the aforesaid label is upstream-assigned. 243 - if all the encapsulated MPLS packets have an upstream-assigned 244 top label, or if all the encapsulated MPLS packets have a 245 downstream-assigned top label, then the ethertype value 0x8847 246 MUST be used. 248 Which of these two situations applies is determined by means outside 249 the scope of this specification. 251 6. IP Protocol Number 253 RFC 4023 is modified as follows: the IPv4 Protocol Number field or 254 the IPv6 Next Header field is always set to 137, whether or not the 255 encapsulated MPLS packet is an MPLS multicast packet. 257 If the IP destination address of the IP encapsulation is an IP 258 multicast address, the IP tunnel may be considered to be a point-to- 259 multipoint tunnel or a multipoint-to-multipoint tunnel. In either 260 case, either all encapsulated MPLS packets in the particular tunnel 261 have a downstream-assigned label at the top of the stack, or all 262 encapsulated MPLS packets in that tunnel have an upstream-assigned 263 label at the top of the stack. The means by which this is determined 264 for a particular tunnel is outside the scope of this specification. 266 7. Ethernet MAC DA for Multicast MPLS 268 When a multicast MPLS packet is carried in a multicast ethernet 269 frame, the Destination MAC Address shall be set to the value 01-00- 270 5e-8a-bc-de, where abcde is the twenty-bit (4-nibble) value of the 271 topmost MPLS label of the MPLS packet. 273 8. IANA Considerations 275 IANA already owns the set of ethernet multicast addresses in the 276 range 01-00-5e-00-00-00 to 01-00-5e-ff-ff-ff. Addresses in the range 277 01-00-5e-00-00-00 to 01-00-5e-7f-ff-ff are reserved for use when an 278 ethernet multicast frame carries an IP multicast packet. IANA shall 279 reserve ethernet addresses in the range 01-00-5e-80-00-00 to 01-00- 280 5e-8f-ff-ff for use when an ethernet multicast frame carries an MPLS 281 multicast packet. 283 9. Security Considerations 285 The security considerations of RFC 3032 and RFC 4023 apply. 287 Malicious changing of the codepoint may result in loss or misrouting 288 of packets. However, altering the codepoint without also altering the 289 label does not result in a predictable effect. 291 Malicious alteration of the MAC DA on an ethernet can result in 292 packets being received by a third party, rather than by the intended 293 recipient. 295 10. Normative References 297 [RFC3031] "Multiprotocol Label Switching Architecture", Rosen, 298 Viswanathan, Callon, January 2001 300 [RFC3032] "MPLS Label Stack Encoding", Rosen, et. al., January 2001 302 [RFC4023] "Encapsulating MPLS in IP or GRE", Worster, Rekhter, Rosen, 303 March 2005 305 11. Informative References 307 12. Authors' Addresses 309 Toerless Eckert 310 Cisco Systems, Inc. 311 170 Tasman Drive 312 San Jose, CA, 95134 313 Email: eckert@cisco.com 315 Eric C. Rosen 316 Cisco Systems, Inc. 317 1414 Massachusetts Avenue 318 Boxborough, MA 01719 319 Email: erosen@cisco.com 321 Rahul Aggarwal 322 Juniper Networks 323 1194 North Mathilda Ave. 324 Sunnyvale, CA 94089 325 Email: rahul@juniper.net 327 Yakov Rekhter 328 Juniper Networks 329 1194 North Mathilda Ave. 330 Sunnyvale, CA 94089 331 Email: yakov@juniper.net 333 13. Full Copyright Statement 335 Copyright (C) The Internet Society (2006). 337 This document is subject to the rights, licenses and restrictions 338 contained in BCP 78, and except as set forth therein, the authors 339 retain all their rights. 341 This document and the information contained herein are provided on an 342 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 343 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET 344 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, 345 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE 346 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 347 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 349 14. 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