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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network Working Group Toerless Eckert 2 Internet Draft Eric C. Rosen (editor) 3 Expiration Date: October 2005 Cisco Systems, Inc. 4 Updates RFCs 3032 and 4023 5 Rahul Aggarwal 6 Yakov Rekhter 7 Juniper Networks, Inc. 9 April 2005 11 MPLS Multicast Encapsulations 13 draft-rosen-mpls-multicast-encaps-00.txt 15 Status of this Memo 17 By submitting this Internet-Draft, each author represents that any 18 applicable patent or other IPR claims of which he or she is aware 19 have been or will be disclosed, and any of which he or she becomes 20 aware will be disclosed, in accordance with Section 6 of BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF), its areas, and its working groups. Note that other 24 groups may also distribute working documents as Internet-Drafts. 26 Internet-Drafts are draft documents valid for a maximum of six months 27 and may be updated, replaced, or obsoleted by other documents at any 28 time. It is inappropriate to use Internet-Drafts as reference 29 material or to cite them other than as "work in progress." 31 The list of current Internet-Drafts can be accessed at 32 http://www.ietf.org/ietf/1id-abstracts.txt. 34 The list of Internet-Draft Shadow Directories can be accessed at 35 http://www.ietf.org/shadow.html. 37 Abstract 39 RFC 3032 established two data link layer codepoints for MPLS: one to 40 indicate that the data link layer frame is carrying an MPLS unicast 41 packet, and the other to indicate that the data link layer frame is 42 carrying an MPLS multicast packet. This specification updates 43 RFC3032 by redefining the meaning of these two codepoints. The 44 former "multicast codepoint" is now to be used only on multiaccess 45 media, and it is to mean "the top label of the following label stack 46 is an upstream-assigned label". The former "unicast codepoint" is to 47 be used in all other cases. Whether the data link layer payload is a 48 unicast MPLS packet or a multicast MPLS packet is now to be 49 determined by looking up the top label, rather than by the codepoint. 51 RFC3032 does not specify the destination address to be placed in the 52 "MAC DA" field of an ethernet frame which carries an MPLS multicast 53 packet. This document provides that specification. 55 This document updates RFC 3032 and RFC 4023. 57 Contents 59 1 Introduction ......................................... 2 60 2 Upstream-Assigned vs. Downstream-Assigned ............ 3 61 3 Ethernet Codepoints .................................. 5 62 4 PPP Protocol Field ................................... 6 63 5 GRE Protocol Type .................................... 6 64 6 IP Protocol Number ................................... 6 65 7 Ethernet MAC DA for Multicast MPLS ................... 7 66 8 IANA Considerations .................................. 7 67 9 Security Considerations .............................. 7 68 10 Normative References ................................. 7 69 11 Informative References ............................... 8 70 12 Authors' Addresses ................................... 8 71 13 Full Copyright Statement ............................. 8 72 14 Intellectual Property ................................ 9 74 1. Introduction 76 RFC 3031 defines the "Next Hop Label Forwarding Entry" (NHLFE). The 77 NHLFE for a particular label maps the label into a next hop (among 78 other things). When an MPLS packet is received, its top label is 79 mapped to an NHLFE, and the packet is sent to the next hop specified 80 by the NHLFE. 82 We define a particular MPLS label to be a "multicast label" in a 83 particular context if the NHLFE to which it is mapped in that context 84 specifies a set of next hops, with the semantics that the packet is 85 to be replicated, and a copy of the packet sent to each of the 86 specified next hops. Note that this definition accommodates the case 87 where the set of next hops contains a single member. What makes a 88 label a multicast label in a particular context is the semantics 89 attached to the set, i.e., the intention to replicate the packet and 90 transmit to all members of the set if the set has more than one 91 member. 93 RFC 3032 established two data link layer codepoints for MPLS: one to 94 indicate that the data link layer frame is carrying an MPLS unicast 95 packet, and the other to indicate that the data link layer frame is 96 carrying an MPLS multicast packet. The term "multicast packet" is 97 not precisely defined in RFC 3032, though one may presume that the 98 "multicast" codepoint is intended to identify the packet's top label 99 as a multicast label. However, the multicast codepoint has never 100 been deployed, and further development of the procedures for MPLS 101 multicast have shown that, while there is a need for two codepoints, 102 the use of the two codepoints is not properly captured by RFC3032. 104 In particular, there is no need for the codepoint to indicate whether 105 the top MPLS label is a multicast label. When the receiver of an 106 MPLS packet looks up the top label, the NHLFE will specify whether 107 the label is a multicast label or not. 109 This document updates RFC 3032 and RFC 4023 by re-specifying the use 110 of the codepoints. 112 While RFC 3032 allows an MPLS packet to be carried in an ethernet 113 multicast frame, it fails to specify how the Medium Access Layer 114 Destination Address (MAC DA) field is to be set in that case. This 115 document provides that specification. 117 2. Upstream-Assigned vs. Downstream-Assigned 119 According to RFC 3031, if two MPLS Label Switching Routers (LSRs) are 120 adjacent in a label switched path (LSP), with respect to that LSP, 121 one of them may be called the "upstream" LSR and the other the 122 "downstream" LSR. Call these Ru and Rd respectively. Before Ru can 123 send an MPLS packet to Rd with label L at the top of the label stack, 124 Ru and Rd must agree on the Forwarding Equivalence Class (FEC) which 125 is bound to L. A particular binding of L to FEC F is called a 126 "downstream-assigned" binding if the binding is first made by Rd and 127 then advertised to Ru. If the binding is first made by Ru and then 128 advertised to Rd, it is called an "upstream-assigned" binding. 130 If Ru and RD are LSP adjacencies, then they transmit a MPLS packet to 131 each other through one of the following mechanisms: 133 1. by putting the MPLS packet in a data link layer frame and 134 transmitting the frame 136 2. by transmitting the MPLS packet through an MPLS tunnel, i.e., 137 by pushing an additional label (or labels) onto the label 138 stack, and then invoking mechanism 1, 140 3. by transmitting the MPLS packet through an IP-based tunnel 141 (e.g., via RFC 4023), and then invoking mechanisms 1 and/or 2. 143 In short, an MPLS packet is transmitted either through a data link or 144 through an MPLS tunnel or through an IP tunnel. In any of those 145 cases, when the packet emerges through the tunnel, the downstream LSR 146 must know whether the label that now appears at the top of the label 147 stack has an upstream-assigned label binding or a downstream-assigned 148 label binding. For convenience, we will speak of a label with an 149 upstream-assigned label binding as an "upstream-assigned label". 151 Unicast labels MUST be downstream-assigned. 153 Under certain conditions, specified below, multicast labels MAY be 154 upstream-assigned. The ability to use upstream-assigned labels is an 155 OPTIONAL feature. Upstream-assigned labels MUST NOT be used unless 156 it is known that the downstream LSR supports them. How this is known 157 is outside the scope of this document. 159 We discuss three different types of data link or tunnel: 161 - Point-to-Point. A point-to-point data link or tunnel associates 162 two systems, such that transmissions on that link or tunnel made 163 by the one are received by the other, and only by the other. 165 When an MPLS packet is transmitted on a point-to-point data link 166 or tunnel, its top label (before applying the data link or tunnel 167 encapsulation) MUST be a downstream-assigned label. 169 - Point-to-Multipoint. A point-to-multipoint link or tunnel 170 associates n systems, such that only one of them can transmit 171 onto the link or tunnel, and the transmissions may be received by 172 the other n-1 systems. 174 The top labels (before applying the data link or tunnel 175 encapsulation) of all MPLS packets which are transmitted on a 176 particular point-to-multipoint data link or tunnel MUST be of the 177 same type; either all upstream-assigned or all downstream- 178 assigned. This means that all the receivers on the MPLS or IP 179 tunnel must know a priori whether upstream-assigned or 180 downstream-assigned labels are being used in the tunnel. How 181 this is known is outside the scope of this document. 183 - Multipoint-to-Multipoint. A multipoint-to-multipoint link or 184 tunnel associates n systems, such that any of them can transmit 185 on the link or tunnel, and the transmissions may be received by 186 the other n-1 systems. 188 If a set of MPLS packets are transmitted on a multipoint-to- 189 multipoint link, their top labels (before applying the data link 190 or tunnel encapsulation) MAY be of different types, i.e., there 191 may be a mixture of upstream-assigned and downstream-assigned top 192 labels. 194 However, if upstream-assigned labels are to be used, the data 195 link or tunnel encapsulation MUST provide a codepoint which 196 specifies whether the top label of the encapsulated MPLS packet 197 is upstream-assigned or downstream-assigned. If a particular 198 type of data link or tunnel does not provide such a codepoint, 199 then upstream-assigned labels MUST NOT be used. 201 The remainder of this document specifies procedures for setting the 202 data link layer codepoints and address fields. 204 3. Ethernet Codepoints 206 Ethernet is an example of a multipoint-to-multipoint data link. 208 Ethertype 0x8847 is used whenever a unicast ethernet frame carries an 209 MPLS packet. 211 Ethertype 0x8847 is also used whenever a multicast ethernet frame 212 carries an MPLS packet, EXCEPT for the case where the top label of 213 the MPLS packet has been upstream-assigned. 215 Ethertype 0x8848, formerly known as the "MPLS multicast codepoint", 216 is to be used only when an MPLS packet whose top label is upstream- 217 assigned is carried in a multicast ethernet frame. 219 4. PPP Protocol Field 221 PPP is an example of a point-to-point data link. When a PPP frame is 222 carrying an MPLS packet, the PPP Protocol field is always set to 223 0x0281. 225 5. GRE Protocol Type 227 RFC 4023 is modified as described below. 229 If the IP destination address of the GRE encapsulation is a unicast 230 IP address, then the ethertype value 0x8847 MUST be used in all cases 231 for the MPLS-in-GRE encapsulation. 233 If the IP destination address of the GRE encapsulation is a multicast 234 IP address, then: 236 - if both upstream-assigned and downstream-assigned labels may 237 appear as the top label of the encapsulated MPLS packets, then 238 the ethertype value 0x8847 MUST be used when the aforesaid label 239 is downstream-assigned, and the ethertype value 0x8848 MUST be 240 used when the aforesaid label is upstream-assigned. 242 - if all the encapsulated MPLS packets have an upstream-assigned 243 top label, or if all the encapsulated MPLS packets have a 244 downstream-assigned top label, then the ethertype value 0x8847 245 MUST be used. 247 Which of these two situations applies is determined by means outside 248 the scope of this specification. 250 6. IP Protocol Number 252 RFC 4023 is modified as follows: the IPv4 Protocol Number field or 253 the IPv6 Next Header field is always set to 137, whether or not the 254 encapsulated MPLS packet is an MPLS multicast packet. 256 If the IP destination address of the IP encapsulation is an IP 257 multicast address, the IP tunnel may be considered to be a point-to- 258 multipoint tunnel or a multipoint-to-multipoint tunnel. In either 259 case, either all encapsulated MPLS packets in the particular tunnel 260 have a downstream-assigned label at the top of the stack, or all 261 encapsulated MPLS packets in that tunnel have an upstream-assigned 262 label at the top of the stack. The means by which this is determined 263 for a particular tunnel is outside the scope of this specification. 265 7. Ethernet MAC DA for Multicast MPLS 267 When a multicast MPLS packet is carried in a multicast ethernet 268 frame, the Destination MAC Address shall be set to the value 01-00- 269 5e-8a-bc-de, where abcde is the twenty-bit (4-nibble) value of the 270 topmost MPLS label of the MPLS packet. 272 8. IANA Considerations 274 IANA already owns the set of ethernet multicast addresses in the 275 range 01-00-5e-00-00-00 to 01-00-5e-ff-ff-ff. Addresses in the range 276 01-00-5e-00-00-00 to 01-00-5e-7f-ff-ff are reserved for use when an 277 ethernet multicast frame carries an IP multicast packet. IANA shall 278 reserve ethernet addresses in the range 01-00-5e-80-00-00 to 01-00- 279 5e-8f-ff-ff for use when an ethernet multicast frame carries an MPLS 280 multicast packet. 282 9. Security Considerations 284 The security considerations of RFC 3032 and RFC 4023 apply. 286 Malicious changing of the codepoint may result in loss or misrouting 287 of packets. However, altering the codepoint without also altering the 288 label does not result in a predictable effect. 290 Malicious alteration of the MAC DA on an ethernet can result in 291 packets being received by a third party, rather than by the intended 292 recipient. 294 10. Normative References 296 [RFC3031] "Multiprotocol Label Switching Architecture", Rosen, 297 Viswanathan, Callon, January 2001 299 [RFC3032] "MPLS Label Stack Encoding", Rosen, et. al., January 2001 301 [RFC4023] "Encapsulating MPLS in IP or GRE", Worster, Rekhter, Rosen, 302 March 2005 304 11. Informative References 306 12. Authors' Addresses 308 Toerless Eckert 309 Cisco Systems, Inc. 310 170 Tasman Drive 311 San Jose, CA, 95134 312 Email: eckert@cisco.com 314 Eric C. Rosen 315 Cisco Systems, Inc. 316 1414 Massachusetts Avenue 317 Boxborough, MA 01719 318 Email: erosen@cisco.com 320 Rahul Aggarwal 321 Juniper Networks 322 1194 North Mathilda Ave. 323 Sunnyvale, CA 94089 324 Email: rahul@juniper.net 326 Yakov Rekhter 327 Juniper Networks 328 1194 North Mathilda Ave. 329 Sunnyvale, CA 94089 330 Email: yakov@juniper.net 332 13. Full Copyright Statement 334 Copyright (C) The Internet Society (2005). 336 This document is subject to the rights, licenses and restrictions 337 contained in BCP 78, and except as set forth therein, the authors 338 retain all their rights. 340 This document and the information contained herein are provided on an 341 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 342 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET 343 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, 344 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE 345 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 346 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 348 14. 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