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Rosen (editor) 4 Intended Status: Standards Track Cisco Systems, Inc. 5 Expires: November 1, 2008 6 Updates: RFCs 3032 and 4023 Rahul Aggarwal 7 Yakov Rekhter 8 Juniper Networks, Inc. 10 May 1, 2008 12 MPLS Multicast Encapsulations 14 draft-ietf-mpls-multicast-encaps-09.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, used to 41 distinguish whether the data link layer frame is carrying an MPLS 42 unicast or an MPLS multicast packet. However, this usage was never 43 deployed. This specification updates RFC 3032 by redefining the 44 meaning of these two codepoints. Both codepoints can now be used to 45 carry multicast packets. The second codepoint (formerly the 46 "multicast codepoint") is now to be used only on multiaccess media, 47 and it is to mean "the top label of the following label stack is an 48 upstream-assigned label". 50 RFC 3032 does not specify the destination address to be placed in the 51 "MAC DA" field of an ethernet frame which carries an MPLS multicast 52 packet. This document provides that specification. 54 This document updates RFC 3032 and RFC 4023. 56 Contents 58 1 Specification of Requirements ........................... 2 59 2 Introduction ............................................ 3 60 3 Upstream-Assigned vs. Downstream-Assigned ............... 4 61 4 Ethernet Codepoints ..................................... 6 62 5 PPP Protocol Field ...................................... 6 63 6 GRE Protocol Type ....................................... 6 64 7 IP Protocol Number ...................................... 7 65 8 Ethernet MAC DA for Multicast MPLS ...................... 7 66 9 IANA Considerations ..................................... 8 67 10 Security Considerations ................................. 9 68 11 Normative References .................................... 9 69 12 Authors' Addresses ...................................... 9 70 13 Full Copyright Statement ................................ 10 71 14 Intellectual Property ................................... 10 73 1. Specification of Requirements 75 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 76 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 77 document are to be interpreted as described in [RFC2119]. 79 2. Introduction 81 RFC 3031 [RFC3031] defines the "Next Hop Label Forwarding Entry" 82 (NHLFE). The NHLFE for a particular label maps the label into a next 83 hop (among other things). When an MPLS packet is received, its top 84 label is mapped to an NHLFE, and the packet is sent to the next hop 85 specified by the NHLFE. 87 We define a particular MPLS label to be a "multicast label" in a 88 particular context if the NHLFE to which it is mapped in that context 89 specifies a set of next hops, with the semantics that the packet is 90 to be replicated, and a copy of the packet sent to each of the 91 specified next hops. Note that this definition accommodates the case 92 where the set of next hops contains a single member. What makes a 93 label a multicast label in a particular context is the semantics 94 attached to the set, i.e., the intention to replicate the packet and 95 transmit to all members of the set if the set has more than one 96 member. 98 RFC 3032 [RFC3032] established two data link layer codepoints for 99 MPLS: one to indicate that the data link layer frame is carrying an 100 MPLS unicast packet, and the other to indicate that the data link 101 layer frame is carrying an MPLS multicast packet. The term 102 "multicast packet" is not precisely defined in RFC 3032, though one 103 may presume that the "multicast" codepoint is intended to identify 104 the packet's top label as a multicast label. However, the multicast 105 codepoint has never been deployed, and further development of the 106 procedures for MPLS multicast have shown that, while there is a need 107 for two codepoints, the use of the two codepoints is not properly 108 captured by RFC 3032. 110 In particular, there is no need for the codepoint to indicate whether 111 the top MPLS label is a multicast label. When the receiver of an 112 MPLS packet looks up the top label, the NHLFE will specify whether 113 the label is a multicast label or not. 115 This document updates RFC 3032 and RFC 4023 by re-specifying the use 116 of the codepoints. Note that an implementation that does MPLS 117 multicast according to RFC 3032 and/or 4023 will be unable to 118 interoperate with implementations that do MPLS multicast according to 119 this document. Any attempt to interoperate two such implementations 120 will result either in black holes or in misrouted packets. However, 121 since to the best of our knowledge MPLS multicast done according to 122 RFC 3032 has never been deployed, it is believed though that this 123 does not present a problem in practice. This document specifically 124 deprecates the multicast data plane as specified in RFC 3032. 126 While RFC 3032 allows an MPLS packet to be carried in an ethernet 127 multicast frame, it fails to specify how the Medium Access Layer 128 Destination Address (MAC DA) field is to be set in that case. This 129 document provides that specification. 131 3. Upstream-Assigned vs. Downstream-Assigned 133 According to RFC 3031 [RFC3031], if two MPLS Label Switching Routers 134 (LSRs) are adjacent in a label switched path (LSP), with respect to 135 that LSP, one of them may be called the "upstream" LSR and the other 136 the "downstream" LSR. Call these Ru and Rd respectively. Before Ru 137 can send an MPLS packet to Rd with label L at the top of the label 138 stack, Ru and Rd must agree on the Forwarding Equivalence Class (FEC) 139 which is bound to L. A particular binding of L to FEC F is called a 140 "downstream-assigned" binding if the binding is first made by Rd and 141 then advertised to Ru. If the binding is first made by Ru and then 142 advertised to Rd, it is called an "upstream-assigned" binding. 144 If Ru and RD are LSP adjacencies, then they transmit a MPLS packet to 145 each other through one of the following mechanisms: 147 1. by putting the MPLS packet in a data link layer frame and 148 transmitting the frame 150 2. by transmitting the MPLS packet through an MPLS tunnel, i.e., 151 by pushing an additional label (or labels) onto the label 152 stack, and then invoking mechanism 1, 154 3. by transmitting the MPLS packet through an IP-based tunnel 155 (e.g., via RFC 4023 [RFC4023]), and then invoking mechanisms 1 156 and/or 2. 158 In short, an MPLS packet is transmitted either through a data link or 159 through an MPLS tunnel or through an IP tunnel. In any of those 160 cases, when the packet emerges through the tunnel, the downstream LSR 161 must know whether the label that now appears at the top of the label 162 stack has an upstream-assigned label binding or a downstream-assigned 163 label binding. For convenience, we will speak of a label with an 164 upstream-assigned label binding as an "upstream-assigned label". 166 Unicast labels MUST be downstream-assigned. 168 Under certain conditions, specified below, multicast labels MAY be 169 upstream-assigned. The ability to use upstream-assigned labels is an 170 OPTIONAL feature. Upstream-assigned labels MUST NOT be used unless 171 it is known that the downstream LSR supports them. How this is known 172 is outside the scope of this document. 174 We discuss three different types of data link or tunnel: 176 - Point-to-Point. A point-to-point data link or tunnel associates 177 two systems, such that transmissions on that link or tunnel made 178 by the one are received by the other, and only by the other. 180 For a given direction of a given point-to-point data link or 181 tunnel, the following MUST be the case: either every MPLS packet 182 will carry an upstream-assigned label, or else every MPLS packet 183 will carry a downstream-assigned label. The procedures for 184 determining whether upstream-assigned or downstream-assigned 185 labels are being used are outside the scope of this 186 specification. However, in the absence of any other information, 187 the use of downstream-assigned labels MUST be presumed by 188 default. 190 - Point-to-Multipoint. A point-to-multipoint link or tunnel 191 associates n systems, such that only one of them can transmit 192 onto the link or tunnel, and the transmissions may be received by 193 the other n-1 systems. 195 The top labels (before applying the data link or tunnel 196 encapsulation) of all MPLS packets which are transmitted on a 197 particular point-to-multipoint data link or tunnel MUST be of the 198 same type; either all upstream-assigned or all downstream- 199 assigned. This means that all the receivers on the MPLS or IP 200 tunnel must know a priori whether upstream-assigned or 201 downstream-assigned labels are being used in the tunnel. How 202 this is known is outside the scope of this document. 204 - Multipoint-to-Multipoint. A multipoint-to-multipoint link or 205 tunnel associates n systems, such that any of them can transmit 206 on the link or tunnel, and the transmissions may be received by 207 the other n-1 systems. 209 If MPLS packets are transmitted on a particular multipoint-to- 210 multipoint link or tunnel, one of the following scenarios 211 applies: 213 1. It is known (by methods outside the scope of this document) 214 that the top label of every MPLS packet on the link or 215 tunnel is downstream-assigned 217 2. It is known (by methods outside the scope of this document) 218 that the top label of every MPLS packet on the link or 219 tunnel is upstream-assigned 221 3. Some MPLS packets on the link may have upstream-assigned 222 top labels while some may have downstream-assigned top 223 labels 225 If (and only if) the third scenario applies, the data link or 226 tunnel encapsulation MUST provide a codepoint which specifies 227 whether the top label of the encapsulated MPLS packet is 228 upstream-assigned or downstream-assigned. If a particular type 229 of data link or tunnel does not provide such a codepoint, then 230 the third scenario MUST NOT be used. 232 The remainder of this document specifies procedures for setting the 233 data link layer codepoints and address fields. 235 4. Ethernet Codepoints 237 Ethernet is an example of a multipoint-to-multipoint data link. 239 Ethertype 0x8847 is used whenever a unicast ethernet frame carries an 240 MPLS packet. 242 Ethertype 0x8847 is also used whenever a multicast ethernet frame 243 carries an MPLS packet, EXCEPT for the case where the top label of 244 the MPLS packet has been upstream-assigned. 246 Ethertype 0x8848, formerly known as the "MPLS multicast codepoint", 247 is to be used only when an MPLS packet whose top label is upstream- 248 assigned is carried in a multicast ethernet frame. 250 5. PPP Protocol Field 252 PPP is an example of a point-to-point data link. When a PPP frame is 253 carrying an MPLS packet, the PPP Protocol field is always set to 254 0x0281. 256 6. GRE Protocol Type 258 RFC 4023 is modified as described below. 260 If the IP destination address of the GRE encapsulation is a unicast 261 IP address, then the ethertype value 0x8847 MUST be used in all cases 262 for the MPLS-in-GRE encapsulation. 264 If the IP destination address of the GRE encapsulation is a multicast 265 IP address, then: 267 - the ethertype value 0x8847 MUST be used when the top label of the 268 encapsulated MPLS packet is downstream-assigned, 270 - the ethertype value 0x8848 MUST be used when the top label of the 271 encapsulated MPLS packet is upstream-assigned. 273 Through procedures which are outside the scope of this specification, 274 it may be known that if the destination address of a GRE packet is a 275 multicast IP address, then the top label of the GRE payload is 276 upstream-assigned. In such a case, the occurrence of the 8847 277 codepoint in a GRE packet with a multicast destination IP address 278 MUST be considered an error, and the packet MUST be discarded. 280 7. IP Protocol Number 282 RFC 4023 is modified as follows: the IPv4 Protocol Number field or 283 the IPv6 Next Header field is always set to 137, whether or not the 284 encapsulated MPLS packet is an MPLS multicast packet. 286 If the IP destination address of the IP encapsulation is an IP 287 multicast address, the IP tunnel may be considered to be a point-to- 288 multipoint tunnel or a multipoint-to-multipoint tunnel. In either 289 case, either all encapsulated MPLS packets in the particular tunnel 290 have a downstream-assigned label at the top of the stack, or all 291 encapsulated MPLS packets in that tunnel have an upstream-assigned 292 label at the top of the stack. The means by which this is determined 293 for a particular tunnel is outside the scope of this specification. 295 8. Ethernet MAC DA for Multicast MPLS 297 When an LSR transmits a multicast MPLS packet in a multicast ethernet 298 frame, it MUST set the Destination MAC Address to the value 299 01-00-5e-8v-wx-yz, where vwxyz is a 20-bit (five-nibble) value set as 300 follows: 302 1. vwxyz MAY be set to 0 304 2. vwxyz MAY be set to the value of one of the MPLS labels on the 305 packet's label stack. 307 Which of these procedures is the default procedure in any particular 308 LSR is implementation-dependent. However, LSRs using the two 309 different procedures MUST interoperate. That is, an LSR MUST NOT 310 filter packets for which vwxyz has been set to zero, and it MUST NOT 311 indiscriminately filter all packets for which vwxyz has not been set 312 to zero. 314 If an LSR follows the procedure of setting vwxyz to the value of one 315 of the MPLS labels on the packet's label stack, and if that label 316 stack contains two or more labels, then by default, vwxyz MUST be set 317 to the value of the second MPLS label on the packet's label stack. 318 By "the second label", we mean the label that is in the label stack 319 entry that immediately follows the topmost label stack entry. The 320 LSR MAY, if configured to do so, allow a a label other than the 321 second to be used for this purpose. If the MPLS packet has only one 322 label, the value of that label will be used instead of the value of 323 the (non-existent) second label. 325 It is expected that the LSR will follow the procedures of [UPSTREAM], 326 pushing on two labels, with the topmost label being a "context label" 327 that is the same for all MPLS packets being transmitted by the LSR 328 onto the ethernet, but with the second label being different for 329 different LSPs. Thus if the MAC DA value is a function of the second 330 label, more of the LSP-specific information about the packet appears 331 in the MAC DA field. This can be used to filter multicast packets 332 with "unexpected" non-zero values of vwxyz. Further discussion of 333 such filtering or its uses is outside the scope of this document. 335 The use of ethernet and/or IP broadcast addresses (as distinguished 336 from multicast addresses) does not fall within the scope of this 337 specification. 339 9. IANA Considerations 341 IANA already owns the set of ethernet multicast addresses in the 342 range 01-00-5e-00-00-00 to 01-00-5e-ff-ff-ff. Addresses in the range 343 01-00-5e-00-00-00 to 01-00-5e-7f-ff-ff are already reserved for use 344 when an ethernet multicast frame carries an IP multicast packet. 346 When this document is accepted, IANA shall reserve ethernet addresses 347 in the range 01-00-5e-80-00-00 to 01-00-5e-8f-ff-ff for use when an 348 ethernet multicast frame carries an MPLS multicast packet. Addresses 349 in this range are to be valid when used with ethertype 8847 or 8848. 351 As this document modifies the usage of ethertypes 8847 and 8848, IANA 352 shall change the description of these ethertypes as follows. 353 Ethertype 8847 shall be defined as "MPLS", as defined in RFC 3032 and 354 in this document. Ethertype 8848 shall be defined as "MPLS with 355 upstream-assigned label", as defined in this document. 357 10. Security Considerations 359 The security considerations of RFC 3032 and RFC 4023 apply. 361 Malicious changing of the codepoint may result in loss or misrouting 362 of packets. However, altering the codepoint without also altering the 363 label does not result in a predictable effect. 365 Malicious alteration of the MAC DA on an ethernet can result in 366 packets being received by a third party, rather than by the intended 367 recipient. 369 11. Normative References 371 [RFC2119] "Key words for use in RFCs to Indicate Requirement 372 Levels.", Bradner, March 1997 374 [RFC3031] "Multiprotocol Label Switching Architecture", Rosen, 375 Viswanathan, Callon, January 2001 377 [RFC3032] "MPLS Label Stack Encoding", Rosen, et. al., January 2001 379 [RFC4023] "Encapsulating MPLS in IP or GRE", Worster, Rekhter, Rosen, 380 March 2005 382 [UPSTREAM] "MPLS Upstream Label Assignment and Context Specific Label 383 Space", Aggarwal, Rekhter, Rosen, draft-ietf-mpls-upstream- 384 label-05.txt, March 2008. 386 12. Authors' Addresses 388 Toerless Eckert 389 Cisco Systems, Inc. 390 170 Tasman Drive 391 San Jose, CA, 95134 392 Email: eckert@cisco.com 394 Eric C. Rosen 395 Cisco Systems, Inc. 396 1414 Massachusetts Avenue 397 Boxborough, MA 01719 398 Email: erosen@cisco.com 399 Rahul Aggarwal 400 Juniper Networks 401 1194 North Mathilda Ave. 402 Sunnyvale, CA 94089 403 Email: rahul@juniper.net 405 Yakov Rekhter 406 Juniper Networks 407 1194 North Mathilda Ave. 408 Sunnyvale, CA 94089 409 Email: yakov@juniper.net 411 13. Full Copyright Statement 413 Copyright (C) The IETF Trust (2008). 415 This document is subject to the rights, licenses and restrictions 416 contained in BCP 78, and except as set forth therein, the authors 417 retain all their rights. 419 This document and the information contained herein are provided on an 420 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 421 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 422 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 423 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 424 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 425 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 427 14. 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