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Rosen (editor) 4 Intended Status: Standards Track Cisco Systems, Inc. 5 Expires: October 28, 2008 6 Updates: RFCs 3032 and 4023 Rahul Aggarwal 7 Yakov Rekhter 8 Juniper Networks, Inc. 10 April 28, 2008 12 MPLS Multicast Encapsulations 14 draft-ietf-mpls-multicast-encaps-08.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. It is 121 believed though that this does not present a problem in practice. 123 While RFC 3032 allows an MPLS packet to be carried in an ethernet 124 multicast frame, it fails to specify how the Medium Access Layer 125 Destination Address (MAC DA) field is to be set in that case. This 126 document provides that specification. 128 3. Upstream-Assigned vs. Downstream-Assigned 130 According to RFC 3031 [RFC3031], if two MPLS Label Switching Routers 131 (LSRs) are adjacent in a label switched path (LSP), with respect to 132 that LSP, one of them may be called the "upstream" LSR and the other 133 the "downstream" LSR. Call these Ru and Rd respectively. Before Ru 134 can send an MPLS packet to Rd with label L at the top of the label 135 stack, Ru and Rd must agree on the Forwarding Equivalence Class (FEC) 136 which is bound to L. A particular binding of L to FEC F is called a 137 "downstream-assigned" binding if the binding is first made by Rd and 138 then advertised to Ru. If the binding is first made by Ru and then 139 advertised to Rd, it is called an "upstream-assigned" binding. 141 If Ru and RD are LSP adjacencies, then they transmit a MPLS packet to 142 each other through one of the following mechanisms: 144 1. by putting the MPLS packet in a data link layer frame and 145 transmitting the frame 147 2. by transmitting the MPLS packet through an MPLS tunnel, i.e., 148 by pushing an additional label (or labels) onto the label 149 stack, and then invoking mechanism 1, 151 3. by transmitting the MPLS packet through an IP-based tunnel 152 (e.g., via RFC 4023 [RFC4023]), and then invoking mechanisms 1 153 and/or 2. 155 In short, an MPLS packet is transmitted either through a data link or 156 through an MPLS tunnel or through an IP tunnel. In any of those 157 cases, when the packet emerges through the tunnel, the downstream LSR 158 must know whether the label that now appears at the top of the label 159 stack has an upstream-assigned label binding or a downstream-assigned 160 label binding. For convenience, we will speak of a label with an 161 upstream-assigned label binding as an "upstream-assigned label". 163 Unicast labels MUST be downstream-assigned. 165 Under certain conditions, specified below, multicast labels MAY be 166 upstream-assigned. The ability to use upstream-assigned labels is an 167 OPTIONAL feature. Upstream-assigned labels MUST NOT be used unless 168 it is known that the downstream LSR supports them. How this is known 169 is outside the scope of this document. 171 We discuss three different types of data link or tunnel: 173 - Point-to-Point. A point-to-point data link or tunnel associates 174 two systems, such that transmissions on that link or tunnel made 175 by the one are received by the other, and only by the other. 177 For a given direction of a given point-to-point data link or 178 tunnel, the following MUST be the case: either every MPLS packet 179 will carry an upstream-assigned label, or else every MPLS packet 180 will carry a downstream-assigned label. The procedures for 181 determining whether upstream-assigned or downstream-assigned 182 labels are being used are outside the scope of this 183 specification. However, in the absence of any other information, 184 the use of downstream-assigned labels MUST be presumed by 185 default. 187 - Point-to-Multipoint. A point-to-multipoint link or tunnel 188 associates n systems, such that only one of them can transmit 189 onto the link or tunnel, and the transmissions may be received by 190 the other n-1 systems. 192 The top labels (before applying the data link or tunnel 193 encapsulation) of all MPLS packets which are transmitted on a 194 particular point-to-multipoint data link or tunnel MUST be of the 195 same type; either all upstream-assigned or all downstream- 196 assigned. This means that all the receivers on the MPLS or IP 197 tunnel must know a priori whether upstream-assigned or 198 downstream-assigned labels are being used in the tunnel. How 199 this is known is outside the scope of this document. 201 - Multipoint-to-Multipoint. A multipoint-to-multipoint link or 202 tunnel associates n systems, such that any of them can transmit 203 on the link or tunnel, and the transmissions may be received by 204 the other n-1 systems. 206 If MPLS packets are transmitted on a particular multipoint-to- 207 multipoint link or tunnel, one of the following scenarios 208 applies: 210 1. It is known (by methods outside the scope of this document) 211 that the top label of every MPLS packet on the link or 212 tunnel is downstream-assigned 214 2. It is known (by methods outside the scope of this document) 215 that the top label of every MPLS packet on the link or 216 tunnel is upstream-assigned 218 3. Some MPLS packets on the link may have upstream-assigned 219 top labels while some may have downstream-assigned top 220 labels 222 If (and only if) the third scenario applies, the data link or 223 tunnel encapsulation MUST provide a codepoint which specifies 224 whether the top label of the encapsulated MPLS packet is 225 upstream-assigned or downstream-assigned. If a particular type 226 of data link or tunnel does not provide such a codepoint, then 227 the third scenario MUST NOT be used. 229 The remainder of this document specifies procedures for setting the 230 data link layer codepoints and address fields. 232 4. Ethernet Codepoints 234 Ethernet is an example of a multipoint-to-multipoint data link. 236 Ethertype 0x8847 is used whenever a unicast ethernet frame carries an 237 MPLS packet. 239 Ethertype 0x8847 is also used whenever a multicast ethernet frame 240 carries an MPLS packet, EXCEPT for the case where the top label of 241 the MPLS packet has been upstream-assigned. 243 Ethertype 0x8848, formerly known as the "MPLS multicast codepoint", 244 is to be used only when an MPLS packet whose top label is upstream- 245 assigned is carried in a multicast ethernet frame. 247 5. PPP Protocol Field 249 PPP is an example of a point-to-point data link. When a PPP frame is 250 carrying an MPLS packet, the PPP Protocol field is always set to 251 0x0281. 253 6. GRE Protocol Type 255 RFC 4023 is modified as described below. 257 If the IP destination address of the GRE encapsulation is a unicast 258 IP address, then the ethertype value 0x8847 MUST be used in all cases 259 for the MPLS-in-GRE encapsulation. 261 If the IP destination address of the GRE encapsulation is a multicast 262 IP address, then: 264 - the ethertype value 0x8847 MUST be used when the top label of the 265 encapsulated MPLS packet is downstream-assigned, 267 - the ethertype value 0x8848 MUST be used when the top label of the 268 encapsulated MPLS packet is upstream-assigned. 270 Through procedures which are outside the scope of this specification, 271 it may be known that if the destination address of a GRE packet is a 272 multicast IP address, then the top label of the GRE payload is 273 upstream-assigned. In such a case, the occurrence of the 8847 274 codepoint in a GRE packet with a multicast destination IP address 275 MUST be considered an error, and the packet MUST be discarded. 277 7. IP Protocol Number 279 RFC 4023 is modified as follows: the IPv4 Protocol Number field or 280 the IPv6 Next Header field is always set to 137, whether or not the 281 encapsulated MPLS packet is an MPLS multicast packet. 283 If the IP destination address of the IP encapsulation is an IP 284 multicast address, the IP tunnel may be considered to be a point-to- 285 multipoint tunnel or a multipoint-to-multipoint tunnel. In either 286 case, either all encapsulated MPLS packets in the particular tunnel 287 have a downstream-assigned label at the top of the stack, or all 288 encapsulated MPLS packets in that tunnel have an upstream-assigned 289 label at the top of the stack. The means by which this is determined 290 for a particular tunnel is outside the scope of this specification. 292 8. Ethernet MAC DA for Multicast MPLS 294 When an LSR transmits a multicast MPLS packet in a multicast ethernet 295 frame, it MUST set the Destination MAC Address to the value 296 01-00-5e-8v-wx-yz, where vwxyz is a 20-bit (five-nibble) value set as 297 follows: 299 1. vwxyz MAY be set to 0 301 2. vwxyz MAY be set to the value of one of the MPLS labels on the 302 packet's label stack. 304 Which of these procedures is the default procedure in any particular 305 LSR is implementation-dependent. However, LSRs using the two 306 different procedures MUST interoperate. That is, an LSR MUST NOT 307 filter packets for which vwxyz has been set to zero, and it MUST NOT 308 indiscriminately filter all packets for which vwxyz has not been set 309 to zero. 311 If an LSR follows the procedure of setting vwxyz to the value of one 312 of the MPLS labels on the packet's label stack, and if that label 313 stack contains two or more labels, then by default, vwxyz MUST be set 314 to the value of the second MPLS label on the packet's label stack. 315 By "the second label", we mean the label that is in the label stack 316 entry that immediately follows the topmost label stack entry. The 317 LSR MAY, if configured to do so, allow a a label other than the 318 second to be used for this purpose. If the MPLS packet has only one 319 label, the value of that label will be used instead of the value of 320 the (non-existent) second label. 322 It is expected that the LSR will follow the procedures of [UPSTREAM], 323 pushing on two labels, with the topmost label being a "context label" 324 that is the same for all MPLS packets being transmitted by the LSR 325 onto the ethernet, but with the second label being different for 326 different LSPs. Thus if the MAC DA value is a function of the second 327 label, more of the LSP-specific information about the packet appears 328 in the MAC DA field. This can be used to filter multicast packets 329 with "unexpected" non-zero values of vwxyz. Further discussion of 330 such filtering or its uses is outside the scope of this document. 332 The use of ethernet and/or IP broadcast addresses (as distinguished 333 from multicast addresses) does not fall within the scope of this 334 specification. 336 9. IANA Considerations 338 IANA already owns the set of ethernet multicast addresses in the 339 range 01-00-5e-00-00-00 to 01-00-5e-ff-ff-ff. Addresses in the range 340 01-00-5e-00-00-00 to 01-00-5e-7f-ff-ff are already reserved for use 341 when an ethernet multicast frame carries an IP multicast packet. 343 When this document is accepted, IANA shall reserve ethernet addresses 344 in the range 01-00-5e-80-00-00 to 01-00-5e-8f-ff-ff for use when an 345 ethernet multicast frame carries an MPLS multicast packet. Addresses 346 in this range are to be valid when used with ethertype 8847 or 8848. 348 As this document modifies the usage of ethertypes 8847 and 8848, IANA 349 shall change the description of these ethertypes as follows. 350 Ethertype 8847 shall be defined as "MPLS", as defined in RFC 3032 and 351 in this document. Ethertype 8848 shall be defined as "MPLS with 352 upstream-assigned label", as defined in this document. 354 10. Security Considerations 356 The security considerations of RFC 3032 and RFC 4023 apply. 358 Malicious changing of the codepoint may result in loss or misrouting 359 of packets. However, altering the codepoint without also altering the 360 label does not result in a predictable effect. 362 Malicious alteration of the MAC DA on an ethernet can result in 363 packets being received by a third party, rather than by the intended 364 recipient. 366 11. Normative References 368 [RFC2119] "Key words for use in RFCs to Indicate Requirement 369 Levels.", Bradner, March 1997 371 [RFC3031] "Multiprotocol Label Switching Architecture", Rosen, 372 Viswanathan, Callon, January 2001 374 [RFC3032] "MPLS Label Stack Encoding", Rosen, et. al., January 2001 376 [RFC4023] "Encapsulating MPLS in IP or GRE", Worster, Rekhter, Rosen, 377 March 2005 379 [UPSTREAM] "MPLS Upstream Label Assignment and Context Specific Label 380 Space", Aggarwal, Rekhter, Rosen, draft-ietf-mpls-upstream- 381 label-04.txt, February 2008. 383 12. Authors' Addresses 385 Toerless Eckert 386 Cisco Systems, Inc. 387 170 Tasman Drive 388 San Jose, CA, 95134 389 Email: eckert@cisco.com 391 Eric C. Rosen 392 Cisco Systems, Inc. 393 1414 Massachusetts Avenue 394 Boxborough, MA 01719 395 Email: erosen@cisco.com 396 Rahul Aggarwal 397 Juniper Networks 398 1194 North Mathilda Ave. 399 Sunnyvale, CA 94089 400 Email: rahul@juniper.net 402 Yakov Rekhter 403 Juniper Networks 404 1194 North Mathilda Ave. 405 Sunnyvale, CA 94089 406 Email: yakov@juniper.net 408 13. Full Copyright Statement 410 Copyright (C) The IETF Trust (2008). 412 This document is subject to the rights, licenses and restrictions 413 contained in BCP 78, and except as set forth therein, the authors 414 retain all their rights. 416 This document and the information contained herein are provided on an 417 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 418 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 419 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 420 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 421 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 422 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 424 14. 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