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Rosen (editor) 4 Intended Status: Standards Track Cisco Systems, Inc. 5 Expires: May 1, 2008 6 Updates: RFCs 3032 and 4023 Rahul Aggarwal 7 Yakov Rekhter 8 Juniper Networks, Inc. 10 November 1, 2007 12 MPLS Multicast Encapsulations 14 draft-ietf-mpls-multicast-encaps-07.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 RFC 44 3032 by redefining the meaning of these two codepoints. The former 45 "multicast codepoint" is now to be used only on multiaccess media, 46 and it is to mean "the top label of the following label stack is an 47 upstream-assigned label". The former "unicast codepoint" is to be 48 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 RFC 3032 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 Specification of Requirements ........................... 3 61 2 Introduction ............................................ 3 62 3 Upstream-Assigned vs. Downstream-Assigned ............... 4 63 4 Ethernet Codepoints ..................................... 6 64 5 PPP Protocol Field ...................................... 6 65 6 GRE Protocol Type ....................................... 6 66 7 IP Protocol Number ...................................... 7 67 8 Ethernet MAC DA for Multicast MPLS ...................... 7 68 9 IANA Considerations ..................................... 8 69 10 Security Considerations ................................. 8 70 11 Normative References .................................... 9 71 12 Informative References .................................. 9 72 13 Authors' Addresses ...................................... 9 73 14 Full Copyright Statement ................................ 10 74 15 Intellectual Property ................................... 10 75 1. Specification of Requirements 77 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 78 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 79 document are to be interpreted as described in [RFC2119]. 81 2. Introduction 83 RFC 3031 [RFC3031] defines the "Next Hop Label Forwarding Entry" 84 (NHLFE). The NHLFE for a particular label maps the label into a next 85 hop (among other things). When an MPLS packet is received, its top 86 label is mapped to an NHLFE, and the packet is sent to the next hop 87 specified by the NHLFE. 89 We define a particular MPLS label to be a "multicast label" in a 90 particular context if the NHLFE to which it is mapped in that context 91 specifies a set of next hops, with the semantics that the packet is 92 to be replicated, and a copy of the packet sent to each of the 93 specified next hops. Note that this definition accommodates the case 94 where the set of next hops contains a single member. What makes a 95 label a multicast label in a particular context is the semantics 96 attached to the set, i.e., the intention to replicate the packet and 97 transmit to all members of the set if the set has more than one 98 member. 100 RFC 3032 [RFC3032] established two data link layer codepoints for 101 MPLS: one to indicate that the data link layer frame is carrying an 102 MPLS unicast packet, and the other to indicate that the data link 103 layer frame is carrying an MPLS multicast packet. The term 104 "multicast packet" is not precisely defined in RFC 3032, though one 105 may presume that the "multicast" codepoint is intended to identify 106 the packet's top label as a multicast label. However, the multicast 107 codepoint has never been deployed, and further development of the 108 procedures for MPLS multicast have shown that, while there is a need 109 for two codepoints, the use of the two codepoints is not properly 110 captured by RFC 3032. 112 In particular, there is no need for the codepoint to indicate whether 113 the top MPLS label is a multicast label. When the receiver of an 114 MPLS packet looks up the top label, the NHLFE will specify whether 115 the label is a multicast label or not. 117 This document updates RFC 3032 and RFC 4023 by re-specifying the use 118 of the codepoints. 120 While RFC 3032 allows an MPLS packet to be carried in an ethernet 121 multicast frame, it fails to specify how the Medium Access Layer 122 Destination Address (MAC DA) field is to be set in that case. This 123 document provides that specification. 125 3. Upstream-Assigned vs. Downstream-Assigned 127 According to RFC 3031 [RFC3031], if two MPLS Label Switching Routers 128 (LSRs) are adjacent in a label switched path (LSP), with respect to 129 that LSP, one of them may be called the "upstream" LSR and the other 130 the "downstream" LSR. Call these Ru and Rd respectively. Before Ru 131 can send an MPLS packet to Rd with label L at the top of the label 132 stack, Ru and Rd must agree on the Forwarding Equivalence Class (FEC) 133 which is bound to L. A particular binding of L to FEC F is called a 134 "downstream-assigned" binding if the binding is first made by Rd and 135 then advertised to Ru. If the binding is first made by Ru and then 136 advertised to Rd, it is called an "upstream-assigned" binding. 138 If Ru and RD are LSP adjacencies, then they transmit a MPLS packet to 139 each other through one of the following mechanisms: 141 1. by putting the MPLS packet in a data link layer frame and 142 transmitting the frame 144 2. by transmitting the MPLS packet through an MPLS tunnel, i.e., 145 by pushing an additional label (or labels) onto the label 146 stack, and then invoking mechanism 1, 148 3. by transmitting the MPLS packet through an IP-based tunnel 149 (e.g., via RFC 4023 [RFC4023]), and then invoking mechanisms 1 150 and/or 2. 152 In short, an MPLS packet is transmitted either through a data link or 153 through an MPLS tunnel or through an IP tunnel. In any of those 154 cases, when the packet emerges through the tunnel, the downstream LSR 155 must know whether the label that now appears at the top of the label 156 stack has an upstream-assigned label binding or a downstream-assigned 157 label binding. For convenience, we will speak of a label with an 158 upstream-assigned label binding as an "upstream-assigned label". 160 Unicast labels MUST be downstream-assigned. 162 Under certain conditions, specified below, multicast labels MAY be 163 upstream-assigned. The ability to use upstream-assigned labels is an 164 OPTIONAL feature. Upstream-assigned labels MUST NOT be used unless 165 it is known that the downstream LSR supports them. How this is known 166 is outside the scope of this document. 168 We discuss three different types of data link or tunnel: 170 - Point-to-Point. A point-to-point data link or tunnel associates 171 two systems, such that transmissions on that link or tunnel made 172 by the one are received by the other, and only by the other. 174 For a given direction of a given point-to-point data link or 175 tunnel, the following MUST be the case: either every MPLS packet 176 will carry an upstream-assigned label, or else every MPLS packet 177 will carry a downstream-assigned label. The procedures for 178 determining whether upstream-assigned or downstream-assigned 179 labels are being used are outside the scope of this 180 specification. However, in the absence of any other information, 181 the use of downstream-assigned labels MUST be presumed by 182 default. 184 - Point-to-Multipoint. A point-to-multipoint link or tunnel 185 associates n systems, such that only one of them can transmit 186 onto the link or tunnel, and the transmissions may be received by 187 the other n-1 systems. 189 The top labels (before applying the data link or tunnel 190 encapsulation) of all MPLS packets which are transmitted on a 191 particular point-to-multipoint data link or tunnel MUST be of the 192 same type; either all upstream-assigned or all downstream- 193 assigned. This means that all the receivers on the MPLS or IP 194 tunnel must know a priori whether upstream-assigned or 195 downstream-assigned labels are being used in the tunnel. How 196 this is known is outside the scope of this document. 198 - Multipoint-to-Multipoint. A multipoint-to-multipoint link or 199 tunnel associates n systems, such that any of them can transmit 200 on the link or tunnel, and the transmissions may be received by 201 the other n-1 systems. 203 If MPLS packets are transmitted on a particular multipoint-to- 204 multipoint link or tunnel, one of the following scenarios 205 applies: 207 1. It is known (by methods outside the scope of this document) 208 that the top label of every MPLS packet on the link or 209 tunnel is downstream-assigned 211 2. It is known (by methods outside the scope of this document) 212 that the top label of every MPLS packet on the link or 213 tunnel is upstream-assigned 215 3. Some MPLS packets on the link may have upstream-assigned 216 top labels while some may have downstream-assigned top 217 labels 219 If (and only if) the third scenario applies, the data link or 220 tunnel encapsulation MUST provide a codepoint which specifies 221 whether the top label of the encapsulated MPLS packet is 222 upstream-assigned or downstream-assigned. If a particular type 223 of data link or tunnel does not provide such a codepoint, then 224 the third scenario MUST NOT be used. 226 The remainder of this document specifies procedures for setting the 227 data link layer codepoints and address fields. 229 4. Ethernet Codepoints 231 Ethernet is an example of a multipoint-to-multipoint data link. 233 Ethertype 0x8847 is used whenever a unicast ethernet frame carries an 234 MPLS packet. 236 Ethertype 0x8847 is also used whenever a multicast ethernet frame 237 carries an MPLS packet, EXCEPT for the case where the top label of 238 the MPLS packet has been upstream-assigned. 240 Ethertype 0x8848, formerly known as the "MPLS multicast codepoint", 241 is to be used only when an MPLS packet whose top label is upstream- 242 assigned is carried in a multicast ethernet frame. 244 5. PPP Protocol Field 246 PPP is an example of a point-to-point data link. When a PPP frame is 247 carrying an MPLS packet, the PPP Protocol field is always set to 248 0x0281. 250 6. GRE Protocol Type 252 RFC 4023 is modified as described below. 254 If the IP destination address of the GRE encapsulation is a unicast 255 IP address, then the ethertype value 0x8847 MUST be used in all cases 256 for the MPLS-in-GRE encapsulation. 258 If the IP destination address of the GRE encapsulation is a multicast 259 IP address, then: 261 - the ethertype value 0x8847 MUST be used when the top label of the 262 encapsulated MPLS packet is downstream-assigned, 264 - the ethertype value 0x8848 MUST be used when the top label of the 265 encapsulated MPLS packet is upstream-assigned. 267 Through procedures which are outside the scope of this specification, 268 it may be known that if the destination address of a GRE packet is a 269 multicast IP address, then the top label of the GRE payload is 270 upstream-assigned. In such a case, the occurrence of the 8847 271 codepoint in a GRE packet with a multicast destination IP address 272 MUST be considered an error, and the packet MUST be discarded. 274 7. IP Protocol Number 276 RFC 4023 is modified as follows: the IPv4 Protocol Number field or 277 the IPv6 Next Header field is always set to 137, whether or not the 278 encapsulated MPLS packet is an MPLS multicast packet. 280 If the IP destination address of the IP encapsulation is an IP 281 multicast address, the IP tunnel may be considered to be a point-to- 282 multipoint tunnel or a multipoint-to-multipoint tunnel. In either 283 case, either all encapsulated MPLS packets in the particular tunnel 284 have a downstream-assigned label at the top of the stack, or all 285 encapsulated MPLS packets in that tunnel have an upstream-assigned 286 label at the top of the stack. The means by which this is determined 287 for a particular tunnel is outside the scope of this specification. 289 8. Ethernet MAC DA for Multicast MPLS 291 When an LSR transmits a multicast MPLS packet in a multicast ethernet 292 frame, it MUST set the Destination MAC Address to the value 293 01-00-5e-8v-wx-yz, where vwxyz is a 20-bit (five-nibble) value set as 294 follows: 296 1. vwxyz MAY be set to 0 298 2. vwxyz MAY be set to the value of one of the MPLS labels on the 299 packet's label stack. 301 Which of these procedures is the default procedure in any particular 302 LSR is implementation-dependent. However, LSRs using the two 303 different procedures MUST interoperate. That is, an LSR MUST NOT 304 filter packets for which vwxyz has been set to zero, and it MUST NOT 305 indiscriminately filter all packets for which vwxyz has not been set 306 to zero. 308 If an LSR follows the procedure of setting vwxyz to the value of one 309 of the MPLS labels on the packet's label stack, and if that label 310 stack contains two or more labels, then by default, vwxyz MUST be set 311 to the value of the second MPLS label on the packet's label stack. 312 By "the second label", we mean the label that is in the label stack 313 entry that immediately follows the topmost label stack entry. The 314 LSR MAY, if configured to do so, allow a a label other than the 315 second to be used for this purpose. If the MPLS packet has only one 316 label, the value of that label will be used instead of the value of 317 the (non-existent) second label. 319 It is expected that the LSR will follow the procedures of [UPSTREAM], 320 pushing on two labels, with the topmost label being a "context label" 321 that is the same for all MPLS packets being transmitted by the LSR 322 onto the ethernet, but with the second label being different for 323 different LSPs. Thus if the MAC DA value is a function of the second 324 label, more of the LSP-specific information about the packet appears 325 in the MAC DA field. This can be used to filter multicast packets 326 with "unexpected" non-zero values of vwxyz. Further discussion of 327 such filtering or its uses is outside the scope of this document. 329 9. IANA Considerations 331 IANA already owns the set of ethernet multicast addresses in the 332 range 01-00-5e-00-00-00 to 01-00-5e-ff-ff-ff. Addresses in the range 333 01-00-5e-00-00-00 to 01-00-5e-7f-ff-ff are reserved for use when an 334 ethernet multicast frame carries an IP multicast packet. IANA shall 335 reserve ethernet addresses in the range 01-00-5e-80-00-00 to 336 01-00-5e-8f-ff-ff for use when an ethernet multicast frame carries an 337 MPLS multicast packet. 339 10. Security Considerations 341 The security considerations of RFC 3032 and RFC 4023 apply. 343 Malicious changing of the codepoint may result in loss or misrouting 344 of packets. However, altering the codepoint without also altering the 345 label does not result in a predictable effect. 347 Malicious alteration of the MAC DA on an ethernet can result in 348 packets being received by a third party, rather than by the intended 349 recipient. 351 11. Normative References 353 [RFC2119] "Key words for use in RFCs to Indicate Requirement 354 Levels.", Bradner, March 1997 356 [RFC3031] "Multiprotocol Label Switching Architecture", Rosen, 357 Viswanathan, Callon, January 2001 359 [RFC3032] "MPLS Label Stack Encoding", Rosen, et. al., January 2001 361 [RFC4023] "Encapsulating MPLS in IP or GRE", Worster, Rekhter, Rosen, 362 March 2005 364 12. Informative References 366 [UPSTREAM] "MPLS Upstream Label Assignment and Context Specific Label 367 Space", Aggarwal, Rekhter, Rosen, draft-ietf-mpls-upstream- 368 label-03.txt, November 2007. 370 13. Authors' Addresses 372 Toerless Eckert 373 Cisco Systems, Inc. 374 170 Tasman Drive 375 San Jose, CA, 95134 376 Email: eckert@cisco.com 378 Eric C. Rosen 379 Cisco Systems, Inc. 380 1414 Massachusetts Avenue 381 Boxborough, MA 01719 382 Email: erosen@cisco.com 384 Rahul Aggarwal 385 Juniper Networks 386 1194 North Mathilda Ave. 387 Sunnyvale, CA 94089 388 Email: rahul@juniper.net 389 Yakov Rekhter 390 Juniper Networks 391 1194 North Mathilda Ave. 392 Sunnyvale, CA 94089 393 Email: yakov@juniper.net 395 14. Full Copyright Statement 397 Copyright (C) The IETF Trust (2007). 399 This document is subject to the rights, licenses and restrictions 400 contained in BCP 78, and except as set forth therein, the authors 401 retain all their rights. 403 This document and the information contained herein are provided on an 404 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 405 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 406 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 407 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 408 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 409 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 411 15. 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