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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: December 2007 Cisco Systems, Inc. 5 Updates RFCs 3032 and 4023 6 Rahul Aggarwal 7 Yakov Rekhter 8 Juniper Networks, Inc. 10 June 2007 12 MPLS Multicast Encapsulations 14 draft-ietf-mpls-multicast-encaps-05.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 62 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 63 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 64 document are to be interpreted as described in [RFC2119]. 66 2. Introduction 68 RFC 3031 [RFC3031] defines the "Next Hop Label Forwarding Entry" 69 (NHLFE). The NHLFE for a particular label maps the label into a next 70 hop (among other things). When an MPLS packet is received, its top 71 label is mapped to an NHLFE, and the packet is sent to the next hop 72 specified by the NHLFE. 74 We define a particular MPLS label to be a "multicast label" in a 75 particular context if the NHLFE to which it is mapped in that context 76 specifies a set of next hops, with the semantics that the packet is 77 to be replicated, and a copy of the packet sent to each of the 78 specified next hops. Note that this definition accommodates the case 79 where the set of next hops contains a single member. What makes a 80 label a multicast label in a particular context is the semantics 81 attached to the set, i.e., the intention to replicate the packet and 82 transmit to all members of the set if the set has more than one 83 member. 85 RFC 3032 [RFC3032] established two data link layer codepoints for 86 MPLS: one to indicate that the data link layer frame is carrying an 87 MPLS unicast packet, and the other to indicate that the data link 88 layer frame is carrying an MPLS multicast packet. The term 89 "multicast packet" is not precisely defined in RFC 3032, though one 90 may presume that the "multicast" codepoint is intended to identify 91 the packet's top label as a multicast label. However, the multicast 92 codepoint has never been deployed, and further development of the 93 procedures for MPLS multicast have shown that, while there is a need 94 for two codepoints, the use of the two codepoints is not properly 95 captured by RFC 3032. 97 In particular, there is no need for the codepoint to indicate whether 98 the top MPLS label is a multicast label. When the receiver of an 99 MPLS packet looks up the top label, the NHLFE will specify whether 100 the label is a multicast label or not. 102 This document updates RFC 3032 and RFC 4023 by re-specifying the use 103 of the codepoints. 105 While RFC 3032 allows an MPLS packet to be carried in an ethernet 106 multicast frame, it fails to specify how the Medium Access Layer 107 Destination Address (MAC DA) field is to be set in that case. This 108 document provides that specification. 110 3. Upstream-Assigned vs. Downstream-Assigned 112 According to RFC 3031 [RFC3031], if two MPLS Label Switching Routers 113 (LSRs) are adjacent in a label switched path (LSP), with respect to 114 that LSP, one of them may be called the "upstream" LSR and the other 115 the "downstream" LSR. Call these Ru and Rd respectively. Before Ru 116 can send an MPLS packet to Rd with label L at the top of the label 117 stack, Ru and Rd must agree on the Forwarding Equivalence Class (FEC) 118 which is bound to L. A particular binding of L to FEC F is called a 119 "downstream-assigned" binding if the binding is first made by Rd and 120 then advertised to Ru. If the binding is first made by Ru and then 121 advertised to Rd, it is called an "upstream-assigned" binding. 123 If Ru and RD are LSP adjacencies, then they transmit a MPLS packet to 124 each other through one of the following mechanisms: 126 1. by putting the MPLS packet in a data link layer frame and 127 transmitting the frame 129 2. by transmitting the MPLS packet through an MPLS tunnel, i.e., 130 by pushing an additional label (or labels) onto the label 131 stack, and then invoking mechanism 1, 133 3. by transmitting the MPLS packet through an IP-based tunnel 134 (e.g., via RFC 4023 [RFC4023]), and then invoking mechanisms 1 135 and/or 2. 137 In short, an MPLS packet is transmitted either through a data link or 138 through an MPLS tunnel or through an IP tunnel. In any of those 139 cases, when the packet emerges through the tunnel, the downstream LSR 140 must know whether the label that now appears at the top of the label 141 stack has an upstream-assigned label binding or a downstream-assigned 142 label binding. For convenience, we will speak of a label with an 143 upstream-assigned label binding as an "upstream-assigned label". 145 Unicast labels MUST be downstream-assigned. 147 Under certain conditions, specified below, multicast labels MAY be 148 upstream-assigned. The ability to use upstream-assigned labels is an 149 OPTIONAL feature. Upstream-assigned labels MUST NOT be used unless 150 it is known that the downstream LSR supports them. How this is known 151 is outside the scope of this document. 153 We discuss three different types of data link or tunnel: 155 - Point-to-Point. A point-to-point data link or tunnel associates 156 two systems, such that transmissions on that link or tunnel made 157 by the one are received by the other, and only by the other. 159 For a given direction of a given point-to-point data link or 160 tunnel, the following MUST be the case: either every MPLS packet 161 will carry an upstream-assigned label, or else every MPLS packet 162 will carry a downstream-assigned label. The procedures for 163 determining whether upstream-assigned or downstream-assigned 164 labels are being used are outside the scope of this 165 specification. However, in the absence of any other information, 166 the use of downstream-assigned labels MUST be presumed by 167 default. 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 MPLS packets are transmitted on a particular multipoint-to- 189 multipoint link or tunnel, one of the following scenarios 190 applies: 192 1. It is known (by methods outside the scope of this document) 193 that the top label of every MPLS packet on the link or 194 tunnel is downstream-assigned 196 2. It is known (by methods outside the scope of this document) 197 that the top label of every MPLS packet on the link or 198 tunnel is upstream-assigned 200 3. Some MPLS packets on the link may have upstream-assigned 201 top labels while some may have downstream-assigned top 202 labels 204 If (and only if) the third scenario applies, the data link or 205 tunnel encapsulation MUST provide a codepoint which specifies 206 whether the top label of the encapsulated MPLS packet is 207 upstream-assigned or downstream-assigned. If a particular type 208 of data link or tunnel does not provide such a codepoint, then 209 the third scenario MUST NOT be used. 211 The remainder of this document specifies procedures for setting the 212 data link layer codepoints and address fields. 214 4. Ethernet Codepoints 216 Ethernet is an example of a multipoint-to-multipoint data link. 218 Ethertype 0x8847 is used whenever a unicast ethernet frame carries an 219 MPLS packet. 221 Ethertype 0x8847 is also used whenever a multicast ethernet frame 222 carries an MPLS packet, EXCEPT for the case where the top label of 223 the MPLS packet has been upstream-assigned. 225 Ethertype 0x8848, formerly known as the "MPLS multicast codepoint", 226 is to be used only when an MPLS packet whose top label is upstream- 227 assigned is carried in a multicast ethernet frame. 229 5. PPP Protocol Field 231 PPP is an example of a point-to-point data link. When a PPP frame is 232 carrying an MPLS packet, the PPP Protocol field is always set to 233 0x0281. 235 6. GRE Protocol Type 237 RFC 4023 is modified as described below. 239 If the IP destination address of the GRE encapsulation is a unicast 240 IP address, then the ethertype value 0x8847 MUST be used in all cases 241 for the MPLS-in-GRE encapsulation. 243 If the IP destination address of the GRE encapsulation is a multicast 244 IP address, then: 246 - the ethertype value 0x8847 MUST be used when the top label of the 247 encapsulated MPLS packet is downstream-assigned, 249 - the ethertype value 0x8848 MUST be used when the top label of the 250 encapsulated MPLS packet is upstream-assigned. 252 Through procedures which are outside the scope of this specification, 253 it may be known that if the destination address of a GRE packet is a 254 multicast IP address, then the top label of the GRE payload is 255 upstream-assigned. In such a case, the occurrence of the 8847 256 codepoint in a GRE packet with a multicast destination IP address 257 MUST be considered an error, and the packet MUST be discarded. 259 7. IP Protocol Number 261 RFC 4023 is modified as follows: the IPv4 Protocol Number field or 262 the IPv6 Next Header field is always set to 137, whether or not the 263 encapsulated MPLS packet is an MPLS multicast packet. 265 If the IP destination address of the IP encapsulation is an IP 266 multicast address, the IP tunnel may be considered to be a point-to- 267 multipoint tunnel or a multipoint-to-multipoint tunnel. In either 268 case, either all encapsulated MPLS packets in the particular tunnel 269 have a downstream-assigned label at the top of the stack, or all 270 encapsulated MPLS packets in that tunnel have an upstream-assigned 271 label at the top of the stack. The means by which this is determined 272 for a particular tunnel is outside the scope of this specification. 274 8. Ethernet MAC DA for Multicast MPLS 276 When an LSR transmits a multicast MPLS packet in a multicast ethernet 277 frame, it MUST set the Destination MAC Address to the value 278 01-00-5e-8a-bc-de, where abcde MUST, by default, be the twenty-bit 279 (five-nibble) value of the second MPLS label on the packet's label 280 stack. By "the second label", we mean the label that is in the label 281 stack entry that immediately follows the topmost label stack entry. 282 The LSR MAY, if configured to do so, allow a a label other than the 283 second to be used for this purpose. However, if the MPLS packet has 284 only one label, the value of that label will be used instead of the 285 value of the (non-existent) second label. 287 It is expected that the LSR will follow the procedures of [UPSTREAM], 288 pushing on two labels, with the topmost label being a "context label" 289 that is the same for all MPLS packets being transmitted by the LSR 290 onto the ethernet, but with the second label being different for 291 different LSPs. Thus if the MAC DA value is a function of the second 292 label, more of the LSP-specific information about the packet appears 293 in the MAC DA field. However, the way in which that information is 294 used, if any, is outside the scope of this document. 296 9. IANA Considerations 298 IANA already owns the set of ethernet multicast addresses in the 299 range 01-00-5e-00-00-00 to 01-00-5e-ff-ff-ff. Addresses in the range 300 01-00-5e-00-00-00 to 01-00-5e-7f-ff-ff are reserved for use when an 301 ethernet multicast frame carries an IP multicast packet. IANA shall 302 reserve ethernet addresses in the range 01-00-5e-80-00-00 to 303 01-00-5e-8f-ff-ff for use when an ethernet multicast frame carries an 304 MPLS multicast packet. 306 10. Security Considerations 308 The security considerations of RFC 3032 and RFC 4023 apply. 310 Malicious changing of the codepoint may result in loss or misrouting 311 of packets. However, altering the codepoint without also altering the 312 label does not result in a predictable effect. 314 Malicious alteration of the MAC DA on an ethernet can result in 315 packets being received by a third party, rather than by the intended 316 recipient. 318 11. Normative References 320 [RFC2119] "Key words for use in RFCs to Indicate Requirement 321 Levels.", Bradner, March 1997 323 [RFC3031] "Multiprotocol Label Switching Architecture", Rosen, 324 Viswanathan, Callon, January 2001 326 [RFC3032] "MPLS Label Stack Encoding", Rosen, et. al., January 2001 328 [RFC4023] "Encapsulating MPLS in IP or GRE", Worster, Rekhter, Rosen, 329 March 2005 331 12. Informative References 333 [UPSTREAM] "MPLS Upstream Label Assignment and Context Specific Label 334 Space", Aggarwal, Rekhter, Rosen, draft-ietf-mpls-upstream- 335 label-02.txt, March 2007. 337 13. Authors' Addresses 339 Toerless Eckert 340 Cisco Systems, Inc. 341 170 Tasman Drive 342 San Jose, CA, 95134 343 Email: eckert@cisco.com 345 Eric C. Rosen 346 Cisco Systems, Inc. 347 1414 Massachusetts Avenue 348 Boxborough, MA 01719 349 Email: erosen@cisco.com 351 Rahul Aggarwal 352 Juniper Networks 353 1194 North Mathilda Ave. 354 Sunnyvale, CA 94089 355 Email: rahul@juniper.net 356 Yakov Rekhter 357 Juniper Networks 358 1194 North Mathilda Ave. 359 Sunnyvale, CA 94089 360 Email: yakov@juniper.net 362 14. 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