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(See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date () is 739382 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- ** Obsolete normative reference: RFC 4601 (Obsoleted by RFC 7761) == Outdated reference: A later version (-09) exists of draft-ietf-pim-bidir-07 == Outdated reference: A later version (-06) exists of draft-ietf-pim-join-attributes-00 == Outdated reference: A later version (-07) exists of draft-ietf-ssm-arch-06 Summary: 5 errors (**), 0 flaws (~~), 4 warnings (==), 7 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 PIM WG IJ. Wijnands 3 Internet-Draft A. Boers 4 Intended status: Informational E. Rosen 5 Expires: April 4, 2007 Cisco Systems, Inc. 6 october 2006 8 The RPF Vector TLV 9 draft-ietf-pim-rpf-vector-03 11 Status of this Memo 13 By submitting this Internet-Draft, each author represents that any 14 applicable patent or other IPR claims of which he or she is aware 15 have been or will be disclosed, and any of which he or she becomes 16 aware will be disclosed, in accordance with Section 6 of BCP 79. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as Internet- 21 Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six months 24 and may be updated, replaced, or obsoleted by other documents at any 25 time. It is inappropriate to use Internet-Drafts as reference 26 material or to cite them other than as "work in progress." 28 The list of current Internet-Drafts can be accessed at 29 http://www.ietf.org/ietf/1id-abstracts.txt. 31 The list of Internet-Draft Shadow Directories can be accessed at 32 http://www.ietf.org/shadow.html. 34 This Internet-Draft will expire on April 4, 2007. 36 Copyright Notice 38 Copyright (C) The Internet Society (2006). 40 Abstract 42 This document describes a use of the PIM Join Attribute as defined in 43 draft-ietf-pim-join-attributes[I-D.ietf-pim-join-attributes] which 44 enables PIM to build multicast trees through an MPLS-enabled network, 45 even if that network's IGP does not have a route to the source of the 46 tree. 48 Table of Contents 50 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 51 2. Use of the RPF Vector TLV . . . . . . . . . . . . . . . . . . 4 52 2.1. Attribute and shared tree joins . . . . . . . . . . . . . 4 53 2.2. Attribute and Bootstrap messages . . . . . . . . . . . . . 5 54 2.3. The Vector Attribute . . . . . . . . . . . . . . . . . . . 5 55 2.3.1. Inserting a Vector Attribute in a Join . . . . . . . . 5 56 2.3.2. Processing a Received Vector Attribute . . . . . . . . 5 57 2.3.3. Vector Attribute and Asserts . . . . . . . . . . . . . 5 58 3. Vector Attribute TLV Format . . . . . . . . . . . . . . . . . 7 59 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 60 5. Security Considerations . . . . . . . . . . . . . . . . . . . 8 61 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8 62 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 63 7.1. Normative References . . . . . . . . . . . . . . . . . . . 8 64 7.2. Informative References . . . . . . . . . . . . . . . . . . 9 65 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9 66 Intellectual Property and Copyright Statements . . . . . . . . . . 10 68 1. Introduction 70 It is sometimes convenient to distinguish the routers of a particular 71 network into two categories: "edge routers" and "core routers". The 72 edge routers attach directly to users or to other networks, but the 73 core routers attach only to other routers of the same network. If 74 the network is MPLS-enabled, then any unicast packet which needs to 75 travel outside the network can be "tunneled" via MPLS from one edge 76 router to another. To handle a unicast packet which must travel 77 outside the network, an edge router needs to know which of the other 78 edge routers is the best exit point from the network for that 79 packet's destination IP address. The core routers, however, do not 80 need to have any knowledge of routes which lead outside the network; 81 as they handle only tunneled packets, they only need to know how to 82 reach the edge routers and the other core routers. 84 Consider, for example, the case where the network is an Autonomous 85 System (AS), the edge routers are EBGP speakers, the core routers may 86 be said to constitute a "BGP-free core". The edge routers must 87 distribute BGP routes to each other, but not to the core routers. 89 However, when multicast packets are considered, the strategy of 90 keeping the core routers free of "external" routes is more 91 problematic. When using PIM-SM[RFC4601], PIM-SSM[I-D.ietf-ssm-arch] 92 or PIM-BIDIR[I-D.ietf-pim-bidir] to create a multicast distribution 93 tree for a particular multicast group, one wants the core routers to 94 be full participants in the PIM protocol, so that multicasting can be 95 done efficiently in the core.This means that the core routers must be 96 able to correctly process PIM Join messages for the group, which in 97 turn means that the core routes must be able to send the Join 98 messages towards the root of the distribution tree. If the root of 99 the tree lies outside the network's borders (e.g., is in a different 100 AS), and the core routers do not maintain routes to external 101 destinations, then the PIM Join messages cannot be processed, and the 102 multicast distribution tree cannot be created. 104 In order to allow PIM to work properly in an environment where the 105 core routers do not maintain external routes, a PIM extension is 106 needed. When an edge router sends a PIM Join message into the core, 107 it must include in that message a "Vector" which specifies the IP 108 address of the next edge router along the path to the root of the 109 multicast distribution tree. The core routers can then process the 110 Join message by sending it towards the specified edge router (i.e., 111 toward the Vector). In effect, the Vector serves as an attribute, 112 within a particular network, for the root of the tree. 114 This document defines a new TLV in the PIM Join Attribute 115 message[I-D.ietf-pim-join-attributes]. It consists of a single 116 Vector which identifies the exit point of the network. 118 2. Use of the RPF Vector TLV 120 Before we can start forwarding multicast packets we need to build a 121 forwarding tree by sending PIM Joins hop by hop. Each router in the 122 path creates a forwarding state and propagates the Join towards the 123 root of the forwarding tree. The building of this tree is receiver 124 driven. See Figure 1. 126 ------------------ BGP ----------------- 127 | | 128 [S]---( Edge 1)--(Core 1)---( Core )--(Core 2)---( Edge 2 )---[R] 129 <--- (S,G) Join 131 Figure 1 133 In this example, the 2 edge routers are BGP speakers. The core 134 routers are not BGP speakers and do not have any BGP distributed 135 routes. The route to S is a BGP distributed route, hence is known to 136 the edge but not to the core. The Edge 2 router determines the 137 interface leading to S, and sends a PIM Join to the upstream router. 138 In this example, though, the upstream router is a core router, with 139 no route to S. Without the PIM extensions specified in this document, 140 the core router cannot determine where the send the Join, so the tree 141 cannot be constructed. 143 To allow the core router to participate in the construction of the 144 tree, the Edge 2 router will include an attribute field in the PIM 145 Join. In this example, the Attribute field will contain the IP 146 address of Edge 1. Edge 2 then forwards the PIM Join towards Edge 1. 147 The intermediate core router do their RPF check on the Attribute (IP 148 address of Edge 1) rather than the Source, this allows the tree to be 149 constructed. 151 2.1. Attribute and shared tree joins 153 In the example above we build a source tree to illustrate the 154 attribute behavior. The attribute is however not restricted to 155 source tree only. The tree may also be constructed towards a 156 Rendezvous Point (RP) IP address. The RP IP address is used in a 157 similar way as the Source in the example above. PIM Attribute 158 procedures defined for sources are equally applicable to (*,G) and 159 (*,*,RP) joins unless otherwise noted. 161 2.2. Attribute and Bootstrap messages 163 The RPF vector does not apply to BSR bootstrap messages. To allow 164 BSR messages to be forwarded across a core where the RP IP address is 165 not routable in the core a solution has the developed in BSR. 167 2.3. The Vector Attribute 169 2.3.1. Inserting a Vector Attribute in a Join 171 In the example of Figure 1, when the Edge 2 router looks up the route 172 to the source of the multicast distribution tree, it will find a BGP- 173 distributed route whose "BGP next-hop" is Edge 1. Edge 2 then looks 174 up the route to Edge 1 to find interface and PIM adjacency which is 175 the next hop to the source, namely Core 2. 177 When Edge 2 sends a PIM Join to Core 2, it includes a Vector 178 Attribute specifying the address of Edge 1. Core 2, and subsequent 179 core routers, will forwarding the Join along the Vector (i.e, towards 180 Edge 1) instead of trying to forward it towards S. 182 Whether an ttribute is actually needed depends on whether the Core 183 routers have a route to the source of the multicast tree. How the 184 Edge router knows whether or not this is the case (and thus how the 185 Edge router determines whether or not to insert an attribute field) 186 is outside the scope of this document. 188 2.3.2. Processing a Received Vector Attribute 190 When processing a received PIM Join which contains a Vector 191 Attribute, a router must first check to see if the Vector IP address 192 is one of its own IP addresses. If so, the Vector Attribute is 193 discarded, and not passed further upstream. Otherwise, the Vector 194 Attribute is used to find the route to the source, and is passed 195 along when a PIM Join is sent upstream. Note that a router which 196 receives a Vector Attribute must use it, even if that router happens 197 to have a route to the source. A router which discards a Vector 198 Attribute may of course insert a new Vector Attribute. This would 199 typically happen if a PIM Join needed to pass through a sequence of 200 Edge routers, each pair of which is separated by a core which does 201 not have external routes. In the absence of periodic refreshment, 202 Vectors expire along with the corresponding (S,G) state. 204 2.3.3. Vector Attribute and Asserts 206 In a PIM Assert message we include the routing protocol's "metric" to 207 the source of the tree. This information is used in the selection of 208 the assert winner. If a PIM Join is being sent towards a Vector, 209 rather than towards the source, the Assert message must have the 210 metric to the Vector instead of the metric to the source. The Assert 211 message however does not have an attribute field and does not mention 212 the Vector. 214 A router may change its upstream neighbor on a particular multicast 215 tree as the result of receiving Assert messages. However a Vector 216 Attribute should not be sent in a PIM Join to an upstream neighbor 217 which is chosen as the result of processing the Assert messages. 218 Reachability of the Vector is only guaranteed by the router that 219 advertises reachability to the Vector in it's IGP. If the assert 220 winner upstream is not our real preferred next-hop, we can't be sure 221 this router knows the path to the Vector. In the worst case the 222 assert winner has a route to the Vector that is on the same interface 223 where the assert was won. That will point the RPF interface to that 224 interface and will result in a O-list being NULL. The Vector 225 attribute is not inserted if the RPF neighbor was chosen via an 226 assert process and the RPF neighbor is different from the RPF 227 neighbor that would have been selected via the local routing table. 228 In all other cases the Vector has to be included in the Join message. 230 3. Vector Attribute TLV Format 232 0 1 2 3 233 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 234 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 235 |F|S| Type | Length | Encoded-Unicast address 236 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-....... 238 F bit 239 ----- 240 Forward Unknown TLV. If this bit is set the TLV is forwarded 241 regardless if the router understands the Type. 243 S bit 244 ----- 245 Bottom of Stack. If this bit is set then this is the last 246 TLV in the stack. 248 Type 249 ---- 250 The Vector Attribute type is 0. 252 Length 253 ------ 254 Length depending on Address Family of Encoded-Unicast address. 256 Value 257 ----- 258 Encoded-Unicast address, see PIM-SM 259 [RFC4601] 261 0 1 2 3 262 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 263 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 264 |F|S| Type | Length | Encoded-Unicast address 265 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-....... 267 F bit 268 ----- 269 Forward Unknown TLV. If this bit is set the TLV is forwarded 270 regardless if the router understands the Type. 272 S bit 273 ----- 274 Bottom of Stack. If this bit is set then this is the last 275 TLV in the stack. 277 Type 278 ---- 279 The Vector Attribute type is 0. 281 Length 282 ------ 283 Length depending on Address Family of Encoded-Unicast address. 285 Value 286 ----- 287 Encoded-Unicast address, see PIM-SM 289 4. IANA Considerations 291 An attribute type needs to be assigned. For now we propose the value 292 0. 294 5. Security Considerations 296 Security of the RPF Vector Attribute is only guaranteed by the 297 security of the PIM packet, so the security considerations for PIM 298 join packets as described in PIM-SM [RFC4601] apply here. 300 6. Acknowledgments 302 The authors would like to thank Yakov Rekhter and Dino Farinacci for 303 their initial ideas on this topic. 305 7. References 307 7.1. Normative References 309 [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, 310 "Protocol Independent Multicast - Sparse Mode (PIM-SM): 311 Protocol Specification (Revised)", RFC 4601, August 2006. 313 [I-D.ietf-pim-bidir] 314 Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 315 "Bi-directional Protocol Independent Multicast (BIDIR- 316 PIM)", draft-ietf-pim-bidir-07 (work in progress), 317 March 2005. 319 [I-D.ietf-pim-join-attributes] 320 Boers, A., "Format for using TLVs in PIM messages", 321 draft-ietf-pim-join-attributes-00 (work in progress), 322 October 2005. 324 [I-D.ietf-ssm-arch] 325 Holbrook, H. and B. Cain, "Source-Specific Multicast for 326 IP", draft-ietf-ssm-arch-06 (work in progress), 327 September 2004. 329 7.2. Informative References 331 Authors' Addresses 333 IJsbrand Wijnands 334 Cisco Systems, Inc. 335 De kleetlaan 6a 336 Diegem 1831 337 Belgium 339 Email: ice@cisco.com 341 Arjen Boers 342 Cisco Systems, Inc. 343 Avda. Diagonal, 682 344 Barcelona 08034 345 Spain 347 Email: aboers@cisco.com 349 Eric Rosen 350 Cisco Systems, Inc. 351 1414 Massachusetts Avenue 352 Boxborough, Ma 01719 354 Email: erosen@cisco.com 356 Full Copyright Statement 358 Copyright (C) The Internet Society (2006). 360 This document is subject to the rights, licenses and restrictions 361 contained in BCP 78, and except as set forth therein, the authors 362 retain all their rights. 364 This document and the information contained herein are provided on an 365 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 366 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET 367 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, 368 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE 369 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 370 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 372 Intellectual Property 374 The IETF takes no position regarding the validity or scope of any 375 Intellectual Property Rights or other rights that might be claimed to 376 pertain to the implementation or use of the technology described in 377 this document or the extent to which any license under such rights 378 might or might not be available; nor does it represent that it has 379 made any independent effort to identify any such rights. 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