idnits 2.17.1 draft-ietf-lisp-multicast-12.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (January 2, 2012) is 4497 days in the past. Is this intentional? Checking references for intended status: Experimental ---------------------------------------------------------------------------- == Outdated reference: A later version (-06) exists of draft-ietf-lisp-interworking-02 == Outdated reference: A later version (-24) exists of draft-ietf-lisp-16 ** Obsolete normative reference: RFC 4601 (Obsoleted by RFC 7761) == Outdated reference: A later version (-10) exists of draft-ietf-lisp-alt-09 == Outdated reference: A later version (-26) exists of draft-ietf-mboned-mtrace-v2-08 Summary: 1 error (**), 0 flaws (~~), 5 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group D. Farinacci 3 Internet-Draft D. Meyer 4 Intended status: Experimental J. Zwiebel 5 Expires: July 5, 2012 S. Venaas 6 cisco Systems 7 January 2, 2012 9 LISP for Multicast Environments 10 draft-ietf-lisp-multicast-12 12 Abstract 14 This draft describes how inter-domain multicast routing will function 15 in an environment where Locator/ID Separation is deployed using the 16 LISP architecture. 18 Status of this Memo 20 This Internet-Draft is submitted in full conformance with the 21 provisions of BCP 78 and BCP 79. 23 Internet-Drafts are working documents of the Internet Engineering 24 Task Force (IETF). Note that other groups may also distribute 25 working documents as Internet-Drafts. The list of current Internet- 26 Drafts is at http://datatracker.ietf.org/drafts/current/. 28 Internet-Drafts are draft documents valid for a maximum of six months 29 and may be updated, replaced, or obsoleted by other documents at any 30 time. It is inappropriate to use Internet-Drafts as reference 31 material or to cite them other than as "work in progress." 33 This Internet-Draft will expire on July 5, 2012. 35 Copyright Notice 37 Copyright (c) 2012 IETF Trust and the persons identified as the 38 document authors. All rights reserved. 40 This document is subject to BCP 78 and the IETF Trust's Legal 41 Provisions Relating to IETF Documents 42 (http://trustee.ietf.org/license-info) in effect on the date of 43 publication of this document. Please review these documents 44 carefully, as they describe your rights and restrictions with respect 45 to this document. Code Components extracted from this document must 46 include Simplified BSD License text as described in Section 4.e of 47 the Trust Legal Provisions and are provided without warranty as 48 described in the Simplified BSD License. 50 Table of Contents 52 1. Requirements Notation . . . . . . . . . . . . . . . . . . . . 4 53 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 54 3. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 7 55 4. Basic Overview . . . . . . . . . . . . . . . . . . . . . . . . 10 56 5. Source Addresses versus Group Addresses . . . . . . . . . . . 13 57 6. Locator Reachability Implications on LISP-Multicast . . . . . 14 58 7. Multicast Protocol Changes . . . . . . . . . . . . . . . . . . 15 59 8. LISP-Multicast Data-Plane Architecture . . . . . . . . . . . . 18 60 8.1. ITR Forwarding Procedure . . . . . . . . . . . . . . . . . 18 61 8.1.1. Multiple RLOCs for an ITR . . . . . . . . . . . . . . 18 62 8.1.2. Multiple ITRs for a LISP Source Site . . . . . . . . . 19 63 8.2. ETR Forwarding Procedure . . . . . . . . . . . . . . . . . 19 64 8.3. Replication Locations . . . . . . . . . . . . . . . . . . 20 65 9. LISP-Multicast Interworking . . . . . . . . . . . . . . . . . 21 66 9.1. LISP and non-LISP Mixed Sites . . . . . . . . . . . . . . 21 67 9.1.1. LISP Source Site to non-LISP Receiver Sites . . . . . 22 68 9.1.2. Non-LISP Source Site to non-LISP Receiver Sites . . . 23 69 9.1.3. Non-LISP Source Site to Any Receiver Site . . . . . . 24 70 9.1.4. Unicast LISP Source Site to Any Receiver Sites . . . . 25 71 9.1.5. LISP Source Site to Any Receiver Sites . . . . . . . . 25 72 9.2. LISP Sites with Mixed Address Families . . . . . . . . . . 26 73 9.3. Making a Multicast Interworking Decision . . . . . . . . . 28 74 10. Considerations when RP Addresses are Embedded in Group 75 Addresses . . . . . . . . . . . . . . . . . . . . . . . . . . 29 76 11. Taking Advantage of Upgrades in the Core . . . . . . . . . . . 30 77 12. Mtrace Considerations . . . . . . . . . . . . . . . . . . . . 31 78 13. Security Considerations . . . . . . . . . . . . . . . . . . . 32 79 14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 33 80 15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 34 81 16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 35 82 16.1. Normative References . . . . . . . . . . . . . . . . . . . 35 83 16.2. Informative References . . . . . . . . . . . . . . . . . . 36 84 Appendix A. Document Change Log . . . . . . . . . . . . . . . . . 37 85 A.1. Changes to draft-ietf-lisp-multicast-12.txt . . . . . . . 37 86 A.2. Changes to draft-ietf-lisp-multicast-11.txt . . . . . . . 37 87 A.3. Changes to draft-ietf-lisp-multicast-10.txt . . . . . . . 37 88 A.4. Changes to draft-ietf-lisp-multicast-09.txt . . . . . . . 37 89 A.5. Changes to draft-ietf-lisp-multicast-08.txt . . . . . . . 37 90 A.6. Changes to draft-ietf-lisp-multicast-07.txt . . . . . . . 37 91 A.7. Changes to draft-ietf-lisp-multicast-06.txt . . . . . . . 37 92 A.8. Changes to draft-ietf-lisp-multicast-05.txt . . . . . . . 38 93 A.9. Changes to draft-ietf-lisp-multicast-04.txt . . . . . . . 38 94 A.10. Changes to draft-ietf-lisp-multicast-03.txt . . . . . . . 38 95 A.11. Changes to draft-ietf-lisp-multicast-02.txt . . . . . . . 38 96 A.12. Changes to draft-ietf-lisp-multicast-01.txt . . . . . . . 39 97 A.13. Changes to draft-ietf-lisp-multicast-00.txt . . . . . . . 39 99 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 40 101 1. Requirements Notation 103 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 104 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 105 document are to be interpreted as described in [RFC2119]. 107 2. Introduction 109 The Locator/ID Separation Architecture [LISP] provides a mechanism to 110 separate out Identification and Location semantics from the current 111 definition of an IP address. By creating two namespaces, an Endpoint 112 ID (EID) namespace used by sites and a Routing Locator (RLOC) 113 namespace used by core routing, the core routing infrastructure can 114 scale by doing topological aggregation of routing information. 116 Since LISP creates a new namespace, a mapping function must exist to 117 map a site's EID prefixes to its associated locators. For unicast 118 packets, both the source address and destination address must be 119 mapped. For multicast packets, only the source address needs to be 120 mapped. The destination group address doesn't need to be mapped 121 because the semantics of an IPv4 or IPv6 group address are logical in 122 nature and not topology-dependent. Therefore, this specification 123 focuses on to map a source EID address of a multicast flow during 124 distribution tree setup and packet delivery. 126 This specification will address the following scenarios: 128 1. How a multicast source host in a LISP site sends multicast 129 packets to receivers inside of its site as well as to receivers 130 in other sites that are LISP enabled. 132 2. How inter-domain (or between LISP sites) multicast distribution 133 trees are built and how forwarding of multicast packets leaving a 134 source site toward receivers sites is performed. 136 3. What protocols are affected and what changes are required to such 137 multicast protocols. 139 4. How ASM-mode (Any Source Multicast), SSM-mode (Single Source 140 Multicast), and Bidir-mode (Bidirectional Shared Trees) service 141 models will operate. 143 5. How multicast packet flow will occur for multiple combinations of 144 LISP and non-LISP capable source and receiver sites, for example: 146 A. How multicast packets from a source host in a LISP site are 147 sent to receivers in other sites when they are all non-LISP 148 sites. 150 B. How multicast packets from a source host in a LISP site are 151 sent to receivers in both LISP-enabled sites and non-LISP 152 sites. 154 C. How multicast packets from a source host in a non-LISP site 155 are sent to receivers in other sites when they are all LISP- 156 enabled sites. 158 D. How multicast packets from a source host in a non-LISP site 159 are sent to receivers in both LISP-enabled sites and non-LISP 160 sites. 162 This specification focuses on what changes are needed to the 163 multicast routing protocols to support LISP-Multicast as well as 164 other protocols used for inter-domain multicast, such as Multi- 165 protocol BGP (MBGP) [RFC4760]. The approach proposed in this 166 specification requires no packet format changes to the protocols and 167 no operational procedural changes to the multicast infrastructure 168 inside of a site when all sources and receivers reside in that site, 169 even when the site is LISP enabled. That is, internal operation of 170 multicast is unchanged regardless of whether or not the site is LISP 171 enabled or whether or not receivers exist in other sites which are 172 LISP-enabled. 174 Therefore, we see changes only to PIM-ASM [RFC4601], MSDP [RFC3618], 175 and PIM-SSM [RFC4607]. Bidir-PIM [RFC5015], which typically does not 176 run in an inter-domain environment is not addressed in depth in this 177 version of the specification. 179 Also, the current version of this specification does not describe 180 multicast-based Traffic Engineering relative to the TE-ITR (Traffic 181 Engineering based Ingress Tunnel Router) and TE-ETR (Traffic 182 Engineering based Egress Tunnel Router) descriptions in [LISP]. 183 Futher work is also needed to determine the detailed behavior for 184 multicast proxy ITRs (mPITRs) (Section 9.1.3), mtrace (Section 12), 185 and locator reachability (Section 6). Finally, further deployment 186 and experimentation would be useful to understand the real-life 187 performance of the LISP-Multicast solution. For instance, the design 188 optimizes for minimal state and control traffic in the core, but can 189 in some cases cause extra multicast traffic to be sent Section 8.1.2. 191 3. Definition of Terms 193 The terminology in this section is consistent with the definitions in 194 [LISP] but is extended specifically to deal with the application of 195 the terminology to multicast routing. 197 LISP-Multicast: a reference to the design in this specification. 198 That is, when any site that is participating in multicast 199 communication has been upgraded to be a LISP site, the operation 200 of control-plane and data-plane protocols is considered part of 201 the LISP-Multicast architecture. 203 Endpoint ID (EID): a 32-bit (for IPv4) or 128-bit (for IPv6) value 204 used in the source address field of the first (most inner) LISP 205 header of a multicast packet. The host obtains a destination 206 group address the same way it obtains one today, as it would when 207 it is a non-LISP site. The source EID is obtained via existing 208 mechanisms used to set a host's "local" IP address. An EID is 209 allocated to a host from an EID prefix block associated with the 210 site the host is located in. An EID can be used by a host to 211 refer to another host, as when it joins an SSM (S-EID,G) route 212 using IGMP version 3 [RFC4604]. LISP uses Provider Independent 213 (PI) blocks for EIDs; such EIDs MUST NOT be used as LISP RLOCs. 214 Note that EID blocks may be assigned in a hierarchical manner, 215 independent of the network topology, to facilitate scaling of the 216 mapping database. In addition, an EID block assigned to a site 217 may have site-local structure (subnetting) for routing within the 218 site; this structure is not visible to the global routing system. 220 Routing Locator (RLOC): the IPv4 or IPv6 address of an ingress 221 tunnel router (ITR), the router in the multicast source host's 222 site that encapsulates multicast packets. It is the output of a 223 EID-to-RLOC mapping lookup. An EID maps to one or more RLOCs. 224 Typically, RLOCs are numbered from topologically-aggregatable 225 blocks that are assigned to a site at each point to which it 226 attaches to the global Internet; where the topology is defined by 227 the connectivity of provider networks, RLOCs can be thought of as 228 Provider Assigned (PA) addresses. Multiple RLOCs can be assigned 229 to the same ITR device or to multiple ITR devices at a site. 231 Ingress Tunnel Router (ITR): a router which accepts an IP multicast 232 packet with a single IP header (more precisely, an IP packet that 233 does not contain a LISP header). The router treats this "inner" 234 IP destination multicast address opaquely so it doesn't need to 235 perform a map lookup on the group address because it is 236 topologically insignificant. The router then prepends an "outer" 237 IP header with one of its globally-routable RLOCs as the source 238 address field. This RLOC is known to other multicast receiver 239 sites which have used the mapping database to join a multicast 240 tree for which the ITR is the root. In general, an ITR receives 241 IP packets from site end systems on one side and sends LISP- 242 encapsulated multicast IP packets out all external interfaces 243 which have been joined. 245 An ITR would receive a multicast packet from a source inside of 246 its site when 1) it is on the path from the multicast source to 247 internally joined receivers, or 2) when it is on the path from the 248 multicast source to externally joined receivers. 250 Egress Tunnel Router (ETR): a router that is on the path from a 251 multicast source host in another site to a multicast receiver in 252 its own site. An ETR accepts a PIM Join/Prune message from a site 253 internal PIM router destined for the source's EID in the multicast 254 source site. The ETR maps the source EID in the Join/Prune 255 message to an RLOC address based on the EID-to-RLOC mapping. This 256 sets up the ETR to accept multicast encapsulated packets from the 257 ITR in the source multicast site. A multicast ETR decapsulates 258 multicast encapsulated packets and replicates them on interfaces 259 leading to internal receivers. 261 xTR: is a reference to an ITR or ETR when direction of data flow is 262 not part of the context description. xTR refers to the router that 263 is the tunnel endpoint. Used synonymously with the term "Tunnel 264 Router". For example, "An xTR can be located at the Customer Edge 265 (CE) router", meaning both ITR and ETR functionality can be at the 266 CE router. 268 LISP Header: a term used in this document to refer to the outer 269 IPv4 or IPv6 header, a UDP header, and a LISP header. An ITR 270 prepends headers and an ETR strips headers. A LISP encapsulated 271 multicast packet will have an "inner" header with the source EID 272 in the source field; an "outer" header with the source RLOC in the 273 source field: and the same globally unique group address in the 274 destination field of both the inner and outer header. 276 (S,G) State: the formal definition is in the PIM Sparse Mode 277 [RFC4601] specification. For this specification, the term is used 278 generally to refer to multicast state. Based on its topological 279 location, the (S,G) state resides in routers can be either 280 (S-EID,G) state (at a location where the (S,G) state resides) or 281 (S-RLOC,G) state (in the Internet core). 283 (S-EID,G) State: refers to multicast state in multicast source and 284 receiver sites where S-EID is the IP address of the multicast 285 source host (its EID). An S-EID can appear in an IGMPv3 report, 286 an MSDP SA message or a PIM Join/Prune message that travels inside 287 of a site. 289 (S-RLOC,G) State: refers to multicast state in the core where S is 290 a source locator (the IP address of a multicast ITR) of a site 291 with a multicast source. The (S-RLOC,G) is mapped from (S-EID,G) 292 entry by doing a mapping database lookup for the EID prefix that 293 S-EID maps to. An S-RLOC can appear in a PIM Join/Prune message 294 when it travels from an ETR to an ITR over the Internet core. 296 uLISP Site: a unicast only LISP site according to [LISP] which has 297 not deployed the procedures of this specification and therefore, 298 for multicast purposes, follows the procedures from Section 9. A 299 uLISP site can be a traditional multicast site. 301 LISP Site: a unicast LISP site (uLISP Site) that is also multicast 302 capable according to the procedures in this specification. 304 mPETR: this is a multicast proxy-ETR that is responsible for 305 advertising a very coarse EID prefix which non-LISP and uLISP 306 sites can target their (S-EID,G) PIM Join/Prune message to. mPETRs 307 are used so LISP source multicast sites can send multicast packets 308 using source addresses from the EID namespace. mPETRs act as Proxy 309 ETRs for supporting multicast routing in a LISP infrastructure. 310 It is likely an uPITR [INTWORK] and a mPETR will be co-located 311 since the single device advertises a coarse EID-prefix in the 312 underlying unicast routing system. 314 Mixed Locator-Sets: this is a locator-set for a LISP database 315 mapping entry where the RLOC addresses in the locator-set are in 316 both IPv4 and IPv6 format. 318 Unicast Encapsulated PIM Join/Prune Message: this is a standard PIM 319 Join/Prune message (LISP encapsulated with destination UDP port 320 4341) which is sent by ETRs at multicast receiver sites to an ITR 321 at a multicast source site. This message is sent periodically as 322 long as there are interfaces in the OIF-list for the (S-EID,G) 323 entry the ETR is joining for. 325 OIF-list: this is notation to describe the outgoing interface list 326 a multicast router stores per multicast routing table entry so it 327 knows what interfaces to replicate multicast packets on. 329 RPF: Reverse Path Forwarding is a procedure used by multicast 330 routers. A router will accept a multicast packet for forwarding 331 if the packet was received on the path that the router would use 332 to forward unicast packets to the multicast packet's source. 334 4. Basic Overview 336 LISP, when used for unicast routing, increases the site's ability to 337 control ingress traffic flows. Egress traffic flows are controlled 338 by the IGP in the source site. For multicast, the IGP coupled with 339 PIM can decide which path multicast packets ingress. By using the 340 traffic engineering features of LISP, a multicast source site can 341 control the egress of its multicast traffic. By controlling the 342 priorities of locators from a mapping database entry, a source 343 multicast site can control which way multicast receiver sites join to 344 the source site. 346 At this point in time, there is no requirement for different locator- 347 sets, priority, and weight policies for multicast than there is for 348 unicast. However, when traffic engineering policies are different 349 for unicast versus multicast flows, it will be desirable to use 350 multicast-based priority and weight values in Map-Reply messages. 352 The fundamental multicast forwarding model is to encapsulate a 353 multicast packet into another multicast packet. An ITR will 354 encapsulate multicast packets received from sources that it serves in 355 a LISP multicast header. The destination group address from the 356 inner header is copied to the destination address of the outer 357 header. The inner source address is the EID of the multicast source 358 host and the outer source address is the RLOC of the encapsulating 359 ITR. 361 The LISP-Multicast architecture will follow this high-level protocol 362 and operational sequence: 364 1. Receiver hosts in multicast sites will join multicast content the 365 way they do today, they use IGMP. When they use IGMPv3 where 366 they specify source addresses, they use source EIDs, that is they 367 join (S-EID,G). If the multicast source is external to this 368 receiver site, the PIM Join/Prune message flows toward the ETRs, 369 finding the shortest exit (that is the closest exit for the Join/ 370 Prune message and the closest entrance for the multicast packet 371 to the receiver). 373 2. The ETR does a mapping database lookup for S-EID. If the mapping 374 is cached from a previous lookup (from either a previous Join/ 375 Prune for the source multicast site or a unicast packet that went 376 to the site), it will use the RLOC information from the mapping. 377 The ETR will use the same priority and weighting mechanism as for 378 unicast. So the source site can decide which way multicast 379 packets egress. 381 3. The ETR will build two PIM Join/Prune messages, one that contains 382 a (S-EID,G) entry that is unicast to the ITR that matches the 383 RLOC the ETR selects, and the other which contains a (S-RLOC,G) 384 entry so the core network can create multicast state from this 385 ETR to the ITR. 387 4. When the ITR gets the unicast Join/Prune message (see Section 3 388 for formal definition), it will process (S-EID,G) entries in the 389 message and propagate them inside of the site where it has 390 explicit routing information for EIDs via the IGP. When the ITR 391 receives the (S-RLOC,G) PIM Join/Prune message it will process it 392 like any other join it would get in today's Internet. The S-RLOC 393 address is the IP address of this ITR. 395 5. At this point there is (S-EID,G) state from the joining host in 396 the receiver multicast site to the ETR of the receiver multicast 397 site. There is (S-RLOC,G) state across the core network from the 398 ETR of the multicast receiver site to the ITR in the multicast 399 source site and (S-EID,G) state in the source multicast site. 400 Note, the (S-EID,G) state is the same S-EID in each multicast 401 site. As other ETRs join the same multicast tree, they can join 402 through the same ITR (in which case the packet replication is 403 done in the core) or a different ITR (in which case the packet 404 replication is done at the source site). 406 6. When a packet is originated by the multicast host in the source 407 site, the packet will flow to one or more ITRs which will prepend 408 a LISP header. By copying the group address to the outer 409 destination address field, the ITR insert its own locator address 410 in the outer source address field. The ITR will look at its 411 (S-RLOC,G) state, where S-RLOC is its own locator address, and 412 replicate the packet on each interface a (S-RLOC,G) joined was 413 received on. The core has (S-RLOC,G) so where fanout occurs to 414 multiple sites, a core router will do packet replication. 416 7. When either the source site or the core replicates the packet, 417 the ETR will receive a LISP packet with a destination group 418 address. It will decapsulate packets because it has receivers 419 for the group. Otherwise, it would have not received the packets 420 because it would not have joined. The ETR decapsulates and does 421 a (S-EID,G) lookup in its multicast FIB to forward packets out 422 one or more interfaces to forward the packet to internal 423 receivers. 425 This architecture is consistent and scalable with the architecture 426 presented in [LISP] where multicast state in the core operates on 427 locators and multicast state at the sites operates on EIDs. 429 Alternatively, [LISP] also has a mechanism where (S-EID,G) state can 430 reside in the core through the use of RPF-vectors [RFC5496] in PIM 431 Join/Prune messages. However, few PIM implementations support RPF 432 vectors and LISP should avoid S-EID state in the core. See Section 5 433 for details. 435 However, some observations can be made on the algorithm above. The 436 control plane can scale but at the expense of sending data to sites 437 which may have not joined the distribution tree where the 438 encapsulated data is being delivered. For example, one site joins 439 (S-EID1,G) and another site joins (S-EID2,G). Both EIDs are in the 440 same multicast source site. Both multicast receiver sites join to 441 the same ITR with state (S-RLOC,G) where S-RLOC is the RLOC for the 442 ITR. The ITR joins both (S-EID1,G) and (S-EID2,G) inside of the 443 site. The ITR receives (S-RLOC,G) joins and populates the OIF-list 444 state for it. Since both (S-EID1,G) and (S-EID2, G) map to the one 445 (S-RLOC,G) packets will be delivered by the core to both multicast 446 receiver sites even though each have joined a single source-based 447 distribution tree. This behavior is a consequence of the many-to-one 448 mapping between S-EIDs and a S-RLOC. 450 There is a possible solution to this problem which reduces the number 451 of many-to-one occurrences of (S-EID,G) entries aggregating into a 452 single (S-RLOC,G) entry. If a physical ITR can be assigned multiple 453 RLOC addresses and these addresses are advertised in mapping database 454 entries, then ETRs at receiver sites have more RLOC address options 455 and therefore can join different (RLOC,G) entries for each (S-EID,G) 456 entry joined at the receiver site. It would not scale to have a one- 457 to-one relationship between the number of S-EID sources at a source 458 site and the number of RLOCs assigned to all ITRs at the site, but 459 "n" can reduce to a smaller number in the "n-to-1" relationship. And 460 in turn, reduce the opportunity for data packets to be delivered to 461 sites for groups not joined. 463 5. Source Addresses versus Group Addresses 465 Multicast group addresses don't have to be associated with either the 466 EID or RLOC namespace. They actually are a namespace of their own 467 that can be treated as logical with relatively opaque allocation. 468 So, by their nature, they don't detract from an incremental 469 deployment of LISP-Multicast. 471 As for source addresses, as in the unicast LISP scenario, there is a 472 decoupling of identification from location. In a LISP site, packets 473 are originated from hosts using their allocated EIDs. EID addresses 474 are used to identify the host as well as where in the site's topology 475 the host resides but not how and where it is attached to the 476 Internet. 478 Therefore, when multicast distribution tree state is created anywhere 479 in the network on the path from any multicast receiver to a multicast 480 source, EID state is maintained at the source and receiver multicast 481 sites, and RLOC state is maintained in the core. That is, a 482 multicast distribution tree will be represented as a 3-tuple of 483 {(S-EID,G) (S-RLOC,G) (S-EID,G)} where the first element of the 484 3-tuple is the state stored in routers from the source to one or more 485 ITRs in the source multicast site, the second element of the 3-tuple 486 is the state stored in routers downstream of the ITR, in the core, to 487 all LISP receiver multicast sites, and the third element in the 488 3-tuple is the state stored in the routers downstream of each ETR, in 489 each receiver multicast site, reaching each receiver. Note that 490 (S-EID,G) is the same in both the source and receiver multicast 491 sites. 493 The concatenation/mapping from the first element to the second 494 element of the 3-tuples is done by the ITR and from the second 495 element to the third element is done at the ETRs. 497 6. Locator Reachability Implications on LISP-Multicast 499 Multicast state as it is stored in the core is always (S,G) state as 500 it exists today or (S-RLOC,G) state as it will exist when LISP sites 501 are deployed. The core routers cannot distinguish one from the 502 other. They don't need to because it is state that RPFs against the 503 core routing tables in the RLOC namespace. The difference is where 504 the root of the distribution tree for a particular source is. In the 505 traditional multicast core, the source S is the source host's IP 506 address. For LISP-Multicast the source S is a single ITR of the 507 multicast source site. 509 An ITR is selected based on the LISP EID-to-RLOC mapping used when an 510 ETR propagates a PIM Join/Prune message out of a receiver multicast 511 site. The selection is based on the same algorithm an ITR would use 512 to select an ETR when sending a unicast packet to the site. In the 513 unicast case, the ITR can change on a per-packet basis depending on 514 the reachability of the ETR. So an ITR can change relatively easily 515 using local reachability state. However, in the multicast case, when 516 an ITR goes unreachable, new distribution tree state must be built 517 because the encapsulating root has changed. This is more significant 518 than an RPF-change event, where any router would typically locally 519 change its RPF-interface for its existing tree state. But when an 520 encapsulating LISP-Multicast ITR goes unreachable, new distribution 521 state must be rebuilt and reflect the new encapsulator. Therefore, 522 when an ITR goes unreachable, all ETRs that are currently joined to 523 that ITR will have to trigger a new Join/Prune message for (S-RLOC,G) 524 to the new ITR as well as send a unicast encapsulated Join/Prune 525 message telling the new ITR which (S-EID,G) is being joined. 527 This issue can be mitigated by using anycast addressing for the ITRs 528 so the problem does reduce to an RPF change in the core, but still 529 requires a unicast encapsulated Join/Prune message to tell the new 530 ITR about (S-EID,G). The problem with this approach is that the ETR 531 really doesn't know when the ITR has changed so the new anycast ITR 532 will get the (S-EID,G) state only when the ETR sends it the next time 533 during its periodic sending procedures. 535 7. Multicast Protocol Changes 537 A number of protocols are used today for inter-domain multicast 538 routing: 540 IGMPv1-v3, MLDv1-v2: These protocols do not require any changes for 541 LISP-Multicast for two reasons. One being that they are link- 542 local and not used over site boundaries and second, they advertise 543 group addresses that don't need translation. Where source 544 addresses are supplied in IGMPv3 and MLDv2 messages, they are 545 semantically regarded as EIDs and don't need to be converted to 546 RLOCs until the multicast tree-building protocol, such as PIM, is 547 received by the ETR at the site boundary. Addresses used for IGMP 548 and MLD come out of the source site's allocated addresses which 549 are therefore from the EID namespace. 551 MBGP: Even though MBGP is not a multicast routing protocol, it is 552 used to find multicast sources when the unicast BGP peering 553 topology and the multicast MBGP peering topology are not 554 congruent. When MBGP is used in a LISP-Multicast environment, the 555 prefixes which are advertised are from the RLOC namespace. This 556 allows receiver multicast sites to find a path to the source 557 multicast site's ITRs. MBGP peering addresses will be from the 558 RLOC namespace. There are no MBGP protocol changes required to 559 support LISP-Multicast. 561 MSDP: MSDP is used to announce active multicast sources to other 562 routing domains (or LISP sites). The announcements come from the 563 PIM Rendezvous Points (RPs) from sites where there are active 564 multicast sources sending to various groups. In the context of 565 LISP-Multicast, the source addresses advertised in MSDP will 566 semantically be from the EID namespace since they describe the 567 identity of a source multicast host. It will be true that the 568 state stored in MSDP caches from core routers will be from the EID 569 namespace. An RP address inside of site will be from the EID 570 namespace so it can be advertised and reached by internal unicast 571 routing mechanism. However, for MSDP peer-RPF checking to work 572 properly across sites, the RP addresses must be converted or 573 mapped into a routable address that is advertised and maintained 574 in the BGP routing tables in the core. MSDP peering addresses can 575 come out of either the EID or a routable address namespace. And 576 the choice can be made unilaterally because the ITR at the site 577 will determine which namespace the destination peer address is out 578 of by looking in the mapping database service. There are no MSDP 579 protocol changes required to support LISP-Multicast. 581 PIM-SSM: In the simplest form of distribution tree building, when 582 PIM operates in SSM mode, a source distribution tree is built and 583 maintained across site boundaries. In this case, there is a small 584 modification to the operation of the PIM protocol. No 585 modifications to any message format, but to support taking a Join/ 586 Prune message originated inside of a LISP site with embedded 587 addresses from the EID namespace and converting them to addresses 588 from the RLOC namespace when the Join/Prune message crosses a site 589 boundary. This is similar to the requirements documented in 590 [RFC5135]. 592 PIM-Bidir: Bidirectional PIM is typically run inside of a routing 593 domain, but if deployed in an inter-domain environment, one would 594 have to decide if the RP address of the shared-tree would be from 595 the EID namespace or the RLOC namespace. If the RP resides in a 596 site-based router, then the RP address is from the EID namespace. 597 If the RP resides in the core where RLOC addresses are routed, 598 then the RP address is from the RLOC namespace. This could be 599 easily distinguishable if the EID address were well-known address 600 allocation block from the RLOC namespace. Also, when using 601 Embedded-RP for RP determination [RFC3956], the format of the 602 group address could indicate the namespace the RP address is from. 603 However, refer to Section 10 for considerations core routers need 604 to make when using Embedded-RP IPv6 group addresses. When using 605 Bidir-PIM for inter-domain multicast routing, it is recommended to 606 use staticly configured RPs. Allowing core routers to associate a 607 Bidir group's RP address with an ITR's RLOC address. And site 608 routers to associate the Bidir group's RP address as an EID 609 address. With respect to DF-election in Bidir PIM, no changes are 610 required since all messaging and addressing is link-local. 612 PIM-ASM: The ASM mode of PIM, the most popular form of PIM, is 613 deployed in the Internet today is by having shared-trees within a 614 site and using source-trees across sites. By the use of MSDP and 615 PIM-SSM techniques described above, multicast connectivity can 616 occur across LISP sites. Having said that, that means there are 617 no special actions required for processing (*,G) or (S,G,R) Join/ 618 Prune messages since they all operate against the shared-tree 619 which is site resident. Just like with ASM, there is no (*,G) in 620 the core when LISP-Multicast is in use. This is also true for the 621 RP-mapping mechanisms Auto-RP and BSR. 623 Based on the protocol description above, the conclusion is that there 624 are no protocol message format changes, just a translation function 625 performed at the control-plane. This will make for an easier and 626 faster transition for LISP since fewer components in the network have 627 to change. 629 It should also be stated just like it is in [LISP] that no host 630 changes, whatsoever, are required to have a multicast source host 631 send multicast packets and for a multicast receiver host to receive 632 multicast packets. 634 8. LISP-Multicast Data-Plane Architecture 636 The LISP-Multicast data-plane operation conforms to the operation and 637 packet formats specified in [LISP]. However, encapsulating a 638 multicast packet from an ITR is a much simpler process. The process 639 is simply to copy the inner group address to the outer destination 640 address. And to have the ITR use its own IP address (its RLOC) as 641 the source address. The process is simpler for multicast because 642 there is no EID-to-RLOC mapping lookup performed during packet 643 forwarding. 645 In the decapsulation case, the ETR simply removes the outer header 646 and performs a multicast routing table lookup on the inner header 647 (S-EID,G) addresses. Then the OIF-list for the (S-EID,G) entry is 648 used to replicate the packet on site-facing interfaces leading to 649 multicast receiver hosts. 651 There is no Data-Probe logic for ETRs as there can be in the unicast 652 forwarding case. 654 8.1. ITR Forwarding Procedure 656 The following procedure is used by an ITR, when it receives a 657 multicast packet from a source inside of its site: 659 1. A multicast data packet sent by a host in a LISP site will have 660 the source address equal to the host's EID and the destination 661 address equal to the group address of the multicast group. It is 662 assumed the group information is obtained by current methods. 663 The same is true for a multicast receiver to obtain the source 664 and group address of a multicast flow. 666 2. When the ITR receives a multicast packet, it will have both S-EID 667 state and S-RLOC state stored. Since the packet was received on 668 a site-facing interface, the RPF lookup is based on the S-EID 669 state. If the RPF check succeeds, then the OIF-list contains 670 interfaces that are site-facing and external-facing. For the 671 site-facing interfaces, no LISP header is prepended. For the 672 external-facing interfaces a LISP header is prepended. When the 673 ITR prepends a LISP header, it uses its own RLOC address as the 674 source address and copies the group address supplied by the IP 675 header the host built as the outer destination address. 677 8.1.1. Multiple RLOCs for an ITR 679 Typically, an ITR will have a single RLOC address but in some cases 680 there could be multiple RLOC addresses assigned from either the same 681 or different service providers. In this case when (S-RLOC,G) Join/ 682 Prune messages are received for each RLOC, there is a OIF-list 683 merging action that must take place. Therefore, when a packet is 684 received from a site-facing interface that matches on a (S-EID,G) 685 entry, the interfaces of the OIF-list from all (RLOC,G) entries 686 joined to the ITR as well as the site-facing OIF-list joined for 687 (S-EID,G) must be part be included in packet replication. In 688 addition to replicating for all types of OIF-lists, each oif entry 689 must be tagged with the RLOC address, so encapsulation uses the outer 690 source address for the RLOC joined. 692 8.1.2. Multiple ITRs for a LISP Source Site 694 Note when ETRs from different multicast receiver sites receive 695 (S-EID,G) joins, they may select a different S-RLOC for a multicast 696 source site due to policy (the multicast ITR can return different 697 multicast priority and weight values per ETR Map-Request). In this 698 case, the same (S-EID,G) is being realized by different (S-RLOC,G) 699 state in the core. This will not result in duplicate packets because 700 each ITR in the multicast source site will choose their own RLOC for 701 the source address for encapsulated multicast traffic. The RLOC 702 addresses are the ones joined by remote multicast ETRs. 704 When different (S-EID,G) traffic is combined into a single (RLOC,G) 705 core distribution tree, this may cause traffic to go to a receiver 706 multicast site when it does not need to. This happens when one 707 receiver multicast site joins (S1-EID,Gi) through a core distribution 708 tree of (RLOC1,Gi) and another multicast receiver site joins (S2- 709 EID,Gi) through the same core distribution tree of (RLOC1,Gi). When 710 ETRs decapsulate such traffic, they should know from their local 711 (S-EID,G) state if the packet should be forwarded. If there is no 712 (S-EID,G) state that matches the inner packet header, the packet is 713 discarded. 715 8.2. ETR Forwarding Procedure 717 The following procedure is used by an ETR, when it receives a 718 multicast packet from a source outside of its site: 720 1. When a multicast data packet is received by an ETR on an 721 external-facing interface, it will do an RPF lookup on the S-RLOC 722 state it has stored. If the RPF check succeeds, the interfaces 723 from the OIF-list are used for replication to interfaces that are 724 site-facing as well as interfaces that are external-facing (this 725 ETR can also be a transit multicast router for receivers outside 726 of its site). When the packet is to be replicated for an 727 external-facing interface, the LISP encapsulation header are not 728 stripped. When the packet is replicated for a site-facing 729 interface, the encapsulation header is stripped. 731 2. The packet without a LISP header is now forwarded down the 732 (S-EID,G) distribution tree in the receiver multicast site. 734 8.3. Replication Locations 736 Multicast packet replication can happen in the following topological 737 locations: 739 o In an IGP multicast router inside a site which operates on S-EIDs. 741 o In a transit multicast router inside of the core which operates on 742 S-RLOCs. 744 o At one or more ETR routers depending on the path a Join/Prune 745 message exits a receiver multicast site. 747 o At one or more ITR routers in a source multicast site depending on 748 what priorities are returned in a Map-Reply to receiver multicast 749 sites. 751 In the last case the source multicast site can do replication rather 752 than having a single exit from the site. But this only can occur 753 when the priorities in the Map-Reply are modified for different 754 receiver multicast site so that the PIM Join/Prune messages arrive at 755 different ITRs. 757 This policy technique, also used in [ALT] for unicast, is useful for 758 multicast to mitigate the problems of changing distribution tree 759 state as discussed in Section 6. 761 9. LISP-Multicast Interworking 763 This section will describe the multicast corollary to [INTWORK] which 764 describes the interworking of multicast routing among LISP and non- 765 LISP sites. 767 9.1. LISP and non-LISP Mixed Sites 769 Since multicast communication can involve more than two entities to 770 communicate together, the combinations of interworking scenarios are 771 more involved. However, the state maintained for distribution trees 772 at the sites is the same regardless of whether or not the site is 773 LISP enabled or not. So most of the implications are in the core 774 with respect to storing routable EID prefixes from either PA or PI 775 blocks. 777 Before enumerating the multicast interworking scenarios, let's define 778 3 deployment states of a site: 780 o A non-LISP site which will run PIM-SSM or PIM-ASM with MSDP as it 781 does today. The addresses for the site are globally routable. 783 o A site that deploys LISP for unicast routing. The addresses for 784 the site are not globally routable. Let's define the name for 785 this type of site as a uLISP site. 787 o A site that deploys LISP for both unicast and multicast routing. 788 The addresses for the site are not globally routable. Let's 789 define the name for this type of site as a LISP-Multicast site. 791 What will not be considered is a LISP site enabled for multicast 792 purposes only but do consider a uLISP site as documented in 793 [INTWORK]. In this section there is no discussion how a LISP site 794 sends multicast packets when all receiver sites are LISP-Multicast 795 enabled; that has been discussed in previous sections. 797 The following scenarios exist to make LISP-Multicast sites interwork 798 with non-LISP-Multicast sites: 800 1. A LISP site must be able to send multicast packets to receiver 801 sites which are a mix of non-LISP sites and uLISP sites. 803 2. A non-LISP site must be able to send multicast packets to 804 receiver sites which are a mix of non-LISP sites and uLISP sites. 806 3. A non-LISP site must be able to send multicast packets to 807 receiver sites which are a mix of LISP sites, uLISP sites, and 808 non-LISP sites. 810 4. A uLISP site must be able to send multicast packets to receiver 811 sites which are a mix of LISP sites, uLISP sites, and non-LISP 812 sites. 814 5. A LISP site must be able to send multicast packets to receiver 815 sites which are a mix of LISP sites, uLISP sites, and non-LISP 816 sites. 818 9.1.1. LISP Source Site to non-LISP Receiver Sites 820 In the first scenario, a site is LISP capable for both unicast and 821 multicast traffic and as such operates on EIDs. Therefore there is a 822 possibility that the EID prefix block is not routable in the core. 823 For LISP receiver multicast sites this isn't a problem but for non- 824 LISP or uLISP receiver multicast sites, when a PIM Join/Prune message 825 is received by the edge router, it has no route to propagate the 826 Join/Prune message out of the site. This is no different than the 827 unicast case that LISP-NAT in [INTWORK] solves. 829 LISP-NAT allows a unicast packet that exits a LISP site to get its 830 source address mapped to a globally routable address before the ITR 831 realizes that it should not encapsulate the packet destined to a non- 832 LISP site. For a multicast packet to leave a LISP site, distribution 833 tree state needs to be built so the ITR can know where to send the 834 packet. So the receiver multicast sites need to know about the 835 multicast source host by its routable address and not its EID 836 address. When this is the case, the routable address is the 837 (S-RLOC,G) state that is stored and maintained in the core routers. 838 It is important to note that the routable address for the host cannot 839 be the same as an RLOC for the site because it is desirable for ITRs 840 to process a received PIM Join/Prune message from an external-facing 841 interface to be propagated inside of the site so the site-part of the 842 distribution tree is built. 844 Using a globally routable source address allows non-LISP and uLISP 845 multicast receiver to join, create, and maintain a multicast 846 distribution tree. However, the LISP multicast receiver site will 847 want to perform an EID-to-RLOC mapping table lookup when a PIM Join/ 848 Prune message is received on a site-facing interface. It does this 849 because it wants to find a (S-RLOC,G) entry to Join in the core. So 850 there is a conflict of behavior between the two types of sites. 852 The solution to this problem is the same as when an ITR wants to send 853 a unicast packet to a destination site but needs determine if the 854 site is LISP capable or not. When it is not LISP capable, the ITR 855 does not encapsulate the packet. So for the multicast case, when ETR 856 receives a PIM Join/Prune message for (S-EID,G) state, it will do a 857 mapping table lookup on S-EID. In this case, S-EID is not in the 858 mapping database because the source multicast site is using a 859 routable address and not an EID prefix address. So the ETR knows to 860 simply propagate the PIM Join/Prune message to a external-facing 861 interface without converting the (S-EID,G) because it is an (S,G) 862 where S is routable and reachable via core routing tables. 864 Now that the multicast distribution tree is built and maintained from 865 any non-LISP or uLISP receiver multicast site, the way packet 866 forwarding model is performed can be explained. 868 Since the ITR in the source multicast site has never received a 869 unicast encapsulated PIM Join/Prune message from any ETR in a 870 receiver multicast site, it knows there are no LISP-Multicast 871 receiver sites. Therefore, there is no need for the ITR to 872 encapsulate data. Since it will know a priori (via configuration) 873 that its site's EIDs are not routable (and not registered to the 874 mapping database system), it assumes that the multicast packets from 875 the source host are sent by a routable address. That is, it is the 876 responsibility of the multicast source host's system administrator to 877 ensure that the source host sends multicast traffic using a routable 878 source address. When this happens, the ITR acts simply as a router 879 and forwards the multicast packet like an ordinary multicast router. 881 There is an alternative to using a LISP-NAT scheme just like there is 882 for unicast [INTWORK] forwarding by using Proxy Tunnel Routers 883 (PxTRs). This can work the same way for multicast routing as well, 884 but the difference is that non-LISP and uLISP sites will send PIM 885 Join/Prune messages for (S-EID,G) which make their way in the core to 886 multicast PxTRs. Let's call this use of a PxTR as a "Multicast 887 Proxy-ETR" (or mPETR). Since the mPETRs advertise very coarse EID 888 prefixes, they draw the PIM Join/Prune control traffic making them 889 the target of the distribution tree. To get multicast packets from 890 the LISP source multicast sites, the tree needs to be built on the 891 path from the mPETR to the LISP source multicast site. To make this 892 happen the mPETR acts as a "Proxy ETR" (where in unicast it acts as a 893 "Proxy ITR", or an uPITR [INTWORK]). 895 The existence of mPETRs in the core allows source multicast site ITRs 896 to encapsulate multicast packets according to (S-RLOC,G) state. The 897 (S-RLOC,G) state is built from the mPETRs to the multicast ITRs. The 898 encapsulated multicast packets are decapsulated by mPETRs and then 899 forwarded according to (S-EID,G) state. The (S-EID,G) state is built 900 from the non-LISP and uLISP receiver multicast sites to the mPETRs. 902 9.1.2. Non-LISP Source Site to non-LISP Receiver Sites 904 Clearly non-LISP multicast sites can send multicast packets to non- 905 LISP receiver multicast sites. That is what they do today. However, 906 discussion is required to show how non-LISP multicast sites send 907 multicast packets to uLISP receiver multicast sites. 909 Since uLISP receiver multicast sites are not targets of any (S,G) 910 state, they simply send (S,G) PIM Join/Prune messages toward the non- 911 LISP source multicast site. Since the source multicast site, in this 912 case has not been upgraded to LISP, all multicast source host 913 addresses are routable. So this case is simplified to where a uLISP 914 receiver multicast site looks to the source multicast site as a non- 915 LISP receiver multicast site. 917 9.1.3. Non-LISP Source Site to Any Receiver Site 919 When a non-LISP source multicast site has receivers in either a non- 920 LISP/uLISP site or a LISP site, one needs to decide how the LISP 921 receiver multicast site will attach to the distribution tree. It is 922 known from Section 9.1.2 that non-LISP and uLISP receiver multicast 923 sites can join the distribution tree, but a LISP receiver multicast 924 site ETR will need to know if the source address of the multicast 925 source host is routable or not. It has been shown in Section 9.1.1 926 that an ETR, before it sends a PIM Join/Prune message on an external- 927 facing interface, does a EID-to-RLOC mapping lookup to determine if 928 it should convert the (S,G) state from a PIM Join/Prune message 929 received on a site-facing interface to a (S-RLOC,G). If the lookup 930 fails, the ETR can conclude the source multicast site is a non-LISP 931 site so it simply forwards the Join/Prune message (it also doesn't 932 need to send a unicast encapsulated Join/Prune message because there 933 is no ITR in a non-LISP site and there is namespace continuity 934 between the ETR and source). 936 For a non-LISP source multicast site, (S-EID,G) state could be 937 limited to the edges of the network with the use of multicast proxy- 938 ITRs (mPITRs). The mPITRs can take native, unencapsulated multicast 939 packets from non-LISP source multicast and uLISP sites and 940 encapsulate them to ETRs in receiver multicast sites or to mPETRs 941 that can decapsulate for non-LISP receiver multicast or uLISP sites. 942 The mPITRs are responsible for sending (S-EID,G) joins to the non- 943 LISP source multicast site. To connect the distribution trees 944 together, multicast ETRs will need to be configured with the mPITR's 945 RLOC addresses so they can send both (S-RLOC,G) joins to build a 946 distribution tree to the mPITR as well as for sending unicast joins 947 to mPITRs so they can propogate (S-EID,G) joins into source multicast 948 sites. The use of mPITRs is undergoing more study and is work in 949 progress. 951 9.1.4. Unicast LISP Source Site to Any Receiver Sites 953 In the last section, it was explained how an ETR in a multicast 954 receiver site can determine if a source multicast site is LISP- 955 enabled by looking into the mapping database. When the source 956 multicast site is a uLISP site, it is LISP enabled but the ITR, by 957 definition is not capable of doing multicast encapsulation. So for 958 the purposes of multicast routing, the uLISP source multicast site is 959 treated as non-LISP source multicast site. 961 Non-LISP receiver multicast sites can join distribution trees to a 962 uLISP source multicast site since the source site behaves, from a 963 forwarding perspective, as a non-LISP source site. This is also the 964 case for a uLISP receiver multicast site since the ETR does not have 965 multicast functionality built-in or enabled. 967 Special considerations are required for LISP receiver multicast sites 968 since they think the source multicast site is LISP capable, the ETR 969 cannot know if ITR is LISP-Multicast capable. To solve this problem, 970 each mapping database entry will have a multicast 2-tuple (Mpriority, 971 Mweight) per RLOC. When the Mpriority is set to 255, the site is 972 considered not multicast capable. So an ETR in a LISP receiver 973 multicast site can distinguish whether a LISP source multicast site 974 is LISP-Multicast site from a uLISP site. 976 9.1.5. LISP Source Site to Any Receiver Sites 978 When a LISP source multicast site has receivers in LISP, non-LISP, 979 and uLISP receiver multicast sites, it has a conflict about how it 980 sends multicast packets. The ITR can either encapsulate or natively 981 forward multicast packets. Since the receiver multicast sites are 982 heterogeneous in their behavior, one packet forwarding mechanism 983 cannot satisfy both. However, if a LISP receiver multicast site acts 984 like a uLISP site then it could receive packets like a non-LISP 985 receiver multicast site making all receiver multicast sites have 986 homogeneous behavior. However, this poses the following issues: 988 o LISP-NAT techniques with routable addresses would be required in 989 all cases. 991 o Or alternatively, mPETR deployment would be required forcing 992 coarse EID prefix advertisement in the core. 994 o But what is most disturbing is that when all sites that 995 participate are LISP-Multicast sites but then a non-LISP or uLISP 996 site joins the distribution tree, then the existing joined LISP 997 receiver multicast sites would have to change their behavior. 998 This would create too much dynamic tree-building churn to be a 999 viable alternative. 1001 So the solution space options are: 1003 1. Make the LISP ITR in the source multicast site send two packets, 1004 one that is encapsulated with (S-RLOC,G) to reach LISP receiver 1005 multicast sites and another that is not encapsulated with 1006 (S-EID,G) to reach non-LISP and uLISP receiver multicast sites. 1008 2. Make the LISP ITR always encapsulate packets with (S-RLOC,G) to 1009 reach LISP-Multicast sites and to reach mPETRs that can 1010 decapsulate and forward (S-EID,G) packets to non-LISP and uLISP 1011 receiver multicast sites. 1013 9.2. LISP Sites with Mixed Address Families 1015 A LISP database mapping entry that describes the locator-set, 1016 Mpriority and Mweight per locator address (RLOC), for an EID prefix 1017 associated with a site could have RLOC addresses in either IPv4 or 1018 IPv6 format. When a mapping entry has a mix of RLOC formatted 1019 addresses, it is an implicit advertisement by the site that it is a 1020 dual-stack site. That is, the site can receive IPv4 or IPv6 unicast 1021 packets. 1023 To distinguish if the site can receive dual-stack unicast packets as 1024 well as dual-stack multicast packets, the Mpriority value setting 1025 will be relative to an IPv4 or IPv6 RLOC See [LISP] for packet format 1026 details. 1028 If one considers the combinations of LISP, non-LISP, and uLISP sites 1029 sharing the same distribution tree and considering the capabilities 1030 of supporting IPv4, IPv6, or dual-stack, the number of total 1031 combinations grows beyond comprehension. 1033 Using some combinatorial math, the following profiles of a site and 1034 the combinations that can occur: 1036 1. LISP-Multicast IPv4 Site 1038 2. LISP-Multicast IPv6 Site 1040 3. LISP-Multicast Dual-Stack Site 1042 4. uLISP IPv4 Site 1044 5. uLISP IPv6 Site 1045 6. uLISP Dual-Stack Site 1047 7. non-LISP IPv4 Site 1049 8. non-LISP IPv6 Site 1051 9. non-LISP Dual-Stack Site 1053 Lets define (m n) = m!/(n!*(m-n)!), pronounced "m choose n" to 1054 illustrate some combinatorial math below. 1056 When 1 site talks to another site, the combinatorial is (9 2), when 1 1057 site talks to another 2 sites, the combinatorial is (9 3). If sum 1058 this up to (9 9), then: 1060 (9 2) + (9 3) + (9 4) + (9 5) + (9 6) + (9 7) + (9 8) + (9 9) = 1062 36 + 84 + 126 + 126 + 84 + 36 + 9 + 1 1064 Which results in the total number of cases to be considered at 502. 1066 This combinatorial gets even worse when one considers a site using 1067 one address family inside of the site and the xTRs use the other 1068 address family (as in using IPv4 EIDs with IPv6 RLOCs or IPv6 EIDs 1069 with IPv4 RLOCs). 1071 To rationalize this combinatorial nightmare, there are some 1072 guidelines which need to be put in place: 1074 o Each distribution tree shared between sites will either be an IPv4 1075 distribution tree or an IPv6 distribution tree. Therefore, head- 1076 end replication can be avoided by building and sending packets on 1077 each address family based distribution tree. Even though there 1078 might be an urge to do multicast packet translation from one 1079 address family format to the other, it is a non-viable over- 1080 complicated urge. Multicast ITRs will only encapsulate packets 1081 where the inner and outer headers are from the same address 1082 family. 1084 o All LISP sites on a multicast distribution tree must share a 1085 common address family which is determined by the source site's 1086 locator-set in its LISP database mapping entry. All receiver 1087 multicast sites will use the best RLOC priority controlled by the 1088 source multicast site. This is true when the source site is 1089 either LISP-Multicast or uLISP capable. This means that priority- 1090 based policy modification is prohibited. When a receiver 1091 multicast site ETR receives a (S-EID,G) join, it must select a 1092 S-RLOC for the same address family as S-EID. 1094 o When a multicast locator-set has more than one locator, only 1095 locators from the same address-family MUST be set to the same best 1096 priority value. A mixed locator-set can exist (for unicast use), 1097 but the multicast priorities MUST be the set for the same address 1098 family locators. 1100 o When the source site is not LISP capable, it is up to how 1101 receivers find the source and group information for a multicast 1102 flow. That mechanism decides the address family for the flow. 1104 9.3. Making a Multicast Interworking Decision 1106 This Multicast Interworking section has shown all combinations of 1107 multicast connectivity that could occur. As already concluded, this 1108 can be quite complicated and if the design is too ambitious, the 1109 dynamics of the protocol could cause a lot of instability. 1111 The trade-off decisions are hard to make and so the same single 1112 solution is desirable to work for both IPv4 and IPv6 multicast. It 1113 is imperative to have an incrementally deployable solution for all of 1114 IPv4 unicast and multicast and IPv6 unicast and multicast while 1115 minimizing (or eliminating) both unicast and multicast EID namespace 1116 state. 1118 Therefore the design decision to go with uPITRs [INTWORK] for unicast 1119 routing and mPETRs for multicast routing seems to be the sweet spot 1120 in the solution space so state requirements can be optimized and 1121 avoid head-end data replication at ITRs. 1123 10. Considerations when RP Addresses are Embedded in Group Addresses 1125 When ASM and PIM-Bidir is used in an IPv6 inter-domain environment, a 1126 technique exists to embed the unicast address of an RP in a IPv6 1127 group address [RFC3956]. When routers in end sites process a PIM 1128 Join/Prune message which contain an embedded-RP group address, they 1129 extract the RP address from the group address and treat it from the 1130 EID namespace. However, core routers do not have state for the EID 1131 namespace, and need to extract an RP address from the RLOC namespace. 1133 Therefore, it is the responsibility of ETRs in multicast receiver 1134 sites to map the group address into a group address where the 1135 embedded-RP address is from the RLOC namespace. The mapped RP- 1136 address is obtained from a EID-to-RLOC mapping database lookup. The 1137 ETR will also send a unicast (*,G) Join/Prune message to the ITR so 1138 the branch of the distribution tree from the source site resident RP 1139 to the ITR is created. 1141 This technique is no different than the techniques described in this 1142 specification for translating (S,G) state and propagating Join/Prune 1143 messages into the core. The only difference is that the (*,G) state 1144 in Join/Prune messages are mapped because they contain unicast 1145 addresses encoded in an Embedded-RP group address. 1147 11. Taking Advantage of Upgrades in the Core 1149 If the core routers are upgraded to support [RFC5496], then the EID 1150 specific data can be passed through the core without, possibly, 1151 having to store the state in the core. 1153 By doing this one can eliminate the ETR from unicast encapsulating 1154 PIM Join/Prune messages to the source site's ITR. 1156 However, this solution is restricted to a small set of workable cases 1157 which would not be good for general use of LISP-Multicast. In 1158 addition due to slow convergence properties, it is not being 1159 recommended for LISP-Multicast. 1161 12. Mtrace Considerations 1163 Mtrace functionality MUST be consistent with unicast traceroute 1164 functionality where all hops from multicast receiver to multicast 1165 source are visible. 1167 The design for mtrace for use in LISP-Multicast environments is to be 1168 determined but should build upon the mtrace version 2 specified in 1169 [MTRACE]. 1171 13. Security Considerations 1173 The security concerns for LISP multicast are mainly the same as for 1174 the base LISP specification [LISP] and for multicast in general, 1175 including PIM-ASM [RFC4601]. 1177 There may be a security concern with respect to unicast PIM messages. 1178 When multiple receiver sites are joining a (S-EID1,G) distribution 1179 tree that maps to a (RLOC1,G) core distribution tree, and a malicious 1180 receiver site joins a (S-EID2,G) distribution tree that also maps to 1181 the (RLOC1,G) core distribution tree, the legitimate sites will 1182 receive data from S-EID2 when they did not ask for it. 1184 Other than as noted above there are currently no known security 1185 differences between multicast with LISP and multicast without LISP. 1186 However this has not been a topic that has been investigated deeply 1187 so far therefore additional issues might arise in future. 1189 14. Acknowledgments 1191 The authors would like to gratefully acknowledge the people who have 1192 contributed discussion, ideas, and commentary to the making of this 1193 proposal and specification. People who provided expert review were 1194 Scott Brim, Greg Shepherd, and Dave Oran. Other commentary from 1195 discussions at Summer 2008 Dublin IETF were Toerless Eckert and 1196 Ijsbrand Wijnands. 1198 The authors would also like to thank the MBONED working group for 1199 constructive and civil verbal feedback when this draft was presented 1200 at the Fall 2008 IETF in Minneapolis. In particular, good commentary 1201 came from Tom Pusateri, Steve Casner, Marshall Eubanks, Dimitri 1202 Papadimitriou, Ron Bonica, Lenny Guardino, Alia Atlas, Jesus Arango, 1203 and Jari Arkko. 1205 An expert review of this specification was done by Yiqun Cai and 1206 Liming Wei. The authors thank them for their detailed comments. 1208 This work originated in the Routing Research Group (RRG) of the IRTF. 1209 The individual submission [MLISP] was converted into this IETF LISP 1210 working group draft. 1212 15. IANA Considerations 1214 This document makes no request of the IANA. 1216 16. References 1218 16.1. Normative References 1220 [INTWORK] Lewis, D., Meyer, D., and D. Farinacci, "Interworking LISP 1221 with IPv4 and IPv6", draft-ietf-lisp-interworking-02.txt 1222 (work in progress). 1224 [LISP] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, 1225 "Locator/ID Separation Protocol (LISP)", 1226 draft-ietf-lisp-16.txt (work in progress). 1228 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1229 Requirement Levels", BCP 14, RFC 2119, March 1997. 1231 [RFC3618] Fenner, B. and D. Meyer, "Multicast Source Discovery 1232 Protocol (MSDP)", RFC 3618, October 2003. 1234 [RFC3956] Savola, P. and B. Haberman, "Embedding the Rendezvous 1235 Point (RP) Address in an IPv6 Multicast Address", 1236 RFC 3956, November 2004. 1238 [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, 1239 "Protocol Independent Multicast - Sparse Mode (PIM-SM): 1240 Protocol Specification (Revised)", RFC 4601, August 2006. 1242 [RFC4604] Holbrook, H., Cain, B., and B. Haberman, "Using Internet 1243 Group Management Protocol Version 3 (IGMPv3) and Multicast 1244 Listener Discovery Protocol Version 2 (MLDv2) for Source- 1245 Specific Multicast", RFC 4604, August 2006. 1247 [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for 1248 IP", RFC 4607, August 2006. 1250 [RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, 1251 "Multiprotocol Extensions for BGP-4", RFC 4760, 1252 January 2007. 1254 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 1255 "Bidirectional Protocol Independent Multicast (BIDIR- 1256 PIM)", RFC 5015, October 2007. 1258 [RFC5135] Wing, D. and T. Eckert, "IP Multicast Requirements for a 1259 Network Address Translator (NAT) and a Network Address 1260 Port Translator (NAPT)", BCP 135, RFC 5135, February 2008. 1262 [RFC5496] Wijnands, IJ., Boers, A., and E. Rosen, "The Reverse Path 1263 Forwarding (RPF) Vector TLV", RFC 5496, March 2009. 1265 16.2. Informative References 1267 [ALT] Farinacci, D., Fuller, V., and D. Meyer, "LISP Alternative 1268 Topology (LISP-ALT)", draft-ietf-lisp-alt-09.txt (work in 1269 progress). 1271 [MLISP] Farinacci, D., Meyer, D., Zwiebel, J., and S. Venaas, 1272 "LISP for Multicast Environments", 1273 draft-farinacci-lisp-multicast-01.txt (work in progress). 1275 [MTRACE] Asaeda, H., Jinmei, T., Fenner, W., and S. Casner, "Mtrace 1276 Version 2: Traceroute Facility for IP Multicast", 1277 draft-ietf-mboned-mtrace-v2-08.txt (work in progress). 1279 Appendix A. Document Change Log 1281 A.1. Changes to draft-ietf-lisp-multicast-12.txt 1283 o Posted January 2012. 1285 o Added more security disclaimers to the Security Considerations 1286 section. 1288 A.2. Changes to draft-ietf-lisp-multicast-11.txt 1290 o Posted November 2011. 1292 o Added Stig text to Security Considerations section to reflect 1293 comments from IESG review comment from Stephen Farrell. 1295 o Changed how an unicast PIM join gets sent. Do not use an ECM or 1296 else an instance-ID cannot be included in the join. So go back to 1297 what we had where the unicast PIM join is encapsulated in a 4341 1298 UDP packet. 1300 A.3. Changes to draft-ietf-lisp-multicast-10.txt 1302 o Posted second half of October 2011. Changes to reflect IESG 1303 review comments from Stephen Farrell. 1305 A.4. Changes to draft-ietf-lisp-multicast-09.txt 1307 o Posted October 2011. Changes to reflect IESG review comments from 1308 Ralph Droms and Kathleen Moriarty. 1310 A.5. Changes to draft-ietf-lisp-multicast-08.txt 1312 o Posted September 2011. Minor editorial changes from Jari's 1313 commentary. 1315 A.6. Changes to draft-ietf-lisp-multicast-07.txt 1317 o Posted July 2011. Fixing IDnits errors. 1319 A.7. Changes to draft-ietf-lisp-multicast-06.txt 1321 o Posted June 2011 to complete working group last call. 1323 o Added paragraph to section 8.1.2 based on Jesus comment about 1324 making it more clear what happens when two (S-EID,G) trees use the 1325 same (RLOC,G) tree. 1327 o Make more references to [INTWORK] when mentioning uPITRs and 1328 uPETRs. 1330 o Made many changes based on editorial and wordsmithing comments 1331 from Alia. 1333 A.8. Changes to draft-ietf-lisp-multicast-05.txt 1335 o Posted April 2011 to reset expiration timer. 1337 o Updated references. 1339 A.9. Changes to draft-ietf-lisp-multicast-04.txt 1341 o Posted October 2010 to reset expiration timer. 1343 o Updated references. 1345 A.10. Changes to draft-ietf-lisp-multicast-03.txt 1347 o Posted April 2010. 1349 o Added section 8.1.2 to address Joel Halpern's comment about 1350 receiver sites joining the same source site via 2 different RLOCs, 1351 each being a separate ITR. 1353 o Change all occurences of "mPTR" to "mPETR" to become more 1354 consistent with uPITRs and uPETRs described in [INTWORK]. That 1355 is, an mPETR is a LISP multicast router that decapsulates 1356 multicast packets that are encapsulated to it by ITRs in multicast 1357 source sites. 1359 o Add clarifications in section 9 about how homogeneous multicast 1360 encapsulation should occur. As well as describing in this 1361 section, how to deal with mixed-locator sets to avoid 1362 heterogeneous encapsulation. 1364 o Introduce concept of mPITRs to help reduce (S-EID,G) to the edges 1365 of LISP global multicast network. 1367 A.11. Changes to draft-ietf-lisp-multicast-02.txt 1369 o Posted September 2009. 1371 o Added Document Change Log appendix. 1373 o Specify that the LISP Encapsulated Control Message be used for 1374 unicasting PIM Join/Prune messages from ETRs to ITRs. 1376 A.12. Changes to draft-ietf-lisp-multicast-01.txt 1378 o Posted November 2008. 1380 o Specified that PIM Join/Prune unicast messages that get sent from 1381 ETRs to ITRs of a source multicast site get LISP encapsulated in 1382 destination UDP port 4342. 1384 o Add multiple RLOCs per ITR per Yiqun's comments. 1386 o Indicate how static RPs can be used when LISP is run using Bidir- 1387 PIM in the core. 1389 o Editorial changes per Liming comments. 1391 o Add Mttrace Considersations section. 1393 A.13. Changes to draft-ietf-lisp-multicast-00.txt 1395 o Posted April 2008. 1397 o Renamed from draft-farinacci-lisp-multicast-01.txt. 1399 Authors' Addresses 1401 Dino Farinacci 1402 cisco Systems 1403 Tasman Drive 1404 San Jose, CA 1405 USA 1407 Email: dino@cisco.com 1409 Dave Meyer 1410 cisco Systems 1411 Tasman Drive 1412 San Jose, CA 1413 USA 1415 Email: dmm@cisco.com 1417 John Zwiebel 1418 cisco Systems 1419 Tasman Drive 1420 San Jose, CA 1421 USA 1423 Email: jzwiebel@cisco.com 1425 Stig Venaas 1426 cisco Systems 1427 Tasman Drive 1428 San Jose, CA 1429 USA 1431 Email: stig@cisco.com