idnits 2.17.1 draft-ietf-lisp-multicast-13.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 (February 7, 2012) is 4455 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for intended status: Experimental ---------------------------------------------------------------------------- == Outdated reference: A later version (-06) exists of draft-ietf-lisp-interworking-02 == Outdated reference: A later version (-24) exists of draft-ietf-lisp-16 ** Obsolete normative reference: RFC 4601 (Obsoleted by RFC 7761) == Outdated reference: A later version (-10) exists of draft-ietf-lisp-alt-09 == Outdated reference: A later version (-26) exists of draft-ietf-mboned-mtrace-v2-08 Summary: 1 error (**), 0 flaws (~~), 5 warnings (==), 1 comment (--).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: August 10, 2012 S. Venaas 6 cisco Systems 7 February 7, 2012 9 LISP for Multicast Environments 10 draft-ietf-lisp-multicast-13 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 August 10, 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-13.txt . . . . . . . 37 86 A.2. Changes to draft-ietf-lisp-multicast-12.txt . . . . . . . 37 87 A.3. Changes to draft-ietf-lisp-multicast-11.txt . . . . . . . 37 88 A.4. Changes to draft-ietf-lisp-multicast-10.txt . . . . . . . 37 89 A.5. Changes to draft-ietf-lisp-multicast-09.txt . . . . . . . 37 90 A.6. Changes to draft-ietf-lisp-multicast-08.txt . . . . . . . 37 91 A.7. Changes to draft-ietf-lisp-multicast-07.txt . . . . . . . 37 92 A.8. Changes to draft-ietf-lisp-multicast-06.txt . . . . . . . 38 93 A.9. Changes to draft-ietf-lisp-multicast-05.txt . . . . . . . 38 94 A.10. Changes to draft-ietf-lisp-multicast-04.txt . . . . . . . 38 95 A.11. Changes to draft-ietf-lisp-multicast-03.txt . . . . . . . 38 96 A.12. Changes to draft-ietf-lisp-multicast-02.txt . . . . . . . 39 97 A.13. Changes to draft-ietf-lisp-multicast-01.txt . . . . . . . 39 98 A.14. 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 only operational (and not protocol) changes for 175 PIM-ASM [RFC4601], MSDP [RFC3618], and PIM-SSM [RFC4607]. Bidir-PIM 176 [RFC5015], which typically does not run in an inter-domain 177 environment is not addressed in depth in this version of the 178 specification. 180 Also, the current version of this specification does not describe 181 multicast-based Traffic Engineering relative to the TE-ITR (Traffic 182 Engineering based Ingress Tunnel Router) and TE-ETR (Traffic 183 Engineering based Egress Tunnel Router) descriptions in [LISP]. 184 Futher work is also needed to determine the detailed behavior for 185 multicast proxy ITRs (mPITRs) (Section 9.1.3), mtrace (Section 12), 186 and locator reachability (Section 6). Finally, further deployment 187 and experimentation would be useful to understand the real-life 188 performance of the LISP-Multicast solution. For instance, the design 189 optimizes for minimal state and control traffic in the core, but can 190 in some cases cause extra multicast traffic to be sent Section 8.1.2. 192 3. Definition of Terms 194 The terminology in this section is consistent with the definitions in 195 [LISP] but is extended specifically to deal with the application of 196 the terminology to multicast routing. 198 LISP-Multicast: a reference to the design in this specification. 199 That is, when any site that is participating in multicast 200 communication has been upgraded to be a LISP site, the operation 201 of control-plane and data-plane protocols is considered part of 202 the LISP-Multicast architecture. 204 Endpoint ID (EID): a 32-bit (for IPv4) or 128-bit (for IPv6) value 205 used in the source address field of the first (most inner) LISP 206 header of a multicast packet. The host obtains a destination 207 group address the same way it obtains one today, as it would when 208 it is a non-LISP site. The source EID is obtained via existing 209 mechanisms used to set a host's "local" IP address. An EID is 210 allocated to a host from an EID prefix block associated with the 211 site the host is located in. An EID can be used by a host to 212 refer to another host, as when it joins an SSM (S-EID,G) route 213 using IGMP version 3 [RFC4604]. LISP uses Provider Independent 214 (PI) blocks for EIDs; such EIDs MUST NOT be used as LISP RLOCs. 215 Note that EID blocks may be assigned in a hierarchical manner, 216 independent of the network topology, to facilitate scaling of the 217 mapping database. In addition, an EID block assigned to a site 218 may have site-local structure (subnetting) for routing within the 219 site; this structure is not visible to the global routing system. 221 Routing Locator (RLOC): the IPv4 or IPv6 address of an ingress 222 tunnel router (ITR), the router in the multicast source host's 223 site that encapsulates multicast packets. It is the output of a 224 EID-to-RLOC mapping lookup. An EID maps to one or more RLOCs. 225 Typically, RLOCs are numbered from topologically-aggregatable 226 blocks that are assigned to a site at each point to which it 227 attaches to the global Internet; where the topology is defined by 228 the connectivity of provider networks, RLOCs can be thought of as 229 Provider Assigned (PA) addresses. Multiple RLOCs can be assigned 230 to the same ITR device or to multiple ITR devices at a site. 232 Ingress Tunnel Router (ITR): a router which accepts an IP multicast 233 packet with a single IP header (more precisely, an IP packet that 234 does not contain a LISP header). The router treats this "inner" 235 IP destination multicast address opaquely so it doesn't need to 236 perform a map lookup on the group address because it is 237 topologically insignificant. The router then prepends an "outer" 238 IP header with one of its globally-routable RLOCs as the source 239 address field. This RLOC is known to other multicast receiver 240 sites which have used the mapping database to join a multicast 241 tree for which the ITR is the root. In general, an ITR receives 242 IP packets from site end systems on one side and sends LISP- 243 encapsulated multicast IP packets out all external interfaces 244 which have been joined. 246 An ITR would receive a multicast packet from a source inside of 247 its site when 1) it is on the path from the multicast source to 248 internally joined receivers, or 2) when it is on the path from the 249 multicast source to externally joined receivers. 251 Egress Tunnel Router (ETR): a router that is on the path from a 252 multicast source host in another site to a multicast receiver in 253 its own site. An ETR accepts a PIM Join/Prune message from a site 254 internal PIM router destined for the source's EID in the multicast 255 source site. The ETR maps the source EID in the Join/Prune 256 message to an RLOC address based on the EID-to-RLOC mapping. This 257 sets up the ETR to accept multicast encapsulated packets from the 258 ITR in the source multicast site. A multicast ETR decapsulates 259 multicast encapsulated packets and replicates them on interfaces 260 leading to internal receivers. 262 xTR: is a reference to an ITR or ETR when direction of data flow is 263 not part of the context description. xTR refers to the router that 264 is the tunnel endpoint. Used synonymously with the term "Tunnel 265 Router". For example, "An xTR can be located at the Customer Edge 266 (CE) router", meaning both ITR and ETR functionality can be at the 267 CE router. 269 LISP Header: a term used in this document to refer to the outer 270 IPv4 or IPv6 header, a UDP header, and a LISP header. An ITR 271 prepends headers and an ETR strips headers. A LISP encapsulated 272 multicast packet will have an "inner" header with the source EID 273 in the source field; an "outer" header with the source RLOC in the 274 source field: and the same globally unique group address in the 275 destination field of both the inner and outer header. 277 (S,G) State: the formal definition is in the PIM Sparse Mode 278 [RFC4601] specification. For this specification, the term is used 279 generally to refer to multicast state. Based on its topological 280 location, the (S,G) state resides in routers can be either 281 (S-EID,G) state (at a location where the (S,G) state resides) or 282 (S-RLOC,G) state (in the Internet core). 284 (S-EID,G) State: refers to multicast state in multicast source and 285 receiver sites where S-EID is the IP address of the multicast 286 source host (its EID). An S-EID can appear in an IGMPv3 report, 287 an MSDP SA message or a PIM Join/Prune message that travels inside 288 of a site. 290 (S-RLOC,G) State: refers to multicast state in the core where S is 291 a source locator (the IP address of a multicast ITR) of a site 292 with a multicast source. The (S-RLOC,G) is mapped from (S-EID,G) 293 entry by doing a mapping database lookup for the EID prefix that 294 S-EID maps to. An S-RLOC can appear in a PIM Join/Prune message 295 when it travels from an ETR to an ITR over the Internet core. 297 uLISP Site: a unicast only LISP site according to [LISP] which has 298 not deployed the procedures of this specification and therefore, 299 for multicast purposes, follows the procedures from Section 9. A 300 uLISP site can be a traditional multicast site. 302 LISP Site: a unicast LISP site (uLISP Site) that is also multicast 303 capable according to the procedures in this specification. 305 mPETR: this is a multicast proxy-ETR that is responsible for 306 advertising a very coarse EID prefix which non-LISP and uLISP 307 sites can target their (S-EID,G) PIM Join/Prune message to. mPETRs 308 are used so LISP source multicast sites can send multicast packets 309 using source addresses from the EID namespace. mPETRs act as Proxy 310 ETRs for supporting multicast routing in a LISP infrastructure. 311 It is likely an uPITR [INTWORK] and a mPETR will be co-located 312 since the single device advertises a coarse EID-prefix in the 313 underlying unicast routing system. 315 Mixed Locator-Sets: this is a locator-set for a LISP database 316 mapping entry where the RLOC addresses in the locator-set are in 317 both IPv4 and IPv6 format. 319 Unicast Encapsulated PIM Join/Prune Message: this is a standard PIM 320 Join/Prune message (LISP encapsulated with destination UDP port 321 4341) which is sent by ETRs at multicast receiver sites to an ITR 322 at a multicast source site. This message is sent periodically as 323 long as there are interfaces in the OIF-list for the (S-EID,G) 324 entry the ETR is joining for. 326 OIF-list: this is notation to describe the outgoing interface list 327 a multicast router stores per multicast routing table entry so it 328 knows what interfaces to replicate multicast packets on. 330 RPF: Reverse Path Forwarding is a procedure used by multicast 331 routers. A router will accept a multicast packet for forwarding 332 if the packet was received on the path that the router would use 333 to forward unicast packets to the multicast packet's source. 335 4. Basic Overview 337 LISP, when used for unicast routing, increases the site's ability to 338 control ingress traffic flows. Egress traffic flows are controlled 339 by the IGP in the source site. For multicast, the IGP coupled with 340 PIM can decide which path multicast packets ingress. By using the 341 traffic engineering features of LISP [LISP], a multicast source site 342 can control the egress of its multicast traffic. By controlling the 343 priorities of locators from a mapping database entry, a source 344 multicast site can control which way multicast receiver sites join to 345 the source site. 347 At this point in time, there is no requirement for different locator- 348 sets, priority, and weight policies for multicast than there is for 349 unicast. However, when traffic engineering policies are different 350 for unicast versus multicast flows, it will be desirable to use 351 multicast-based priority and weight values in Map-Reply messages. 353 The fundamental multicast forwarding model is to encapsulate a 354 multicast packet into another multicast packet. An ITR will 355 encapsulate multicast packets received from sources that it serves in 356 a LISP multicast header. The destination group address from the 357 inner header is copied to the destination address of the outer 358 header. The inner source address is the EID of the multicast source 359 host and the outer source address is the RLOC of the encapsulating 360 ITR. 362 The LISP-Multicast architecture will follow this high-level protocol 363 and operational sequence: 365 1. Receiver hosts in multicast sites will join multicast content the 366 way they do today, they use IGMP. When they use IGMPv3 where 367 they specify source addresses, they use source EIDs, that is they 368 join (S-EID,G). If the multicast source is external to this 369 receiver site, the PIM Join/Prune message flows toward the ETRs, 370 finding the shortest exit (that is the closest exit for the Join/ 371 Prune message and the closest entrance for the multicast packet 372 to the receiver). 374 2. The ETR does a mapping database lookup for S-EID. If the mapping 375 is cached from a previous lookup (from either a previous Join/ 376 Prune for the source multicast site or a unicast packet that went 377 to the site), it will use the RLOC information from the mapping. 378 The ETR will use the same priority and weighting mechanism as for 379 unicast. So the source site can decide which way multicast 380 packets egress. 382 3. The ETR will build two PIM Join/Prune messages, one that contains 383 a (S-EID,G) entry that is unicast to the ITR that matches the 384 RLOC the ETR selects, and the other which contains a (S-RLOC,G) 385 entry so the core network can create multicast state from this 386 ETR to the ITR. 388 4. When the ITR gets the unicast Join/Prune message (see Section 3 389 for formal definition), it will process (S-EID,G) entries in the 390 message and propagate them inside of the site where it has 391 explicit routing information for EIDs via the IGP. When the ITR 392 receives the (S-RLOC,G) PIM Join/Prune message it will process it 393 like any other join it would get in today's Internet. The S-RLOC 394 address is the IP address of this ITR. 396 5. At this point there is (S-EID,G) state from the joining host in 397 the receiver multicast site to the ETR of the receiver multicast 398 site. There is (S-RLOC,G) state across the core network from the 399 ETR of the multicast receiver site to the ITR in the multicast 400 source site and (S-EID,G) state in the source multicast site. 401 Note, the (S-EID,G) state is the same S-EID in each multicast 402 site. As other ETRs join the same multicast tree, they can join 403 through the same ITR (in which case the packet replication is 404 done in the core) or a different ITR (in which case the packet 405 replication is done at the source site). 407 6. When a packet is originated by the multicast host in the source 408 site, the packet will flow to one or more ITRs which will prepend 409 a LISP header. By copying the group address to the outer 410 destination address field, the ITR insert its own locator address 411 in the outer source address field. The ITR will look at its 412 (S-RLOC,G) state, where S-RLOC is its own locator address, and 413 replicate the packet on each interface a (S-RLOC,G) joined was 414 received on. The core has (S-RLOC,G) so where fanout occurs to 415 multiple sites, a core router will do packet replication. 417 7. When either the source site or the core replicates the packet, 418 the ETR will receive a LISP packet with a destination group 419 address. It will decapsulate packets because it has receivers 420 for the group. Otherwise, it would have not received the packets 421 because it would not have joined. The ETR decapsulates and does 422 a (S-EID,G) lookup in its multicast FIB to forward packets out 423 one or more interfaces to forward the packet to internal 424 receivers. 426 This architecture is consistent and scalable with the architecture 427 presented in [LISP] where multicast state in the core operates on 428 locators and multicast state at the sites operates on EIDs. 430 Alternatively, [LISP] also has a mechanism where (S-EID,G) state can 431 reside in the core through the use of RPF-vectors [RFC5496] in PIM 432 Join/Prune messages. However, few PIM implementations support RPF 433 vectors and LISP should avoid S-EID state in the core. See Section 5 434 for details. 436 However, some observations can be made on the algorithm above. The 437 control plane can scale but at the expense of sending data to sites 438 which may have not joined the distribution tree where the 439 encapsulated data is being delivered. For example, one site joins 440 (S-EID1,G) and another site joins (S-EID2,G). Both EIDs are in the 441 same multicast source site. Both multicast receiver sites join to 442 the same ITR with state (S-RLOC,G) where S-RLOC is the RLOC for the 443 ITR. The ITR joins both (S-EID1,G) and (S-EID2,G) inside of the 444 site. The ITR receives (S-RLOC,G) joins and populates the OIF-list 445 state for it. Since both (S-EID1,G) and (S-EID2, G) map to the one 446 (S-RLOC,G) packets will be delivered by the core to both multicast 447 receiver sites even though each have joined a single source-based 448 distribution tree. This behavior is a consequence of the many-to-one 449 mapping between S-EIDs and a S-RLOC. 451 There is a possible solution to this problem which reduces the number 452 of many-to-one occurrences of (S-EID,G) entries aggregating into a 453 single (S-RLOC,G) entry. If a physical ITR can be assigned multiple 454 RLOC addresses and these addresses are advertised in mapping database 455 entries, then ETRs at receiver sites have more RLOC address options 456 and therefore can join different (RLOC,G) entries for each (S-EID,G) 457 entry joined at the receiver site. It would not scale to have a one- 458 to-one relationship between the number of S-EID sources at a source 459 site and the number of RLOCs assigned to all ITRs at the site, but 460 "n" can reduce to a smaller number in the "n-to-1" relationship. And 461 in turn, reduce the opportunity for data packets to be delivered to 462 sites for groups not joined. 464 5. Source Addresses versus Group Addresses 466 Multicast group addresses don't have to be associated with either the 467 EID or RLOC namespace. They actually are a namespace of their own 468 that can be treated as logical with relatively opaque allocation. 469 So, by their nature, they don't detract from an incremental 470 deployment of LISP-Multicast. 472 As for source addresses, as in the unicast LISP scenario, there is a 473 decoupling of identification from location. In a LISP site, packets 474 are originated from hosts using their allocated EIDs. EID addresses 475 are used to identify the host as well as where in the site's topology 476 the host resides but not how and where it is attached to the 477 Internet. 479 Therefore, when multicast distribution tree state is created anywhere 480 in the network on the path from any multicast receiver to a multicast 481 source, EID state is maintained at the source and receiver multicast 482 sites, and RLOC state is maintained in the core. That is, a 483 multicast distribution tree will be represented as a 3-tuple of 484 {(S-EID,G) (S-RLOC,G) (S-EID,G)} where the first element of the 485 3-tuple is the state stored in routers from the source to one or more 486 ITRs in the source multicast site, the second element of the 3-tuple 487 is the state stored in routers downstream of the ITR, in the core, to 488 all LISP receiver multicast sites, and the third element in the 489 3-tuple is the state stored in the routers downstream of each ETR, in 490 each receiver multicast site, reaching each receiver. Note that 491 (S-EID,G) is the same in both the source and receiver multicast 492 sites. 494 The concatenation/mapping from the first element to the second 495 element of the 3-tuples is done by the ITR and from the second 496 element to the third element is done at the ETRs. 498 6. Locator Reachability Implications on LISP-Multicast 500 Multicast state as it is stored in the core is always (S,G) state as 501 it exists today or (S-RLOC,G) state as it will exist when LISP sites 502 are deployed. The core routers cannot distinguish one from the 503 other. They don't need to because it is state that RPFs against the 504 core routing tables in the RLOC namespace. The difference is where 505 the root of the distribution tree for a particular source is. In the 506 traditional multicast core, the source S is the source host's IP 507 address. For LISP-Multicast the source S is a single ITR of the 508 multicast source site. 510 An ITR is selected based on the LISP EID-to-RLOC mapping used when an 511 ETR propagates a PIM Join/Prune message out of a receiver multicast 512 site. The selection is based on the same algorithm an ITR would use 513 to select an ETR when sending a unicast packet to the site. In the 514 unicast case, the ITR can change on a per-packet basis depending on 515 the reachability of the ETR. So an ITR can change relatively easily 516 using local reachability state. However, in the multicast case, when 517 an ITR goes unreachable, new distribution tree state must be built 518 because the encapsulating root has changed. This is more significant 519 than an RPF-change event, where any router would typically locally 520 change its RPF-interface for its existing tree state. But when an 521 encapsulating LISP-Multicast ITR goes unreachable, new distribution 522 state must be rebuilt and reflect the new encapsulator. Therefore, 523 when an ITR goes unreachable, all ETRs that are currently joined to 524 that ITR will have to trigger a new Join/Prune message for (S-RLOC,G) 525 to the new ITR as well as send a unicast encapsulated Join/Prune 526 message telling the new ITR which (S-EID,G) is being joined. 528 This issue can be mitigated by using anycast addressing for the ITRs 529 so the problem does reduce to an RPF change in the core, but still 530 requires a unicast encapsulated Join/Prune message to tell the new 531 ITR about (S-EID,G). The problem with this approach is that the ETR 532 really doesn't know when the ITR has changed so the new anycast ITR 533 will get the (S-EID,G) state only when the ETR sends it the next time 534 during its periodic sending procedures. 536 7. Multicast Protocol Changes 538 A number of protocols are used today for inter-domain multicast 539 routing: 541 IGMPv1-v3, MLDv1-v2: These protocols [RFC4604] do not require any 542 changes for LISP-Multicast for two reasons. One being that they 543 are link-local and not used over site boundaries and second, they 544 advertise group addresses that don't need translation. Where 545 source addresses are supplied in IGMPv3 and MLDv2 messages, they 546 are semantically regarded as EIDs and don't need to be converted 547 to RLOCs until the multicast tree-building protocol, such as PIM, 548 is received by the ETR at the site boundary. Addresses used for 549 IGMP and MLD come out of the source site's allocated addresses 550 which are therefore from the EID namespace. 552 MBGP: Even though MBGP [RFC4760] is not a multicast routing 553 protocol, it is used to find multicast sources when the unicast 554 BGP peering topology and the multicast MBGP peering topology are 555 not congruent. When MBGP is used in a LISP-Multicast environment, 556 the prefixes which are advertised are from the RLOC namespace. 557 This allows receiver multicast sites to find a path to the source 558 multicast site's ITRs. MBGP peering addresses will be from the 559 RLOC namespace. There are no MBGP protocol changes required to 560 support LISP-Multicast. 562 MSDP: MSDP [RFC3618] is used to announce active multicast sources 563 to other routing domains (or LISP sites). The announcements come 564 from the PIM Rendezvous Points (RPs) from sites where there are 565 active multicast sources sending to various groups. In the 566 context of LISP-Multicast, the source addresses advertised in MSDP 567 will semantically be from the EID namespace since they describe 568 the identity of a source multicast host. It will be true that the 569 state stored in MSDP caches from core routers will be from the EID 570 namespace. An RP address inside of site will be from the EID 571 namespace so it can be advertised and reached by internal unicast 572 routing mechanism. However, for MSDP peer-RPF checking to work 573 properly across sites, the RP addresses must be converted or 574 mapped into a routable address that is advertised and maintained 575 in the BGP routing tables in the core. MSDP peering addresses can 576 come out of either the EID or a routable address namespace. And 577 the choice can be made unilaterally because the ITR at the site 578 will determine which namespace the destination peer address is out 579 of by looking in the mapping database service. There are no MSDP 580 protocol changes required to support LISP-Multicast. 582 PIM-SSM: In the simplest form of distribution tree building, when 583 PIM operates in SSM mode [RFC4607], a source distribution tree is 584 built and maintained across site boundaries. In this case, there 585 is a small modification to how PIM Join/Prune messages are sent by 586 the LISP-Multicast component. No modifications to any message 587 format, but to support taking a Join/Prune message originated 588 inside of a LISP site with embedded addresses from the EID 589 namespace and converting them to addresses from the RLOC namespace 590 when the Join/Prune message crosses a site boundary. This is 591 similar to the requirements documented in [RFC5135]. 593 PIM-Bidir: Bidirectional PIM [RFC5015] is typically run inside of a 594 routing domain, but if deployed in an inter-domain environment, 595 one would have to decide if the RP address of the shared-tree 596 would be from the EID namespace or the RLOC namespace. If the RP 597 resides in a site-based router, then the RP address is from the 598 EID namespace. If the RP resides in the core where RLOC addresses 599 are routed, then the RP address is from the RLOC namespace. This 600 could be easily distinguishable if the EID address were well-known 601 address allocation block from the RLOC namespace. Also, when 602 using Embedded-RP for RP determination [RFC3956], the format of 603 the group address could indicate the namespace the RP address is 604 from. However, refer to Section 10 for considerations core 605 routers need to make when using Embedded-RP IPv6 group addresses. 606 When using Bidir-PIM for inter-domain multicast routing, it is 607 recommended to use staticly configured RPs. Allowing core routers 608 to associate a Bidir group's RP address with an ITR's RLOC 609 address. And site routers to associate the Bidir group's RP 610 address as an EID address. With respect to DF-election in Bidir 611 PIM, no changes are required since all messaging and addressing is 612 link-local. 614 PIM-ASM: The ASM mode of PIM [RFC4601], the most popular form of 615 PIM, is deployed in the Internet today is by having shared-trees 616 within a site and using source-trees across sites. By the use of 617 MSDP and PIM-SSM techniques described above, multicast 618 connectivity can occur across LISP sites. Having said that, that 619 means there are no special actions required for processing (*,G) 620 or (S,G,R) Join/Prune messages since they all operate against the 621 shared-tree which is site resident. Just like with ASM, there is 622 no (*,G) in the core when LISP-Multicast is in use. This is also 623 true for the RP-mapping mechanisms Auto-RP and BSR. 625 Based on the protocol description above, the conclusion is that there 626 are no protocol message format changes, just a translation function 627 performed at the control-plane. This will make for an easier and 628 faster transition for LISP since fewer components in the network have 629 to change. 631 It should also be stated just like it is in [LISP] that no host 632 changes, whatsoever, are required to have a multicast source host 633 send multicast packets and for a multicast receiver host to receive 634 multicast packets. 636 8. LISP-Multicast Data-Plane Architecture 638 The LISP-Multicast data-plane operation conforms to the operation and 639 packet formats specified in [LISP]. However, encapsulating a 640 multicast packet from an ITR is a much simpler process. The process 641 is simply to copy the inner group address to the outer destination 642 address. And to have the ITR use its own IP address (its RLOC) as 643 the source address. The process is simpler for multicast because 644 there is no EID-to-RLOC mapping lookup performed during packet 645 forwarding. 647 In the decapsulation case, the ETR simply removes the outer header 648 and performs a multicast routing table lookup on the inner header 649 (S-EID,G) addresses. Then the OIF-list for the (S-EID,G) entry is 650 used to replicate the packet on site-facing interfaces leading to 651 multicast receiver hosts. 653 There is no Data-Probe logic for ETRs as there can be in the unicast 654 forwarding case. 656 8.1. ITR Forwarding Procedure 658 The following procedure is used by an ITR, when it receives a 659 multicast packet from a source inside of its site: 661 1. A multicast data packet sent by a host in a LISP site will have 662 the source address equal to the host's EID and the destination 663 address equal to the group address of the multicast group. It is 664 assumed the group information is obtained by current methods. 665 The same is true for a multicast receiver to obtain the source 666 and group address of a multicast flow. 668 2. When the ITR receives a multicast packet, it will have both S-EID 669 state and S-RLOC state stored. Since the packet was received on 670 a site-facing interface, the RPF lookup is based on the S-EID 671 state. If the RPF check succeeds, then the OIF-list contains 672 interfaces that are site-facing and external-facing. For the 673 site-facing interfaces, no LISP header is prepended. For the 674 external-facing interfaces a LISP header is prepended. When the 675 ITR prepends a LISP header, it uses its own RLOC address as the 676 source address and copies the group address supplied by the IP 677 header the host built as the outer destination address. 679 8.1.1. Multiple RLOCs for an ITR 681 Typically, an ITR will have a single RLOC address but in some cases 682 there could be multiple RLOC addresses assigned from either the same 683 or different service providers. In this case when (S-RLOC,G) Join/ 684 Prune messages are received for each RLOC, there is a OIF-list 685 merging action that must take place. Therefore, when a packet is 686 received from a site-facing interface that matches on a (S-EID,G) 687 entry, the interfaces of the OIF-list from all (RLOC,G) entries 688 joined to the ITR as well as the site-facing OIF-list joined for 689 (S-EID,G) must be part be included in packet replication. In 690 addition to replicating for all types of OIF-lists, each oif entry 691 must be tagged with the RLOC address, so encapsulation uses the outer 692 source address for the RLOC joined. 694 8.1.2. Multiple ITRs for a LISP Source Site 696 Note when ETRs from different multicast receiver sites receive 697 (S-EID,G) joins, they may select a different S-RLOC for a multicast 698 source site due to policy (the multicast ITR can return different 699 multicast priority and weight values per ETR Map-Request). In this 700 case, the same (S-EID,G) is being realized by different (S-RLOC,G) 701 state in the core. This will not result in duplicate packets because 702 each ITR in the multicast source site will choose their own RLOC for 703 the source address for encapsulated multicast traffic. The RLOC 704 addresses are the ones joined by remote multicast ETRs. 706 When different (S-EID,G) traffic is combined into a single (RLOC,G) 707 core distribution tree, this may cause traffic to go to a receiver 708 multicast site when it does not need to. This happens when one 709 receiver multicast site joins (S1-EID,Gi) through a core distribution 710 tree of (RLOC1,Gi) and another multicast receiver site joins (S2- 711 EID,Gi) through the same core distribution tree of (RLOC1,Gi). When 712 ETRs decapsulate such traffic, they should know from their local 713 (S-EID,G) state if the packet should be forwarded. If there is no 714 (S-EID,G) state that matches the inner packet header, the packet is 715 discarded. 717 8.2. ETR Forwarding Procedure 719 The following procedure is used by an ETR, when it receives a 720 multicast packet from a source outside of its site: 722 1. When a multicast data packet is received by an ETR on an 723 external-facing interface, it will do an RPF lookup on the S-RLOC 724 state it has stored. If the RPF check succeeds, the interfaces 725 from the OIF-list are used for replication to interfaces that are 726 site-facing as well as interfaces that are external-facing (this 727 ETR can also be a transit multicast router for receivers outside 728 of its site). When the packet is to be replicated for an 729 external-facing interface, the LISP encapsulation header are not 730 stripped. When the packet is replicated for a site-facing 731 interface, the encapsulation header is stripped. 733 2. The packet without a LISP header is now forwarded down the 734 (S-EID,G) distribution tree in the receiver multicast site. 736 8.3. Replication Locations 738 Multicast packet replication can happen in the following topological 739 locations: 741 o In an IGP multicast router inside a site which operates on S-EIDs. 743 o In a transit multicast router inside of the core which operates on 744 S-RLOCs. 746 o At one or more ETR routers depending on the path a Join/Prune 747 message exits a receiver multicast site. 749 o At one or more ITR routers in a source multicast site depending on 750 what priorities are returned in a Map-Reply to receiver multicast 751 sites. 753 In the last case the source multicast site can do replication rather 754 than having a single exit from the site. But this only can occur 755 when the priorities in the Map-Reply are modified for different 756 receiver multicast site so that the PIM Join/Prune messages arrive at 757 different ITRs. 759 This policy technique, also used in [ALT] for unicast, is useful for 760 multicast to mitigate the problems of changing distribution tree 761 state as discussed in Section 6. 763 9. LISP-Multicast Interworking 765 This section will describe the multicast corollary to [INTWORK] which 766 describes the interworking of multicast routing among LISP and non- 767 LISP sites. 769 9.1. LISP and non-LISP Mixed Sites 771 Since multicast communication can involve more than two entities to 772 communicate together, the combinations of interworking scenarios are 773 more involved. However, the state maintained for distribution trees 774 at the sites is the same regardless of whether or not the site is 775 LISP enabled or not. So most of the implications are in the core 776 with respect to storing routable EID prefixes from either PA or PI 777 blocks. 779 Before enumerating the multicast interworking scenarios, let's define 780 3 deployment states of a site: 782 o A non-LISP site which will run PIM-SSM or PIM-ASM with MSDP as it 783 does today. The addresses for the site are globally routable. 785 o A site that deploys LISP for unicast routing. The addresses for 786 the site are not globally routable. Let's define the name for 787 this type of site as a uLISP site. 789 o A site that deploys LISP for both unicast and multicast routing. 790 The addresses for the site are not globally routable. Let's 791 define the name for this type of site as a LISP-Multicast site. 793 What will not be considered is a LISP site enabled for multicast 794 purposes only but do consider a uLISP site as documented in 795 [INTWORK]. In this section there is no discussion how a LISP site 796 sends multicast packets when all receiver sites are LISP-Multicast 797 enabled; that has been discussed in previous sections. 799 The following scenarios exist to make LISP-Multicast sites interwork 800 with non-LISP-Multicast sites: 802 1. A LISP site must be able to send multicast packets to receiver 803 sites which are a mix of non-LISP sites and uLISP sites. 805 2. A non-LISP site must be able to send multicast packets to 806 receiver sites which are a mix of non-LISP sites and uLISP sites. 808 3. A non-LISP site must be able to send multicast packets to 809 receiver sites which are a mix of LISP sites, uLISP sites, and 810 non-LISP sites. 812 4. A uLISP site must be able to send multicast packets to receiver 813 sites which are a mix of LISP sites, uLISP sites, and non-LISP 814 sites. 816 5. A LISP site must be able to send multicast packets to receiver 817 sites which are a mix of LISP sites, uLISP sites, and non-LISP 818 sites. 820 9.1.1. LISP Source Site to non-LISP Receiver Sites 822 In the first scenario, a site is LISP capable for both unicast and 823 multicast traffic and as such operates on EIDs. Therefore there is a 824 possibility that the EID prefix block is not routable in the core. 825 For LISP receiver multicast sites this isn't a problem but for non- 826 LISP or uLISP receiver multicast sites, when a PIM Join/Prune message 827 is received by the edge router, it has no route to propagate the 828 Join/Prune message out of the site. This is no different than the 829 unicast case that LISP-NAT in [INTWORK] solves. 831 LISP-NAT allows a unicast packet that exits a LISP site to get its 832 source address mapped to a globally routable address before the ITR 833 realizes that it should not encapsulate the packet destined to a non- 834 LISP site. For a multicast packet to leave a LISP site, distribution 835 tree state needs to be built so the ITR can know where to send the 836 packet. So the receiver multicast sites need to know about the 837 multicast source host by its routable address and not its EID 838 address. When this is the case, the routable address is the 839 (S-RLOC,G) state that is stored and maintained in the core routers. 840 It is important to note that the routable address for the host cannot 841 be the same as an RLOC for the site because it is desirable for ITRs 842 to process a received PIM Join/Prune message from an external-facing 843 interface to be propagated inside of the site so the site-part of the 844 distribution tree is built. 846 Using a globally routable source address allows non-LISP and uLISP 847 multicast receiver to join, create, and maintain a multicast 848 distribution tree. However, the LISP multicast receiver site will 849 want to perform an EID-to-RLOC mapping table lookup when a PIM Join/ 850 Prune message is received on a site-facing interface. It does this 851 because it wants to find a (S-RLOC,G) entry to Join in the core. So 852 there is a conflict of behavior between the two types of sites. 854 The solution to this problem is the same as when an ITR wants to send 855 a unicast packet to a destination site but needs determine if the 856 site is LISP capable or not. When it is not LISP capable, the ITR 857 does not encapsulate the packet. So for the multicast case, when ETR 858 receives a PIM Join/Prune message for (S-EID,G) state, it will do a 859 mapping table lookup on S-EID. In this case, S-EID is not in the 860 mapping database because the source multicast site is using a 861 routable address and not an EID prefix address. So the ETR knows to 862 simply propagate the PIM Join/Prune message to a external-facing 863 interface without converting the (S-EID,G) because it is an (S,G) 864 where S is routable and reachable via core routing tables. 866 Now that the multicast distribution tree is built and maintained from 867 any non-LISP or uLISP receiver multicast site, the way packet 868 forwarding model is performed can be explained. 870 Since the ITR in the source multicast site has never received a 871 unicast encapsulated PIM Join/Prune message from any ETR in a 872 receiver multicast site, it knows there are no LISP-Multicast 873 receiver sites. Therefore, there is no need for the ITR to 874 encapsulate data. Since it will know a priori (via configuration) 875 that its site's EIDs are not routable (and not registered to the 876 mapping database system), it assumes that the multicast packets from 877 the source host are sent by a routable address. That is, it is the 878 responsibility of the multicast source host's system administrator to 879 ensure that the source host sends multicast traffic using a routable 880 source address. When this happens, the ITR acts simply as a router 881 and forwards the multicast packet like an ordinary multicast router. 883 There is an alternative to using a LISP-NAT scheme just like there is 884 for unicast [INTWORK] forwarding by using Proxy Tunnel Routers 885 (PxTRs). This can work the same way for multicast routing as well, 886 but the difference is that non-LISP and uLISP sites will send PIM 887 Join/Prune messages for (S-EID,G) which make their way in the core to 888 multicast PxTRs. Let's call this use of a PxTR as a "Multicast 889 Proxy-ETR" (or mPETR). Since the mPETRs advertise very coarse EID 890 prefixes, they draw the PIM Join/Prune control traffic making them 891 the target of the distribution tree. To get multicast packets from 892 the LISP source multicast sites, the tree needs to be built on the 893 path from the mPETR to the LISP source multicast site. To make this 894 happen the mPETR acts as a "Proxy ETR" (where in unicast it acts as a 895 "Proxy ITR", or an uPITR [INTWORK]). 897 The existence of mPETRs in the core allows source multicast site ITRs 898 to encapsulate multicast packets according to (S-RLOC,G) state. The 899 (S-RLOC,G) state is built from the mPETRs to the multicast ITRs. The 900 encapsulated multicast packets are decapsulated by mPETRs and then 901 forwarded according to (S-EID,G) state. The (S-EID,G) state is built 902 from the non-LISP and uLISP receiver multicast sites to the mPETRs. 904 9.1.2. Non-LISP Source Site to non-LISP Receiver Sites 906 Clearly non-LISP multicast sites can send multicast packets to non- 907 LISP receiver multicast sites. That is what they do today. However, 908 discussion is required to show how non-LISP multicast sites send 909 multicast packets to uLISP receiver multicast sites. 911 Since uLISP receiver multicast sites are not targets of any (S,G) 912 state, they simply send (S,G) PIM Join/Prune messages toward the non- 913 LISP source multicast site. Since the source multicast site, in this 914 case has not been upgraded to LISP, all multicast source host 915 addresses are routable. So this case is simplified to where a uLISP 916 receiver multicast site looks to the source multicast site as a non- 917 LISP receiver multicast site. 919 9.1.3. Non-LISP Source Site to Any Receiver Site 921 When a non-LISP source multicast site has receivers in either a non- 922 LISP/uLISP site or a LISP site, one needs to decide how the LISP 923 receiver multicast site will attach to the distribution tree. It is 924 known from Section 9.1.2 that non-LISP and uLISP receiver multicast 925 sites can join the distribution tree, but a LISP receiver multicast 926 site ETR will need to know if the source address of the multicast 927 source host is routable or not. It has been shown in Section 9.1.1 928 that an ETR, before it sends a PIM Join/Prune message on an external- 929 facing interface, does a EID-to-RLOC mapping lookup to determine if 930 it should convert the (S,G) state from a PIM Join/Prune message 931 received on a site-facing interface to a (S-RLOC,G). If the lookup 932 fails, the ETR can conclude the source multicast site is a non-LISP 933 site so it simply forwards the Join/Prune message (it also doesn't 934 need to send a unicast encapsulated Join/Prune message because there 935 is no ITR in a non-LISP site and there is namespace continuity 936 between the ETR and source). 938 For a non-LISP source multicast site, (S-EID,G) state could be 939 limited to the edges of the network with the use of multicast proxy- 940 ITRs (mPITRs). The mPITRs can take native, unencapsulated multicast 941 packets from non-LISP source multicast and uLISP sites and 942 encapsulate them to ETRs in receiver multicast sites or to mPETRs 943 that can decapsulate for non-LISP receiver multicast or uLISP sites. 944 The mPITRs are responsible for sending (S-EID,G) joins to the non- 945 LISP source multicast site. To connect the distribution trees 946 together, multicast ETRs will need to be configured with the mPITR's 947 RLOC addresses so they can send both (S-RLOC,G) joins to build a 948 distribution tree to the mPITR as well as for sending unicast joins 949 to mPITRs so they can propogate (S-EID,G) joins into source multicast 950 sites. The use of mPITRs is undergoing more study and is work in 951 progress. 953 9.1.4. Unicast LISP Source Site to Any Receiver Sites 955 In the last section, it was explained how an ETR in a multicast 956 receiver site can determine if a source multicast site is LISP- 957 enabled by looking into the mapping database. When the source 958 multicast site is a uLISP site, it is LISP enabled but the ITR, by 959 definition is not capable of doing multicast encapsulation. So for 960 the purposes of multicast routing, the uLISP source multicast site is 961 treated as non-LISP source multicast site. 963 Non-LISP receiver multicast sites can join distribution trees to a 964 uLISP source multicast site since the source site behaves, from a 965 forwarding perspective, as a non-LISP source site. This is also the 966 case for a uLISP receiver multicast site since the ETR does not have 967 multicast functionality built-in or enabled. 969 Special considerations are required for LISP receiver multicast sites 970 since they think the source multicast site is LISP capable, the ETR 971 cannot know if ITR is LISP-Multicast capable. To solve this problem, 972 each mapping database entry will have a multicast 2-tuple (Mpriority, 973 Mweight) per RLOC [LISP]. When the Mpriority is set to 255, the site 974 is considered not multicast capable. So an ETR in a LISP receiver 975 multicast site can distinguish whether a LISP source multicast site 976 is LISP-Multicast site from a uLISP site. 978 9.1.5. LISP Source Site to Any Receiver Sites 980 When a LISP source multicast site has receivers in LISP, non-LISP, 981 and uLISP receiver multicast sites, it has a conflict about how it 982 sends multicast packets. The ITR can either encapsulate or natively 983 forward multicast packets. Since the receiver multicast sites are 984 heterogeneous in their behavior, one packet forwarding mechanism 985 cannot satisfy both. However, if a LISP receiver multicast site acts 986 like a uLISP site then it could receive packets like a non-LISP 987 receiver multicast site making all receiver multicast sites have 988 homogeneous behavior. However, this poses the following issues: 990 o LISP-NAT techniques with routable addresses would be required in 991 all cases. 993 o Or alternatively, mPETR deployment would be required forcing 994 coarse EID prefix advertisement in the core. 996 o But what is most disturbing is that when all sites that 997 participate are LISP-Multicast sites but then a non-LISP or uLISP 998 site joins the distribution tree, then the existing joined LISP 999 receiver multicast sites would have to change their behavior. 1000 This would create too much dynamic tree-building churn to be a 1001 viable alternative. 1003 So the solution space options are: 1005 1. Make the LISP ITR in the source multicast site send two packets, 1006 one that is encapsulated with (S-RLOC,G) to reach LISP receiver 1007 multicast sites and another that is not encapsulated with 1008 (S-EID,G) to reach non-LISP and uLISP receiver multicast sites. 1010 2. Make the LISP ITR always encapsulate packets with (S-RLOC,G) to 1011 reach LISP-Multicast sites and to reach mPETRs that can 1012 decapsulate and forward (S-EID,G) packets to non-LISP and uLISP 1013 receiver multicast sites. 1015 9.2. LISP Sites with Mixed Address Families 1017 A LISP database mapping entry that describes the locator-set, 1018 Mpriority and Mweight per locator address (RLOC), for an EID prefix 1019 associated with a site could have RLOC addresses in either IPv4 or 1020 IPv6 format. When a mapping entry has a mix of RLOC formatted 1021 addresses, it is an implicit advertisement by the site that it is a 1022 dual-stack site. That is, the site can receive IPv4 or IPv6 unicast 1023 packets. 1025 To distinguish if the site can receive dual-stack unicast packets as 1026 well as dual-stack multicast packets, the Mpriority value setting 1027 will be relative to an IPv4 or IPv6 RLOC See [LISP] for packet format 1028 details. 1030 If one considers the combinations of LISP, non-LISP, and uLISP sites 1031 sharing the same distribution tree and considering the capabilities 1032 of supporting IPv4, IPv6, or dual-stack, the number of total 1033 combinations grows beyond comprehension. 1035 Using some combinatorial math, the following profiles of a site and 1036 the combinations that can occur: 1038 1. LISP-Multicast IPv4 Site 1040 2. LISP-Multicast IPv6 Site 1042 3. LISP-Multicast Dual-Stack Site 1044 4. uLISP IPv4 Site 1046 5. uLISP IPv6 Site 1047 6. uLISP Dual-Stack Site 1049 7. non-LISP IPv4 Site 1051 8. non-LISP IPv6 Site 1053 9. non-LISP Dual-Stack Site 1055 Lets define (m n) = m!/(n!*(m-n)!), pronounced "m choose n" to 1056 illustrate some combinatorial math below. 1058 When 1 site talks to another site, the combinatorial is (9 2), when 1 1059 site talks to another 2 sites, the combinatorial is (9 3). If sum 1060 this up to (9 9), then: 1062 (9 2) + (9 3) + (9 4) + (9 5) + (9 6) + (9 7) + (9 8) + (9 9) = 1064 36 + 84 + 126 + 126 + 84 + 36 + 9 + 1 1066 Which results in the total number of cases to be considered at 502. 1068 This combinatorial gets even worse when one considers a site using 1069 one address family inside of the site and the xTRs use the other 1070 address family (as in using IPv4 EIDs with IPv6 RLOCs or IPv6 EIDs 1071 with IPv4 RLOCs). 1073 To rationalize this combinatorial nightmare, there are some 1074 guidelines which need to be put in place: 1076 o Each distribution tree shared between sites will either be an IPv4 1077 distribution tree or an IPv6 distribution tree. Therefore, head- 1078 end replication can be avoided by building and sending packets on 1079 each address family based distribution tree. Even though there 1080 might be an urge to do multicast packet translation from one 1081 address family format to the other, it is a non-viable over- 1082 complicated urge. Multicast ITRs will only encapsulate packets 1083 where the inner and outer headers are from the same address 1084 family. 1086 o All LISP sites on a multicast distribution tree must share a 1087 common address family which is determined by the source site's 1088 locator-set in its LISP database mapping entry. All receiver 1089 multicast sites will use the best RLOC priority controlled by the 1090 source multicast site. This is true when the source site is 1091 either LISP-Multicast or uLISP capable. This means that priority- 1092 based policy modification is prohibited. When a receiver 1093 multicast site ETR receives a (S-EID,G) join, it must select a 1094 S-RLOC for the same address family as S-EID. 1096 o When a multicast locator-set has more than one locator, only 1097 locators from the same address-family MUST be set to the same best 1098 priority value. A mixed locator-set can exist (for unicast use), 1099 but the multicast priorities MUST be the set for the same address 1100 family locators. 1102 o When the source site is not LISP capable, it is up to how 1103 receivers find the source and group information for a multicast 1104 flow. That mechanism decides the address family for the flow. 1106 9.3. Making a Multicast Interworking Decision 1108 This Multicast Interworking section has shown all combinations of 1109 multicast connectivity that could occur. As already concluded, this 1110 can be quite complicated and if the design is too ambitious, the 1111 dynamics of the protocol could cause a lot of instability. 1113 The trade-off decisions are hard to make and so the same single 1114 solution is desirable to work for both IPv4 and IPv6 multicast. It 1115 is imperative to have an incrementally deployable solution for all of 1116 IPv4 unicast and multicast and IPv6 unicast and multicast while 1117 minimizing (or eliminating) both unicast and multicast EID namespace 1118 state. 1120 Therefore the design decision to go with uPITRs [INTWORK] for unicast 1121 routing and mPETRs for multicast routing seems to be the sweet spot 1122 in the solution space so state requirements can be optimized and 1123 avoid head-end data replication at ITRs. 1125 10. Considerations when RP Addresses are Embedded in Group Addresses 1127 When ASM and PIM-Bidir is used in an IPv6 inter-domain environment, a 1128 technique exists to embed the unicast address of an RP in a IPv6 1129 group address [RFC3956]. When routers in end sites process a PIM 1130 Join/Prune message which contain an embedded-RP group address, they 1131 extract the RP address from the group address and treat it from the 1132 EID namespace. However, core routers do not have state for the EID 1133 namespace, and need to extract an RP address from the RLOC namespace. 1135 Therefore, it is the responsibility of ETRs in multicast receiver 1136 sites to map the group address into a group address where the 1137 embedded-RP address is from the RLOC namespace. The mapped RP- 1138 address is obtained from a EID-to-RLOC mapping database lookup. The 1139 ETR will also send a unicast (*,G) Join/Prune message to the ITR so 1140 the branch of the distribution tree from the source site resident RP 1141 to the ITR is created. 1143 This technique is no different than the techniques described in this 1144 specification for translating (S,G) state and propagating Join/Prune 1145 messages into the core. The only difference is that the (*,G) state 1146 in Join/Prune messages are mapped because they contain unicast 1147 addresses encoded in an Embedded-RP group address. 1149 11. Taking Advantage of Upgrades in the Core 1151 If the core routers are upgraded to support [RFC5496], then the EID 1152 specific data can be passed through the core without, possibly, 1153 having to store the state in the core. 1155 By doing this one can eliminate the ETR from unicast encapsulating 1156 PIM Join/Prune messages to the source site's ITR. 1158 However, this solution is restricted to a small set of workable cases 1159 which would not be good for general use of LISP-Multicast. In 1160 addition due to slow convergence properties, it is not being 1161 recommended for LISP-Multicast. 1163 12. Mtrace Considerations 1165 Mtrace functionality MUST be consistent with unicast traceroute 1166 functionality where all hops from multicast receiver to multicast 1167 source are visible. 1169 The design for mtrace for use in LISP-Multicast environments is to be 1170 determined but should build upon the mtrace version 2 specified in 1171 [MTRACE]. 1173 13. Security Considerations 1175 The security concerns for LISP multicast are mainly the same as for 1176 the base LISP specification [LISP] and for multicast in general, 1177 including PIM-ASM [RFC4601]. 1179 There may be a security concern with respect to unicast PIM messages. 1180 When multiple receiver sites are joining a (S-EID1,G) distribution 1181 tree that maps to a (RLOC1,G) core distribution tree, and a malicious 1182 receiver site joins a (S-EID2,G) distribution tree that also maps to 1183 the (RLOC1,G) core distribution tree, the legitimate sites will 1184 receive data from S-EID2 when they did not ask for it. 1186 Other than as noted above there are currently no known security 1187 differences between multicast with LISP and multicast without LISP. 1188 However this has not been a topic that has been investigated deeply 1189 so far therefore additional issues might arise in future. 1191 14. Acknowledgments 1193 The authors would like to gratefully acknowledge the people who have 1194 contributed discussion, ideas, and commentary to the making of this 1195 proposal and specification. People who provided expert review were 1196 Scott Brim, Greg Shepherd, and Dave Oran. Other commentary from 1197 discussions at Summer 2008 Dublin IETF were Toerless Eckert and 1198 Ijsbrand Wijnands. 1200 The authors would also like to thank the MBONED working group for 1201 constructive and civil verbal feedback when this draft was presented 1202 at the Fall 2008 IETF in Minneapolis. In particular, good commentary 1203 came from Tom Pusateri, Steve Casner, Marshall Eubanks, Dimitri 1204 Papadimitriou, Ron Bonica, Lenny Guardino, Alia Atlas, Jesus Arango, 1205 and Jari Arkko. 1207 An expert review of this specification was done by Yiqun Cai and 1208 Liming Wei. The authors thank them for their detailed comments. 1210 This work originated in the Routing Research Group (RRG) of the IRTF. 1211 The individual submission [MLISP] was converted into this IETF LISP 1212 working group draft. 1214 15. IANA Considerations 1216 This document makes no request of the IANA. 1218 16. References 1220 16.1. Normative References 1222 [INTWORK] Lewis, D., Meyer, D., and D. Farinacci, "Interworking LISP 1223 with IPv4 and IPv6", draft-ietf-lisp-interworking-02.txt 1224 (work in progress). 1226 [LISP] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, 1227 "Locator/ID Separation Protocol (LISP)", 1228 draft-ietf-lisp-16.txt (work in progress). 1230 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1231 Requirement Levels", BCP 14, RFC 2119, March 1997. 1233 [RFC3618] Fenner, B. and D. Meyer, "Multicast Source Discovery 1234 Protocol (MSDP)", RFC 3618, October 2003. 1236 [RFC3956] Savola, P. and B. Haberman, "Embedding the Rendezvous 1237 Point (RP) Address in an IPv6 Multicast Address", 1238 RFC 3956, November 2004. 1240 [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, 1241 "Protocol Independent Multicast - Sparse Mode (PIM-SM): 1242 Protocol Specification (Revised)", RFC 4601, August 2006. 1244 [RFC4604] Holbrook, H., Cain, B., and B. Haberman, "Using Internet 1245 Group Management Protocol Version 3 (IGMPv3) and Multicast 1246 Listener Discovery Protocol Version 2 (MLDv2) for Source- 1247 Specific Multicast", RFC 4604, August 2006. 1249 [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for 1250 IP", RFC 4607, August 2006. 1252 [RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, 1253 "Multiprotocol Extensions for BGP-4", RFC 4760, 1254 January 2007. 1256 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 1257 "Bidirectional Protocol Independent Multicast (BIDIR- 1258 PIM)", RFC 5015, October 2007. 1260 [RFC5135] Wing, D. and T. Eckert, "IP Multicast Requirements for a 1261 Network Address Translator (NAT) and a Network Address 1262 Port Translator (NAPT)", BCP 135, RFC 5135, February 2008. 1264 [RFC5496] Wijnands, IJ., Boers, A., and E. Rosen, "The Reverse Path 1265 Forwarding (RPF) Vector TLV", RFC 5496, March 2009. 1267 16.2. Informative References 1269 [ALT] Farinacci, D., Fuller, V., and D. Meyer, "LISP Alternative 1270 Topology (LISP-ALT)", draft-ietf-lisp-alt-09.txt (work in 1271 progress). 1273 [MLISP] Farinacci, D., Meyer, D., Zwiebel, J., and S. Venaas, 1274 "LISP for Multicast Environments", 1275 draft-farinacci-lisp-multicast-01.txt (work in progress). 1277 [MTRACE] Asaeda, H., Jinmei, T., Fenner, W., and S. Casner, "Mtrace 1278 Version 2: Traceroute Facility for IP Multicast", 1279 draft-ietf-mboned-mtrace-v2-08.txt (work in progress). 1281 Appendix A. Document Change Log 1283 A.1. Changes to draft-ietf-lisp-multicast-13.txt 1285 o Posted February 2012. 1287 o Resolution to Stewart Bryant's and Adrian Farrel's comments. 1289 A.2. Changes to draft-ietf-lisp-multicast-12.txt 1291 o Posted January 2012. 1293 o Added more security disclaimers to the Security Considerations 1294 section. 1296 A.3. Changes to draft-ietf-lisp-multicast-11.txt 1298 o Posted November 2011. 1300 o Added Stig text to Security Considerations section to reflect 1301 comments from IESG review comment from Stephen Farrell. 1303 o Changed how an unicast PIM join gets sent. Do not use an ECM or 1304 else an instance-ID cannot be included in the join. So go back to 1305 what we had where the unicast PIM join is encapsulated in a 4341 1306 UDP packet. 1308 A.4. Changes to draft-ietf-lisp-multicast-10.txt 1310 o Posted second half of October 2011. Changes to reflect IESG 1311 review comments from Stephen Farrell. 1313 A.5. Changes to draft-ietf-lisp-multicast-09.txt 1315 o Posted October 2011. Changes to reflect IESG review comments from 1316 Ralph Droms and Kathleen Moriarty. 1318 A.6. Changes to draft-ietf-lisp-multicast-08.txt 1320 o Posted September 2011. Minor editorial changes from Jari's 1321 commentary. 1323 A.7. Changes to draft-ietf-lisp-multicast-07.txt 1325 o Posted July 2011. Fixing IDnits errors. 1327 A.8. Changes to draft-ietf-lisp-multicast-06.txt 1329 o Posted June 2011 to complete working group last call. 1331 o Added paragraph to section 8.1.2 based on Jesus comment about 1332 making it more clear what happens when two (S-EID,G) trees use the 1333 same (RLOC,G) tree. 1335 o Make more references to [INTWORK] when mentioning uPITRs and 1336 uPETRs. 1338 o Made many changes based on editorial and wordsmithing comments 1339 from Alia. 1341 A.9. Changes to draft-ietf-lisp-multicast-05.txt 1343 o Posted April 2011 to reset expiration timer. 1345 o Updated references. 1347 A.10. Changes to draft-ietf-lisp-multicast-04.txt 1349 o Posted October 2010 to reset expiration timer. 1351 o Updated references. 1353 A.11. Changes to draft-ietf-lisp-multicast-03.txt 1355 o Posted April 2010. 1357 o Added section 8.1.2 to address Joel Halpern's comment about 1358 receiver sites joining the same source site via 2 different RLOCs, 1359 each being a separate ITR. 1361 o Change all occurences of "mPTR" to "mPETR" to become more 1362 consistent with uPITRs and uPETRs described in [INTWORK]. That 1363 is, an mPETR is a LISP multicast router that decapsulates 1364 multicast packets that are encapsulated to it by ITRs in multicast 1365 source sites. 1367 o Add clarifications in section 9 about how homogeneous multicast 1368 encapsulation should occur. As well as describing in this 1369 section, how to deal with mixed-locator sets to avoid 1370 heterogeneous encapsulation. 1372 o Introduce concept of mPITRs to help reduce (S-EID,G) to the edges 1373 of LISP global multicast network. 1375 A.12. Changes to draft-ietf-lisp-multicast-02.txt 1377 o Posted September 2009. 1379 o Added Document Change Log appendix. 1381 o Specify that the LISP Encapsulated Control Message be used for 1382 unicasting PIM Join/Prune messages from ETRs to ITRs. 1384 A.13. Changes to draft-ietf-lisp-multicast-01.txt 1386 o Posted November 2008. 1388 o Specified that PIM Join/Prune unicast messages that get sent from 1389 ETRs to ITRs of a source multicast site get LISP encapsulated in 1390 destination UDP port 4342. 1392 o Add multiple RLOCs per ITR per Yiqun's comments. 1394 o Indicate how static RPs can be used when LISP is run using Bidir- 1395 PIM in the core. 1397 o Editorial changes per Liming comments. 1399 o Add Mttrace Considersations section. 1401 A.14. Changes to draft-ietf-lisp-multicast-00.txt 1403 o Posted April 2008. 1405 o Renamed from draft-farinacci-lisp-multicast-01.txt. 1407 Authors' Addresses 1409 Dino Farinacci 1410 cisco Systems 1411 Tasman Drive 1412 San Jose, CA 1413 USA 1415 Email: dino@cisco.com 1417 Dave Meyer 1418 cisco Systems 1419 Tasman Drive 1420 San Jose, CA 1421 USA 1423 Email: dmm@cisco.com 1425 John Zwiebel 1426 cisco Systems 1427 Tasman Drive 1428 San Jose, CA 1429 USA 1431 Email: jzwiebel@cisco.com 1433 Stig Venaas 1434 cisco Systems 1435 Tasman Drive 1436 San Jose, CA 1437 USA 1439 Email: stig@cisco.com