idnits 2.17.1 draft-ietf-lisp-multicast-11.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 (November 4, 2011) is 4556 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for intended status: Experimental ---------------------------------------------------------------------------- == Outdated reference: A later version (-06) exists of draft-ietf-lisp-interworking-02 == Outdated reference: A later version (-24) exists of draft-ietf-lisp-16 ** Obsolete normative reference: RFC 4601 (Obsoleted by RFC 7761) == Outdated reference: A later version (-10) exists of draft-ietf-lisp-alt-09 == Outdated reference: A later version (-26) exists of draft-ietf-mboned-mtrace-v2-08 Summary: 1 error (**), 0 flaws (~~), 5 warnings (==), 1 comment (--).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: May 7, 2012 S. Venaas 6 cisco Systems 7 November 4, 2011 9 LISP for Multicast Environments 10 draft-ietf-lisp-multicast-11 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 May 7, 2012. 35 Copyright Notice 37 Copyright (c) 2011 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 . . . . . . . . . . . . . . . . . . . . 3 53 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 54 3. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 6 55 4. Basic Overview . . . . . . . . . . . . . . . . . . . . . . . . 9 56 5. Source Addresses versus Group Addresses . . . . . . . . . . . 12 57 6. Locator Reachability Implications on LISP-Multicast . . . . . 13 58 7. Multicast Protocol Changes . . . . . . . . . . . . . . . . . . 14 59 8. LISP-Multicast Data-Plane Architecture . . . . . . . . . . . . 17 60 8.1. ITR Forwarding Procedure . . . . . . . . . . . . . . . . . 17 61 8.1.1. Multiple RLOCs for an ITR . . . . . . . . . . . . . . 17 62 8.1.2. Multiple ITRs for a LISP Source Site . . . . . . . . . 18 63 8.2. ETR Forwarding Procedure . . . . . . . . . . . . . . . . . 18 64 8.3. Replication Locations . . . . . . . . . . . . . . . . . . 19 65 9. LISP-Multicast Interworking . . . . . . . . . . . . . . . . . 20 66 9.1. LISP and non-LISP Mixed Sites . . . . . . . . . . . . . . 20 67 9.1.1. LISP Source Site to non-LISP Receiver Sites . . . . . 21 68 9.1.2. Non-LISP Source Site to non-LISP Receiver Sites . . . 22 69 9.1.3. Non-LISP Source Site to Any Receiver Site . . . . . . 23 70 9.1.4. Unicast LISP Source Site to Any Receiver Sites . . . . 24 71 9.1.5. LISP Source Site to Any Receiver Sites . . . . . . . . 24 72 9.2. LISP Sites with Mixed Address Families . . . . . . . . . . 25 73 9.3. Making a Multicast Interworking Decision . . . . . . . . . 27 74 10. Considerations when RP Addresses are Embedded in Group 75 Addresses . . . . . . . . . . . . . . . . . . . . . . . . . . 28 76 11. Taking Advantage of Upgrades in the Core . . . . . . . . . . . 29 77 12. Mtrace Considerations . . . . . . . . . . . . . . . . . . . . 30 78 13. Security Considerations . . . . . . . . . . . . . . . . . . . 31 79 14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 32 80 15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 33 81 16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 34 82 16.1. Normative References . . . . . . . . . . . . . . . . . . . 34 83 16.2. Informative References . . . . . . . . . . . . . . . . . . 35 84 Appendix A. Document Change Log . . . . . . . . . . . . . . . . . 36 85 A.1. Changes to draft-ietf-lisp-multicast-11.txt . . . . . . . 36 86 A.2. Changes to draft-ietf-lisp-multicast-10.txt . . . . . . . 36 87 A.3. Changes to draft-ietf-lisp-multicast-09.txt . . . . . . . 36 88 A.4. Changes to draft-ietf-lisp-multicast-08.txt . . . . . . . 36 89 A.5. Changes to draft-ietf-lisp-multicast-07.txt . . . . . . . 36 90 A.6. Changes to draft-ietf-lisp-multicast-06.txt . . . . . . . 36 91 A.7. Changes to draft-ietf-lisp-multicast-05.txt . . . . . . . 37 92 A.8. Changes to draft-ietf-lisp-multicast-04.txt . . . . . . . 37 93 A.9. Changes to draft-ietf-lisp-multicast-03.txt . . . . . . . 37 94 A.10. Changes to draft-ietf-lisp-multicast-02.txt . . . . . . . 37 95 A.11. Changes to draft-ietf-lisp-multicast-01.txt . . . . . . . 37 96 A.12. Changes to draft-ietf-lisp-multicast-00.txt . . . . . . . 38 97 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 39 99 1. Requirements Notation 101 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 102 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 103 document are to be interpreted as described in [RFC2119]. 105 2. Introduction 107 The Locator/ID Separation Architecture [LISP] provides a mechanism to 108 separate out Identification and Location semantics from the current 109 definition of an IP address. By creating two namespaces, an Endpoint 110 ID (EID) namespace used by sites and a Routing Locator (RLOC) 111 namespace used by core routing, the core routing infrastructure can 112 scale by doing topological aggregation of routing information. 114 Since LISP creates a new namespace, a mapping function must exist to 115 map a site's EID prefixes to its associated locators. For unicast 116 packets, both the source address and destination address must be 117 mapped. For multicast packets, only the source address needs to be 118 mapped. The destination group address doesn't need to be mapped 119 because the semantics of an IPv4 or IPv6 group address are logical in 120 nature and not topology-dependent. Therefore, this specification 121 focuses on to map a source EID address of a multicast flow during 122 distribution tree setup and packet delivery. 124 This specification will address the following scenarios: 126 1. How a multicast source host in a LISP site sends multicast 127 packets to receivers inside of its site as well as to receivers 128 in other sites that are LISP enabled. 130 2. How inter-domain (or between LISP sites) multicast distribution 131 trees are built and how forwarding of multicast packets leaving a 132 source site toward receivers sites is performed. 134 3. What protocols are affected and what changes are required to such 135 multicast protocols. 137 4. How ASM-mode (Any Source Multicast), SSM-mode (Single Source 138 Multicast), and Bidir-mode (Bidirectional Shared Trees) service 139 models will operate. 141 5. How multicast packet flow will occur for multiple combinations of 142 LISP and non-LISP capable source and receiver sites, for example: 144 A. How multicast packets from a source host in a LISP site are 145 sent to receivers in other sites when they are all non-LISP 146 sites. 148 B. How multicast packets from a source host in a LISP site are 149 sent to receivers in both LISP-enabled sites and non-LISP 150 sites. 152 C. How multicast packets from a source host in a non-LISP site 153 are sent to receivers in other sites when they are all LISP- 154 enabled sites. 156 D. How multicast packets from a source host in a non-LISP site 157 are sent to receivers in both LISP-enabled sites and non-LISP 158 sites. 160 This specification focuses on what changes are needed to the 161 multicast routing protocols to support LISP-Multicast as well as 162 other protocols used for inter-domain multicast, such as Multi- 163 protocol BGP (MBGP) [RFC4760]. The approach proposed in this 164 specification requires no packet format changes to the protocols and 165 no operational procedural changes to the multicast infrastructure 166 inside of a site when all sources and receivers reside in that site, 167 even when the site is LISP enabled. That is, internal operation of 168 multicast is unchanged regardless of whether or not the site is LISP 169 enabled or whether or not receivers exist in other sites which are 170 LISP-enabled. 172 Therefore, we see changes only to PIM-ASM [RFC4601], MSDP [RFC3618], 173 and PIM-SSM [RFC4607]. Bidir-PIM [RFC5015], which typically does not 174 run in an inter-domain environment is not addressed in depth in this 175 version of the specification. 177 Also, the current version of this specification does not describe 178 multicast-based Traffic Engineering relative to the TE-ITR (Traffic 179 Engineering based Ingress Tunnel Router) and TE-ETR (Traffic 180 Engineering based Egress Tunnel Router) descriptions in [LISP]. 181 Futher work is also needed to determine the detailed behavior for 182 multicast proxy ITRs (mPITRs) (Section 9.1.3), mtrace (Section 12), 183 and locator reachability (Section 6). Finally, further deployment 184 and experimentation would be useful to understand the real-life 185 performance of the LISP-Multicast solution. For instance, the design 186 optimizes for minimal state and control traffic in the core, but can 187 in some cases cause extra multicast traffic to be sent Section 8.1.2. 189 3. Definition of Terms 191 The terminology in this section is consistent with the definitions in 192 [LISP] but is extended specifically to deal with the application of 193 the terminology to multicast routing. 195 LISP-Multicast: a reference to the design in this specification. 196 That is, when any site that is participating in multicast 197 communication has been upgraded to be a LISP site, the operation 198 of control-plane and data-plane protocols is considered part of 199 the LISP-Multicast architecture. 201 Endpoint ID (EID): a 32-bit (for IPv4) or 128-bit (for IPv6) value 202 used in the source address field of the first (most inner) LISP 203 header of a multicast packet. The host obtains a destination 204 group address the same way it obtains one today, as it would when 205 it is a non-LISP site. The source EID is obtained via existing 206 mechanisms used to set a host's "local" IP address. An EID is 207 allocated to a host from an EID prefix block associated with the 208 site the host is located in. An EID can be used by a host to 209 refer to another host, as when it joins an SSM (S-EID,G) route 210 using IGMP version 3 [RFC4604]. LISP uses Provider Independent 211 (PI) blocks for EIDs; such EIDs MUST NOT be used as LISP RLOCs. 212 Note that EID blocks may be assigned in a hierarchical manner, 213 independent of the network topology, to facilitate scaling of the 214 mapping database. In addition, an EID block assigned to a site 215 may have site-local structure (subnetting) for routing within the 216 site; this structure is not visible to the global routing system. 218 Routing Locator (RLOC): the IPv4 or IPv6 address of an ingress 219 tunnel router (ITR), the router in the multicast source host's 220 site that encapsulates multicast packets. It is the output of a 221 EID-to-RLOC mapping lookup. An EID maps to one or more RLOCs. 222 Typically, RLOCs are numbered from topologically-aggregatable 223 blocks that are assigned to a site at each point to which it 224 attaches to the global Internet; where the topology is defined by 225 the connectivity of provider networks, RLOCs can be thought of as 226 Provider Assigned (PA) addresses. Multiple RLOCs can be assigned 227 to the same ITR device or to multiple ITR devices at a site. 229 Ingress Tunnel Router (ITR): a router which accepts an IP multicast 230 packet with a single IP header (more precisely, an IP packet that 231 does not contain a LISP header). The router treats this "inner" 232 IP destination multicast address opaquely so it doesn't need to 233 perform a map lookup on the group address because it is 234 topologically insignificant. The router then prepends an "outer" 235 IP header with one of its globally-routable RLOCs as the source 236 address field. This RLOC is known to other multicast receiver 237 sites which have used the mapping database to join a multicast 238 tree for which the ITR is the root. In general, an ITR receives 239 IP packets from site end systems on one side and sends LISP- 240 encapsulated multicast IP packets out all external interfaces 241 which have been joined. 243 An ITR would receive a multicast packet from a source inside of 244 its site when 1) it is on the path from the multicast source to 245 internally joined receivers, or 2) when it is on the path from the 246 multicast source to externally joined receivers. 248 Egress Tunnel Router (ETR): a router that is on the path from a 249 multicast source host in another site to a multicast receiver in 250 its own site. An ETR accepts a PIM Join/Prune message from a site 251 internal PIM router destined for the source's EID in the multicast 252 source site. The ETR maps the source EID in the Join/Prune 253 message to an RLOC address based on the EID-to-RLOC mapping. This 254 sets up the ETR to accept multicast encapsulated packets from the 255 ITR in the source multicast site. A multicast ETR decapsulates 256 multicast encapsulated packets and replicates them on interfaces 257 leading to internal receivers. 259 xTR: is a reference to an ITR or ETR when direction of data flow is 260 not part of the context description. xTR refers to the router that 261 is the tunnel endpoint. Used synonymously with the term "Tunnel 262 Router". For example, "An xTR can be located at the Customer Edge 263 (CE) router", meaning both ITR and ETR functionality can be at the 264 CE router. 266 LISP Header: a term used in this document to refer to the outer 267 IPv4 or IPv6 header, a UDP header, and a LISP header. An ITR 268 prepends headers and an ETR strips headers. A LISP encapsulated 269 multicast packet will have an "inner" header with the source EID 270 in the source field; an "outer" header with the source RLOC in the 271 source field: and the same globally unique group address in the 272 destination field of both the inner and outer header. 274 (S,G) State: the formal definition is in the PIM Sparse Mode 275 [RFC4601] specification. For this specification, the term is used 276 generally to refer to multicast state. Based on its topological 277 location, the (S,G) state resides in routers can be either 278 (S-EID,G) state (at a location where the (S,G) state resides) or 279 (S-RLOC,G) state (in the Internet core). 281 (S-EID,G) State: refers to multicast state in multicast source and 282 receiver sites where S-EID is the IP address of the multicast 283 source host (its EID). An S-EID can appear in an IGMPv3 report, 284 an MSDP SA message or a PIM Join/Prune message that travels inside 285 of a site. 287 (S-RLOC,G) State: refers to multicast state in the core where S is 288 a source locator (the IP address of a multicast ITR) of a site 289 with a multicast source. The (S-RLOC,G) is mapped from (S-EID,G) 290 entry by doing a mapping database lookup for the EID prefix that 291 S-EID maps to. An S-RLOC can appear in a PIM Join/Prune message 292 when it travels from an ETR to an ITR over the Internet core. 294 uLISP Site: a unicast only LISP site according to [LISP] which has 295 not deployed the procedures of this specification and therefore, 296 for multicast purposes, follows the procedures from Section 9. A 297 uLISP site can be a traditional multicast site. 299 LISP Site: a unicast LISP site (uLISP Site) that is also multicast 300 capable according to the procedures in this specification. 302 mPETR: this is a multicast proxy-ETR that is responsible for 303 advertising a very coarse EID prefix which non-LISP and uLISP 304 sites can target their (S-EID,G) PIM Join/Prune message to. mPETRs 305 are used so LISP source multicast sites can send multicast packets 306 using source addresses from the EID namespace. mPETRs act as Proxy 307 ETRs for supporting multicast routing in a LISP infrastructure. 308 It is likely an uPITR [INTWORK] and a mPETR will be co-located 309 since the single device advertises a coarse EID-prefix in the 310 underlying unicast routing system. 312 Mixed Locator-Sets: this is a locator-set for a LISP database 313 mapping entry where the RLOC addresses in the locator-set are in 314 both IPv4 and IPv6 format. 316 Unicast Encapsulated PIM Join/Prune Message: this is a standard PIM 317 Join/Prune message (LISP encapsulated with destination UDP port 318 4341) which is sent by ETRs at multicast receiver sites to an ITR 319 at a multicast source site. This message is sent periodically as 320 long as there are interfaces in the OIF-list for the (S-EID,G) 321 entry the ETR is joining for. 323 OIF-list: this is notation to describe the outgoing interface list 324 a multicast router stores per multicast routing table entry so it 325 knows what interfaces to replicate multicast packets on. 327 RPF: Reverse Path Forwarding is a procedure used by multicast 328 routers. A router will accept a multicast packet for forwarding 329 if the packet was received on the path that the router would use 330 to forward unicast packets to the multicast packet's source. 332 4. Basic Overview 334 LISP, when used for unicast routing, increases the site's ability to 335 control ingress traffic flows. Egress traffic flows are controlled 336 by the IGP in the source site. For multicast, the IGP coupled with 337 PIM can decide which path multicast packets ingress. By using the 338 traffic engineering features of LISP, a multicast source site can 339 control the egress of its multicast traffic. By controlling the 340 priorities of locators from a mapping database entry, a source 341 multicast site can control which way multicast receiver sites join to 342 the source site. 344 At this point in time, there is no requirement for different locator- 345 sets, priority, and weight policies for multicast than there is for 346 unicast. However, when traffic engineering policies are different 347 for unicast versus multicast flows, it will be desirable to use 348 multicast-based priority and weight values in Map-Reply messages. 350 The fundamental multicast forwarding model is to encapsulate a 351 multicast packet into another multicast packet. An ITR will 352 encapsulate multicast packets received from sources that it serves in 353 a LISP multicast header. The destination group address from the 354 inner header is copied to the destination address of the outer 355 header. The inner source address is the EID of the multicast source 356 host and the outer source address is the RLOC of the encapsulating 357 ITR. 359 The LISP-Multicast architecture will follow this high-level protocol 360 and operational sequence: 362 1. Receiver hosts in multicast sites will join multicast content the 363 way they do today, they use IGMP. When they use IGMPv3 where 364 they specify source addresses, they use source EIDs, that is they 365 join (S-EID,G). If the multicast source is external to this 366 receiver site, the PIM Join/Prune message flows toward the ETRs, 367 finding the shortest exit (that is the closest exit for the Join/ 368 Prune message and the closest entrance for the multicast packet 369 to the receiver). 371 2. The ETR does a mapping database lookup for S-EID. If the mapping 372 is cached from a previous lookup (from either a previous Join/ 373 Prune for the source multicast site or a unicast packet that went 374 to the site), it will use the RLOC information from the mapping. 375 The ETR will use the same priority and weighting mechanism as for 376 unicast. So the source site can decide which way multicast 377 packets egress. 379 3. The ETR will build two PIM Join/Prune messages, one that contains 380 a (S-EID,G) entry that is unicast to the ITR that matches the 381 RLOC the ETR selects, and the other which contains a (S-RLOC,G) 382 entry so the core network can create multicast state from this 383 ETR to the ITR. 385 4. When the ITR gets the unicast Join/Prune message (see Section 3 386 for formal definition), it will process (S-EID,G) entries in the 387 message and propagate them inside of the site where it has 388 explicit routing information for EIDs via the IGP. When the ITR 389 receives the (S-RLOC,G) PIM Join/Prune message it will process it 390 like any other join it would get in today's Internet. The S-RLOC 391 address is the IP address of this ITR. 393 5. At this point there is (S-EID,G) state from the joining host in 394 the receiver multicast site to the ETR of the receiver multicast 395 site. There is (S-RLOC,G) state across the core network from the 396 ETR of the multicast receiver site to the ITR in the multicast 397 source site and (S-EID,G) state in the source multicast site. 398 Note, the (S-EID,G) state is the same S-EID in each multicast 399 site. As other ETRs join the same multicast tree, they can join 400 through the same ITR (in which case the packet replication is 401 done in the core) or a different ITR (in which case the packet 402 replication is done at the source site). 404 6. When a packet is originated by the multicast host in the source 405 site, the packet will flow to one or more ITRs which will prepend 406 a LISP header. By copying the group address to the outer 407 destination address field, the ITR insert its own locator address 408 in the outer source address field. The ITR will look at its 409 (S-RLOC,G) state, where S-RLOC is its own locator address, and 410 replicate the packet on each interface a (S-RLOC,G) joined was 411 received on. The core has (S-RLOC,G) so where fanout occurs to 412 multiple sites, a core router will do packet replication. 414 7. When either the source site or the core replicates the packet, 415 the ETR will receive a LISP packet with a destination group 416 address. It will decapsulate packets because it has receivers 417 for the group. Otherwise, it would have not received the packets 418 because it would not have joined. The ETR decapsulates and does 419 a (S-EID,G) lookup in its multicast FIB to forward packets out 420 one or more interfaces to forward the packet to internal 421 receivers. 423 This architecture is consistent and scalable with the architecture 424 presented in [LISP] where multicast state in the core operates on 425 locators and multicast state at the sites operates on EIDs. 427 Alternatively, [LISP] also has a mechanism where (S-EID,G) state can 428 reside in the core through the use of RPF-vectors [RFC5496] in PIM 429 Join/Prune messages. However, few PIM implementations support RPF 430 vectors and LISP should avoid S-EID state in the core. See Section 5 431 for details. 433 However, some observations can be made on the algorithm above. The 434 control plane can scale but at the expense of sending data to sites 435 which may have not joined the distribution tree where the 436 encapsulated data is being delivered. For example, one site joins 437 (S-EID1,G) and another site joins (S-EID2,G). Both EIDs are in the 438 same multicast source site. Both multicast receiver sites join to 439 the same ITR with state (S-RLOC,G) where S-RLOC is the RLOC for the 440 ITR. The ITR joins both (S-EID1,G) and (S-EID2,G) inside of the 441 site. The ITR receives (S-RLOC,G) joins and populates the OIF-list 442 state for it. Since both (S-EID1,G) and (S-EID2, G) map to the one 443 (S-RLOC,G) packets will be delivered by the core to both multicast 444 receiver sites even though each have joined a single source-based 445 distribution tree. This behavior is a consequence of the many-to-one 446 mapping between S-EIDs and a S-RLOC. 448 There is a possible solution to this problem which reduces the number 449 of many-to-one occurrences of (S-EID,G) entries aggregating into a 450 single (S-RLOC,G) entry. If a physical ITR can be assigned multiple 451 RLOC addresses and these addresses are advertised in mapping database 452 entries, then ETRs at receiver sites have more RLOC address options 453 and therefore can join different (RLOC,G) entries for each (S-EID,G) 454 entry joined at the receiver site. It would not scale to have a one- 455 to-one relationship between the number of S-EID sources at a source 456 site and the number of RLOCs assigned to all ITRs at the site, but 457 "n" can reduce to a smaller number in the "n-to-1" relationship. And 458 in turn, reduce the opportunity for data packets to be delivered to 459 sites for groups not joined. 461 5. Source Addresses versus Group Addresses 463 Multicast group addresses don't have to be associated with either the 464 EID or RLOC namespace. They actually are a namespace of their own 465 that can be treated as logical with relatively opaque allocation. 466 So, by their nature, they don't detract from an incremental 467 deployment of LISP-Multicast. 469 As for source addresses, as in the unicast LISP scenario, there is a 470 decoupling of identification from location. In a LISP site, packets 471 are originated from hosts using their allocated EIDs. EID addresses 472 are used to identify the host as well as where in the site's topology 473 the host resides but not how and where it is attached to the 474 Internet. 476 Therefore, when multicast distribution tree state is created anywhere 477 in the network on the path from any multicast receiver to a multicast 478 source, EID state is maintained at the source and receiver multicast 479 sites, and RLOC state is maintained in the core. That is, a 480 multicast distribution tree will be represented as a 3-tuple of 481 {(S-EID,G) (S-RLOC,G) (S-EID,G)} where the first element of the 482 3-tuple is the state stored in routers from the source to one or more 483 ITRs in the source multicast site, the second element of the 3-tuple 484 is the state stored in routers downstream of the ITR, in the core, to 485 all LISP receiver multicast sites, and the third element in the 486 3-tuple is the state stored in the routers downstream of each ETR, in 487 each receiver multicast site, reaching each receiver. Note that 488 (S-EID,G) is the same in both the source and receiver multicast 489 sites. 491 The concatenation/mapping from the first element to the second 492 element of the 3-tuples is done by the ITR and from the second 493 element to the third element is done at the ETRs. 495 6. Locator Reachability Implications on LISP-Multicast 497 Multicast state as it is stored in the core is always (S,G) state as 498 it exists today or (S-RLOC,G) state as it will exist when LISP sites 499 are deployed. The core routers cannot distinguish one from the 500 other. They don't need to because it is state that RPFs against the 501 core routing tables in the RLOC namespace. The difference is where 502 the root of the distribution tree for a particular source is. In the 503 traditional multicast core, the source S is the source host's IP 504 address. For LISP-Multicast the source S is a single ITR of the 505 multicast source site. 507 An ITR is selected based on the LISP EID-to-RLOC mapping used when an 508 ETR propagates a PIM Join/Prune message out of a receiver multicast 509 site. The selection is based on the same algorithm an ITR would use 510 to select an ETR when sending a unicast packet to the site. In the 511 unicast case, the ITR can change on a per-packet basis depending on 512 the reachability of the ETR. So an ITR can change relatively easily 513 using local reachability state. However, in the multicast case, when 514 an ITR goes unreachable, new distribution tree state must be built 515 because the encapsulating root has changed. This is more significant 516 than an RPF-change event, where any router would typically locally 517 change its RPF-interface for its existing tree state. But when an 518 encapsulating LISP-Multicast ITR goes unreachable, new distribution 519 state must be rebuilt and reflect the new encapsulator. Therefore, 520 when an ITR goes unreachable, all ETRs that are currently joined to 521 that ITR will have to trigger a new Join/Prune message for (S-RLOC,G) 522 to the new ITR as well as send a unicast encapsulated Join/Prune 523 message telling the new ITR which (S-EID,G) is being joined. 525 This issue can be mitigated by using anycast addressing for the ITRs 526 so the problem does reduce to an RPF change in the core, but still 527 requires a unicast encapsulated Join/Prune message to tell the new 528 ITR about (S-EID,G). The problem with this approach is that the ETR 529 really doesn't know when the ITR has changed so the new anycast ITR 530 will get the (S-EID,G) state only when the ETR sends it the next time 531 during its periodic sending procedures. 533 7. Multicast Protocol Changes 535 A number of protocols are used today for inter-domain multicast 536 routing: 538 IGMPv1-v3, MLDv1-v2: These protocols do not require any changes for 539 LISP-Multicast for two reasons. One being that they are link- 540 local and not used over site boundaries and second, they advertise 541 group addresses that don't need translation. Where source 542 addresses are supplied in IGMPv3 and MLDv2 messages, they are 543 semantically regarded as EIDs and don't need to be converted to 544 RLOCs until the multicast tree-building protocol, such as PIM, is 545 received by the ETR at the site boundary. Addresses used for IGMP 546 and MLD come out of the source site's allocated addresses which 547 are therefore from the EID namespace. 549 MBGP: Even though MBGP is not a multicast routing protocol, it is 550 used to find multicast sources when the unicast BGP peering 551 topology and the multicast MBGP peering topology are not 552 congruent. When MBGP is used in a LISP-Multicast environment, the 553 prefixes which are advertised are from the RLOC namespace. This 554 allows receiver multicast sites to find a path to the source 555 multicast site's ITRs. MBGP peering addresses will be from the 556 RLOC namespace. There are no MBGP protocol changes required to 557 support LISP-Multicast. 559 MSDP: MSDP is used to announce active multicast sources to other 560 routing domains (or LISP sites). The announcements come from the 561 PIM Rendezvous Points (RPs) from sites where there are active 562 multicast sources sending to various groups. In the context of 563 LISP-Multicast, the source addresses advertised in MSDP will 564 semantically be from the EID namespace since they describe the 565 identity of a source multicast host. It will be true that the 566 state stored in MSDP caches from core routers will be from the EID 567 namespace. An RP address inside of site will be from the EID 568 namespace so it can be advertised and reached by internal unicast 569 routing mechanism. However, for MSDP peer-RPF checking to work 570 properly across sites, the RP addresses must be converted or 571 mapped into a routable address that is advertised and maintained 572 in the BGP routing tables in the core. MSDP peering addresses can 573 come out of either the EID or a routable address namespace. And 574 the choice can be made unilaterally because the ITR at the site 575 will determine which namespace the destination peer address is out 576 of by looking in the mapping database service. There are no MSDP 577 protocol changes required to support LISP-Multicast. 579 PIM-SSM: In the simplest form of distribution tree building, when 580 PIM operates in SSM mode, a source distribution tree is built and 581 maintained across site boundaries. In this case, there is a small 582 modification to the operation of the PIM protocol. No 583 modifications to any message format, but to support taking a Join/ 584 Prune message originated inside of a LISP site with embedded 585 addresses from the EID namespace and converting them to addresses 586 from the RLOC namespace when the Join/Prune message crosses a site 587 boundary. This is similar to the requirements documented in 588 [RFC5135]. 590 PIM-Bidir: Bidirectional PIM is typically run inside of a routing 591 domain, but if deployed in an inter-domain environment, one would 592 have to decide if the RP address of the shared-tree would be from 593 the EID namespace or the RLOC namespace. If the RP resides in a 594 site-based router, then the RP address is from the EID namespace. 595 If the RP resides in the core where RLOC addresses are routed, 596 then the RP address is from the RLOC namespace. This could be 597 easily distinguishable if the EID address were well-known address 598 allocation block from the RLOC namespace. Also, when using 599 Embedded-RP for RP determination [RFC3956], the format of the 600 group address could indicate the namespace the RP address is from. 601 However, refer to Section 10 for considerations core routers need 602 to make when using Embedded-RP IPv6 group addresses. When using 603 Bidir-PIM for inter-domain multicast routing, it is recommended to 604 use staticly configured RPs. Allowing core routers to associate a 605 Bidir group's RP address with an ITR's RLOC address. And site 606 routers to associate the Bidir group's RP address as an EID 607 address. With respect to DF-election in Bidir PIM, no changes are 608 required since all messaging and addressing is link-local. 610 PIM-ASM: The ASM mode of PIM, the most popular form of PIM, is 611 deployed in the Internet today is by having shared-trees within a 612 site and using source-trees across sites. By the use of MSDP and 613 PIM-SSM techniques described above, multicast connectivity can 614 occur across LISP sites. Having said that, that means there are 615 no special actions required for processing (*,G) or (S,G,R) Join/ 616 Prune messages since they all operate against the shared-tree 617 which is site resident. Just like with ASM, there is no (*,G) in 618 the core when LISP-Multicast is in use. This is also true for the 619 RP-mapping mechanisms Auto-RP and BSR. 621 Based on the protocol description above, the conclusion is that there 622 are no protocol message format changes, just a translation function 623 performed at the control-plane. This will make for an easier and 624 faster transition for LISP since fewer components in the network have 625 to change. 627 It should also be stated just like it is in [LISP] that no host 628 changes, whatsoever, are required to have a multicast source host 629 send multicast packets and for a multicast receiver host to receive 630 multicast packets. 632 8. LISP-Multicast Data-Plane Architecture 634 The LISP-Multicast data-plane operation conforms to the operation and 635 packet formats specified in [LISP]. However, encapsulating a 636 multicast packet from an ITR is a much simpler process. The process 637 is simply to copy the inner group address to the outer destination 638 address. And to have the ITR use its own IP address (its RLOC) as 639 the source address. The process is simpler for multicast because 640 there is no EID-to-RLOC mapping lookup performed during packet 641 forwarding. 643 In the decapsulation case, the ETR simply removes the outer header 644 and performs a multicast routing table lookup on the inner header 645 (S-EID,G) addresses. Then the OIF-list for the (S-EID,G) entry is 646 used to replicate the packet on site-facing interfaces leading to 647 multicast receiver hosts. 649 There is no Data-Probe logic for ETRs as there can be in the unicast 650 forwarding case. 652 8.1. ITR Forwarding Procedure 654 The following procedure is used by an ITR, when it receives a 655 multicast packet from a source inside of its site: 657 1. A multicast data packet sent by a host in a LISP site will have 658 the source address equal to the host's EID and the destination 659 address equal to the group address of the multicast group. It is 660 assumed the group information is obtained by current methods. 661 The same is true for a multicast receiver to obtain the source 662 and group address of a multicast flow. 664 2. When the ITR receives a multicast packet, it will have both S-EID 665 state and S-RLOC state stored. Since the packet was received on 666 a site-facing interface, the RPF lookup is based on the S-EID 667 state. If the RPF check succeeds, then the OIF-list contains 668 interfaces that are site-facing and external-facing. For the 669 site-facing interfaces, no LISP header is prepended. For the 670 external-facing interfaces a LISP header is prepended. When the 671 ITR prepends a LISP header, it uses its own RLOC address as the 672 source address and copies the group address supplied by the IP 673 header the host built as the outer destination address. 675 8.1.1. Multiple RLOCs for an ITR 677 Typically, an ITR will have a single RLOC address but in some cases 678 there could be multiple RLOC addresses assigned from either the same 679 or different service providers. In this case when (S-RLOC,G) Join/ 680 Prune messages are received for each RLOC, there is a OIF-list 681 merging action that must take place. Therefore, when a packet is 682 received from a site-facing interface that matches on a (S-EID,G) 683 entry, the interfaces of the OIF-list from all (RLOC,G) entries 684 joined to the ITR as well as the site-facing OIF-list joined for 685 (S-EID,G) must be part be included in packet replication. In 686 addition to replicating for all types of OIF-lists, each oif entry 687 must be tagged with the RLOC address, so encapsulation uses the outer 688 source address for the RLOC joined. 690 8.1.2. Multiple ITRs for a LISP Source Site 692 Note when ETRs from different multicast receiver sites receive 693 (S-EID,G) joins, they may select a different S-RLOC for a multicast 694 source site due to policy (the multicast ITR can return different 695 multicast priority and weight values per ETR Map-Request). In this 696 case, the same (S-EID,G) is being realized by different (S-RLOC,G) 697 state in the core. This will not result in duplicate packets because 698 each ITR in the multicast source site will choose their own RLOC for 699 the source address for encapsulated multicast traffic. The RLOC 700 addresses are the ones joined by remote multicast ETRs. 702 When different (S-EID,G) traffic is combined into a single (RLOC,G) 703 core distribution tree, this may cause traffic to go to a receiver 704 multicast site when it does not need to. This happens when one 705 receiver multicast site joins (S1-EID,Gi) through a core distribution 706 tree of (RLOC1,Gi) and another multicast receiver site joins (S2- 707 EID,Gi) through the same core distribution tree of (RLOC1,Gi). When 708 ETRs decapsulate such traffic, they should know from their local 709 (S-EID,G) state if the packet should be forwarded. If there is no 710 (S-EID,G) state that matches the inner packet header, the packet is 711 discarded. 713 8.2. ETR Forwarding Procedure 715 The following procedure is used by an ETR, when it receives a 716 multicast packet from a source outside of its site: 718 1. When a multicast data packet is received by an ETR on an 719 external-facing interface, it will do an RPF lookup on the S-RLOC 720 state it has stored. If the RPF check succeeds, the interfaces 721 from the OIF-list are used for replication to interfaces that are 722 site-facing as well as interfaces that are external-facing (this 723 ETR can also be a transit multicast router for receivers outside 724 of its site). When the packet is to be replicated for an 725 external-facing interface, the LISP encapsulation header are not 726 stripped. When the packet is replicated for a site-facing 727 interface, the encapsulation header is stripped. 729 2. The packet without a LISP header is now forwarded down the 730 (S-EID,G) distribution tree in the receiver multicast site. 732 8.3. Replication Locations 734 Multicast packet replication can happen in the following topological 735 locations: 737 o In an IGP multicast router inside a site which operates on S-EIDs. 739 o In a transit multicast router inside of the core which operates on 740 S-RLOCs. 742 o At one or more ETR routers depending on the path a Join/Prune 743 message exits a receiver multicast site. 745 o At one or more ITR routers in a source multicast site depending on 746 what priorities are returned in a Map-Reply to receiver multicast 747 sites. 749 In the last case the source multicast site can do replication rather 750 than having a single exit from the site. But this only can occur 751 when the priorities in the Map-Reply are modified for different 752 receiver multicast site so that the PIM Join/Prune messages arrive at 753 different ITRs. 755 This policy technique, also used in [ALT] for unicast, is useful for 756 multicast to mitigate the problems of changing distribution tree 757 state as discussed in Section 6. 759 9. LISP-Multicast Interworking 761 This section will describe the multicast corollary to [INTWORK] which 762 describes the interworking of multicast routing among LISP and non- 763 LISP sites. 765 9.1. LISP and non-LISP Mixed Sites 767 Since multicast communication can involve more than two entities to 768 communicate together, the combinations of interworking scenarios are 769 more involved. However, the state maintained for distribution trees 770 at the sites is the same regardless of whether or not the site is 771 LISP enabled or not. So most of the implications are in the core 772 with respect to storing routable EID prefixes from either PA or PI 773 blocks. 775 Before enumerating the multicast interworking scenarios, let's define 776 3 deployment states of a site: 778 o A non-LISP site which will run PIM-SSM or PIM-ASM with MSDP as it 779 does today. The addresses for the site are globally routable. 781 o A site that deploys LISP for unicast routing. The addresses for 782 the site are not globally routable. Let's define the name for 783 this type of site as a uLISP site. 785 o A site that deploys LISP for both unicast and multicast routing. 786 The addresses for the site are not globally routable. Let's 787 define the name for this type of site as a LISP-Multicast site. 789 What will not be considered is a LISP site enabled for multicast 790 purposes only but do consider a uLISP site as documented in 791 [INTWORK]. In this section there is no discussion how a LISP site 792 sends multicast packets when all receiver sites are LISP-Multicast 793 enabled; that has been discussed in previous sections. 795 The following scenarios exist to make LISP-Multicast sites interwork 796 with non-LISP-Multicast sites: 798 1. A LISP site must be able to send multicast packets to receiver 799 sites which are a mix of non-LISP sites and uLISP sites. 801 2. A non-LISP site must be able to send multicast packets to 802 receiver sites which are a mix of non-LISP sites and uLISP sites. 804 3. A non-LISP site must be able to send multicast packets to 805 receiver sites which are a mix of LISP sites, uLISP sites, and 806 non-LISP sites. 808 4. A uLISP site must be able to send multicast packets to receiver 809 sites which are a mix of LISP sites, uLISP sites, and non-LISP 810 sites. 812 5. A LISP 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 9.1.1. LISP Source Site to non-LISP Receiver Sites 818 In the first scenario, a site is LISP capable for both unicast and 819 multicast traffic and as such operates on EIDs. Therefore there is a 820 possibility that the EID prefix block is not routable in the core. 821 For LISP receiver multicast sites this isn't a problem but for non- 822 LISP or uLISP receiver multicast sites, when a PIM Join/Prune message 823 is received by the edge router, it has no route to propagate the 824 Join/Prune message out of the site. This is no different than the 825 unicast case that LISP-NAT in [INTWORK] solves. 827 LISP-NAT allows a unicast packet that exits a LISP site to get its 828 source address mapped to a globally routable address before the ITR 829 realizes that it should not encapsulate the packet destined to a non- 830 LISP site. For a multicast packet to leave a LISP site, distribution 831 tree state needs to be built so the ITR can know where to send the 832 packet. So the receiver multicast sites need to know about the 833 multicast source host by its routable address and not its EID 834 address. When this is the case, the routable address is the 835 (S-RLOC,G) state that is stored and maintained in the core routers. 836 It is important to note that the routable address for the host cannot 837 be the same as an RLOC for the site because it is desirable for ITRs 838 to process a received PIM Join/Prune message from an external-facing 839 interface to be propagated inside of the site so the site-part of the 840 distribution tree is built. 842 Using a globally routable source address allows non-LISP and uLISP 843 multicast receiver to join, create, and maintain a multicast 844 distribution tree. However, the LISP multicast receiver site will 845 want to perform an EID-to-RLOC mapping table lookup when a PIM Join/ 846 Prune message is received on a site-facing interface. It does this 847 because it wants to find a (S-RLOC,G) entry to Join in the core. So 848 there is a conflict of behavior between the two types of sites. 850 The solution to this problem is the same as when an ITR wants to send 851 a unicast packet to a destination site but needs determine if the 852 site is LISP capable or not. When it is not LISP capable, the ITR 853 does not encapsulate the packet. So for the multicast case, when ETR 854 receives a PIM Join/Prune message for (S-EID,G) state, it will do a 855 mapping table lookup on S-EID. In this case, S-EID is not in the 856 mapping database because the source multicast site is using a 857 routable address and not an EID prefix address. So the ETR knows to 858 simply propagate the PIM Join/Prune message to a external-facing 859 interface without converting the (S-EID,G) because it is an (S,G) 860 where S is routable and reachable via core routing tables. 862 Now that the multicast distribution tree is built and maintained from 863 any non-LISP or uLISP receiver multicast site, the way packet 864 forwarding model is performed can be explained. 866 Since the ITR in the source multicast site has never received a 867 unicast encapsulated PIM Join/Prune message from any ETR in a 868 receiver multicast site, it knows there are no LISP-Multicast 869 receiver sites. Therefore, there is no need for the ITR to 870 encapsulate data. Since it will know a priori (via configuration) 871 that its site's EIDs are not routable (and not registered to the 872 mapping database system), it assumes that the multicast packets from 873 the source host are sent by a routable address. That is, it is the 874 responsibility of the multicast source host's system administrator to 875 ensure that the source host sends multicast traffic using a routable 876 source address. When this happens, the ITR acts simply as a router 877 and forwards the multicast packet like an ordinary multicast router. 879 There is an alternative to using a LISP-NAT scheme just like there is 880 for unicast [INTWORK] forwarding by using Proxy Tunnel Routers 881 (PxTRs). This can work the same way for multicast routing as well, 882 but the difference is that non-LISP and uLISP sites will send PIM 883 Join/Prune messages for (S-EID,G) which make their way in the core to 884 multicast PxTRs. Let's call this use of a PxTR as a "Multicast 885 Proxy-ETR" (or mPETR). Since the mPETRs advertise very coarse EID 886 prefixes, they draw the PIM Join/Prune control traffic making them 887 the target of the distribution tree. To get multicast packets from 888 the LISP source multicast sites, the tree needs to be built on the 889 path from the mPETR to the LISP source multicast site. To make this 890 happen the mPETR acts as a "Proxy ETR" (where in unicast it acts as a 891 "Proxy ITR", or an uPITR [INTWORK]). 893 The existence of mPETRs in the core allows source multicast site ITRs 894 to encapsulate multicast packets according to (S-RLOC,G) state. The 895 (S-RLOC,G) state is built from the mPETRs to the multicast ITRs. The 896 encapsulated multicast packets are decapsulated by mPETRs and then 897 forwarded according to (S-EID,G) state. The (S-EID,G) state is built 898 from the non-LISP and uLISP receiver multicast sites to the mPETRs. 900 9.1.2. Non-LISP Source Site to non-LISP Receiver Sites 902 Clearly non-LISP multicast sites can send multicast packets to non- 903 LISP receiver multicast sites. That is what they do today. However, 904 discussion is required to show how non-LISP multicast sites send 905 multicast packets to uLISP receiver multicast sites. 907 Since uLISP receiver multicast sites are not targets of any (S,G) 908 state, they simply send (S,G) PIM Join/Prune messages toward the non- 909 LISP source multicast site. Since the source multicast site, in this 910 case has not been upgraded to LISP, all multicast source host 911 addresses are routable. So this case is simplified to where a uLISP 912 receiver multicast site looks to the source multicast site as a non- 913 LISP receiver multicast site. 915 9.1.3. Non-LISP Source Site to Any Receiver Site 917 When a non-LISP source multicast site has receivers in either a non- 918 LISP/uLISP site or a LISP site, one needs to decide how the LISP 919 receiver multicast site will attach to the distribution tree. It is 920 known from Section 9.1.2 that non-LISP and uLISP receiver multicast 921 sites can join the distribution tree, but a LISP receiver multicast 922 site ETR will need to know if the source address of the multicast 923 source host is routable or not. It has been shown in Section 9.1.1 924 that an ETR, before it sends a PIM Join/Prune message on an external- 925 facing interface, does a EID-to-RLOC mapping lookup to determine if 926 it should convert the (S,G) state from a PIM Join/Prune message 927 received on a site-facing interface to a (S-RLOC,G). If the lookup 928 fails, the ETR can conclude the source multicast site is a non-LISP 929 site so it simply forwards the Join/Prune message (it also doesn't 930 need to send a unicast encapsulated Join/Prune message because there 931 is no ITR in a non-LISP site and there is namespace continuity 932 between the ETR and source). 934 For a non-LISP source multicast site, (S-EID,G) state could be 935 limited to the edges of the network with the use of multicast proxy- 936 ITRs (mPITRs). The mPITRs can take native, unencapsulated multicast 937 packets from non-LISP source multicast and uLISP sites and 938 encapsulate them to ETRs in receiver multicast sites or to mPETRs 939 that can decapsulate for non-LISP receiver multicast or uLISP sites. 940 The mPITRs are responsible for sending (S-EID,G) joins to the non- 941 LISP source multicast site. To connect the distribution trees 942 together, multicast ETRs will need to be configured with the mPITR's 943 RLOC addresses so they can send both (S-RLOC,G) joins to build a 944 distribution tree to the mPITR as well as for sending unicast joins 945 to mPITRs so they can propogate (S-EID,G) joins into source multicast 946 sites. The use of mPITRs is undergoing more study and is work in 947 progress. 949 9.1.4. Unicast LISP Source Site to Any Receiver Sites 951 In the last section, it was explained how an ETR in a multicast 952 receiver site can determine if a source multicast site is LISP- 953 enabled by looking into the mapping database. When the source 954 multicast site is a uLISP site, it is LISP enabled but the ITR, by 955 definition is not capable of doing multicast encapsulation. So for 956 the purposes of multicast routing, the uLISP source multicast site is 957 treated as non-LISP source multicast site. 959 Non-LISP receiver multicast sites can join distribution trees to a 960 uLISP source multicast site since the source site behaves, from a 961 forwarding perspective, as a non-LISP source site. This is also the 962 case for a uLISP receiver multicast site since the ETR does not have 963 multicast functionality built-in or enabled. 965 Special considerations are required for LISP receiver multicast sites 966 since they think the source multicast site is LISP capable, the ETR 967 cannot know if ITR is LISP-Multicast capable. To solve this problem, 968 each mapping database entry will have a multicast 2-tuple (Mpriority, 969 Mweight) per RLOC. When the Mpriority is set to 255, the site is 970 considered not multicast capable. So an ETR in a LISP receiver 971 multicast site can distinguish whether a LISP source multicast site 972 is LISP-Multicast site from a uLISP site. 974 9.1.5. LISP Source Site to Any Receiver Sites 976 When a LISP source multicast site has receivers in LISP, non-LISP, 977 and uLISP receiver multicast sites, it has a conflict about how it 978 sends multicast packets. The ITR can either encapsulate or natively 979 forward multicast packets. Since the receiver multicast sites are 980 heterogeneous in their behavior, one packet forwarding mechanism 981 cannot satisfy both. However, if a LISP receiver multicast site acts 982 like a uLISP site then it could receive packets like a non-LISP 983 receiver multicast site making all receiver multicast sites have 984 homogeneous behavior. However, this poses the following issues: 986 o LISP-NAT techniques with routable addresses would be required in 987 all cases. 989 o Or alternatively, mPETR deployment would be required forcing 990 coarse EID prefix advertisement in the core. 992 o But what is most disturbing is that when all sites that 993 participate are LISP-Multicast sites but then a non-LISP or uLISP 994 site joins the distribution tree, then the existing joined LISP 995 receiver multicast sites would have to change their behavior. 996 This would create too much dynamic tree-building churn to be a 997 viable alternative. 999 So the solution space options are: 1001 1. Make the LISP ITR in the source multicast site send two packets, 1002 one that is encapsulated with (S-RLOC,G) to reach LISP receiver 1003 multicast sites and another that is not encapsulated with 1004 (S-EID,G) to reach non-LISP and uLISP receiver multicast sites. 1006 2. Make the LISP ITR always encapsulate packets with (S-RLOC,G) to 1007 reach LISP-Multicast sites and to reach mPETRs that can 1008 decapsulate and forward (S-EID,G) packets to non-LISP and uLISP 1009 receiver multicast sites. 1011 9.2. LISP Sites with Mixed Address Families 1013 A LISP database mapping entry that describes the locator-set, 1014 Mpriority and Mweight per locator address (RLOC), for an EID prefix 1015 associated with a site could have RLOC addresses in either IPv4 or 1016 IPv6 format. When a mapping entry has a mix of RLOC formatted 1017 addresses, it is an implicit advertisement by the site that it is a 1018 dual-stack site. That is, the site can receive IPv4 or IPv6 unicast 1019 packets. 1021 To distinguish if the site can receive dual-stack unicast packets as 1022 well as dual-stack multicast packets, the Mpriority value setting 1023 will be relative to an IPv4 or IPv6 RLOC See [LISP] for packet format 1024 details. 1026 If one considers the combinations of LISP, non-LISP, and uLISP sites 1027 sharing the same distribution tree and considering the capabilities 1028 of supporting IPv4, IPv6, or dual-stack, the number of total 1029 combinations grows beyond comprehension. 1031 Using some combinatorial math, the following profiles of a site and 1032 the combinations that can occur: 1034 1. LISP-Multicast IPv4 Site 1036 2. LISP-Multicast IPv6 Site 1038 3. LISP-Multicast Dual-Stack Site 1040 4. uLISP IPv4 Site 1042 5. uLISP IPv6 Site 1043 6. uLISP Dual-Stack Site 1045 7. non-LISP IPv4 Site 1047 8. non-LISP IPv6 Site 1049 9. non-LISP Dual-Stack Site 1051 Lets define (m n) = m!/(n!*(m-n)!), pronounced "m choose n" to 1052 illustrate some combinatorial math below. 1054 When 1 site talks to another site, the combinatorial is (9 2), when 1 1055 site talks to another 2 sites, the combinatorial is (9 3). If sum 1056 this up to (9 9), then: 1058 (9 2) + (9 3) + (9 4) + (9 5) + (9 6) + (9 7) + (9 8) + (9 9) = 1060 36 + 84 + 126 + 126 + 84 + 36 + 9 + 1 1062 Which results in the total number of cases to be considered at 502. 1064 This combinatorial gets even worse when one considers a site using 1065 one address family inside of the site and the xTRs use the other 1066 address family (as in using IPv4 EIDs with IPv6 RLOCs or IPv6 EIDs 1067 with IPv4 RLOCs). 1069 To rationalize this combinatorial nightmare, there are some 1070 guidelines which need to be put in place: 1072 o Each distribution tree shared between sites will either be an IPv4 1073 distribution tree or an IPv6 distribution tree. Therefore, head- 1074 end replication can be avoided by building and sending packets on 1075 each address family based distribution tree. Even though there 1076 might be an urge to do multicast packet translation from one 1077 address family format to the other, it is a non-viable over- 1078 complicated urge. Multicast ITRs will only encapsulate packets 1079 where the inner and outer headers are from the same address 1080 family. 1082 o All LISP sites on a multicast distribution tree must share a 1083 common address family which is determined by the source site's 1084 locator-set in its LISP database mapping entry. All receiver 1085 multicast sites will use the best RLOC priority controlled by the 1086 source multicast site. This is true when the source site is 1087 either LISP-Multicast or uLISP capable. This means that priority- 1088 based policy modification is prohibited. When a receiver 1089 multicast site ETR receives a (S-EID,G) join, it must select a 1090 S-RLOC for the same address family as S-EID. 1092 o When a multicast locator-set has more than one locator, only 1093 locators from the same address-family MUST be set to the same best 1094 priority value. A mixed locator-set can exist (for unicast use), 1095 but the multicast priorities MUST be the set for the same address 1096 family locators. 1098 o When the source site is not LISP capable, it is up to how 1099 receivers find the source and group information for a multicast 1100 flow. That mechanism decides the address family for the flow. 1102 9.3. Making a Multicast Interworking Decision 1104 This Multicast Interworking section has shown all combinations of 1105 multicast connectivity that could occur. As already concluded, this 1106 can be quite complicated and if the design is too ambitious, the 1107 dynamics of the protocol could cause a lot of instability. 1109 The trade-off decisions are hard to make and so the same single 1110 solution is desirable to work for both IPv4 and IPv6 multicast. It 1111 is imperative to have an incrementally deployable solution for all of 1112 IPv4 unicast and multicast and IPv6 unicast and multicast while 1113 minimizing (or eliminating) both unicast and multicast EID namespace 1114 state. 1116 Therefore the design decision to go with uPITRs [INTWORK] for unicast 1117 routing and mPETRs for multicast routing seems to be the sweet spot 1118 in the solution space so state requirements can be optimized and 1119 avoid head-end data replication at ITRs. 1121 10. Considerations when RP Addresses are Embedded in Group Addresses 1123 When ASM and PIM-Bidir is used in an IPv6 inter-domain environment, a 1124 technique exists to embed the unicast address of an RP in a IPv6 1125 group address [RFC3956]. When routers in end sites process a PIM 1126 Join/Prune message which contain an embedded-RP group address, they 1127 extract the RP address from the group address and treat it from the 1128 EID namespace. However, core routers do not have state for the EID 1129 namespace, and need to extract an RP address from the RLOC namespace. 1131 Therefore, it is the responsibility of ETRs in multicast receiver 1132 sites to map the group address into a group address where the 1133 embedded-RP address is from the RLOC namespace. The mapped RP- 1134 address is obtained from a EID-to-RLOC mapping database lookup. The 1135 ETR will also send a unicast (*,G) Join/Prune message to the ITR so 1136 the branch of the distribution tree from the source site resident RP 1137 to the ITR is created. 1139 This technique is no different than the techniques described in this 1140 specification for translating (S,G) state and propagating Join/Prune 1141 messages into the core. The only difference is that the (*,G) state 1142 in Join/Prune messages are mapped because they contain unicast 1143 addresses encoded in an Embedded-RP group address. 1145 11. Taking Advantage of Upgrades in the Core 1147 If the core routers are upgraded to support [RFC5496], then the EID 1148 specific data can be passed through the core without, possibly, 1149 having to store the state in the core. 1151 By doing this one can eliminate the ETR from unicast encapsulating 1152 PIM Join/Prune messages to the source site's ITR. 1154 However, this solution is restricted to a small set of workable cases 1155 which would not be good for general use of LISP-Multicast. In 1156 addition due to slow convergence properties, it is not being 1157 recommended for LISP-Multicast. 1159 12. Mtrace Considerations 1161 Mtrace functionality MUST be consistent with unicast traceroute 1162 functionality where all hops from multicast receiver to multicast 1163 source are visible. 1165 The design for mtrace for use in LISP-Multicast environments is to be 1166 determined but should build upon the mtrace version 2 specified in 1167 [MTRACE]. 1169 13. Security Considerations 1171 The security concerns for LISP multicast are mainly the same as for 1172 the base LISP specification [LISP] and for multicast in general, 1173 including PIM-ASM [RFC4601]. 1175 There may be a security concern with respect to unicast PIM messages. 1176 When multiple receiver sites are joining a (S-EID1,G) distribution 1177 tree that maps to a (RLOC1,G) core distribution tree, and a malicious 1178 receiver site joins a (S-EID2,G) distribution tree that also maps to 1179 the (RLOC1,G) core distribution tree, the legitimate sites will 1180 receive data from S-EID2 when they did not ask for it. 1182 14. Acknowledgments 1184 The authors would like to gratefully acknowledge the people who have 1185 contributed discussion, ideas, and commentary to the making of this 1186 proposal and specification. People who provided expert review were 1187 Scott Brim, Greg Shepherd, and Dave Oran. Other commentary from 1188 discussions at Summer 2008 Dublin IETF were Toerless Eckert and 1189 Ijsbrand Wijnands. 1191 The authors would also like to thank the MBONED working group for 1192 constructive and civil verbal feedback when this draft was presented 1193 at the Fall 2008 IETF in Minneapolis. In particular, good commentary 1194 came from Tom Pusateri, Steve Casner, Marshall Eubanks, Dimitri 1195 Papadimitriou, Ron Bonica, Lenny Guardino, Alia Atlas, Jesus Arango, 1196 and Jari Arkko. 1198 An expert review of this specification was done by Yiqun Cai and 1199 Liming Wei. The authors thank them for their detailed comments. 1201 This work originated in the Routing Research Group (RRG) of the IRTF. 1202 The individual submission [MLISP] was converted into this IETF LISP 1203 working group draft. 1205 15. IANA Considerations 1207 This document makes no request of the IANA. 1209 16. References 1211 16.1. Normative References 1213 [INTWORK] Lewis, D., Meyer, D., and D. Farinacci, "Interworking LISP 1214 with IPv4 and IPv6", draft-ietf-lisp-interworking-02.txt 1215 (work in progress). 1217 [LISP] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, 1218 "Locator/ID Separation Protocol (LISP)", 1219 draft-ietf-lisp-16.txt (work in progress). 1221 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1222 Requirement Levels", BCP 14, RFC 2119, March 1997. 1224 [RFC3618] Fenner, B. and D. Meyer, "Multicast Source Discovery 1225 Protocol (MSDP)", RFC 3618, October 2003. 1227 [RFC3956] Savola, P. and B. Haberman, "Embedding the Rendezvous 1228 Point (RP) Address in an IPv6 Multicast Address", 1229 RFC 3956, November 2004. 1231 [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, 1232 "Protocol Independent Multicast - Sparse Mode (PIM-SM): 1233 Protocol Specification (Revised)", RFC 4601, August 2006. 1235 [RFC4604] Holbrook, H., Cain, B., and B. Haberman, "Using Internet 1236 Group Management Protocol Version 3 (IGMPv3) and Multicast 1237 Listener Discovery Protocol Version 2 (MLDv2) for Source- 1238 Specific Multicast", RFC 4604, August 2006. 1240 [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for 1241 IP", RFC 4607, August 2006. 1243 [RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, 1244 "Multiprotocol Extensions for BGP-4", RFC 4760, 1245 January 2007. 1247 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 1248 "Bidirectional Protocol Independent Multicast (BIDIR- 1249 PIM)", RFC 5015, October 2007. 1251 [RFC5135] Wing, D. and T. Eckert, "IP Multicast Requirements for a 1252 Network Address Translator (NAT) and a Network Address 1253 Port Translator (NAPT)", BCP 135, RFC 5135, February 2008. 1255 [RFC5496] Wijnands, IJ., Boers, A., and E. Rosen, "The Reverse Path 1256 Forwarding (RPF) Vector TLV", RFC 5496, March 2009. 1258 16.2. Informative References 1260 [ALT] Farinacci, D., Fuller, V., and D. Meyer, "LISP Alternative 1261 Topology (LISP-ALT)", draft-ietf-lisp-alt-09.txt (work in 1262 progress). 1264 [MLISP] Farinacci, D., Meyer, D., Zwiebel, J., and S. Venaas, 1265 "LISP for Multicast Environments", 1266 draft-farinacci-lisp-multicast-01.txt (work in progress). 1268 [MTRACE] Asaeda, H., Jinmei, T., Fenner, W., and S. Casner, "Mtrace 1269 Version 2: Traceroute Facility for IP Multicast", 1270 draft-ietf-mboned-mtrace-v2-08.txt (work in progress). 1272 Appendix A. Document Change Log 1274 A.1. Changes to draft-ietf-lisp-multicast-11.txt 1276 o Posted November 2011. 1278 o Added Stig text to Security Considerations section to reflect 1279 comments from IESG review comment from Stephen Farrell. 1281 o Changed how an unicast PIM join gets sent. Do not use an ECM or 1282 else an instance-ID cannot be included in the join. So go back to 1283 what we had where the unicast PIM join is encapsulated in a 4341 1284 UDP packet. 1286 A.2. Changes to draft-ietf-lisp-multicast-10.txt 1288 o Posted second half of October 2011. Changes to reflect IESG 1289 review comments from Stephen Farrell. 1291 A.3. Changes to draft-ietf-lisp-multicast-09.txt 1293 o Posted October 2011. Changes to reflect IESG review comments from 1294 Ralph Droms and Kathleen Moriarty. 1296 A.4. Changes to draft-ietf-lisp-multicast-08.txt 1298 o Posted September 2011. Minor editorial changes from Jari's 1299 commentary. 1301 A.5. Changes to draft-ietf-lisp-multicast-07.txt 1303 o Posted July 2011. Fixing IDnits errors. 1305 A.6. Changes to draft-ietf-lisp-multicast-06.txt 1307 o Posted June 2011 to complete working group last call. 1309 o Added paragraph to section 8.1.2 based on Jesus comment about 1310 making it more clear what happens when two (S-EID,G) trees use the 1311 same (RLOC,G) tree. 1313 o Make more references to [INTWORK] when mentioning uPITRs and 1314 uPETRs. 1316 o Made many changes based on editorial and wordsmithing comments 1317 from Alia. 1319 A.7. Changes to draft-ietf-lisp-multicast-05.txt 1321 o Posted April 2011 to reset expiration timer. 1323 o Updated references. 1325 A.8. Changes to draft-ietf-lisp-multicast-04.txt 1327 o Posted October 2010 to reset expiration timer. 1329 o Updated references. 1331 A.9. Changes to draft-ietf-lisp-multicast-03.txt 1333 o Posted April 2010. 1335 o Added section 8.1.2 to address Joel Halpern's comment about 1336 receiver sites joining the same source site via 2 different RLOCs, 1337 each being a separate ITR. 1339 o Change all occurences of "mPTR" to "mPETR" to become more 1340 consistent with uPITRs and uPETRs described in [INTWORK]. That 1341 is, an mPETR is a LISP multicast router that decapsulates 1342 multicast packets that are encapsulated to it by ITRs in multicast 1343 source sites. 1345 o Add clarifications in section 9 about how homogeneous multicast 1346 encapsulation should occur. As well as describing in this 1347 section, how to deal with mixed-locator sets to avoid 1348 heterogeneous encapsulation. 1350 o Introduce concept of mPITRs to help reduce (S-EID,G) to the edges 1351 of LISP global multicast network. 1353 A.10. Changes to draft-ietf-lisp-multicast-02.txt 1355 o Posted September 2009. 1357 o Added Document Change Log appendix. 1359 o Specify that the LISP Encapsulated Control Message be used for 1360 unicasting PIM Join/Prune messages from ETRs to ITRs. 1362 A.11. Changes to draft-ietf-lisp-multicast-01.txt 1364 o Posted November 2008. 1366 o Specified that PIM Join/Prune unicast messages that get sent from 1367 ETRs to ITRs of a source multicast site get LISP encapsulated in 1368 destination UDP port 4342. 1370 o Add multiple RLOCs per ITR per Yiqun's comments. 1372 o Indicate how static RPs can be used when LISP is run using Bidir- 1373 PIM in the core. 1375 o Editorial changes per Liming comments. 1377 o Add Mttrace Considersations section. 1379 A.12. Changes to draft-ietf-lisp-multicast-00.txt 1381 o Posted April 2008. 1383 o Renamed from draft-farinacci-lisp-multicast-01.txt. 1385 Authors' Addresses 1387 Dino Farinacci 1388 cisco Systems 1389 Tasman Drive 1390 San Jose, CA 1391 USA 1393 Email: dino@cisco.com 1395 Dave Meyer 1396 cisco Systems 1397 Tasman Drive 1398 San Jose, CA 1399 USA 1401 Email: dmm@cisco.com 1403 John Zwiebel 1404 cisco Systems 1405 Tasman Drive 1406 San Jose, CA 1407 USA 1409 Email: jzwiebel@cisco.com 1411 Stig Venaas 1412 cisco Systems 1413 Tasman Drive 1414 San Jose, CA 1415 USA 1417 Email: stig@cisco.com