idnits 2.17.1 draft-ietf-lisp-multicast-10.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 (October 17, 2011) is 4573 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for intended status: Experimental ---------------------------------------------------------------------------- == Outdated reference: A later version (-06) exists of draft-ietf-lisp-interworking-02 == Outdated reference: A later version (-24) exists of draft-ietf-lisp-15 ** Obsolete normative reference: RFC 4601 (Obsoleted by RFC 7761) == Outdated reference: A later version (-10) exists of draft-ietf-lisp-alt-08 == Outdated reference: A later version (-26) exists of draft-ietf-mboned-mtrace-v2-08 Summary: 1 error (**), 0 flaws (~~), 5 warnings (==), 1 comment (--).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: April 19, 2012 S. Venaas 6 cisco Systems 7 October 17, 2011 9 LISP for Multicast Environments 10 draft-ietf-lisp-multicast-10 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 April 19, 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-10.txt . . . . . . . 36 86 A.2. Changes to draft-ietf-lisp-multicast-09.txt . . . . . . . 36 87 A.3. Changes to draft-ietf-lisp-multicast-08.txt . . . . . . . 36 88 A.4. Changes to draft-ietf-lisp-multicast-07.txt . . . . . . . 36 89 A.5. Changes to draft-ietf-lisp-multicast-06.txt . . . . . . . 36 90 A.6. Changes to draft-ietf-lisp-multicast-05.txt . . . . . . . 36 91 A.7. Changes to draft-ietf-lisp-multicast-04.txt . . . . . . . 36 92 A.8. Changes to draft-ietf-lisp-multicast-03.txt . . . . . . . 37 93 A.9. Changes to draft-ietf-lisp-multicast-02.txt . . . . . . . 37 94 A.10. Changes to draft-ietf-lisp-multicast-01.txt . . . . . . . 37 95 A.11. Changes to draft-ietf-lisp-multicast-00.txt . . . . . . . 38 96 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 39 98 1. Requirements Notation 100 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 101 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 102 document are to be interpreted as described in [RFC2119]. 104 2. Introduction 106 The Locator/ID Separation Architecture [LISP] provides a mechanism to 107 separate out Identification and Location semantics from the current 108 definition of an IP address. By creating two namespaces, an Endpoint 109 ID (EID) namespace used by sites and a Routing Locator (RLOC) 110 namespace used by core routing, the core routing infrastructure can 111 scale by doing topological aggregation of routing information. 113 Since LISP creates a new namespace, a mapping function must exist to 114 map a site's EID prefixes to its associated locators. For unicast 115 packets, both the source address and destination address must be 116 mapped. For multicast packets, only the source address needs to be 117 mapped. The destination group address doesn't need to be mapped 118 because the semantics of an IPv4 or IPv6 group address are logical in 119 nature and not topology-dependent. Therefore, this specification 120 focuses on to map a source EID address of a multicast flow during 121 distribution tree setup and packet delivery. 123 This specification will address the following scenarios: 125 1. How a multicast source host in a LISP site sends multicast 126 packets to receivers inside of its site as well as to receivers 127 in other sites that are LISP enabled. 129 2. How inter-domain (or between LISP sites) multicast distribution 130 trees are built and how forwarding of multicast packets leaving a 131 source site toward receivers sites is performed. 133 3. What protocols are affected and what changes are required to such 134 multicast protocols. 136 4. How ASM-mode (Any Source Multicast), SSM-mode (Single Source 137 Multicast), and Bidir-mode (Bidirectional Shared Trees) service 138 models will operate. 140 5. How multicast packet flow will occur for multiple combinations of 141 LISP and non-LISP capable source and receiver sites, for example: 143 A. How multicast packets from a source host in a LISP site are 144 sent to receivers in other sites when they are all non-LISP 145 sites. 147 B. How multicast packets from a source host in a LISP site are 148 sent to receivers in both LISP-enabled sites and non-LISP 149 sites. 151 C. How multicast packets from a source host in a non-LISP site 152 are sent to receivers in other sites when they are all LISP- 153 enabled sites. 155 D. How multicast packets from a source host in a non-LISP site 156 are sent to receivers in both LISP-enabled sites and non-LISP 157 sites. 159 This specification focuses on what changes are needed to the 160 multicast routing protocols to support LISP-Multicast as well as 161 other protocols used for inter-domain multicast, such as Multi- 162 protocol BGP (MBGP) [RFC4760]. The approach proposed in this 163 specification requires no packet format changes to the protocols and 164 no operational procedural changes to the multicast infrastructure 165 inside of a site when all sources and receivers reside in that site, 166 even when the site is LISP enabled. That is, internal operation of 167 multicast is unchanged regardless of whether or not the site is LISP 168 enabled or whether or not receivers exist in other sites which are 169 LISP-enabled. 171 Therefore, we see changes only to PIM-ASM [RFC4601], MSDP [RFC3618], 172 and PIM-SSM [RFC4607]. Bidir-PIM [RFC5015], which typically does not 173 run in an inter-domain environment is not addressed in depth in this 174 version of the specification. 176 Also, the current version of this specification does not describe 177 multicast-based Traffic Engineering relative to the TE-ITR (Traffic 178 Engineering based Ingress Tunnel Router) and TE-ETR (Traffic 179 Engineering based Egress Tunnel Router) descriptions in [LISP]. 180 Futher work is also needed to determine the detailed behavior for 181 multicast proxy ITRs (mPITRs) (Section 9.1.3), mtrace (Section 12), 182 and locator reachability (Section 6). Finally, further deployment 183 and experimentation would be useful to understand the real-life 184 performance of the LISP-Multicast solution. For instance, the design 185 optimizes for minimal state and control traffic in the core, but can 186 in some cases cause extra multicast traffic to be sent Section 8.1.2. 188 3. Definition of Terms 190 The terminology in this section is consistent with the definitions in 191 [LISP] but is extended specifically to deal with the application of 192 the terminology to multicast routing. 194 LISP-Multicast: a reference to the design in this specification. 195 That is, when any site that is participating in multicast 196 communication has been upgraded to be a LISP site, the operation 197 of control-plane and data-plane protocols is considered part of 198 the LISP-Multicast architecture. 200 Endpoint ID (EID): a 32-bit (for IPv4) or 128-bit (for IPv6) value 201 used in the source address field of the first (most inner) LISP 202 header of a multicast packet. The host obtains a destination 203 group address the same way it obtains one today, as it would when 204 it is a non-LISP site. The source EID is obtained via existing 205 mechanisms used to set a host's "local" IP address. An EID is 206 allocated to a host from an EID prefix block associated with the 207 site the host is located in. An EID can be used by a host to 208 refer to another host, as when it joins an SSM (S-EID,G) route 209 using IGMP version 3 [RFC4604]. LISP uses Provider Independent 210 (PI) blocks for EIDs; such EIDs MUST NOT be used as LISP RLOCs. 211 Note that EID blocks may be assigned in a hierarchical manner, 212 independent of the network topology, to facilitate scaling of the 213 mapping database. In addition, an EID block assigned to a site 214 may have site-local structure (subnetting) for routing within the 215 site; this structure is not visible to the global routing system. 217 Routing Locator (RLOC): the IPv4 or IPv6 address of an ingress 218 tunnel router (ITR), the router in the multicast source host's 219 site that encapsulates multicast packets. It is the output of a 220 EID-to-RLOC mapping lookup. An EID maps to one or more RLOCs. 221 Typically, RLOCs are numbered from topologically-aggregatable 222 blocks that are assigned to a site at each point to which it 223 attaches to the global Internet; where the topology is defined by 224 the connectivity of provider networks, RLOCs can be thought of as 225 Provider Assigned (PA) addresses. Multiple RLOCs can be assigned 226 to the same ITR device or to multiple ITR devices at a site. 228 Ingress Tunnel Router (ITR): a router which accepts an IP multicast 229 packet with a single IP header (more precisely, an IP packet that 230 does not contain a LISP header). The router treats this "inner" 231 IP destination multicast address opaquely so it doesn't need to 232 perform a map lookup on the group address because it is 233 topologically insignificant. The router then prepends an "outer" 234 IP header with one of its globally-routable RLOCs as the source 235 address field. This RLOC is known to other multicast receiver 236 sites which have used the mapping database to join a multicast 237 tree for which the ITR is the root. In general, an ITR receives 238 IP packets from site end systems on one side and sends LISP- 239 encapsulated multicast IP packets out all external interfaces 240 which have been joined. 242 An ITR would receive a multicast packet from a source inside of 243 its site when 1) it is on the path from the multicast source to 244 internally joined receivers, or 2) when it is on the path from the 245 multicast source to externally joined receivers. 247 Egress Tunnel Router (ETR): a router that is on the path from a 248 multicast source host in another site to a multicast receiver in 249 its own site. An ETR accepts a PIM Join/Prune message from a site 250 internal PIM router destined for the source's EID in the multicast 251 source site. The ETR maps the source EID in the Join/Prune 252 message to an RLOC address based on the EID-to-RLOC mapping. This 253 sets up the ETR to accept multicast encapsulated packets from the 254 ITR in the source multicast site. A multicast ETR decapsulates 255 multicast encapsulated packets and replicates them on interfaces 256 leading to internal receivers. 258 xTR: is a reference to an ITR or ETR when direction of data flow is 259 not part of the context description. xTR refers to the router that 260 is the tunnel endpoint. Used synonymously with the term "Tunnel 261 Router". For example, "An xTR can be located at the Customer Edge 262 (CE) router", meaning both ITR and ETR functionality can be at the 263 CE router. 265 LISP Header: a term used in this document to refer to the outer 266 IPv4 or IPv6 header, a UDP header, and a LISP header. An ITR 267 prepends headers and an ETR strips headers. A LISP encapsulated 268 multicast packet will have an "inner" header with the source EID 269 in the source field; an "outer" header with the source RLOC in the 270 source field: and the same globally unique group address in the 271 destination field of both the inner and outer header. 273 (S,G) State: the formal definition is in the PIM Sparse Mode 274 [RFC4601] specification. For this specification, the term is used 275 generally to refer to multicast state. Based on its topological 276 location, the (S,G) state resides in routers can be either 277 (S-EID,G) state (at a location where the (S,G) state resides) or 278 (S-RLOC,G) state (in the Internet core). 280 (S-EID,G) State: refers to multicast state in multicast source and 281 receiver sites where S-EID is the IP address of the multicast 282 source host (its EID). An S-EID can appear in an IGMPv3 report, 283 an MSDP SA message or a PIM Join/Prune message that travels inside 284 of a site. 286 (S-RLOC,G) State: refers to multicast state in the core where S is 287 a source locator (the IP address of a multicast ITR) of a site 288 with a multicast source. The (S-RLOC,G) is mapped from (S-EID,G) 289 entry by doing a mapping database lookup for the EID prefix that 290 S-EID maps to. An S-RLOC can appear in a PIM Join/Prune message 291 when it travels from an ETR to an ITR over the Internet core. 293 uLISP Site: a unicast only LISP site according to [LISP] which has 294 not deployed the procedures of this specification and therefore, 295 for multicast purposes, follows the procedures from Section 9. A 296 uLISP site can be a traditional multicast site. 298 LISP Site: a unicast LISP site (uLISP Site) that is also multicast 299 capable according to the procedures in this specification. 301 mPETR: this is a multicast proxy-ETR that is responsible for 302 advertising a very coarse EID prefix which non-LISP and uLISP 303 sites can target their (S-EID,G) PIM Join/Prune message to. mPETRs 304 are used so LISP source multicast sites can send multicast packets 305 using source addresses from the EID namespace. mPETRs act as Proxy 306 ETRs for supporting multicast routing in a LISP infrastructure. 307 It is likely an uPITR [INTWORK] and a mPETR will be co-located 308 since the single device advertises a coarse EID-prefix in the 309 underlying unicast routing system. 311 Mixed Locator-Sets: this is a locator-set for a LISP database 312 mapping entry where the RLOC addresses in the locator-set are in 313 both IPv4 and IPv6 format. 315 Unicast Encapsulated PIM Join/Prune Message: this is a standard PIM 316 Join/Prune message (encapsulated in a LISP Encapsulated Control 317 Message with destination UDP port 4342) which is sent by ETRs at 318 multicast receiver sites to an ITR at a multicast source site. 319 This message is sent periodically as long as there are interfaces 320 in the OIF-list for the (S-EID,G) entry the ETR is joining for. 322 OIF-list: this is notation to describe the outgoing interface list 323 a multicast router stores per multicast routing table entry so it 324 knows what interfaces to replicate multicast packets on. 326 RPF: Reverse Path Forwarding is a procedure used by multicast 327 routers. A router will accept a multicast packet for forwarding 328 if the packet was received on the path that the router would use 329 to forward unicast packets to the multicast packet's source. 331 4. Basic Overview 333 LISP, when used for unicast routing, increases the site's ability to 334 control ingress traffic flows. Egress traffic flows are controlled 335 by the IGP in the source site. For multicast, the IGP coupled with 336 PIM can decide which path multicast packets ingress. By using the 337 traffic engineering features of LISP, a multicast source site can 338 control the egress of its multicast traffic. By controlling the 339 priorities of locators from a mapping database entry, a source 340 multicast site can control which way multicast receiver sites join to 341 the source site. 343 At this point in time, there is no requirement for different locator- 344 sets, priority, and weight policies for multicast than there is for 345 unicast. However, when traffic engineering policies are different 346 for unicast versus multicast flows, it will be desirable to use 347 multicast-based priority and weight values in Map-Reply messages. 349 The fundamental multicast forwarding model is to encapsulate a 350 multicast packet into another multicast packet. An ITR will 351 encapsulate multicast packets received from sources that it serves in 352 a LISP multicast header. The destination group address from the 353 inner header is copied to the destination address of the outer 354 header. The inner source address is the EID of the multicast source 355 host and the outer source address is the RLOC of the encapsulating 356 ITR. 358 The LISP-Multicast architecture will follow this high-level protocol 359 and operational sequence: 361 1. Receiver hosts in multicast sites will join multicast content the 362 way they do today, they use IGMP. When they use IGMPv3 where 363 they specify source addresses, they use source EIDs, that is they 364 join (S-EID,G). If the multicast source is external to this 365 receiver site, the PIM Join/Prune message flows toward the ETRs, 366 finding the shortest exit (that is the closest exit for the Join/ 367 Prune message and the closest entrance for the multicast packet 368 to the receiver). 370 2. The ETR does a mapping database lookup for S-EID. If the mapping 371 is cached from a previous lookup (from either a previous Join/ 372 Prune for the source multicast site or a unicast packet that went 373 to the site), it will use the RLOC information from the mapping. 374 The ETR will use the same priority and weighting mechanism as for 375 unicast. So the source site can decide which way multicast 376 packets egress. 378 3. The ETR will build two PIM Join/Prune messages, one that contains 379 a (S-EID,G) entry that is unicast to the ITR that matches the 380 RLOC the ETR selects, and the other which contains a (S-RLOC,G) 381 entry so the core network can create multicast state from this 382 ETR to the ITR. 384 4. When the ITR gets the unicast Join/Prune message (see Section 3 385 for formal definition), it will process (S-EID,G) entries in the 386 message and propagate them inside of the site where it has 387 explicit routing information for EIDs via the IGP. When the ITR 388 receives the (S-RLOC,G) PIM Join/Prune message it will process it 389 like any other join it would get in today's Internet. The S-RLOC 390 address is the IP address of this ITR. 392 5. At this point there is (S-EID,G) state from the joining host in 393 the receiver multicast site to the ETR of the receiver multicast 394 site. There is (S-RLOC,G) state across the core network from the 395 ETR of the multicast receiver site to the ITR in the multicast 396 source site and (S-EID,G) state in the source multicast site. 397 Note, the (S-EID,G) state is the same S-EID in each multicast 398 site. As other ETRs join the same multicast tree, they can join 399 through the same ITR (in which case the packet replication is 400 done in the core) or a different ITR (in which case the packet 401 replication is done at the source site). 403 6. When a packet is originated by the multicast host in the source 404 site, the packet will flow to one or more ITRs which will prepend 405 a LISP header. By copying the group address to the outer 406 destination address field, the ITR insert its own locator address 407 in the outer source address field. The ITR will look at its 408 (S-RLOC,G) state, where S-RLOC is its own locator address, and 409 replicate the packet on each interface a (S-RLOC,G) joined was 410 received on. The core has (S-RLOC,G) so where fanout occurs to 411 multiple sites, a core router will do packet replication. 413 7. When either the source site or the core replicates the packet, 414 the ETR will receive a LISP packet with a destination group 415 address. It will decapsulate packets because it has receivers 416 for the group. Otherwise, it would have not received the packets 417 because it would not have joined. The ETR decapsulates and does 418 a (S-EID,G) lookup in its multicast FIB to forward packets out 419 one or more interfaces to forward the packet to internal 420 receivers. 422 This architecture is consistent and scalable with the architecture 423 presented in [LISP] where multicast state in the core operates on 424 locators and multicast state at the sites operates on EIDs. 426 Alternatively, [LISP] also has a mechanism where (S-EID,G) state can 427 reside in the core through the use of RPF-vectors [RFC5496] in PIM 428 Join/Prune messages. However, few PIM implementations support RPF 429 vectors and LISP should avoid S-EID state in the core. See Section 5 430 for details. 432 However, some observations can be made on the algorithm above. The 433 control plane can scale but at the expense of sending data to sites 434 which may have not joined the distribution tree where the 435 encapsulated data is being delivered. For example, one site joins 436 (S-EID1,G) and another site joins (S-EID2,G). Both EIDs are in the 437 same multicast source site. Both multicast receiver sites join to 438 the same ITR with state (S-RLOC,G) where S-RLOC is the RLOC for the 439 ITR. The ITR joins both (S-EID1,G) and (S-EID2,G) inside of the 440 site. The ITR receives (S-RLOC,G) joins and populates the OIF-list 441 state for it. Since both (S-EID1,G) and (S-EID2, G) map to the one 442 (S-RLOC,G) packets will be delivered by the core to both multicast 443 receiver sites even though each have joined a single source-based 444 distribution tree. This behavior is a consequence of the many-to-one 445 mapping between S-EIDs and a S-RLOC. 447 There is a possible solution to this problem which reduces the number 448 of many-to-one occurrences of (S-EID,G) entries aggregating into a 449 single (S-RLOC,G) entry. If a physical ITR can be assigned multiple 450 RLOC addresses and these addresses are advertised in mapping database 451 entries, then ETRs at receiver sites have more RLOC address options 452 and therefore can join different (RLOC,G) entries for each (S-EID,G) 453 entry joined at the receiver site. It would not scale to have a one- 454 to-one relationship between the number of S-EID sources at a source 455 site and the number of RLOCs assigned to all ITRs at the site, but 456 "n" can reduce to a smaller number in the "n-to-1" relationship. And 457 in turn, reduce the opportunity for data packets to be delivered to 458 sites for groups not joined. 460 5. Source Addresses versus Group Addresses 462 Multicast group addresses don't have to be associated with either the 463 EID or RLOC namespace. They actually are a namespace of their own 464 that can be treated as logical with relatively opaque allocation. 465 So, by their nature, they don't detract from an incremental 466 deployment of LISP-Multicast. 468 As for source addresses, as in the unicast LISP scenario, there is a 469 decoupling of identification from location. In a LISP site, packets 470 are originated from hosts using their allocated EIDs. EID addresses 471 are used to identify the host as well as where in the site's topology 472 the host resides but not how and where it is attached to the 473 Internet. 475 Therefore, when multicast distribution tree state is created anywhere 476 in the network on the path from any multicast receiver to a multicast 477 source, EID state is maintained at the source and receiver multicast 478 sites, and RLOC state is maintained in the core. That is, a 479 multicast distribution tree will be represented as a 3-tuple of 480 {(S-EID,G) (S-RLOC,G) (S-EID,G)} where the first element of the 481 3-tuple is the state stored in routers from the source to one or more 482 ITRs in the source multicast site, the second element of the 3-tuple 483 is the state stored in routers downstream of the ITR, in the core, to 484 all LISP receiver multicast sites, and the third element in the 485 3-tuple is the state stored in the routers downstream of each ETR, in 486 each receiver multicast site, reaching each receiver. Note that 487 (S-EID,G) is the same in both the source and receiver multicast 488 sites. 490 The concatenation/mapping from the first element to the second 491 element of the 3-tuples is done by the ITR and from the second 492 element to the third element is done at the ETRs. 494 6. Locator Reachability Implications on LISP-Multicast 496 Multicast state as it is stored in the core is always (S,G) state as 497 it exists today or (S-RLOC,G) state as it will exist when LISP sites 498 are deployed. The core routers cannot distinguish one from the 499 other. They don't need to because it is state that RPFs against the 500 core routing tables in the RLOC namespace. The difference is where 501 the root of the distribution tree for a particular source is. In the 502 traditional multicast core, the source S is the source host's IP 503 address. For LISP-Multicast the source S is a single ITR of the 504 multicast source site. 506 An ITR is selected based on the LISP EID-to-RLOC mapping used when an 507 ETR propagates a PIM Join/Prune message out of a receiver multicast 508 site. The selection is based on the same algorithm an ITR would use 509 to select an ETR when sending a unicast packet to the site. In the 510 unicast case, the ITR can change on a per-packet basis depending on 511 the reachability of the ETR. So an ITR can change relatively easily 512 using local reachability state. However, in the multicast case, when 513 an ITR goes unreachable, new distribution tree state must be built 514 because the encapsulating root has changed. This is more significant 515 than an RPF-change event, where any router would typically locally 516 change its RPF-interface for its existing tree state. But when an 517 encapsulating LISP-Multicast ITR goes unreachable, new distribution 518 state must be rebuilt and reflect the new encapsulator. Therefore, 519 when an ITR goes unreachable, all ETRs that are currently joined to 520 that ITR will have to trigger a new Join/Prune message for (S-RLOC,G) 521 to the new ITR as well as send a unicast encapsulated Join/Prune 522 message telling the new ITR which (S-EID,G) is being joined. 524 This issue can be mitigated by using anycast addressing for the ITRs 525 so the problem does reduce to an RPF change in the core, but still 526 requires a unicast encapsulated Join/Prune message to tell the new 527 ITR about (S-EID,G). The problem with this approach is that the ETR 528 really doesn't know when the ITR has changed so the new anycast ITR 529 will get the (S-EID,G) state only when the ETR sends it the next time 530 during its periodic sending procedures. 532 7. Multicast Protocol Changes 534 A number of protocols are used today for inter-domain multicast 535 routing: 537 IGMPv1-v3, MLDv1-v2: These protocols do not require any changes for 538 LISP-Multicast for two reasons. One being that they are link- 539 local and not used over site boundaries and second, they advertise 540 group addresses that don't need translation. Where source 541 addresses are supplied in IGMPv3 and MLDv2 messages, they are 542 semantically regarded as EIDs and don't need to be converted to 543 RLOCs until the multicast tree-building protocol, such as PIM, is 544 received by the ETR at the site boundary. Addresses used for IGMP 545 and MLD come out of the source site's allocated addresses which 546 are therefore from the EID namespace. 548 MBGP: Even though MBGP is not a multicast routing protocol, it is 549 used to find multicast sources when the unicast BGP peering 550 topology and the multicast MBGP peering topology are not 551 congruent. When MBGP is used in a LISP-Multicast environment, the 552 prefixes which are advertised are from the RLOC namespace. This 553 allows receiver multicast sites to find a path to the source 554 multicast site's ITRs. MBGP peering addresses will be from the 555 RLOC namespace. There are no MBGP protocol changes required to 556 support LISP-Multicast. 558 MSDP: MSDP is used to announce active multicast sources to other 559 routing domains (or LISP sites). The announcements come from the 560 PIM Rendezvous Points (RPs) from sites where there are active 561 multicast sources sending to various groups. In the context of 562 LISP-Multicast, the source addresses advertised in MSDP will 563 semantically be from the EID namespace since they describe the 564 identity of a source multicast host. It will be true that the 565 state stored in MSDP caches from core routers will be from the EID 566 namespace. An RP address inside of site will be from the EID 567 namespace so it can be advertised and reached by internal unicast 568 routing mechanism. However, for MSDP peer-RPF checking to work 569 properly across sites, the RP addresses must be converted or 570 mapped into a routable address that is advertised and maintained 571 in the BGP routing tables in the core. MSDP peering addresses can 572 come out of either the EID or a routable address namespace. And 573 the choice can be made unilaterally because the ITR at the site 574 will determine which namespace the destination peer address is out 575 of by looking in the mapping database service. There are no MSDP 576 protocol changes required to support LISP-Multicast. 578 PIM-SSM: In the simplest form of distribution tree building, when 579 PIM operates in SSM mode, a source distribution tree is built and 580 maintained across site boundaries. In this case, there is a small 581 modification to the operation of the PIM protocol. No 582 modifications to any message format, but to support taking a Join/ 583 Prune message originated inside of a LISP site with embedded 584 addresses from the EID namespace and converting them to addresses 585 from the RLOC namespace when the Join/Prune message crosses a site 586 boundary. This is similar to the requirements documented in 587 [RFC5135]. 589 PIM-Bidir: Bidirectional PIM is typically run inside of a routing 590 domain, but if deployed in an inter-domain environment, one would 591 have to decide if the RP address of the shared-tree would be from 592 the EID namespace or the RLOC namespace. If the RP resides in a 593 site-based router, then the RP address is from the EID namespace. 594 If the RP resides in the core where RLOC addresses are routed, 595 then the RP address is from the RLOC namespace. This could be 596 easily distinguishable if the EID address were well-known address 597 allocation block from the RLOC namespace. Also, when using 598 Embedded-RP for RP determination [RFC3956], the format of the 599 group address could indicate the namespace the RP address is from. 600 However, refer to Section 10 for considerations core routers need 601 to make when using Embedded-RP IPv6 group addresses. When using 602 Bidir-PIM for inter-domain multicast routing, it is recommended to 603 use staticly configured RPs. Allowing core routers to associate a 604 Bidir group's RP address with an ITR's RLOC address. And site 605 routers to associate the Bidir group's RP address as an EID 606 address. With respect to DF-election in Bidir PIM, no changes are 607 required since all messaging and addressing is link-local. 609 PIM-ASM: The ASM mode of PIM, the most popular form of PIM, is 610 deployed in the Internet today is by having shared-trees within a 611 site and using source-trees across sites. By the use of MSDP and 612 PIM-SSM techniques described above, multicast connectivity can 613 occur across LISP sites. Having said that, that means there are 614 no special actions required for processing (*,G) or (S,G,R) Join/ 615 Prune messages since they all operate against the shared-tree 616 which is site resident. Just like with ASM, there is no (*,G) in 617 the core when LISP-Multicast is in use. This is also true for the 618 RP-mapping mechanisms Auto-RP and BSR. 620 Based on the protocol description above, the conclusion is that there 621 are no protocol message format changes, just a translation function 622 performed at the control-plane. This will make for an easier and 623 faster transition for LISP since fewer components in the network have 624 to change. 626 It should also be stated just like it is in [LISP] that no host 627 changes, whatsoever, are required to have a multicast source host 628 send multicast packets and for a multicast receiver host to receive 629 multicast packets. 631 8. LISP-Multicast Data-Plane Architecture 633 The LISP-Multicast data-plane operation conforms to the operation and 634 packet formats specified in [LISP]. However, encapsulating a 635 multicast packet from an ITR is a much simpler process. The process 636 is simply to copy the inner group address to the outer destination 637 address. And to have the ITR use its own IP address (its RLOC) as 638 the source address. The process is simpler for multicast because 639 there is no EID-to-RLOC mapping lookup performed during packet 640 forwarding. 642 In the decapsulation case, the ETR simply removes the outer header 643 and performs a multicast routing table lookup on the inner header 644 (S-EID,G) addresses. Then the OIF-list for the (S-EID,G) entry is 645 used to replicate the packet on site-facing interfaces leading to 646 multicast receiver hosts. 648 There is no Data-Probe logic for ETRs as there can be in the unicast 649 forwarding case. 651 8.1. ITR Forwarding Procedure 653 The following procedure is used by an ITR, when it receives a 654 multicast packet from a source inside of its site: 656 1. A multicast data packet sent by a host in a LISP site will have 657 the source address equal to the host's EID and the destination 658 address equal to the group address of the multicast group. It is 659 assumed the group information is obtained by current methods. 660 The same is true for a multicast receiver to obtain the source 661 and group address of a multicast flow. 663 2. When the ITR receives a multicast packet, it will have both S-EID 664 state and S-RLOC state stored. Since the packet was received on 665 a site-facing interface, the RPF lookup is based on the S-EID 666 state. If the RPF check succeeds, then the OIF-list contains 667 interfaces that are site-facing and external-facing. For the 668 site-facing interfaces, no LISP header is prepended. For the 669 external-facing interfaces a LISP header is prepended. When the 670 ITR prepends a LISP header, it uses its own RLOC address as the 671 source address and copies the group address supplied by the IP 672 header the host built as the outer destination address. 674 8.1.1. Multiple RLOCs for an ITR 676 Typically, an ITR will have a single RLOC address but in some cases 677 there could be multiple RLOC addresses assigned from either the same 678 or different service providers. In this case when (S-RLOC,G) Join/ 679 Prune messages are received for each RLOC, there is a OIF-list 680 merging action that must take place. Therefore, when a packet is 681 received from a site-facing interface that matches on a (S-EID,G) 682 entry, the interfaces of the OIF-list from all (RLOC,G) entries 683 joined to the ITR as well as the site-facing OIF-list joined for 684 (S-EID,G) must be part be included in packet replication. In 685 addition to replicating for all types of OIF-lists, each oif entry 686 must be tagged with the RLOC address, so encapsulation uses the outer 687 source address for the RLOC joined. 689 8.1.2. Multiple ITRs for a LISP Source Site 691 Note when ETRs from different multicast receiver sites receive 692 (S-EID,G) joins, they may select a different S-RLOC for a multicast 693 source site due to policy (the multicast ITR can return different 694 multicast priority and weight values per ETR Map-Request). In this 695 case, the same (S-EID,G) is being realized by different (S-RLOC,G) 696 state in the core. This will not result in duplicate packets because 697 each ITR in the multicast source site will choose their own RLOC for 698 the source address for encapsulated multicast traffic. The RLOC 699 addresses are the ones joined by remote multicast ETRs. 701 When different (S-EID,G) traffic is combined into a single (RLOC,G) 702 core distribution tree, this may cause traffic to go to a receiver 703 multicast site when it does not need to. This happens when one 704 receiver multicast site joins (S1-EID,Gi) through a core distribution 705 tree of (RLOC1,Gi) and another multicast receiver site joins (S2- 706 EID,Gi) through the same core distribution tree of (RLOC1,Gi). When 707 ETRs decapsulate such traffic, they should know from their local 708 (S-EID,G) state if the packet should be forwarded. If there is no 709 (S-EID,G) state that matches the inner packet header, the packet is 710 discarded. 712 8.2. ETR Forwarding Procedure 714 The following procedure is used by an ETR, when it receives a 715 multicast packet from a source outside of its site: 717 1. When a multicast data packet is received by an ETR on an 718 external-facing interface, it will do an RPF lookup on the S-RLOC 719 state it has stored. If the RPF check succeeds, the interfaces 720 from the OIF-list are used for replication to interfaces that are 721 site-facing as well as interfaces that are external-facing (this 722 ETR can also be a transit multicast router for receivers outside 723 of its site). When the packet is to be replicated for an 724 external-facing interface, the LISP encapsulation header are not 725 stripped. When the packet is replicated for a site-facing 726 interface, the encapsulation header is stripped. 728 2. The packet without a LISP header is now forwarded down the 729 (S-EID,G) distribution tree in the receiver multicast site. 731 8.3. Replication Locations 733 Multicast packet replication can happen in the following topological 734 locations: 736 o In an IGP multicast router inside a site which operates on S-EIDs. 738 o In a transit multicast router inside of the core which operates on 739 S-RLOCs. 741 o At one or more ETR routers depending on the path a Join/Prune 742 message exits a receiver multicast site. 744 o At one or more ITR routers in a source multicast site depending on 745 what priorities are returned in a Map-Reply to receiver multicast 746 sites. 748 In the last case the source multicast site can do replication rather 749 than having a single exit from the site. But this only can occur 750 when the priorities in the Map-Reply are modified for different 751 receiver multicast site so that the PIM Join/Prune messages arrive at 752 different ITRs. 754 This policy technique, also used in [ALT] for unicast, is useful for 755 multicast to mitigate the problems of changing distribution tree 756 state as discussed in Section 6. 758 9. LISP-Multicast Interworking 760 This section will describe the multicast corollary to [INTWORK] which 761 describes the interworking of multicast routing among LISP and non- 762 LISP sites. 764 9.1. LISP and non-LISP Mixed Sites 766 Since multicast communication can involve more than two entities to 767 communicate together, the combinations of interworking scenarios are 768 more involved. However, the state maintained for distribution trees 769 at the sites is the same regardless of whether or not the site is 770 LISP enabled or not. So most of the implications are in the core 771 with respect to storing routable EID prefixes from either PA or PI 772 blocks. 774 Before enumerating the multicast interworking scenarios, let's define 775 3 deployment states of a site: 777 o A non-LISP site which will run PIM-SSM or PIM-ASM with MSDP as it 778 does today. The addresses for the site are globally routable. 780 o A site that deploys LISP for unicast routing. The addresses for 781 the site are not globally routable. Let's define the name for 782 this type of site as a uLISP site. 784 o A site that deploys LISP for both unicast and multicast routing. 785 The addresses for the site are not globally routable. Let's 786 define the name for this type of site as a LISP-Multicast site. 788 What will not be considered is a LISP site enabled for multicast 789 purposes only but do consider a uLISP site as documented in 790 [INTWORK]. In this section there is no discussion how a LISP site 791 sends multicast packets when all receiver sites are LISP-Multicast 792 enabled; that has been discussed in previous sections. 794 The following scenarios exist to make LISP-Multicast sites interwork 795 with non-LISP-Multicast sites: 797 1. A LISP site must be able to send multicast packets to receiver 798 sites which are a mix of non-LISP sites and uLISP sites. 800 2. A non-LISP site must be able to send multicast packets to 801 receiver sites which are a mix of non-LISP sites and uLISP sites. 803 3. A non-LISP site must be able to send multicast packets to 804 receiver sites which are a mix of LISP sites, uLISP sites, and 805 non-LISP sites. 807 4. A uLISP site must be able to send multicast packets to receiver 808 sites which are a mix of LISP sites, uLISP sites, and non-LISP 809 sites. 811 5. A LISP site must be able to send multicast packets to receiver 812 sites which are a mix of LISP sites, uLISP sites, and non-LISP 813 sites. 815 9.1.1. LISP Source Site to non-LISP Receiver Sites 817 In the first scenario, a site is LISP capable for both unicast and 818 multicast traffic and as such operates on EIDs. Therefore there is a 819 possibility that the EID prefix block is not routable in the core. 820 For LISP receiver multicast sites this isn't a problem but for non- 821 LISP or uLISP receiver multicast sites, when a PIM Join/Prune message 822 is received by the edge router, it has no route to propagate the 823 Join/Prune message out of the site. This is no different than the 824 unicast case that LISP-NAT in [INTWORK] solves. 826 LISP-NAT allows a unicast packet that exits a LISP site to get its 827 source address mapped to a globally routable address before the ITR 828 realizes that it should not encapsulate the packet destined to a non- 829 LISP site. For a multicast packet to leave a LISP site, distribution 830 tree state needs to be built so the ITR can know where to send the 831 packet. So the receiver multicast sites need to know about the 832 multicast source host by its routable address and not its EID 833 address. When this is the case, the routable address is the 834 (S-RLOC,G) state that is stored and maintained in the core routers. 835 It is important to note that the routable address for the host cannot 836 be the same as an RLOC for the site because it is desirable for ITRs 837 to process a received PIM Join/Prune message from an external-facing 838 interface to be propagated inside of the site so the site-part of the 839 distribution tree is built. 841 Using a globally routable source address allows non-LISP and uLISP 842 multicast receiver to join, create, and maintain a multicast 843 distribution tree. However, the LISP multicast receiver site will 844 want to perform an EID-to-RLOC mapping table lookup when a PIM Join/ 845 Prune message is received on a site-facing interface. It does this 846 because it wants to find a (S-RLOC,G) entry to Join in the core. So 847 there is a conflict of behavior between the two types of sites. 849 The solution to this problem is the same as when an ITR wants to send 850 a unicast packet to a destination site but needs determine if the 851 site is LISP capable or not. When it is not LISP capable, the ITR 852 does not encapsulate the packet. So for the multicast case, when ETR 853 receives a PIM Join/Prune message for (S-EID,G) state, it will do a 854 mapping table lookup on S-EID. In this case, S-EID is not in the 855 mapping database because the source multicast site is using a 856 routable address and not an EID prefix address. So the ETR knows to 857 simply propagate the PIM Join/Prune message to a external-facing 858 interface without converting the (S-EID,G) because it is an (S,G) 859 where S is routable and reachable via core routing tables. 861 Now that the multicast distribution tree is built and maintained from 862 any non-LISP or uLISP receiver multicast site, the way packet 863 forwarding model is performed can be explained. 865 Since the ITR in the source multicast site has never received a 866 unicast encapsulated PIM Join/Prune message from any ETR in a 867 receiver multicast site, it knows there are no LISP-Multicast 868 receiver sites. Therefore, there is no need for the ITR to 869 encapsulate data. Since it will know a priori (via configuration) 870 that its site's EIDs are not routable (and not registered to the 871 mapping database system), it assumes that the multicast packets from 872 the source host are sent by a routable address. That is, it is the 873 responsibility of the multicast source host's system administrator to 874 ensure that the source host sends multicast traffic using a routable 875 source address. When this happens, the ITR acts simply as a router 876 and forwards the multicast packet like an ordinary multicast router. 878 There is an alternative to using a LISP-NAT scheme just like there is 879 for unicast [INTWORK] forwarding by using Proxy Tunnel Routers 880 (PxTRs). This can work the same way for multicast routing as well, 881 but the difference is that non-LISP and uLISP sites will send PIM 882 Join/Prune messages for (S-EID,G) which make their way in the core to 883 multicast PxTRs. Let's call this use of a PxTR as a "Multicast 884 Proxy-ETR" (or mPETR). Since the mPETRs advertise very coarse EID 885 prefixes, they draw the PIM Join/Prune control traffic making them 886 the target of the distribution tree. To get multicast packets from 887 the LISP source multicast sites, the tree needs to be built on the 888 path from the mPETR to the LISP source multicast site. To make this 889 happen the mPETR acts as a "Proxy ETR" (where in unicast it acts as a 890 "Proxy ITR", or an uPITR [INTWORK]). 892 The existence of mPETRs in the core allows source multicast site ITRs 893 to encapsulate multicast packets according to (S-RLOC,G) state. The 894 (S-RLOC,G) state is built from the mPETRs to the multicast ITRs. The 895 encapsulated multicast packets are decapsulated by mPETRs and then 896 forwarded according to (S-EID,G) state. The (S-EID,G) state is built 897 from the non-LISP and uLISP receiver multicast sites to the mPETRs. 899 9.1.2. Non-LISP Source Site to non-LISP Receiver Sites 901 Clearly non-LISP multicast sites can send multicast packets to non- 902 LISP receiver multicast sites. That is what they do today. However, 903 discussion is required to show how non-LISP multicast sites send 904 multicast packets to uLISP receiver multicast sites. 906 Since uLISP receiver multicast sites are not targets of any (S,G) 907 state, they simply send (S,G) PIM Join/Prune messages toward the non- 908 LISP source multicast site. Since the source multicast site, in this 909 case has not been upgraded to LISP, all multicast source host 910 addresses are routable. So this case is simplified to where a uLISP 911 receiver multicast site looks to the source multicast site as a non- 912 LISP receiver multicast site. 914 9.1.3. Non-LISP Source Site to Any Receiver Site 916 When a non-LISP source multicast site has receivers in either a non- 917 LISP/uLISP site or a LISP site, one needs to decide how the LISP 918 receiver multicast site will attach to the distribution tree. It is 919 known from Section 9.1.2 that non-LISP and uLISP receiver multicast 920 sites can join the distribution tree, but a LISP receiver multicast 921 site ETR will need to know if the source address of the multicast 922 source host is routable or not. It has been shown in Section 9.1.1 923 that an ETR, before it sends a PIM Join/Prune message on an external- 924 facing interface, does a EID-to-RLOC mapping lookup to determine if 925 it should convert the (S,G) state from a PIM Join/Prune message 926 received on a site-facing interface to a (S-RLOC,G). If the lookup 927 fails, the ETR can conclude the source multicast site is a non-LISP 928 site so it simply forwards the Join/Prune message (it also doesn't 929 need to send a unicast encapsulated Join/Prune message because there 930 is no ITR in a non-LISP site and there is namespace continuity 931 between the ETR and source). 933 For a non-LISP source multicast site, (S-EID,G) state could be 934 limited to the edges of the network with the use of multicast proxy- 935 ITRs (mPITRs). The mPITRs can take native, unencapsulated multicast 936 packets from non-LISP source multicast and uLISP sites and 937 encapsulate them to ETRs in receiver multicast sites or to mPETRs 938 that can decapsulate for non-LISP receiver multicast or uLISP sites. 939 The mPITRs are responsible for sending (S-EID,G) joins to the non- 940 LISP source multicast site. To connect the distribution trees 941 together, multicast ETRs will need to be configured with the mPITR's 942 RLOC addresses so they can send both (S-RLOC,G) joins to build a 943 distribution tree to the mPITR as well as for sending unicast joins 944 to mPITRs so they can propogate (S-EID,G) joins into source multicast 945 sites. The use of mPITRs is undergoing more study and is work in 946 progress. 948 9.1.4. Unicast LISP Source Site to Any Receiver Sites 950 In the last section, it was explained how an ETR in a multicast 951 receiver site can determine if a source multicast site is LISP- 952 enabled by looking into the mapping database. When the source 953 multicast site is a uLISP site, it is LISP enabled but the ITR, by 954 definition is not capable of doing multicast encapsulation. So for 955 the purposes of multicast routing, the uLISP source multicast site is 956 treated as non-LISP source multicast site. 958 Non-LISP receiver multicast sites can join distribution trees to a 959 uLISP source multicast site since the source site behaves, from a 960 forwarding perspective, as a non-LISP source site. This is also the 961 case for a uLISP receiver multicast site since the ETR does not have 962 multicast functionality built-in or enabled. 964 Special considerations are required for LISP receiver multicast sites 965 since they think the source multicast site is LISP capable, the ETR 966 cannot know if ITR is LISP-Multicast capable. To solve this problem, 967 each mapping database entry will have a multicast 2-tuple (Mpriority, 968 Mweight) per RLOC. When the Mpriority is set to 255, the site is 969 considered not multicast capable. So an ETR in a LISP receiver 970 multicast site can distinguish whether a LISP source multicast site 971 is LISP-Multicast site from a uLISP site. 973 9.1.5. LISP Source Site to Any Receiver Sites 975 When a LISP source multicast site has receivers in LISP, non-LISP, 976 and uLISP receiver multicast sites, it has a conflict about how it 977 sends multicast packets. The ITR can either encapsulate or natively 978 forward multicast packets. Since the receiver multicast sites are 979 heterogeneous in their behavior, one packet forwarding mechanism 980 cannot satisfy both. However, if a LISP receiver multicast site acts 981 like a uLISP site then it could receive packets like a non-LISP 982 receiver multicast site making all receiver multicast sites have 983 homogeneous behavior. However, this poses the following issues: 985 o LISP-NAT techniques with routable addresses would be required in 986 all cases. 988 o Or alternatively, mPETR deployment would be required forcing 989 coarse EID prefix advertisement in the core. 991 o But what is most disturbing is that when all sites that 992 participate are LISP-Multicast sites but then a non-LISP or uLISP 993 site joins the distribution tree, then the existing joined LISP 994 receiver multicast sites would have to change their behavior. 995 This would create too much dynamic tree-building churn to be a 996 viable alternative. 998 So the solution space options are: 1000 1. Make the LISP ITR in the source multicast site send two packets, 1001 one that is encapsulated with (S-RLOC,G) to reach LISP receiver 1002 multicast sites and another that is not encapsulated with 1003 (S-EID,G) to reach non-LISP and uLISP receiver multicast sites. 1005 2. Make the LISP ITR always encapsulate packets with (S-RLOC,G) to 1006 reach LISP-Multicast sites and to reach mPETRs that can 1007 decapsulate and forward (S-EID,G) packets to non-LISP and uLISP 1008 receiver multicast sites. 1010 9.2. LISP Sites with Mixed Address Families 1012 A LISP database mapping entry that describes the locator-set, 1013 Mpriority and Mweight per locator address (RLOC), for an EID prefix 1014 associated with a site could have RLOC addresses in either IPv4 or 1015 IPv6 format. When a mapping entry has a mix of RLOC formatted 1016 addresses, it is an implicit advertisement by the site that it is a 1017 dual-stack site. That is, the site can receive IPv4 or IPv6 unicast 1018 packets. 1020 To distinguish if the site can receive dual-stack unicast packets as 1021 well as dual-stack multicast packets, the Mpriority value setting 1022 will be relative to an IPv4 or IPv6 RLOC See [LISP] for packet format 1023 details. 1025 If one considers the combinations of LISP, non-LISP, and uLISP sites 1026 sharing the same distribution tree and considering the capabilities 1027 of supporting IPv4, IPv6, or dual-stack, the number of total 1028 combinations grows beyond comprehension. 1030 Using some combinatorial math, the following profiles of a site and 1031 the combinations that can occur: 1033 1. LISP-Multicast IPv4 Site 1035 2. LISP-Multicast IPv6 Site 1037 3. LISP-Multicast Dual-Stack Site 1039 4. uLISP IPv4 Site 1041 5. uLISP IPv6 Site 1042 6. uLISP Dual-Stack Site 1044 7. non-LISP IPv4 Site 1046 8. non-LISP IPv6 Site 1048 9. non-LISP Dual-Stack Site 1050 Lets define (m n) = m!/(n!*(m-n)!), pronounced "m choose n" to 1051 illustrate some combinatorial math below. 1053 When 1 site talks to another site, the combinatorial is (9 2), when 1 1054 site talks to another 2 sites, the combinatorial is (9 3). If sum 1055 this up to (9 9), then: 1057 (9 2) + (9 3) + (9 4) + (9 5) + (9 6) + (9 7) + (9 8) + (9 9) = 1059 36 + 84 + 126 + 126 + 84 + 36 + 9 + 1 1061 Which results in the total number of cases to be considered at 502. 1063 This combinatorial gets even worse when one considers a site using 1064 one address family inside of the site and the xTRs use the other 1065 address family (as in using IPv4 EIDs with IPv6 RLOCs or IPv6 EIDs 1066 with IPv4 RLOCs). 1068 To rationalize this combinatorial nightmare, there are some 1069 guidelines which need to be put in place: 1071 o Each distribution tree shared between sites will either be an IPv4 1072 distribution tree or an IPv6 distribution tree. Therefore, head- 1073 end replication can be avoided by building and sending packets on 1074 each address family based distribution tree. Even though there 1075 might be an urge to do multicast packet translation from one 1076 address family format to the other, it is a non-viable over- 1077 complicated urge. Multicast ITRs will only encapsulate packets 1078 where the inner and outer headers are from the same address 1079 family. 1081 o All LISP sites on a multicast distribution tree must share a 1082 common address family which is determined by the source site's 1083 locator-set in its LISP database mapping entry. All receiver 1084 multicast sites will use the best RLOC priority controlled by the 1085 source multicast site. This is true when the source site is 1086 either LISP-Multicast or uLISP capable. This means that priority- 1087 based policy modification is prohibited. When a receiver 1088 multicast site ETR receives a (S-EID,G) join, it must select a 1089 S-RLOC for the same address family as S-EID. 1091 o When a multicast locator-set has more than one locator, only 1092 locators from the same address-family MUST be set to the same best 1093 priority value. A mixed locator-set can exist (for unicast use), 1094 but the multicast priorities MUST be the set for the same address 1095 family locators. 1097 o When the source site is not LISP capable, it is up to how 1098 receivers find the source and group information for a multicast 1099 flow. That mechanism decides the address family for the flow. 1101 9.3. Making a Multicast Interworking Decision 1103 This Multicast Interworking section has shown all combinations of 1104 multicast connectivity that could occur. As already concluded, this 1105 can be quite complicated and if the design is too ambitious, the 1106 dynamics of the protocol could cause a lot of instability. 1108 The trade-off decisions are hard to make and so the same single 1109 solution is desirable to work for both IPv4 and IPv6 multicast. It 1110 is imperative to have an incrementally deployable solution for all of 1111 IPv4 unicast and multicast and IPv6 unicast and multicast while 1112 minimizing (or eliminating) both unicast and multicast EID namespace 1113 state. 1115 Therefore the design decision to go with uPITRs [INTWORK] for unicast 1116 routing and mPETRs for multicast routing seems to be the sweet spot 1117 in the solution space so state requirements can be optimized and 1118 avoid head-end data replication at ITRs. 1120 10. Considerations when RP Addresses are Embedded in Group Addresses 1122 When ASM and PIM-Bidir is used in an IPv6 inter-domain environment, a 1123 technique exists to embed the unicast address of an RP in a IPv6 1124 group address [RFC3956]. When routers in end sites process a PIM 1125 Join/Prune message which contain an embedded-RP group address, they 1126 extract the RP address from the group address and treat it from the 1127 EID namespace. However, core routers do not have state for the EID 1128 namespace, and need to extract an RP address from the RLOC namespace. 1130 Therefore, it is the responsibility of ETRs in multicast receiver 1131 sites to map the group address into a group address where the 1132 embedded-RP address is from the RLOC namespace. The mapped RP- 1133 address is obtained from a EID-to-RLOC mapping database lookup. The 1134 ETR will also send a unicast (*,G) Join/Prune message to the ITR so 1135 the branch of the distribution tree from the source site resident RP 1136 to the ITR is created. 1138 This technique is no different than the techniques described in this 1139 specification for translating (S,G) state and propagating Join/Prune 1140 messages into the core. The only difference is that the (*,G) state 1141 in Join/Prune messages are mapped because they contain unicast 1142 addresses encoded in an Embedded-RP group address. 1144 11. Taking Advantage of Upgrades in the Core 1146 If the core routers are upgraded to support [RFC5496], then the EID 1147 specific data can be passed through the core without, possibly, 1148 having to store the state in the core. 1150 By doing this one can eliminate the ETR from unicast encapsulating 1151 PIM Join/Prune messages to the source site's ITR. 1153 However, this solution is restricted to a small set of workable cases 1154 which would not be good for general use of LISP-Multicast. In 1155 addition due to slow convergence properties, it is not being 1156 recommended for LISP-Multicast. 1158 12. Mtrace Considerations 1160 Mtrace functionality MUST be consistent with unicast traceroute 1161 functionality where all hops from multicast receiver to multicast 1162 source are visible. 1164 The design for mtrace for use in LISP-Multicast environments is to be 1165 determined but should build upon the mtrace version 2 specified in 1166 [MTRACE]. 1168 13. Security Considerations 1170 This document introduces no additional security concerns beyond those 1171 specified in the base LISP specification [LISP]. 1173 14. Acknowledgments 1175 The authors would like to gratefully acknowledge the people who have 1176 contributed discussion, ideas, and commentary to the making of this 1177 proposal and specification. People who provided expert review were 1178 Scott Brim, Greg Shepherd, and Dave Oran. Other commentary from 1179 discussions at Summer 2008 Dublin IETF were Toerless Eckert and 1180 Ijsbrand Wijnands. 1182 The authors would also like to thank the MBONED working group for 1183 constructive and civil verbal feedback when this draft was presented 1184 at the Fall 2008 IETF in Minneapolis. In particular, good commentary 1185 came from Tom Pusateri, Steve Casner, Marshall Eubanks, Dimitri 1186 Papadimitriou, Ron Bonica, Lenny Guardino, Alia Atlas, Jesus Arango, 1187 and Jari Arkko. 1189 An expert review of this specification was done by Yiqun Cai and 1190 Liming Wei. The authors thank them for their detailed comments. 1192 This work originated in the Routing Research Group (RRG) of the IRTF. 1193 The individual submission [MLISP] was converted into this IETF LISP 1194 working group draft. 1196 15. IANA Considerations 1198 This document makes no request of the IANA. 1200 16. References 1202 16.1. Normative References 1204 [INTWORK] Lewis, D., Meyer, D., and D. Farinacci, "Interworking LISP 1205 with IPv4 and IPv6", draft-ietf-lisp-interworking-02.txt 1206 (work in progress). 1208 [LISP] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, 1209 "Locator/ID Separation Protocol (LISP)", 1210 draft-ietf-lisp-15.txt (work in progress). 1212 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1213 Requirement Levels", BCP 14, RFC 2119, March 1997. 1215 [RFC3618] Fenner, B. and D. Meyer, "Multicast Source Discovery 1216 Protocol (MSDP)", RFC 3618, October 2003. 1218 [RFC3956] Savola, P. and B. Haberman, "Embedding the Rendezvous 1219 Point (RP) Address in an IPv6 Multicast Address", 1220 RFC 3956, November 2004. 1222 [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, 1223 "Protocol Independent Multicast - Sparse Mode (PIM-SM): 1224 Protocol Specification (Revised)", RFC 4601, August 2006. 1226 [RFC4604] Holbrook, H., Cain, B., and B. Haberman, "Using Internet 1227 Group Management Protocol Version 3 (IGMPv3) and Multicast 1228 Listener Discovery Protocol Version 2 (MLDv2) for Source- 1229 Specific Multicast", RFC 4604, August 2006. 1231 [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for 1232 IP", RFC 4607, August 2006. 1234 [RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, 1235 "Multiprotocol Extensions for BGP-4", RFC 4760, 1236 January 2007. 1238 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 1239 "Bidirectional Protocol Independent Multicast (BIDIR- 1240 PIM)", RFC 5015, October 2007. 1242 [RFC5135] Wing, D. and T. Eckert, "IP Multicast Requirements for a 1243 Network Address Translator (NAT) and a Network Address 1244 Port Translator (NAPT)", BCP 135, RFC 5135, February 2008. 1246 [RFC5496] Wijnands, IJ., Boers, A., and E. Rosen, "The Reverse Path 1247 Forwarding (RPF) Vector TLV", RFC 5496, March 2009. 1249 16.2. Informative References 1251 [ALT] Farinacci, D., Fuller, V., and D. Meyer, "LISP Alternative 1252 Topology (LISP-ALT)", draft-ietf-lisp-alt-08.txt (work in 1253 progress). 1255 [MLISP] Farinacci, D., Meyer, D., Zwiebel, J., and S. Venaas, 1256 "LISP for Multicast Environments", 1257 draft-farinacci-lisp-multicast-01.txt (work in progress). 1259 [MTRACE] Asaeda, H., Jinmei, T., Fenner, W., and S. Casner, "Mtrace 1260 Version 2: Traceroute Facility for IP Multicast", 1261 draft-ietf-mboned-mtrace-v2-08.txt (work in progress). 1263 Appendix A. Document Change Log 1265 A.1. Changes to draft-ietf-lisp-multicast-10.txt 1267 o Posted second half of October 2011. Changes to reflect IESG 1268 review comments from Stephen Farrell. 1270 A.2. Changes to draft-ietf-lisp-multicast-09.txt 1272 o Posted October 2011. Changes to reflect IESG review comments from 1273 Ralph Droms and Kathleen Moriarty. 1275 A.3. Changes to draft-ietf-lisp-multicast-08.txt 1277 o Posted September 2011. Minor editorial changes from Jari's 1278 commentary. 1280 A.4. Changes to draft-ietf-lisp-multicast-07.txt 1282 o Posted July 2011. Fixing IDnits errors. 1284 A.5. Changes to draft-ietf-lisp-multicast-06.txt 1286 o Posted June 2011 to complete working group last call. 1288 o Added paragraph to section 8.1.2 based on Jesus comment about 1289 making it more clear what happens when two (S-EID,G) trees use the 1290 same (RLOC,G) tree. 1292 o Make more references to [INTWORK] when mentioning uPITRs and 1293 uPETRs. 1295 o Made many changes based on editorial and wordsmithing comments 1296 from Alia. 1298 A.6. Changes to draft-ietf-lisp-multicast-05.txt 1300 o Posted April 2011 to reset expiration timer. 1302 o Updated references. 1304 A.7. Changes to draft-ietf-lisp-multicast-04.txt 1306 o Posted October 2010 to reset expiration timer. 1308 o Updated references. 1310 A.8. Changes to draft-ietf-lisp-multicast-03.txt 1312 o Posted April 2010. 1314 o Added section 8.1.2 to address Joel Halpern's comment about 1315 receiver sites joining the same source site via 2 different RLOCs, 1316 each being a separate ITR. 1318 o Change all occurences of "mPTR" to "mPETR" to become more 1319 consistent with uPITRs and uPETRs described in [INTWORK]. That 1320 is, an mPETR is a LISP multicast router that decapsulates 1321 multicast packets that are encapsulated to it by ITRs in multicast 1322 source sites. 1324 o Add clarifications in section 9 about how homogeneous multicast 1325 encapsulation should occur. As well as describing in this 1326 section, how to deal with mixed-locator sets to avoid 1327 heterogeneous encapsulation. 1329 o Introduce concept of mPITRs to help reduce (S-EID,G) to the edges 1330 of LISP global multicast network. 1332 A.9. Changes to draft-ietf-lisp-multicast-02.txt 1334 o Posted September 2009. 1336 o Added Document Change Log appendix. 1338 o Specify that the LISP Encapsulated Control Message be used for 1339 unicasting PIM Join/Prune messages from ETRs to ITRs. 1341 A.10. Changes to draft-ietf-lisp-multicast-01.txt 1343 o Posted November 2008. 1345 o Specified that PIM Join/Prune unicast messages that get sent from 1346 ETRs to ITRs of a source multicast site get LISP encapsulated in 1347 destination UDP port 4342. 1349 o Add multiple RLOCs per ITR per Yiqun's comments. 1351 o Indicate how static RPs can be used when LISP is run using Bidir- 1352 PIM in the core. 1354 o Editorial changes per Liming comments. 1356 o Add Mttrace Considersations section. 1358 A.11. Changes to draft-ietf-lisp-multicast-00.txt 1360 o Posted April 2008. 1362 o Renamed from draft-farinacci-lisp-multicast-01.txt. 1364 Authors' Addresses 1366 Dino Farinacci 1367 cisco Systems 1368 Tasman Drive 1369 San Jose, CA 1370 USA 1372 Email: dino@cisco.com 1374 Dave Meyer 1375 cisco Systems 1376 Tasman Drive 1377 San Jose, CA 1378 USA 1380 Email: dmm@cisco.com 1382 John Zwiebel 1383 cisco Systems 1384 Tasman Drive 1385 San Jose, CA 1386 USA 1388 Email: jzwiebel@cisco.com 1390 Stig Venaas 1391 cisco Systems 1392 Tasman Drive 1393 San Jose, CA 1394 USA 1396 Email: stig@cisco.com