idnits 2.17.1 draft-ietf-lisp-multicast-09.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 5, 2011) is 4588 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for intended status: Experimental ---------------------------------------------------------------------------- == Outdated reference: A later version (-06) exists of draft-ietf-lisp-interworking-02 == Outdated reference: A later version (-24) exists of draft-ietf-lisp-15 ** Obsolete normative reference: RFC 4601 (Obsoleted by RFC 7761) == Outdated reference: A later version (-10) exists of draft-ietf-lisp-alt-08 == Outdated reference: A later version (-26) exists of draft-ietf-mboned-mtrace-v2-08 Summary: 1 error (**), 0 flaws (~~), 5 warnings (==), 1 comment (--).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 7, 2012 S. Venaas 6 cisco Systems 7 October 5, 2011 9 LISP for Multicast Environments 10 draft-ietf-lisp-multicast-09 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 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-09.txt . . . . . . . 36 86 A.2. Changes to draft-ietf-lisp-multicast-08.txt . . . . . . . 36 87 A.3. Changes to draft-ietf-lisp-multicast-07.txt . . . . . . . 36 88 A.4. Changes to draft-ietf-lisp-multicast-06.txt . . . . . . . 36 89 A.5. Changes to draft-ietf-lisp-multicast-05.txt . . . . . . . 36 90 A.6. Changes to draft-ietf-lisp-multicast-04.txt . . . . . . . 36 91 A.7. Changes to draft-ietf-lisp-multicast-03.txt . . . . . . . 36 92 A.8. Changes to draft-ietf-lisp-multicast-02.txt . . . . . . . 37 93 A.9. Changes to draft-ietf-lisp-multicast-01.txt . . . . . . . 37 94 A.10. Changes to draft-ietf-lisp-multicast-00.txt . . . . . . . 37 95 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 38 97 1. Requirements Notation 99 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 100 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 101 document are to be interpreted as described in [RFC2119]. 103 2. Introduction 105 The Locator/ID Separation Architecture [LISP] provides a mechanism to 106 separate out Identification and Location semantics from the current 107 definition of an IP address. By creating two namespaces, an Endpoint 108 ID (EID) namespace used by sites and a Routing Locator (RLOC) 109 namespace used by core routing, the core routing infrastructure can 110 scale by doing topological aggregation of routing information. 112 Since LISP creates a new namespace, a mapping function must exist to 113 map a site's EID prefixes to its associated locators. For unicast 114 packets, both the source address and destination address must be 115 mapped. For multicast packets, only the source address needs to be 116 mapped. The destination group address doesn't need to be mapped 117 because the semantics of an IPv4 or IPv6 group address are logical in 118 nature and not topology-dependent. Therefore, this specification 119 focuses on to map a source EID address of a multicast flow during 120 distribution tree setup and packet delivery. 122 This specification will address the following scenarios: 124 1. How a multicast source host in a LISP site sends multicast 125 packets to receivers inside of its site as well as to receivers 126 in other sites that are LISP enabled. 128 2. How inter-domain (or between LISP sites) multicast distribution 129 trees are built and how forwarding of multicast packets leaving a 130 source site toward receivers sites is performed. 132 3. What protocols are affected and what changes are required to such 133 multicast protocols. 135 4. How ASM-mode (Any Source Multicast), SSM-mode (Single Source 136 Multicast), and Bidir-mode (Bidirectional Shared Trees) service 137 models will operate. 139 5. How multicast packet flow will occur for multiple combinations of 140 LISP and non-LISP capable source and receiver sites, for example: 142 A. How multicast packets from a source host in a LISP site are 143 sent to receivers in other sites when they are all non-LISP 144 sites. 146 B. How multicast packets from a source host in a LISP site are 147 sent to receivers in both LISP-enabled sites and non-LISP 148 sites. 150 C. How multicast packets from a source host in a non-LISP site 151 are sent to receivers in other sites when they are all LISP- 152 enabled sites. 154 D. How multicast packets from a source host in a non-LISP site 155 are sent to receivers in both LISP-enabled sites and non-LISP 156 sites. 158 This specification focuses on what changes are needed to the 159 multicast routing protocols to support LISP-Multicast as well as 160 other protocols used for inter-domain multicast, such as Multi- 161 protocol BGP (MBGP) [RFC4760]. The approach proposed in this 162 specification requires no packet format changes to the protocol and 163 no operational procedural changes to the multicast infrastructure 164 inside of a site when all sources and receivers reside in that site, 165 even when the site is LISP enabled. That is, internal operation of 166 multicast is unchanged regardless of whether or not the site is LISP 167 enabled or whether or not receivers exist in other sites which are 168 LISP-enabled. 170 Therefore, we see changes only to PIM-ASM [RFC4601], MSDP [RFC3618], 171 and PIM-SSM [RFC4607]. Bidir-PIM [RFC5015], which typically does not 172 run in an inter-domain environment is not addressed in depth in this 173 version of the specification. 175 Also, the current version of this specification does not describe 176 multicast-based Traffic Engineering relative to the TE-ITR (Traffic 177 Engineering based Ingress Tunnel Router) and TE-ETR (Traffic 178 Engineering based Egress Tunnel Router) descriptions in [LISP]. 179 Futher work is also needed to determine the detailed behavior for 180 multicast proxy ITRs (mPITRs) (Section 9.1.3), mtrace (Section 12), 181 and locator reachability (Section 6). Finally, further deployment 182 and experimentation would be useful to understand the real-life 183 performance of the LISP-Multicast solution. For instance, the design 184 optimizes for minimal state and control traffic in the core, but can 185 in some cases cause extra multicast traffic to be sent Section 8.1.2. 187 3. Definition of Terms 189 The terminology in this section is consistent with the definitions in 190 [LISP] but is extended specifically to deal with the application of 191 the terminology to multicast routing. 193 LISP-Multicast: a reference to the design in this specification. 194 That is, when any site that is participating in multicast 195 communication has been upgraded to be a LISP site, the operation 196 of control-plane and data-plane protocols is considered part of 197 the LISP-Multicast architecture. 199 Endpoint ID (EID): a 32-bit (for IPv4) or 128-bit (for IPv6) value 200 used in the source address field of the first (most inner) LISP 201 header of a multicast packet. The host obtains a destination 202 group address the same way it obtains one today, as it would when 203 it is a non-LISP site. The source EID is obtained via existing 204 mechanisms used to set a host's "local" IP address. An EID is 205 allocated to a host from an EID prefix block associated with the 206 site the host is located in. An EID can be used by a host to 207 refer to another host, as when it joins an SSM (S-EID,G) route 208 using IGMP version 3 [RFC4604]. LISP uses Provider Independent 209 (PI) blocks for EIDs; such EIDs MUST NOT be used as LISP RLOCs. 210 Note that EID blocks may be assigned in a hierarchical manner, 211 independent of the network topology, to facilitate scaling of the 212 mapping database. In addition, an EID block assigned to a site 213 may have site-local structure (subnetting) for routing within the 214 site; this structure is not visible to the global routing system. 216 Routing Locator (RLOC): the IPv4 or IPv6 address of an ingress 217 tunnel router (ITR), the router in the multicast source host's 218 site that encapsulates multicast packets. It is the output of a 219 EID-to-RLOC mapping lookup. An EID maps to one or more RLOCs. 220 Typically, RLOCs are numbered from topologically-aggregatable 221 blocks that are assigned to a site at each point to which it 222 attaches to the global Internet; where the topology is defined by 223 the connectivity of provider networks, RLOCs can be thought of as 224 Provider Assigned (PA) addresses. Multiple RLOCs can be assigned 225 to the same ITR device or to multiple ITR devices at a site. 227 Ingress Tunnel Router (ITR): a router which accepts an IP multicast 228 packet with a single IP header (more precisely, an IP packet that 229 does not contain a LISP header). The router treats this "inner" 230 IP destination multicast address opaquely so it doesn't need to 231 perform a map lookup on the group address because it is 232 topologically insignificant. The router then prepends an "outer" 233 IP header with one of its globally-routable RLOCs as the source 234 address field. This RLOC is known to other multicast receiver 235 sites which have used the mapping database to join a multicast 236 tree for which the ITR is the root. In general, an ITR receives 237 IP packets from site end systems on one side and sends LISP- 238 encapsulated multicast IP packets out all external interfaces 239 which have been joined. 241 An ITR would receive a multicast packet from a source inside of 242 its site when 1) it is on the path from the multicast source to 243 internally joined receivers, or 2) when it is on the path from the 244 multicast source to externally joined receivers. 246 Egress Tunnel Router (ETR): a router that is on the path from a 247 multicast source host in another site to a multicast receiver in 248 its own site. An ETR accepts a PIM Join/Prune message from a site 249 internal PIM router destined for the source's EID in the multicast 250 source site. The ETR maps the source EID in the Join/Prune 251 message to an RLOC address based on the EID-to-RLOC mapping. This 252 sets up the ETR to accept multicast encapsulated packets from the 253 ITR in the source multicast site. A multicast ETR decapsulates 254 multicast encapsulated packets and replicates them on interfaces 255 leading to internal receivers. 257 xTR: is a reference to an ITR or ETR when direction of data flow is 258 not part of the context description. xTR refers to the router that 259 is the tunnel endpoint. Used synonymously with the term "Tunnel 260 Router". For example, "An xTR can be located at the Customer Edge 261 (CE) router", meaning both ITR and ETR functionality can be at the 262 CE router. 264 LISP Header: a term used in this document to refer to the outer 265 IPv4 or IPv6 header, a UDP header, and a LISP header. An ITR 266 prepends headers and an ETR strips headers. A LISP encapsulated 267 multicast packet will have an "inner" header with the source EID 268 in the source field; an "outer" header with the source RLOC in the 269 source field: and the same globally unique group address in the 270 destination field of both the inner and outer header. 272 (S,G) State: the formal definition is in the PIM Sparse Mode 273 [RFC4601] specification. For this specification, the term is used 274 generally to refer to multicast state. Based on its topological 275 location, the (S,G) state resides in routers can be either 276 (S-EID,G) state (at a location where the (S,G) state resides) or 277 (S-RLOC,G) state (in the Internet core). 279 (S-EID,G) State: refers to multicast state in multicast source and 280 receiver sites where S-EID is the IP address of the multicast 281 source host (its EID). An S-EID can appear in an IGMPv3 report, 282 an MSDP SA message or a PIM Join/Prune message that travels inside 283 of a site. 285 (S-RLOC,G) State: refers to multicast state in the core where S is 286 a source locator (the IP address of a multicast ITR) of a site 287 with a multicast source. The (S-RLOC,G) is mapped from (S-EID,G) 288 entry by doing a mapping database lookup for the EID prefix that 289 S-EID maps to. An S-RLOC can appear in a PIM Join/Prune message 290 when it travels from an ETR to an ITR over the Internet core. 292 uLISP Site: a unicast only LISP site according to [LISP] which has 293 not deployed the procedures of this specification and therefore, 294 for multicast purposes, follows the procedures from Section 9. A 295 uLISP site can be a traditional multicast site. 297 LISP Site: a unicast LISP site (uLISP Site) that is also multicast 298 capable according to the procedures in this specification. 300 mPETR: this is a multicast proxy-ETR that is responsible for 301 advertising a very coarse EID prefix which non-LISP and uLISP 302 sites can target their (S-EID,G) PIM Join/Prune message to. mPETRs 303 are used so LISP source multicast sites can send multicast packets 304 using source addresses from the EID namespace. mPETRs act as Proxy 305 ETRs for supporting multicast routing in a LISP infrastructure. 306 It is likely an uPITR [INTWORK] and a mPETR will be co-located 307 since the single device advertises a coarse EID-prefix in the 308 underlying unicast routing system. 310 Mixed Locator-Sets: this is a locator-set for a LISP database 311 mapping entry where the RLOC addresses in the locator-set are in 312 both IPv4 and IPv6 format. 314 Unicast Encapsulated PIM Join/Prune Message: this is a standard PIM 315 Join/Prune message (encapsulated in a LISP Encapsulated Control 316 Message with destination UDP port 4342) which is sent by ETRs at 317 multicast receiver sites to an ITR at a multicast source site. 318 This message is sent periodically as long as there are interfaces 319 in the OIF-list for the (S-EID,G) entry the ETR is joining for. 321 OIF-list: this is notation to describe the outgoing interface list 322 a multicast router stores per multicast routing table entry so it 323 knows what interfaces to replicate multicast packets on. 325 4. Basic Overview 327 LISP, when used for unicast routing, increases the site's ability to 328 control ingress traffic flows. Egress traffic flows are controlled 329 by the IGP in the source site. For multicast, the IGP coupled with 330 PIM can decide which path multicast packets ingress. By using the 331 traffic engineering features of LISP, a multicast source site can 332 control the egress of its multicast traffic. By controlling the 333 priorities of locators from a mapping database entry, a source 334 multicast site can control which way multicast receiver sites join to 335 the source site. 337 At this point in time, there is no requirement for different locator- 338 sets, priority, and weight policies for multicast than there is for 339 unicast. However, when traffic engineering policies are different 340 for unicast versus multicast flows, it will be desirable to use 341 multicast-based priority and weight values in Map-Reply messages. 343 The fundamental multicast forwarding model is to encapsulate a 344 multicast packet into another multicast packet. An ITR will 345 encapsulate multicast packets received from sources that it serves in 346 a LISP multicast header. The destination group address from the 347 inner header is copied to the destination address of the outer 348 header. The inner source address is the EID of the multicast source 349 host and the outer source address is the RLOC of the encapsulating 350 ITR. 352 The LISP-Multicast architecture will follow this high-level protocol 353 and operational sequence: 355 1. Receiver hosts in multicast sites will join multicast content the 356 way they do today, they use IGMP. When they use IGMPv3 where 357 they specify source addresses, they use source EIDs, that is they 358 join (S-EID,G). If the multicast source is external to this 359 receiver site, the PIM Join/Prune message flows toward the ETRs, 360 finding the shortest exit (that is the closest exit for the Join/ 361 Prune message and the closest entrance for the multicast packet 362 to the receiver). 364 2. The ETR does a mapping database lookup for S-EID. If the mapping 365 is cached from a previous lookup (from either a previous Join/ 366 Prune for the source multicast site or a unicast packet that went 367 to the site), it will use the RLOC information from the mapping. 368 The ETR will use the same priority and weighting mechanism as for 369 unicast. So the source site can decide which way multicast 370 packets egress. 372 3. The ETR will build two PIM Join/Prune messages, one that contains 373 a (S-EID,G) entry that is unicast to the ITR that matches the 374 RLOC the ETR selects, and the other which contains a (S-RLOC,G) 375 entry so the core network can create multicast state from this 376 ETR to the ITR. 378 4. When the ITR gets the unicast Join/Prune message (see Section 3 379 for formal definition), it will process (S-EID,G) entries in the 380 message and propagate them inside of the site where it has 381 explicit routing information for EIDs via the IGP. When the ITR 382 receives the (S-RLOC,G) PIM Join/Prune message it will process it 383 like any other join it would get in today's Internet. The S-RLOC 384 address is the IP address of this ITR. 386 5. At this point there is (S-EID,G) state from the joining host in 387 the receiver multicast site to the ETR of the receiver multicast 388 site. There is (S-RLOC,G) state across the core network from the 389 ETR of the multicast receiver site to the ITR in the multicast 390 source site and (S-EID,G) state in the source multicast site. 391 Note, the (S-EID,G) state is the same S-EID in each multicast 392 site. As other ETRs join the same multicast tree, they can join 393 through the same ITR (in which case the packet replication is 394 done in the core) or a different ITR (in which case the packet 395 replication is done at the source site). 397 6. When a packet is originated by the multicast host in the source 398 site, the packet will flow to one or more ITRs which will prepend 399 a LISP header. By copying the group address to the outer 400 destination address field, the ITR insert its own locator address 401 in the outer source address field. The ITR will look at its 402 (S-RLOC,G) state, where S-RLOC is its own locator address, and 403 replicate the packet on each interface a (S-RLOC,G) joined was 404 received on. The core has (S-RLOC,G) so where fanout occurs to 405 multiple sites, a core router will do packet replication. 407 7. When either the source site or the core replicates the packet, 408 the ETR will receive a LISP packet with a destination group 409 address. It will decapsulate packets because it has receivers 410 for the group. Otherwise, it would have not received the packets 411 because it would not have joined. The ETR decapsulates and does 412 a (S-EID,G) lookup in its multicast FIB to forward packets out 413 one or more interfaces to forward the packet to internal 414 receivers. 416 This architecture is consistent and scalable with the architecture 417 presented in [LISP] where multicast state in the core operates on 418 locators and multicast state at the sites operates on EIDs. 420 Alternatively, [LISP] also has a mechanism where (S-EID,G) state can 421 reside in the core through the use of RPF-vectors [RFC5496] in PIM 422 Join/Prune messages. However, few PIM implementations support RPF 423 vectors and LISP should avoid S-EID state in the core. See Section 5 424 for details. 426 However, some observations can be made on the algorithm above. The 427 control plane can scale but at the expense of sending data to sites 428 which may have not joined the distribution tree where the 429 encapsulated data is being delivered. For example, one site joins 430 (S-EID1,G) and another site joins (S-EID2,G). Both EIDs are in the 431 same multicast source site. Both multicast receiver sites join to 432 the same ITR with state (S-RLOC,G) where S-RLOC is the RLOC for the 433 ITR. The ITR joins both (S-EID1,G) and (S-EID2,G) inside of the 434 site. The ITR receives (S-RLOC,G) joins and populates the OIF-list 435 state for it. Since both (S-EID1,G) and (S-EID2, G) map to the one 436 (S-RLOC,G) packets will be delivered by the core to both multicast 437 receiver sites even though each have joined a single source-based 438 distribution tree. This behavior is a consequence of the many-to-one 439 mapping between S-EIDs and a S-RLOC. 441 There is a possible solution to this problem which reduces the number 442 of many-to-one occurrences of (S-EID,G) entries aggregating into a 443 single (S-RLOC,G) entry. If a physical ITR can be assigned multiple 444 RLOC addresses and these addresses are advertised in mapping database 445 entries, then ETRs at receiver sites have more RLOC address options 446 and therefore can join different (RLOC,G) entries for each (S-EID,G) 447 entry joined at the receiver site. It would not scale to have a one- 448 to-one relationship between the number of S-EID sources at a source 449 site and the number of RLOCs assigned to all ITRs at the site, but 450 "n" can reduce to a smaller number in the "n-to-1" relationship. And 451 in turn, reduce the opportunity for data packets to be delivered to 452 sites for groups not joined. 454 5. Source Addresses versus Group Addresses 456 Multicast group addresses don't have to be associated with either the 457 EID or RLOC namespace. They actually are a namespace of their own 458 that can be treated as logical with relatively opaque allocation. 459 So, by their nature, they don't detract from an incremental 460 deployment of LISP-Multicast. 462 As for source addresses, as in the unicast LISP scenario, there is a 463 decoupling of identification from location. In a LISP site, packets 464 are originated from hosts using their allocated EIDs. EID addresses 465 are used to identify the host as well as where in the site's topology 466 the host resides but not how and where it is attached to the 467 Internet. 469 Therefore, when multicast distribution tree state is created anywhere 470 in the network on the path from any multicast receiver to a multicast 471 source, EID state is maintained at the source and receiver multicast 472 sites, and RLOC state is maintained in the core. That is, a 473 multicast distribution tree will be represented as a 3-tuple of 474 {(S-EID,G) (S-RLOC,G) (S-EID,G)} where the first element of the 475 3-tuple is the state stored in routers from the source to one or more 476 ITRs in the source multicast site, the second element of the 3-tuple 477 is the state stored in routers downstream of the ITR, in the core, to 478 all LISP receiver multicast sites, and the third element in the 479 3-tuple is the state stored in the routers downstream of each ETR, in 480 each receiver multicast site, reaching each receiver. Note that 481 (S-EID,G) is the same in both the source and receiver multicast 482 sites. 484 The concatenation/mapping from the first element to the second 485 element of the 3-tuples is done by the ITR and from the second 486 element to the third element is done at the ETRs. 488 6. Locator Reachability Implications on LISP-Multicast 490 Multicast state as it is stored in the core is always (S,G) state as 491 it exists today or (S-RLOC,G) state as it will exist when LISP sites 492 are deployed. The core routers cannot distinguish one from the 493 other. They don't need to because it is state that RPFs against the 494 core routing tables in the RLOC namespace. The difference is where 495 the root of the distribution tree for a particular source is. In the 496 traditional multicast core, the source S is the source host's IP 497 address. For LISP-Multicast the source S is a single ITR of the 498 multicast source site. 500 An ITR is selected based on the LISP EID-to-RLOC mapping used when an 501 ETR propagates a PIM Join/Prune message out of a receiver multicast 502 site. The selection is based on the same algorithm an ITR would use 503 to select an ETR when sending a unicast packet to the site. In the 504 unicast case, the ITR can change on a per-packet basis depending on 505 the reachability of the ETR. So an ITR can change relatively easily 506 using local reachability state. However, in the multicast case, when 507 an ITR goes unreachable, new distribution tree state must be built 508 because the encapsulating root has changed. This is more significant 509 than an RPF-change event, where any router would typically locally 510 change its RPF-interface for its existing tree state. But when an 511 encapsulating LISP-Multicast ITR goes unreachable, new distribution 512 state must be rebuilt and reflect the new encapsulator. Therefore, 513 when an ITR goes unreachable, all ETRs that are currently joined to 514 that ITR will have to trigger a new Join/Prune message for (S-RLOC,G) 515 to the new ITR as well as send a unicast encapsulated Join/Prune 516 message telling the new ITR which (S-EID,G) is being joined. 518 This issue can be mitigated by using anycast addressing for the ITRs 519 so the problem does reduce to an RPF change in the core, but still 520 requires a unicast encapsulated Join/Prune message to tell the new 521 ITR about (S-EID,G). The problem with this approach is that the ETR 522 really doesn't know when the ITR has changed so the new anycast ITR 523 will get the (S-EID,G) state only when the ETR sends it the next time 524 during its periodic sending procedures. 526 7. Multicast Protocol Changes 528 A number of protocols are used today for inter-domain multicast 529 routing: 531 IGMPv1-v3, MLDv1-v2: These protocols do not require any changes for 532 LISP-Multicast for two reasons. One being that they are link- 533 local and not used over site boundaries and second, they advertise 534 group addresses that don't need translation. Where source 535 addresses are supplied in IGMPv3 and MLDv2 messages, they are 536 semantically regarded as EIDs and don't need to be converted to 537 RLOCs until the multicast tree-building protocol, such as PIM, is 538 received by the ETR at the site boundary. Addresses used for IGMP 539 and MLD come out of the source site's allocated addresses which 540 are therefore from the EID namespace. 542 MBGP: Even though MBGP is not a multicast routing protocol, it is 543 used to find multicast sources when the unicast BGP peering 544 topology and the multicast MBGP peering topology are not 545 congruent. When MBGP is used in a LISP-Multicast environment, the 546 prefixes which are advertised are from the RLOC namespace. This 547 allows receiver multicast sites to find a path to the source 548 multicast site's ITRs. MBGP peering addresses will be from the 549 RLOC namespace. There are no MBGP protocol changes required to 550 support LISP-Multicast. 552 MSDP: MSDP is used to announce active multicast sources to other 553 routing domains (or LISP sites). The announcements come from the 554 PIM Rendezvous Points (RPs) from sites where there are active 555 multicast sources sending to various groups. In the context of 556 LISP-Multicast, the source addresses advertised in MSDP will 557 semantically be from the EID namespace since they describe the 558 identity of a source multicast host. It will be true that the 559 state stored in MSDP caches from core routers will be from the EID 560 namespace. An RP address inside of site will be from the EID 561 namespace so it can be advertised and reached by internal unicast 562 routing mechanism. However, for MSDP peer-RPF checking to work 563 properly across sites, the RP addresses must be converted or 564 mapped into a routable address that is advertised and maintained 565 in the BGP routing tables in the core. MSDP peering addresses can 566 come out of either the EID or a routable address namespace. And 567 the choice can be made unilaterally because the ITR at the site 568 will determine which namespace the destination peer address is out 569 of by looking in the mapping database service. There are no MSDP 570 protocol changes required to support LISP-Multicast. 572 PIM-SSM: In the simplest form of distribution tree building, when 573 PIM operates in SSM mode, a source distribution tree is built and 574 maintained across site boundaries. In this case, there is a small 575 modification to the operation of the PIM protocol. No 576 modifications to any message format, but to support taking a Join/ 577 Prune message originated inside of a LISP site with embedded 578 addresses from the EID namespace and converting them to addresses 579 from the RLOC namespace when the Join/Prune message crosses a site 580 boundary. This is similar to the requirements documented in 581 [RFC5135]. 583 PIM-Bidir: Bidirectional PIM is typically run inside of a routing 584 domain, but if deployed in an inter-domain environment, one would 585 have to decide if the RP address of the shared-tree would be from 586 the EID namespace or the RLOC namespace. If the RP resides in a 587 site-based router, then the RP address is from the EID namespace. 588 If the RP resides in the core where RLOC addresses are routed, 589 then the RP address is from the RLOC namespace. This could be 590 easily distinguishable if the EID address were well-known address 591 allocation block from the RLOC namespace. Also, when using 592 Embedded-RP for RP determination [RFC3956], the format of the 593 group address could indicate the namespace the RP address is from. 594 However, refer to Section 10 for considerations core routers need 595 to make when using Embedded-RP IPv6 group addresses. When using 596 Bidir-PIM for inter-domain multicast routing, it is recommended to 597 use staticly configured RPs. Allowing core routers to associate a 598 Bidir group's RP address with an ITR's RLOC address. And site 599 routers to associate the Bidir group's RP address as an EID 600 address. With respect to DF-election in Bidir PIM, no changes are 601 required since all messaging and addressing is link-local. 603 PIM-ASM: The ASM mode of PIM, the most popular form of PIM, is 604 deployed in the Internet today is by having shared-trees within a 605 site and using source-trees across sites. By the use of MSDP and 606 PIM-SSM techniques described above, multicast connectivity can 607 occur across LISP sites. Having said that, that means there are 608 no special actions required for processing (*,G) or (S,G,R) Join/ 609 Prune messages since they all operate against the shared-tree 610 which is site resident. Just like with ASM, there is no (*,G) in 611 the core when LISP-Multicast is in use. This is also true for the 612 RP-mapping mechanisms Auto-RP and BSR. 614 Based on the protocol description above, the conclusion is that there 615 are no protocol message format changes, just a translation function 616 performed at the control-plane. This will make for an easier and 617 faster transition for LISP since fewer components in the network have 618 to change. 620 It should also be stated just like it is in [LISP] that no host 621 changes, whatsoever, are required to have a multicast source host 622 send multicast packets and for a multicast receiver host to receive 623 multicast packets. 625 8. LISP-Multicast Data-Plane Architecture 627 The LISP-Multicast data-plane operation conforms to the operation and 628 packet formats specified in [LISP]. However, encapsulating a 629 multicast packet from an ITR is a much simpler process. The process 630 is simply to copy the inner group address to the outer destination 631 address. And to have the ITR use its own IP address (its RLOC) as 632 the source address. The process is simpler for multicast because 633 there is no EID-to-RLOC mapping lookup performed during packet 634 forwarding. 636 In the decapsulation case, the ETR simply removes the outer header 637 and performs a multicast routing table lookup on the inner header 638 (S-EID,G) addresses. Then the OIF-list for the (S-EID,G) entry is 639 used to replicate the packet on site-facing interfaces leading to 640 multicast receiver hosts. 642 There is no Data-Probe logic for ETRs as there can be in the unicast 643 forwarding case. 645 8.1. ITR Forwarding Procedure 647 The following procedure is used by an ITR, when it receives a 648 multicast packet from a source inside of its site: 650 1. A multicast data packet sent by a host in a LISP site will have 651 the source address equal to the host's EID and the destination 652 address equal to the group address of the multicast group. It is 653 assumed the group information is obtained by current methods. 654 The same is true for a multicast receiver to obtain the source 655 and group address of a multicast flow. 657 2. When the ITR receives a multicast packet, it will have both S-EID 658 state and S-RLOC state stored. Since the packet was received on 659 a site-facing interface, the RPF lookup is based on the S-EID 660 state. If the RPF check succeeds, then the OIF-list contains 661 interfaces that are site-facing and external-facing. For the 662 site-facing interfaces, no LISP header is prepended. For the 663 external-facing interfaces a LISP header is prepended. When the 664 ITR prepends a LISP header, it uses its own RLOC address as the 665 source address and copies the group address supplied by the IP 666 header the host built as the outer destination address. 668 8.1.1. Multiple RLOCs for an ITR 670 Typically, an ITR will have a single RLOC address but in some cases 671 there could be multiple RLOC addresses assigned from either the same 672 or different service providers. In this case when (S-RLOC,G) Join/ 673 Prune messages are received for each RLOC, there is a OIF-list 674 merging action that must take place. Therefore, when a packet is 675 received from a site-facing interface that matches on a (S-EID,G) 676 entry, the interfaces of the OIF-list from all (RLOC,G) entries 677 joined to the ITR as well as the site-facing OIF-list joined for 678 (S-EID,G) must be part be included in packet replication. In 679 addition to replicating for all types of OIF-lists, each oif entry 680 must be tagged with the RLOC address, so encapsulation uses the outer 681 source address for the RLOC joined. 683 8.1.2. Multiple ITRs for a LISP Source Site 685 Note when ETRs from different multicast receiver sites receive 686 (S-EID,G) joins, they may select a different S-RLOC for a multicast 687 source site due to policy (the multicast ITR can return different 688 multicast priority and weight values per ETR Map-Request). In this 689 case, the same (S-EID,G) is being realized by different (S-RLOC,G) 690 state in the core. This will not result in duplicate packets because 691 each ITR in the multicast source site will choose their own RLOC for 692 the source address for encapsulated multicast traffic. The RLOC 693 addresses are the ones joined by remote multicast ETRs. 695 When different (S-EID,G) traffic is combined into a single (RLOC,G) 696 core distribution tree, this may cause traffic to go to a receiver 697 multicast site when it does not need to. This happens when one 698 receiver multicast site joins (S1-EID,Gi) through a core distribution 699 tree of (RLOC1,Gi) and another multicast receiver site joins (S2- 700 EID,Gi) through the same core distribution tree of (RLOC1,Gi). When 701 ETRs decapsulate such traffic, they should know from their local 702 (S-EID,G) state if the packet should be forwarded. If there is no 703 (S-EID,G) state that matches the inner packet header, the packet is 704 discarded. 706 8.2. ETR Forwarding Procedure 708 The following procedure is used by an ETR, when it receives a 709 multicast packet from a source outside of its site: 711 1. When a multicast data packet is received by an ETR on an 712 external-facing interface, it will do an RPF lookup on the S-RLOC 713 state it has stored. If the RPF check succeeds, the interfaces 714 from the OIF-list are used for replication to interfaces that are 715 site-facing as well as interfaces that are external-facing (this 716 ETR can also be a transit multicast router for receivers outside 717 of its site). When the packet is to be replicated for an 718 external-facing interface, the LISP encapsulation header are not 719 stripped. When the packet is replicated for a site-facing 720 interface, the encapsulation header is stripped. 722 2. The packet without a LISP header is now forwarded down the 723 (S-EID,G) distribution tree in the receiver multicast site. 725 8.3. Replication Locations 727 Multicast packet replication can happen in the following topological 728 locations: 730 o In an IGP multicast router inside a site which operates on S-EIDs. 732 o In a transit multicast router inside of the core which operates on 733 S-RLOCs. 735 o At one or more ETR routers depending on the path a Join/Prune 736 message exits a receiver multicast site. 738 o At one or more ITR routers in a source multicast site depending on 739 what priorities are returned in a Map-Reply to receiver multicast 740 sites. 742 In the last case the source multicast site can do replication rather 743 than having a single exit from the site. But this only can occur 744 when the priorities in the Map-Reply are modified for different 745 receiver multicast site so that the PIM Join/Prune messages arrive at 746 different ITRs. 748 This policy technique, also used in [ALT] for unicast, is useful for 749 multicast to mitigate the problems of changing distribution tree 750 state as discussed in Section 6. 752 9. LISP-Multicast Interworking 754 This section will describe the multicast corollary to [INTWORK] which 755 describes the interworking of multicast routing among LISP and non- 756 LISP sites. 758 9.1. LISP and non-LISP Mixed Sites 760 Since multicast communication can involve more than two entities to 761 communicate together, the combinations of interworking scenarios are 762 more involved. However, the state maintained for distribution trees 763 at the sites is the same regardless of whether or not the site is 764 LISP enabled or not. So most of the implications are in the core 765 with respect to storing routable EID prefixes from either PA or PI 766 blocks. 768 Before enumerating the multicast interworking scenarios, let's define 769 3 deployment states of a site: 771 o A non-LISP site which will run PIM-SSM or PIM-ASM with MSDP as it 772 does today. The addresses for the site are globally routable. 774 o A site that deploys LISP for unicast routing. The addresses for 775 the site are not globally routable. Let's define the name for 776 this type of site as a uLISP site. 778 o A site that deploys LISP for both unicast and multicast routing. 779 The addresses for the site are not globally routable. Let's 780 define the name for this type of site as a LISP-Multicast site. 782 What will not be considered is a LISP site enabled for multicast 783 purposes only but do consider a uLISP site as documented in 784 [INTWORK]. In this section there is no discussion how a LISP site 785 sends multicast packets when all receiver sites are LISP-Multicast 786 enabled; that has been discussed in previous sections. 788 The following scenarios exist to make LISP-Multicast sites interwork 789 with non-LISP-Multicast sites: 791 1. A LISP site must be able to send multicast packets to receiver 792 sites which are a mix of non-LISP sites and uLISP sites. 794 2. A non-LISP site must be able to send multicast packets to 795 receiver sites which are a mix of non-LISP sites and uLISP sites. 797 3. A non-LISP site must be able to send multicast packets to 798 receiver sites which are a mix of LISP sites, uLISP sites, and 799 non-LISP sites. 801 4. A uLISP site must be able to send multicast packets to receiver 802 sites which are a mix of LISP sites, uLISP sites, and non-LISP 803 sites. 805 5. A LISP site must be able to send multicast packets to receiver 806 sites which are a mix of LISP sites, uLISP sites, and non-LISP 807 sites. 809 9.1.1. LISP Source Site to non-LISP Receiver Sites 811 In the first scenario, a site is LISP capable for both unicast and 812 multicast traffic and as such operates on EIDs. Therefore there is a 813 possibility that the EID prefix block is not routable in the core. 814 For LISP receiver multicast sites this isn't a problem but for non- 815 LISP or uLISP receiver multicast sites, when a PIM Join/Prune message 816 is received by the edge router, it has no route to propagate the 817 Join/Prune message out of the site. This is no different than the 818 unicast case that LISP-NAT in [INTWORK] solves. 820 LISP-NAT allows a unicast packet that exits a LISP site to get its 821 source address mapped to a globally routable address before the ITR 822 realizes that it should not encapsulate the packet destined to a non- 823 LISP site. For a multicast packet to leave a LISP site, distribution 824 tree state needs to be built so the ITR can know where to send the 825 packet. So the receiver multicast sites need to know about the 826 multicast source host by its routable address and not its EID 827 address. When this is the case, the routable address is the 828 (S-RLOC,G) state that is stored and maintained in the core routers. 829 It is important to note that the routable address for the host cannot 830 be the same as an RLOC for the site because it is desirable for ITRs 831 to process a received PIM Join/Prune message from an external-facing 832 interface to be propagated inside of the site so the site-part of the 833 distribution tree is built. 835 Using a globally routable source address allows non-LISP and uLISP 836 multicast receiver to join, create, and maintain a multicast 837 distribution tree. However, the LISP multicast receiver site will 838 want to perform an EID-to-RLOC mapping table lookup when a PIM Join/ 839 Prune message is received on a site-facing interface. It does this 840 because it wants to find a (S-RLOC,G) entry to Join in the core. So 841 there is a conflict of behavior between the two types of sites. 843 The solution to this problem is the same as when an ITR wants to send 844 a unicast packet to a destination site but needs determine if the 845 site is LISP capable or not. When it is not LISP capable, the ITR 846 does not encapsulate the packet. So for the multicast case, when ETR 847 receives a PIM Join/Prune message for (S-EID,G) state, it will do a 848 mapping table lookup on S-EID. In this case, S-EID is not in the 849 mapping database because the source multicast site is using a 850 routable address and not an EID prefix address. So the ETR knows to 851 simply propagate the PIM Join/Prune message to a external-facing 852 interface without converting the (S-EID,G) because it is an (S,G) 853 where S is routable and reachable via core routing tables. 855 Now that the multicast distribution tree is built and maintained from 856 any non-LISP or uLISP receiver multicast site, the way packet 857 forwarding model is performed can be explained. 859 Since the ITR in the source multicast site has never received a 860 unicast encapsulated PIM Join/Prune message from any ETR in a 861 receiver multicast site, it knows there are no LISP-Multicast 862 receiver sites. Therefore, there is no need for the ITR to 863 encapsulate data. Since it will know a priori (via configuration) 864 that its site's EIDs are not routable (and not registered to the 865 mapping database system), it assumes that the multicast packets from 866 the source host are sent by a routable address. That is, it is the 867 responsibility of the multicast source host's system administrator to 868 ensure that the source host sends multicast traffic using a routable 869 source address. When this happens, the ITR acts simply as a router 870 and forwards the multicast packet like an ordinary multicast router. 872 There is an alternative to using a LISP-NAT scheme just like there is 873 for unicast [INTWORK] forwarding by using Proxy Tunnel Routers 874 (PxTRs). This can work the same way for multicast routing as well, 875 but the difference is that non-LISP and uLISP sites will send PIM 876 Join/Prune messages for (S-EID,G) which make their way in the core to 877 multicast PxTRs. Let's call this use of a PxTR as a "Multicast 878 Proxy-ETR" (or mPETR). Since the mPETRs advertise very coarse EID 879 prefixes, they draw the PIM Join/Prune control traffic making them 880 the target of the distribution tree. To get multicast packets from 881 the LISP source multicast sites, the tree needs to be built on the 882 path from the mPETR to the LISP source multicast site. To make this 883 happen the mPETR acts as a "Proxy ETR" (where in unicast it acts as a 884 "Proxy ITR", or an uPITR [INTWORK]). 886 The existence of mPETRs in the core allows source multicast site ITRs 887 to encapsulate multicast packets according to (S-RLOC,G) state. The 888 (S-RLOC,G) state is built from the mPETRs to the multicast ITRs. The 889 encapsulated multicast packets are decapsulated by mPETRs and then 890 forwarded according to (S-EID,G) state. The (S-EID,G) state is built 891 from the non-LISP and uLISP receiver multicast sites to the mPETRs. 893 9.1.2. Non-LISP Source Site to non-LISP Receiver Sites 895 Clearly non-LISP multicast sites can send multicast packets to non- 896 LISP receiver multicast sites. That is what they do today. However, 897 discussion is required to show how non-LISP multicast sites send 898 multicast packets to uLISP receiver multicast sites. 900 Since uLISP receiver multicast sites are not targets of any (S,G) 901 state, they simply send (S,G) PIM Join/Prune messages toward the non- 902 LISP source multicast site. Since the source multicast site, in this 903 case has not been upgraded to LISP, all multicast source host 904 addresses are routable. So this case is simplified to where a uLISP 905 receiver multicast site looks to the source multicast site as a non- 906 LISP receiver multicast site. 908 9.1.3. Non-LISP Source Site to Any Receiver Site 910 When a non-LISP source multicast site has receivers in either a non- 911 LISP/uLISP site or a LISP site, one needs to decide how the LISP 912 receiver multicast site will attach to the distribution tree. It is 913 known from Section 9.1.2 that non-LISP and uLISP receiver multicast 914 sites can join the distribution tree, but a LISP receiver multicast 915 site ETR will need to know if the source address of the multicast 916 source host is routable or not. It has been shown in Section 9.1.1 917 that an ETR, before it sends a PIM Join/Prune message on an external- 918 facing interface, does a EID-to-RLOC mapping lookup to determine if 919 it should convert the (S,G) state from a PIM Join/Prune message 920 received on a site-facing interface to a (S-RLOC,G). If the lookup 921 fails, the ETR can conclude the source multicast site is a non-LISP 922 site so it simply forwards the Join/Prune message (it also doesn't 923 need to send a unicast encapsulated Join/Prune message because there 924 is no ITR in a non-LISP site and there is namespace continuity 925 between the ETR and source). 927 For a non-LISP source multicast site, (S-EID,G) state could be 928 limited to the edges of the network with the use of multicast proxy- 929 ITRs (mPITRs). The mPITRs can take native, unencapsulated multicast 930 packets from non-LISP source multicast and uLISP sites and 931 encapsulate them to ETRs in receiver multicast sites or to mPETRs 932 that can decapsulate for non-LISP receiver multicast or uLISP sites. 933 The mPITRs are responsible for sending (S-EID,G) joins to the non- 934 LISP source multicast site. To connect the distribution trees 935 together, multicast ETRs will need to be configured with the mPITR's 936 RLOC addresses so they can send both (S-RLOC,G) joins to build a 937 distribution tree to the mPITR as well as for sending unicast joins 938 to mPITRs so they can propogate (S-EID,G) joins into source multicast 939 sites. The use of mPITRs is undergoing more study and is work in 940 progress. 942 9.1.4. Unicast LISP Source Site to Any Receiver Sites 944 In the last section, it was explained how an ETR in a multicast 945 receiver site can determine if a source multicast site is LISP- 946 enabled by looking into the mapping database. When the source 947 multicast site is a uLISP site, it is LISP enabled but the ITR, by 948 definition is not capable of doing multicast encapsulation. So for 949 the purposes of multicast routing, the uLISP source multicast site is 950 treated as non-LISP source multicast site. 952 Non-LISP receiver multicast sites can join distribution trees to a 953 uLISP source multicast site since the source site behaves, from a 954 forwarding perspective, as a non-LISP source site. This is also the 955 case for a uLISP receiver multicast site since the ETR does not have 956 multicast functionality built-in or enabled. 958 Special considerations are required for LISP receiver multicast sites 959 since they think the source multicast site is LISP capable, the ETR 960 cannot know if ITR is LISP-Multicast capable. To solve this problem, 961 each mapping database entry will have a multicast 2-tuple (Mpriority, 962 Mweight) per RLOC. When the Mpriority is set to 255, the site is 963 considered not multicast capable. So an ETR in a LISP receiver 964 multicast site can distinguish whether a LISP source multicast site 965 is LISP-Multicast site from a uLISP site. 967 9.1.5. LISP Source Site to Any Receiver Sites 969 When a LISP source multicast site has receivers in LISP, non-LISP, 970 and uLISP receiver multicast sites, it has a conflict about how it 971 sends multicast packets. The ITR can either encapsulate or natively 972 forward multicast packets. Since the receiver multicast sites are 973 heterogeneous in their behavior, one packet forwarding mechanism 974 cannot satisfy both. However, if a LISP receiver multicast site acts 975 like a uLISP site then it could receive packets like a non-LISP 976 receiver multicast site making all receiver multicast sites have 977 homogeneous behavior. However, this poses the following issues: 979 o LISP-NAT techniques with routable addresses would be required in 980 all cases. 982 o Or alternatively, mPETR deployment would be required forcing 983 coarse EID prefix advertisement in the core. 985 o But what is most disturbing is that when all sites that 986 participate are LISP-Multicast sites but then a non-LISP or uLISP 987 site joins the distribution tree, then the existing joined LISP 988 receiver multicast sites would have to change their behavior. 989 This would create too much dynamic tree-building churn to be a 990 viable alternative. 992 So the solution space options are: 994 1. Make the LISP ITR in the source multicast site send two packets, 995 one that is encapsulated with (S-RLOC,G) to reach LISP receiver 996 multicast sites and another that is not encapsulated with 997 (S-EID,G) to reach non-LISP and uLISP receiver multicast sites. 999 2. Make the LISP ITR always encapsulate packets with (S-RLOC,G) to 1000 reach LISP-Multicast sites and to reach mPETRs that can 1001 decapsulate and forward (S-EID,G) packets to non-LISP and uLISP 1002 receiver multicast sites. 1004 9.2. LISP Sites with Mixed Address Families 1006 A LISP database mapping entry that describes the locator-set, 1007 Mpriority and Mweight per locator address (RLOC), for an EID prefix 1008 associated with a site could have RLOC addresses in either IPv4 or 1009 IPv6 format. When a mapping entry has a mix of RLOC formatted 1010 addresses, it is an implicit advertisement by the site that it is a 1011 dual-stack site. That is, the site can receive IPv4 or IPv6 unicast 1012 packets. 1014 To distinguish if the site can receive dual-stack unicast packets as 1015 well as dual-stack multicast packets, the Mpriority value setting 1016 will be relative to an IPv4 or IPv6 RLOC See [LISP] for packet format 1017 details. 1019 If one considers the combinations of LISP, non-LISP, and uLISP sites 1020 sharing the same distribution tree and considering the capabilities 1021 of supporting IPv4, IPv6, or dual-stack, the number of total 1022 combinations grows beyond comprehension. 1024 Using some combinatorial math, the following profiles of a site and 1025 the combinations that can occur: 1027 1. LISP-Multicast IPv4 Site 1029 2. LISP-Multicast IPv6 Site 1031 3. LISP-Multicast Dual-Stack Site 1033 4. uLISP IPv4 Site 1035 5. uLISP IPv6 Site 1036 6. uLISP Dual-Stack Site 1038 7. non-LISP IPv4 Site 1040 8. non-LISP IPv6 Site 1042 9. non-LISP Dual-Stack Site 1044 Lets define (m n) = m!/(n!*(m-n)!), pronounced "m choose n" to 1045 illustrate some combinatorial math below. 1047 When 1 site talks to another site, the combinatorial is (9 2), when 1 1048 site talks to another 2 sites, the combinatorial is (9 3). If sum 1049 this up to (9 9), then: 1051 (9 2) + (9 3) + (9 4) + (9 5) + (9 6) + (9 7) + (9 8) + (9 9) = 1053 36 + 84 + 126 + 126 + 84 + 36 + 9 + 1 1055 Which results in the total number of cases to be considered at 502. 1057 This combinatorial gets even worse when one considers a site using 1058 one address family inside of the site and the xTRs use the other 1059 address family (as in using IPv4 EIDs with IPv6 RLOCs or IPv6 EIDs 1060 with IPv4 RLOCs). 1062 To rationalize this combinatorial nightmare, there are some 1063 guidelines which need to be put in place: 1065 o Each distribution tree shared between sites will either be an IPv4 1066 distribution tree or an IPv6 distribution tree. Therefore, head- 1067 end replication can be avoided by building and sending packets on 1068 each address family based distribution tree. Even though there 1069 might be an urge to do multicast packet translation from one 1070 address family format to the other, it is a non-viable over- 1071 complicated urge. Multicast ITRs will only encapsulate packets 1072 where the inner and outer headers are from the same address 1073 family. 1075 o All LISP sites on a multicast distribution tree must share a 1076 common address family which is determined by the source site's 1077 locator-set in its LISP database mapping entry. All receiver 1078 multicast sites will use the best RLOC priority controlled by the 1079 source multicast site. This is true when the source site is 1080 either LISP-Multicast or uLISP capable. This means that priority- 1081 based policy modification is prohibited. When a receiver 1082 multicast site ETR receives a (S-EID,G) join, it must select a 1083 S-RLOC for the same address family as S-EID. 1085 o When a multicast locator-set has more than one locator, only 1086 locators from the same address-family MUST be set to the same best 1087 priority value. A mixed locator-set can exist (for unicast use), 1088 but the multicast priorities MUST be the set for the same address 1089 family locators. 1091 o When the source site is not LISP capable, it is up to how 1092 receivers find the source and group information for a multicast 1093 flow. That mechanism decides the address family for the flow. 1095 9.3. Making a Multicast Interworking Decision 1097 This Multicast Interworking section has shown all combinations of 1098 multicast connectivity that could occur. As already concluded, this 1099 can be quite complicated and if the design is too ambitious, the 1100 dynamics of the protocol could cause a lot of instability. 1102 The trade-off decisions are hard to make and so the same single 1103 solution is desirable to work for both IPv4 and IPv6 multicast. It 1104 is imperative to have an incrementally deployable solution for all of 1105 IPv4 unicast and multicast and IPv6 unicast and multicast while 1106 minimizing (or eliminating) both unicast and multicast EID namespace 1107 state. 1109 Therefore the design decision to go with uPITRs [INTWORK] for unicast 1110 routing and mPETRs for multicast routing seems to be the sweet spot 1111 in the solution space so state requirements can be optimized and 1112 avoid head-end data replication at ITRs. 1114 10. Considerations when RP Addresses are Embedded in Group Addresses 1116 When ASM and PIM-Bidir is used in an IPv6 inter-domain environment, a 1117 technique exists to embed the unicast address of an RP in a IPv6 1118 group address [RFC3956]. When routers in end sites process a PIM 1119 Join/Prune message which contain an embedded-RP group address, they 1120 extract the RP address from the group address and treat it from the 1121 EID namespace. However, core routers do not have state for the EID 1122 namespace, need to extract an RP address from the RLOC namespace. 1124 Therefore, it is the responsibility of ETRs in multicast receiver 1125 sites to map the group address into a group address where the 1126 embedded-RP address is from the RLOC namespace. The mapped RP- 1127 address is obtained from a EID-to-RLOC mapping database lookup. The 1128 ETR will also send a unicast (*,G) Join/Prune message to the ITR so 1129 the branch of the distribution tree from the source site resident RP 1130 to the ITR is created. 1132 This technique is no different than the techniques described in this 1133 specification for translating (S,G) state and propagating Join/Prune 1134 messages into the core. The only difference is that the (*,G) state 1135 in Join/Prune messages are mapped because they contain unicast 1136 addresses encoded in an Embedded-RP group address. 1138 11. Taking Advantage of Upgrades in the Core 1140 If the core routers are upgraded to support [RFC5496], then the EID 1141 specific data can be passed through the core without, possibly, 1142 having to store the state in the core. 1144 By doing this one can eliminate the ETR from unicast encapsulating 1145 PIM Join/Prune messages to the source site's ITR. 1147 However, this solution is restricted to a small set of workable cases 1148 which would not be good for general use of LISP-Multicast. In 1149 addition due to slow convergence properties, it is not being 1150 recommended for LISP-Multicast. 1152 12. Mtrace Considerations 1154 Mtrace functionality MUST be consistent with unicast traceroute 1155 functionality where all hops from multicast receiver to multicast 1156 source are visible. 1158 The design for mtrace for use in LISP-Multicast environments is to be 1159 determined but should build upon the mtrace version 2 specified in 1160 [MTRACE]. 1162 13. Security Considerations 1164 This document introduces no additional security concerns beyond those 1165 specified in the base LISP specification [LISP]. 1167 14. Acknowledgments 1169 The authors would like to gratefully acknowledge the people who have 1170 contributed discussion, ideas, and commentary to the making of this 1171 proposal and specification. People who provided expert review were 1172 Scott Brim, Greg Shepherd, and Dave Oran. Other commentary from 1173 discussions at Summer 2008 Dublin IETF were Toerless Eckert and 1174 Ijsbrand Wijnands. 1176 The authors would also like to thank the MBONED working group for 1177 constructive and civil verbal feedback when this draft was presented 1178 at the Fall 2008 IETF in Minneapolis. In particular, good commentary 1179 came from Tom Pusateri, Steve Casner, Marshall Eubanks, Dimitri 1180 Papadimitriou, Ron Bonica, Lenny Guardino, Alia Atlas, Jesus Arango, 1181 and Jari Arkko. 1183 An expert review of this specification was done by Yiqun Cai and 1184 Liming Wei. The authors thank them for their detailed comments. 1186 This work originated in the Routing Research Group (RRG) of the IRTF. 1187 The individual submission [MLISP] was converted into this IETF LISP 1188 working group draft. 1190 15. IANA Considerations 1192 This document makes no request of the IANA. 1194 16. References 1196 16.1. Normative References 1198 [INTWORK] Lewis, D., Meyer, D., and D. Farinacci, "Interworking LISP 1199 with IPv4 and IPv6", draft-ietf-lisp-interworking-02.txt 1200 (work in progress). 1202 [LISP] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, 1203 "Locator/ID Separation Protocol (LISP)", 1204 draft-ietf-lisp-15.txt (work in progress). 1206 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1207 Requirement Levels", BCP 14, RFC 2119, March 1997. 1209 [RFC3618] Fenner, B. and D. Meyer, "Multicast Source Discovery 1210 Protocol (MSDP)", RFC 3618, October 2003. 1212 [RFC3956] Savola, P. and B. Haberman, "Embedding the Rendezvous 1213 Point (RP) Address in an IPv6 Multicast Address", 1214 RFC 3956, November 2004. 1216 [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, 1217 "Protocol Independent Multicast - Sparse Mode (PIM-SM): 1218 Protocol Specification (Revised)", RFC 4601, August 2006. 1220 [RFC4604] Holbrook, H., Cain, B., and B. Haberman, "Using Internet 1221 Group Management Protocol Version 3 (IGMPv3) and Multicast 1222 Listener Discovery Protocol Version 2 (MLDv2) for Source- 1223 Specific Multicast", RFC 4604, August 2006. 1225 [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for 1226 IP", RFC 4607, August 2006. 1228 [RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, 1229 "Multiprotocol Extensions for BGP-4", RFC 4760, 1230 January 2007. 1232 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 1233 "Bidirectional Protocol Independent Multicast (BIDIR- 1234 PIM)", RFC 5015, October 2007. 1236 [RFC5135] Wing, D. and T. Eckert, "IP Multicast Requirements for a 1237 Network Address Translator (NAT) and a Network Address 1238 Port Translator (NAPT)", BCP 135, RFC 5135, February 2008. 1240 [RFC5496] Wijnands, IJ., Boers, A., and E. Rosen, "The Reverse Path 1241 Forwarding (RPF) Vector TLV", RFC 5496, March 2009. 1243 16.2. Informative References 1245 [ALT] Farinacci, D., Fuller, V., and D. Meyer, "LISP Alternative 1246 Topology (LISP-ALT)", draft-ietf-lisp-alt-08.txt (work in 1247 progress). 1249 [MLISP] Farinacci, D., Meyer, D., Zwiebel, J., and S. Venaas, 1250 "LISP for Multicast Environments", 1251 draft-farinacci-lisp-multicast-01.txt (work in progress). 1253 [MTRACE] Asaeda, H., Jinmei, T., Fenner, W., and S. Casner, "Mtrace 1254 Version 2: Traceroute Facility for IP Multicast", 1255 draft-ietf-mboned-mtrace-v2-08.txt (work in progress). 1257 Appendix A. Document Change Log 1259 A.1. Changes to draft-ietf-lisp-multicast-09.txt 1261 o Posted October 2011. Changes to reflect IESG review comments from 1262 Ralph Droms and Kathleen Moriarty. 1264 A.2. Changes to draft-ietf-lisp-multicast-08.txt 1266 o Posted September 2011. Minor editorial changes from Jari's 1267 commentary. 1269 A.3. Changes to draft-ietf-lisp-multicast-07.txt 1271 o Posted July 2011. Fixing IDnits errors. 1273 A.4. Changes to draft-ietf-lisp-multicast-06.txt 1275 o Posted June 2011 to complete working group last call. 1277 o Added paragraph to section 8.1.2 based on Jesus comment about 1278 making it more clear what happens when two (S-EID,G) trees use the 1279 same (RLOC,G) tree. 1281 o Make more references to [INTWORK] when mentioning uPITRs and 1282 uPETRs. 1284 o Made many changes based on editorial and wordsmithing comments 1285 from Alia. 1287 A.5. Changes to draft-ietf-lisp-multicast-05.txt 1289 o Posted April 2011 to reset expiration timer. 1291 o Updated references. 1293 A.6. Changes to draft-ietf-lisp-multicast-04.txt 1295 o Posted October 2010 to reset expiration timer. 1297 o Updated references. 1299 A.7. Changes to draft-ietf-lisp-multicast-03.txt 1301 o Posted April 2010. 1303 o Added section 8.1.2 to address Joel Halpern's comment about 1304 receiver sites joining the same source site via 2 different RLOCs, 1305 each being a separate ITR. 1307 o Change all occurences of "mPTR" to "mPETR" to become more 1308 consistent with uPITRs and uPETRs described in [INTWORK]. That 1309 is, an mPETR is a LISP multicast router that decapsulates 1310 multicast packets that are encapsulated to it by ITRs in multicast 1311 source sites. 1313 o Add clarifications in section 9 about how homogeneous multicast 1314 encapsulation should occur. As well as describing in this 1315 section, how to deal with mixed-locator sets to avoid 1316 heterogeneous encapsulation. 1318 o Introduce concept of mPITRs to help reduce (S-EID,G) to the edges 1319 of LISP global multicast network. 1321 A.8. Changes to draft-ietf-lisp-multicast-02.txt 1323 o Posted September 2009. 1325 o Added Document Change Log appendix. 1327 o Specify that the LISP Encapsulated Control Message be used for 1328 unicasting PIM Join/Prune messages from ETRs to ITRs. 1330 A.9. Changes to draft-ietf-lisp-multicast-01.txt 1332 o Posted November 2008. 1334 o Specified that PIM Join/Prune unicast messages that get sent from 1335 ETRs to ITRs of a source multicast site get LISP encapsulated in 1336 destination UDP port 4342. 1338 o Add multiple RLOCs per ITR per Yiqun's comments. 1340 o Indicate how static RPs can be used when LISP is run using Bidir- 1341 PIM in the core. 1343 o Editorial changes per Liming comments. 1345 o Add Mttrace Considersations section. 1347 A.10. Changes to draft-ietf-lisp-multicast-00.txt 1349 o Posted April 2008. 1351 o Renamed from draft-farinacci-lisp-multicast-01.txt. 1353 Authors' Addresses 1355 Dino Farinacci 1356 cisco Systems 1357 Tasman Drive 1358 San Jose, CA 1359 USA 1361 Email: dino@cisco.com 1363 Dave Meyer 1364 cisco Systems 1365 Tasman Drive 1366 San Jose, CA 1367 USA 1369 Email: dmm@cisco.com 1371 John Zwiebel 1372 cisco Systems 1373 Tasman Drive 1374 San Jose, CA 1375 USA 1377 Email: jzwiebel@cisco.com 1379 Stig Venaas 1380 cisco Systems 1381 Tasman Drive 1382 San Jose, CA 1383 USA 1385 Email: stig@cisco.com