idnits 2.17.1 draft-ietf-ssm-arch-03.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- ** Looks like you're using RFC 2026 boilerplate. This must be updated to follow RFC 3978/3979, as updated by RFC 4748. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- ** The document seems to lack a 1id_guidelines paragraph about 6 months document validity -- however, there's a paragraph with a matching beginning. Boilerplate error? ** The document is more than 15 pages and seems to lack a Table of Contents. == No 'Intended status' indicated for this document; assuming Proposed Standard Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- == There are 9 instances of lines with multicast IPv4 addresses in the document. If these are generic example addresses, they should be changed to use the 233.252.0.x range defined in RFC 5771 Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the RFC 3978 Section 5.4 Copyright Line does not match the current year == Line 709 has weird spacing: '...imed to perta...' -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (7 May 2003) is 7660 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'RFC 2119' is mentioned on line 34, but not defined == Missing Reference: 'IPv6-UBM' is mentioned on line 65, but not defined == Missing Reference: 'IPv6-MALLOC' is mentioned on line 323, but not defined == Missing Reference: 'SCOPED-ARCH' is mentioned on line 553, but not defined == Unused Reference: 'IGMPv2' is defined on line 653, but no explicit reference was found in the text == Unused Reference: 'RFC2119' is defined on line 674, but no explicit reference was found in the text == Unused Reference: 'RFC2710' is defined on line 677, but no explicit reference was found in the text ** Obsolete normative reference: RFC 2401 (ref. 'IPSEC') (Obsoleted by RFC 4301) ** Obsolete normative reference: RFC 2373 (Obsoleted by RFC 3513) -- Obsolete informational reference (is this intentional?): RFC 2434 (ref. 'IANA-CONSIDERATIONS') (Obsoleted by RFC 5226) -- Obsolete informational reference (is this intentional?): RFC 2362 (ref. 'PIM-SM') (Obsoleted by RFC 4601, RFC 5059) Summary: 5 errors (**), 0 flaws (~~), 11 warnings (==), 4 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 INTERNET-DRAFT Source-Specific Multicast H. Holbrook 3 Expires Nov 7, 2003 Cisco Systems 4 B. Cain 5 Storigen Systems 6 7 May 2003 8 Source-Specific Multicast for IP 9 11 Status of this Memo 13 This document is an Internet-Draft and is in full conformance with all 14 provisions of Section 10 of RFC2026. 16 Internet-Drafts are working documents of the Internet Engineering Task 17 Force (IETF), its areas, and its working groups. Note that other groups 18 may also distribute working documents as Internet-Drafts. 20 Internet-Drafts are draft documents valid for a maximum of six months 21 and may be updated, replaced, or obsoleted by other documents at any 22 time. It is inappropriate to use Internet- Drafts as reference material 23 or to cite them other than as "work in progress." 25 The list of current Internet-Drafts can be accessed at 26 http://www.ietf.org/ietf/1id-abstracts.txt 28 The list of Internet-Draft Shadow Directories can be accessed at 29 http://www.ietf.org/shadow.html. 31 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 32 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 33 document are to be interpreted as described in RFC 2119 [RFC 2119]. 35 Abstract 37 IP addresses in the 232/8 (232.0.0.0 to 232.255.255.255) range are 38 designated as source-specific multicast (SSM) destination addresses and 39 are reserved for use by source-specific applications and protocols. For 40 IP version 6 (IPv6), the address prefix FF3x::/32 is reserved for 41 source-specific multicast use. It defines an extension to the Internet 42 network service that applies to datagrams sent to SSM addresses and 43 defines the host and router requirements to support this extension. 45 1. Introduction 47 The Internet Protocol (IP) multicast service model is defined in RFC 48 1112 [RFC1112]. RFC 1112 specifies that a datagram sent to an IP 49 multicast address (224.0.0.0 through 239.255.255.255) G is delivered to 50 each "upper-layer protocol module" that has requested reception of 51 datagrams sent to address G. RFC 1112 calls the network service 52 identified by a multicast destination address G a "host group." This 53 model supports both one-to-many and many-to-many group communication. 54 This document uses the term "Any-Source Multicast" (ASM) to refer to 55 model of multicast defined in RFC 1112. RFC 2373 [RFC2373] specifies 56 the form of IPv6 multicast addresses with ASM semantics. 58 IP addresses in the 232/8 (232.0.0.0 to 232.255.255.255) range are 59 currently designated as source-specific multicast (SSM) destination 60 addresses and are reserved for use by source-specific applications and 61 protocols [IANA-ALLOCATION]. 63 For IPv6, the address prefix FF3x::/32 is reserved for source-specific 64 multicast use, where 'x' is any valid scope identifier, by [IPV6-UBM]. 65 Using the terminology of [IPv6-UBM], all SSM addresses must have P=1, 66 T=1, and plen=0. [IPv6-MALLOC] mandates that the network prefix field 67 of an SSM address also be set to zero, hence all SSM addresses fall in 68 the FF3x::/96 range. Future documents may allow a non-zero network 69 prefix field if, for instance, a new IP address to MAC address mapping 70 is defined. Thus, address allocation should occur within the FF3x::/96 71 range, but a system should treat all of FF3x::/32 as SSM addresses, to 72 allow for compatibility with possible future uses of the network prefix 73 field. 75 Addresses in the range FF3x::4000:0000 through FF3x::7FFF:FFFF are 76 reserved in [IPv6-MALLOC] for allocation by IANA. Addresses in the 77 range FF3x::8000:0000 through FF3x::FFFF:FFFF are allowed for dynamic 78 allocation by a host, as described in [IPV6-MALLOC]. Addresses in the 79 range FF3x::0000:0000 through FF3x::3FFF:FFFF are invalid IPv6 SSM 80 addresses. ([IPV6-MALLOC] indicates that FF3x::0000:0001 to 81 FF3x:3FFF:FFFF must set P=0 and T=0, but for SSM, [IPV6-UBM] mandates 82 that P=1 and T=1, hence their designation as invalid). The treatment 83 of a packet sent to such an invalid address is undefined -- a router or 84 host MAY choose to drop such a packet. 86 Source-specific multicast delivery semantics are provided for a datagram 87 sent to an SSM address. That is, a datagram with source IP address S 88 and SSM destination address G is delivered to each upper-layer "socket" 89 that has specifically requested the reception of datagrams sent to 90 address G by source S, and only to those sockets. The network service 91 identified by (S,G), for SSM address G and source host address S, is 92 referred to as a "channel." In contrast to the ASM model of RFC 1112, 93 SSM provides network-layer support for one-to-many delivery only. 95 The benefits of source-specific multicast include: 97 Elimination of cross-delivery of traffic when two sources 98 simultaneously use the same source-specific destination address. 99 The simultaneous use of an SSM destination address by multiple 100 sources and different applications is explicitly supported. 102 Avoidance of the need for inter-host coordination when choosing 103 source-specific addresses, as a consequence of the above. 105 Avoidance of many of the router protocols and algorithms that are 106 needed to provide the ASM service model. For instance, the "shared 107 trees" and Rendezvous Points of the PIM-Sparse Mode (PIM-SM) 108 protocol [PIM-SM] are not necessary to support the source-specific 109 model. The router mechanisms required to support SSM are in fact 110 largely a subset of those that are used to support ASM. For 111 example, the shortest-path tree mechanism of the PIM-SM protocol can 112 be adapted to provide SSM semantics. 114 Like ASM, the set of receivers is unknown to an SSM sender. An SSM 115 source is provided with neither the identity of receivers nor their 116 number. 118 SSM is particularly well-suited to dissemination-style applications with 119 one or more senders whose identities are known before the application 120 begins. For instance, a data dissemination application that desires to 121 provide a secondary data source in case the primary source fails over 122 might implement this by using one channel for each source and 123 advertising both of them to receivers. SSM can be used to build multi- 124 source applications where all participants' identities are not known in 125 advance, but the multi-source "rendezvous" functionality does not occur 126 in the network layer in this case. Just like in an application that 127 uses unicast as the underlying transport, this functionality can be 128 implemented by the application or by an application-layer library. 130 Multicast resource discovery of the form in which a client sends a 131 multicast query directly to a "service location group" to which servers 132 listen is not directly supported by SSM. 134 This document defines the semantics of source-specific multicast 135 addresses and specifies the policies governing their use. In 136 particular, it defines an extension to the Internet network service that 137 applies to datagrams sent to SSM addresses and defines host extensions 138 to support the network service. Hosts, routers, applications, and 139 protocols that use these addresses MUST comply with the policies 140 outlined in this document. Failure of a host to comply may prevent that 141 host or other hosts on the same LAN from receiving traffic sent to an 142 SSM channel. Failure of a router to comply may cause SSM traffic to be 143 delivered to parts of the network where it is unwanted, unnecessarily 144 burdening the network. 146 2. Semantics of Source-Specific Multicast Addresses 148 The source-specific multicast service is defined as follows: 150 A datagram sent with source IP address S and destination IP address 151 G in the SSM range is delivered to each host socket that has 152 specifically requested delivery of datagrams sent by S to G, and 153 only to those sockets. 155 Where, using the terminology of [IGMPv3], 157 "socket" is an implementation-specific parameter used to distinguish 158 among different requesting entities (e.g., programs or processes or 159 communication end-points within a program or process) within the 160 requesting host; the socket parameter of BSD Unix system calls is a 161 specific example. 163 Any host may send a datagram to any SSM address, and delivery is 164 provided according to the above semantics. 166 The IP module interface to upper-layer protocols is extended to allow a 167 socket to "Subscribe" to or "Unsubscribe" from a particular channel 168 identified by an SSM destination address and a source IP address. The 169 extended interface is defined in section 4.1. It is meaningless for an 170 application or host to request reception of datagrams sent to an SSM 171 destination address G, as is supported in the any-source multicast 172 model, without also specifying a corresponding source address, and 173 routers MUST ignore any such request. 175 Multiple source applications on different hosts can use the same SSM 176 destination address G without conflict because datagrams sent by each 177 source host Si are delivered only to those sockets that requested 178 delivery of datagrams sent to G specifically by Si. 180 The key distinguishing property of the model is that a channel is 181 identified (addressed) by the combination of a unicast source address 182 and a multicast destination address in the SSM range. So, for example, 183 the channel 185 S,G = (192.0.2.1, 232.7.8.9) 187 differs from 189 S,G = (192.0.2.2, 232.7.8.9), 191 even though they have the same destination address portion. Similarly, 192 for IPv6, 194 S,G = (2001:3618::1, FF33::1234) 196 and 198 S,G = (2001:3618::2, FF33::1234) 200 are different channels. 202 3. Terminology 204 To reduce confusion when talking about the any-source and source- 205 specific multicast models, we use different terminology when discussing 206 them. 208 We use the term "channel" to refer to the service associated with an SSM 209 address. A channel is identified by the combination of an SSM 210 destination address and a specific source, e.g., an (S,G) pair. 212 We use the term "host group" (used in RFC 1112) to refer to the service 213 associated with "regular" ASM multicast addresses (excluding those in 214 the SSM range). A host group is identified by a single multicast 215 address. 217 Any host can send to a host group, and similarly, any host can send to 218 an SSM destination address. A packet sent by a host S to an ASM 219 destination address G is delivered to the host group identified by G. A 220 packet sent by host S to an SSM destination address G is delivered to 221 the channel identified by (S,G). The receiver operations allowed on a 222 host group are called "join(G)" and "leave(G)" (as per RFC 1112). The 223 receiver operations allowed on a channel are called "Subscribe(S,G)" and 224 "Unsubscribe(S,G)." 225 The following table summarizes the terminology: 227 Service Model: any-source source-specific 228 Network Abstraction: group channel 229 Identifier: G S,G 230 Receiver Operations: Join, Leave Subscribe, Unsubscribe 232 We note that, although this document specifies a new service model 233 available to applications, the protocols and techniques necessary to 234 support the service model are largely a subset of those used to support 235 ASM. 237 4. Host Requirements 239 This section describes requirements on hosts that support source- 240 specific multicast, including: 242 - Extensions to the IP Module Interface 244 - Extensions to the IP Module 246 - Allocation of SSM Addresses 248 4.1. Extensions to the IP Module Interface 250 The IP module interface to upper-layer protocols is extended to allow 251 protocols to request reception of all datagrams sent to a particular 252 channel. 254 Subscribe ( socket, source-address, group-address, interface ) 256 Unsubscribe ( socket, source-address, group-address, interface ) 258 where 260 "socket" is as previously defined in Section 2, 262 and, paraphrasing [IGMPv3], 264 "interface" is a local identifier of the network interface on which 265 reception of the channel identified by the (source-address,group- 266 address) pair is to be enabled or disabled. A special value may be 267 used to indicate a "default" interface. If reception of the same 268 channel is desired on multiple interfaces, Subscribe is invoked once 269 for each. 271 The above are strictly abstract functional interfaces -- the 272 functionality can be provided in an implementation-specific way. On a 273 host that supports the multicast source filtering application 274 programming interface of [MSFAPI], for instance, the Subscribe and 275 Unsubscribe interfaces may be supported via that API. When a host has 276 been configured to know the SSM address range, (whether the 277 configuration mechanism is manual or through a protocol) the host's 278 operating system SHOULD return an error to an application that makes a 279 non-source-specific request to receive multicast sent to an SSM 280 destination address. 282 Widespread implementations of the IP packet reception interface (e.g., 283 the recvfrom() system call in BSD unix) do not allow a receiver to 284 determine the destination address to which a datagram was sent. On a 285 host with such an implementation, the destination address of a datagram 286 cannot be inferred when the socket on which the datagram is received is 287 Subscribed to multiple channels. Host operating systems SHOULD provide 288 a way for a host to determine both the source and the destination 289 address to which a datagram was sent. (As one example, the Linux 290 operating system provides the destination of a packet as part of the 291 response to the recvmsg() system call.) Until this capability is 292 present, applications may be forced to use higher-layer mechanisms to 293 identify the channel to which a datagram was sent. 295 4.2. Requirements on the Host IP Module 297 An incoming datagram destined to an SSM address MUST be delivered by the 298 IP module to all sockets that have indicated (via Subscribe) a desire to 299 receive data that matches the datagram's source address, destination 300 address, and arriving interface. It MUST NOT be delivered to other 301 sockets. 303 When the first socket on host H subscribes to a channel (S,G) on 304 interface I, the host IP module on H sends a request on interface I to 305 indicate to neighboring routers that the host wishes to receive traffic 306 sent by source S to source-specific multicast destination G. Similarly, 307 when the last socket on a host unsubscribes from a channel on interface 308 I, the host IP module sends an unsubscription request for that channel 309 to interface I. 311 These requests will typically be Internet Group Management Protocol 312 version 3 messages for IPv4, or Multicast Listener Discovery Version 2 313 messages for IPv6 [IGMPv3,MLDv2]. A separate document describes how 314 IGMPv3 and MLDv2 are adapted to support source-specific multicast. 316 4.3. Allocation of Source-Specific Multicast Addresses 318 The SSM destination address 232.0.0.0 is reserved, and a system MUST NOT 319 send a datagram with a destination address of 232.0.0.0. The address 320 range 232.0.0.1-232.0.0.255 is currently reserved for allocation by 321 IANA. SSM destination addresses in the range FF3x::4000:0000 through 322 FF3x::7FFF:FFFF are similarly reserved for IANA allocation 323 [IPv6-MALLOC]. 325 The policy for allocating the rest of the SSM addresses to sending 326 applications is strictly locally determined by the sending host. 328 When allocating SSM addresses dynamically, a host or host operating 329 system MUST NOT allocate sequentially starting at the first allowed 330 address. It is RECOMMENDED to allocate SSM addresses to applications 331 randomly, while ensuring that allocated addresses are not given 332 simultaneously to multiple applications (and avoiding the reserved 333 addresses). For IPv6, the randomization should apply to the lowest 31 334 bits of the address. 336 As described in Section 6, the mapping of an IP packet with SSM 337 destination address onto a link-layer multicast address does not take 338 into account the datagram's source IP address (on commonly-used link 339 layers like Ethernet). If all hosts started at the first allowed 340 address, then with high probability, many source-specific channels on 341 shared-medium local area networks would use the same link-layer 342 multicast address. As a result, traffic destined for one channel 343 subscriber would be delivered to another's IP module, which would then 344 have to discard the datagram. 346 A host operating system SHOULD provide an interface to allow an 347 application to request a unique allocation of a channel destination 348 address in advance of a session's commencement, and this allocation 349 database SHOULD persist across host reboots. By providing persistent 350 allocations, a host application can advertise the session in advance of 351 its start time on a web page or in another directory. (We note that 352 this issue is not specific to SSM applications -- the same problem 353 arises for ASM.) 355 This document neither defines the interfaces for requesting or returning 356 addresses nor specifies the host algorithms for storing those 357 allocations. One plausible abstract API is defined in RFC 2771 358 [RFC2771]. Note that RFC 2771 allows an application to request an 359 address within a specific range of addresses. If this interface is 360 used, the starting address of the range SHOULD be selected at random by 361 the application. 363 For IPv6, administratively scoped SSM channel addresses are created by 364 choosing an appropriate scope identifier for the SSM destination 365 address. Normal IPv6 multicast scope boundaries [SCOPINGV6] are applied 366 to traffic sent to an SSM destination address, including any relevant 367 boundaries applied to both the source and destination address. 369 No globally agreed-upon administratively-scoped address range [ADMIN- 370 SCOPE] is currently defined for IPv4 source-specific multicast. For 371 IPv4, administrative scoping of SSM addresses can be implemented within 372 an administrative domain by filtering outgoing SSM traffic sent to a 373 scoped address at the domain's boundary routers. 375 5. Router Requirements 377 5.1. Packet Forwarding 379 A router that receives an IP datagram with a source-specific destination 380 address MUST silently drop it unless a neighboring host or router has 381 communicated a desire to receive packets sent from the source and to the 382 destination address of the received packet. 384 5.2. Protocols 386 Certain IP multicast routing protocols already have the ability to 387 communicate source-specific joins to neighboring routers (in particular, 388 PIM-SM [PIM-SM]), and these protocols can, with slight modifications, be 389 used to provide source-specific semantics. Companion documents will 390 specify the required modifications to those protocols to support SSM. 392 A network can concurrently support SSM in the SSM address range and any- 393 source multicast in the rest of the multicast address space, and it is 394 expected that this will be commonplace. In such a network, a router may 395 receive a non-source-specific, or "(*,G)" in conventional terminology, 396 request for delivery of traffic in the SSM range from a neighbor that 397 does not implement source-specific multicast in a manner compliant with 398 this document. A router that receives such a non-source-specific 399 request for data in the SSM range MUST NOT use the request to establish 400 forwarding state and MUST NOT propagate the request to other neighboring 401 routers. A router MAY log an error in such a case. This applies both 402 to any request received from a host, e.g., an IGMPv1 or IGMPv2 host 403 report, and to any request received from a routing protocol, e.g., a 404 PIM-SM (*,G) join. The inter-router case is further discussed in 405 section 8, Transition Considerations. 407 It is essential that all routers in the network give source-specific 408 semantics to the same range of addresses in order to achieve the full 409 benefit of SSM. To comply with this specification, a router MUST treat 410 ALL IANA-allocated SSM addresses with source-specific semantics. 412 6. Link-Layer Transmission of Datagrams 414 Source-specific multicast packets are transmitted on link-layer networks 415 as specified in RFC 1112 for IPv4 and as in [ETHERv6] for IPv6. On most 416 shared-medium link-layer networks that support multicast (e.g., 417 Ethernet), the IP source address is not used in the selection of the 418 link-layer destination address. Consequently, on such a network, all 419 packets sent to destination address G will be delivered to any host that 420 has subscribed to any channel (S,G), regardless of S. And therefore, 421 the IP module MUST filter packets it receives from the link layer before 422 delivering them to the socket layer. 424 7. Security Considerations 426 This section outlines security issues pertaining to SSM. The following 427 topics are addressed: limitations of IPSec, denial of service attacks, 428 source spoofing, and security issues related to administrative scoping. 430 7.1. IPSec and SSM 432 The IPSec Authentication Header (AH) and Encapsulating Security Payload 433 (ESP) protocols [IPSEC] can be used to secure SSM traffic. As of this 434 writing, however, the IPSec protocols have some limitations when used 435 with SSM. This section describes those limitations. 437 [IPSEC] specifies that every incoming packet that requires IPSec 438 processing is ultimately looked up in a local Security Association 439 Database (SAD) to determine the Security Association (SA) that is to be 440 applied to the packet. The resulting SA determines the decryption 441 and/or authentication key to use and the anti-replay window, if one is 442 used. The key used for the SAD lookup is: 444 - the packet's destination IP address 446 - the IPSec protocol (ESP or AH) 448 - the Security Parameter Index (SPI) 450 A problem arises for SSM because the source address is not included in 451 the SAD lookup. IPSec does not currently provide any way to ensure that 452 two unrelated SSM channels will have unique SAD entries at all 453 receivers. Two senders that happen to choose the same SSM destination 454 address and the same Security Parameter Index will "collide" in the SAD 455 at any host that is receiving both channels. Because the channel 456 addresses and SPIs are both allocated autonomously by the senders, there 457 is no reasonable means to ensure that each sender uses a unique 458 destination address or SPI. 460 In practice, this problem only arises if a receiver subscribes 461 simultaneously to two unrelated channels using IPSec whose sources 462 happen to have chosen the same IP destination address (IPDA) and the 463 same IPSec SPI. The tuple, however, consists of 56 bits that 464 are generally randomly chosen, and a conflict is unlikely to occur 465 through random chance. 467 But when this problem occurs, however unlikely, a host will not be able 468 to simultaneously receive IPSec-protected traffic from the two colliding 469 sources under the current IPSec model. 471 This problem is under investigation and a solution will appear in a 472 separate document. One possible solution is to include the source 473 address in the SAD lookup when the destination is an SSM address. 475 7.2. Denial of Service 477 A subscription request creates (S,G) state in a router to record the 478 subscription, invokes processing on that router, and possibly causes 479 processing at neighboring routers. A host can mount a denial of service 480 attack by requesting a large number of subscriptions. A denial of 481 service can result if: 483 - a large amount of traffic arrives when it was otherwise undesired, 484 consuming network resources to deliver it and host resources to drop 485 it 487 - a large amount of source-specific multicast state is created in 488 network routers, using router memory and CPU resources to store and 489 process the state 491 - a large amount of control traffic is generated to manage the 492 source-specific state, using router CPU and network bandwidth 494 To reduce the damage from such an attack, a router MAY have 495 configuration options to limit, for example, the following items: 497 - The total rate at which all hosts on any one interface are allowed 498 to initiate subscriptions (to limit the damage caused by forged 499 source-address attacks) 501 - The total number of subscriptions that can be initiated from any 502 single interface or host. 504 Any decision by an implementor to artificially limit the rate or number 505 of subscriptions should be taken carefully, however, as future 506 applications may use large numbers of channels. Tight limits on the 507 rate or number of channel subscriptions would inhibit the deployment of 508 such applications. 510 A router SHOULD verify that the source of a subscription request is a 511 valid address for the interface on which it was received. Failure to do 512 so would exacerbate a spoofed-source address attack. 514 We note that these attacks are not unique to SSM -- they are also 515 present for any-source multicast. 517 7.3. Spoofed Source Addresses 519 By forging the source address in a datagram, an attacker can potentially 520 violate the SSM service model by transmitting datagrams on a channel 521 belonging to another host. Thus, an application requiring strong 522 authentication should not assume that all packets that arrive on a 523 channel were sent by the requested source without higher-layer 524 authentication mechanisms. The IPSEC Authentication Header [IPSEC] may 525 be used to authenticate the source of an SSM transmission, for instance. 527 Some degree of protection against spoofed source addresses in multicast 528 is already fairly widespread, because the commonly deployed IP multicast 529 routing protocols [PIM-DM, PIM-SM, DVMRP] incorporate a "reverse-path 530 forwarding check" that validates that a multicast packet arrived on the 531 expected interface for its source address. Routing protocols used for 532 SSM SHOULD incorporate such a check. 534 Source Routing [RFC791] (both Loose and Strict) in combination with 535 source address spoofing may be used to allow an impostor of the true 536 channel source to inject packets onto an SSM channel. An SSM router 537 SHOULD by default disallow source routing to an SSM destination address. 538 A router MAY have a configuration option to allow source routing. Anti- 539 source spoofing mechanisms such as source address filtering at the edges 540 of the network are also strongly encouraged. 542 7.4. Administrative Scoping 544 Administrative scoping should not relied upon as a security measure 545 [ADMIN-SCOPE]; however, in some cases it is part of a security solution. 546 It should be noted that no administrative scoping exists for IPv4 547 source-specific multicast. An alternative approach is to manually 548 configure traffic filters on routers to create such scoping if 549 necessary. 551 Furthermore, for IPv6, neither source nor destination address scoping 552 should be used as a security measure. In some currently-deployed IPv6 553 routers (those that do not conform to [SCOPED-ARCH]), scope boundaries 554 are not always applied to all source address (for instance, an 555 implentation may filter link-local addresses but nothing else). Such a 556 router may incorrectly forward an SSM channel (S,G) through a scope 557 boundary for S. 559 8. Transition Considerations 561 A host that complies with this document will send ONLY source-specific 562 host reports for addresses in the SSM range. As stated above, a router 563 that receives a non-source-specific (e.g., IGMPv1 or IGMPv2 or MLDv1) 564 host report for a source-specific multicast destination address MUST 565 ignore these reports. Failure to do so would violate the SSM service 566 model promised to the sender: that a packet sent to (S,G) would only be 567 delivered to hosts that specifically requested delivery of packets sent 568 to G by S. 570 During a transition period, it would be possible to deliver SSM 571 datagrams in a domain where the routers do not support SSM semantics by 572 simply forwarding any packet destined to G to all hosts that have 573 requested subscription of (S,G) for any S. However, this implementation 574 risks unduly burdening the network infrastructure by delivering (S,G) 575 datagrams to hosts that did not request them. Such an implementation 576 for addresses in the SSM range is specifically not compliant with 577 Section 5.2 of this document. 579 9. IANA Considerations 581 Addresses in the range 232.0.0.1 through 232.0.0.255 and IPv6 addresses 582 in the range FF3x:4000:0000 to FF3x::7FFF:FFFF are reserved for services 583 with wide applicability that either require or would strongly benefit if 584 all hosts used a well-known SSM destination address for that service. 585 IANA shall allocate addresses in this range according to IETF Consensus 586 [IANA-CONSIDERATIONS]. Any proposal for allocation must consider the 587 fact that, on an Ethernet network, all datagrams sent to any SSM 588 destination address will be transmitted with the same link-layer 589 destination address, regardless of the source. Furthermore, the fact 590 that SSM destinations in 232.0.0.0/24 and 232.128.0.0/24 use the same 591 link-layer addresses as the reserved IP multicast group range 592 224.0.0.0/24 must also be considered. Similar consideration should be 593 given to the IPv6 reserved multicast addresses. 595 Except for the aforementioned addresses, IANA SHALL NOT allocate any SSM 596 destination address to a particular entity or application. To do so 597 would compromise one of the important benefits of the source-specific 598 model: the ability for a host to simply and autonomously allocate a 599 source-specific multicast address from a large flat address space. 601 10. Acknowledgments 603 The SSM service model draws on a variety of prior work on alternative 604 approaches to IP multicast, including the EXPRESS multicast model of 605 Holbrook and Cheriton [EXPRESS], Green's [SMRP] and the Simple Multicast 606 proposal of Perlman et. al. [SIMPLE]. We would also like to thank Jon 607 Postel and David Cheriton for their support in reassigning the 232/8 608 address range to SSM. Brian Haberman contributed to the IPv6 portion of 609 this document. Thanks to Pekka Savola for a careful review. 611 11. Normative References 613 [ETHERv6] Crawford, M., "Transmission of IPv6 Packets over Ethernet 614 Networks", RFC2464, Dec 1998. 616 [IPSEC] S. Kent, R. Atkinson, "Security Architecture for the Internet 617 Protocol.", RFC 2401. 619 [IPV6-UBM] B. Haberman, D. Thaler, "Unicast-Prefix-based IPv6 Multicast 620 Addresses.", RFC 3306, August 2002. 622 [IPV6-MALLOC] B. Haberman, "Dynamic Allocation Guidelines for IPv6 623 Multicast Addresses", RFC 3307, August 2002. 625 [RFC791] Postel, J., ed., "Internet Protocol, Darpa Internet Program 626 Protocol Specification," September 1981. 628 [RFC1112] Deering, S., "Host Extensions for IP Multicasting," RFC 1112, 629 August 1989. 631 [RFC2373] Hinden, R. and Deering, S. "IP Version 6 Addressing 632 Architecture." RFC 2373, July 1998. 634 12. Informative References 636 [ADMIN-SCOPE] Meyer, D., "Administratively Scoped IP Multicast", BCP 23, 637 RFC 2365, July 1998. 639 [DVMRP] Waitzman, D., Partridge, C., and S. Deering., "Distance Vector 640 Multicast Routing Protocol," RFC 1075, Nov 1988. 642 [EXPRESS] Holbrook, H., and Cheriton, D. "Explicitly Requested Source- 643 Specific Multicast: EXPRESS support for Large-scale Single-source 644 Applications." Proceedings of ACM SIGCOMM '99, Cambridge, MA, September 645 1999. 647 [IANA-ALLOCATION] Internet Assigned Numbers Authority, 648 http://www.iana.org/assignments/multicast-addresses. 650 [IANA-CONSIDERATIONS] Narten, T., and H. Alvestrand, "Guidelines for 651 Writing an IANA Considerations Section in RFCs," RFC 2434, October 1998. 653 [IGMPv2] Fenner, W., "Internet Group Management Protocol, Version 2," 654 RFC 2236, November 1997. 656 [IGMPv3] Cain, B., Deering, S., and A. Thyagarajan, "Internet Group 657 Management Protocol, Version 3," RFC 3376, October 2002. 659 [MLDv2] R. Vida, and L. Costa. "Multicast Listener Discovery Version 2 660 (MLDv2) for IPv6." Work in Progress. 662 [MSFAPI] Thaler, D., Fenner, B., and Quinn, B. "Socket Interface 663 Extensions for Multicast Source Filters." Work in Progress. 665 [PIM-SM] Estrin, D., Farinacci, D., Helmy, A., Thaler, D., Deering, S., 666 Handley, M., Jacobson, V., Liu, C., Sharma, P. and L. Wei, "Protocol 667 Independent Multicast-Sparse Mode (PIM-SM): Protocol Specification," RFC 668 2362, June 1998. 670 [PIM-DM] Deering, S., Estrin, D., Farinacci, D., Jacobson, V., Helmy, 671 A., Meyer, D., and L. Wei, "Protocol Independent Multicast Version 2 672 Dense Mode Specification," Work in Progress. 674 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 675 Requirement Levels," RFC 2119, March 1997. 677 [RFC2710] S. Deering, W. Fenner, B. Haberman, "Multicast Listener 678 Discovery (MLD) for IPv6", RFC 2710, October 1999. 680 [RFC2771] Finlayson, R., "An Abstract API for Multicast Address 681 Allocation," RFC 2771, February 2000. 683 [SCOPINGV6] Deering, S. et. al, "IP Version 6 Scoped Address 684 Architecture", Work in Progress. 686 [SIMPLE] R. Perlman, C-Y Lee, A. Ballardie, J. Crowcroft, Z. Wang, T. 687 Maufer, C. Diot, and M. Green. "Simple Multicast: A Design for Simple, 688 Low-Overhead Multicast." Work in Progress. 690 [SMRP] Green, M. "Method and System of Multicast Routing for Groups 691 with a Single Transmitter." United States Patent Number 5,517,494. 693 Authors' Addresses 694 Brad Cain 695 Storigen Systems 696 650 Suffolk St. 697 Lowell, MA 01854 698 bcain@storigen.com 700 Hugh Holbrook 701 Cisco Systems 702 170 W. Tasman Drive 703 San Jose, CA 95134 704 holbrook@cisco.com 706 Intellectual Property Rights Notice 708 The IETF takes no position regarding the validity or scope of any 709 intellectual property or other rights that might be claimed to pertain 710 to the implementation or use of the technology described in this 711 document or the extent to which any license under such rights might or 712 might not be available; neither does it represent that it has made any 713 effort to identify any such rights. Information on the IETF's 714 procedures with respect to rights in standards-track and standards- 715 related documentation can be found in BCP-11. Copies of claims of 716 rights made available for publication and any assurances of licenses to 717 be made available, or the result of an attempt made to obtain a general 718 license or permission for the use of such proprietary rights by 719 implementors or users of this specification can be obtained from the 720 IETF Secretariat. 722 The IETF invites any interested party to bring to its attention any 723 copyrights, patents or patent applications, or other proprietary rights 724 which may cover technology that may be required to practice this 725 standard. Please address the information to the IETF Executive 726 Director. 728 Full Copyright Statement 730 Copyright (C) The Internet Society (2002). All Rights Reserved. 732 This document and translations of it may be copied and furnished to 733 others, and derivative works that comment on or otherwise explain it or 734 assist in its implementation may be prepared, copied, published and 735 distributed, in whole or in part, without restriction of any kind, 736 provided that the above copyright notice and this paragraph are included 737 on all such copies and derivative works. However, this document itself 738 may not be modified in any way, such as by removing the copyright notice 739 or references to the Internet Society or other Internet organizations, 740 except as needed for the purpose of developing Internet standards in 741 which case the procedures for copyrights defined in the Internet 742 Standards process must be followed, or as required to translate it into 743 languages other than English. 745 The limited permissions granted above are perpetual and will not be 746 revoked by the Internet Society or its successors or assigns. 748 This document and the information contained herein is provided on an "AS 749 IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK 750 FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT 751 LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT 752 INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR 753 FITNESS FOR A PARTICULAR PURPOSE. 755 This document expires Nov 7, 2003.