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Morin, Ed. 3 Internet-Draft France Telecom - Orange Labs 4 Intended status: Experimental B. Haberman 5 Expires: January 12, 2009 The Johns Hopkins University, 6 Applied Physics Laboratory 7 July 11, 2008 9 IGMP/MLD Error Feedback 10 draft-morin-mboned-igmpmld-error-feedback-01 12 Status of this Memo 14 By submitting this Internet-Draft, each author represents that any 15 applicable patent or other IPR claims of which he or she is aware 16 have been or will be disclosed, and any of which he or she becomes 17 aware will be disclosed, in accordance with Section 6 of BCP 79. 19 Internet-Drafts are working documents of the Internet Engineering 20 Task Force (IETF), its areas, and its working groups. Note that 21 other groups may also distribute working documents as Internet- 22 Drafts. 24 Internet-Drafts are draft documents valid for a maximum of six months 25 and may be updated, replaced, or obsoleted by other documents at any 26 time. It is inappropriate to use Internet-Drafts as reference 27 material or to cite them other than as "work in progress." 29 The list of current Internet-Drafts can be accessed at 30 http://www.ietf.org/ietf/1id-abstracts.txt. 32 The list of Internet-Draft Shadow Directories can be accessed at 33 http://www.ietf.org/shadow.html. 35 This Internet-Draft will expire on January 12, 2009. 37 Abstract 39 This document describes messages and procedures that can optionally 40 be implemented in IGMP/MLD Queriers and Hosts, to provide information 41 to multicast receivers on the reason why the IGMP/MLD Querier didn't 42 take into account a Membership Report message. 44 Requirements Language 46 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 47 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 48 document are to be interpreted as described in RFC 2119 [RFC2119]. 50 Table of Contents 52 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 53 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 54 3. History and problem statement . . . . . . . . . . . . . . . . 3 55 4. Principle . . . . . . . . . . . . . . . . . . . . . . . . . . 4 56 5. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . 4 57 5.1. Procedures on the IGMP/MLD Querier . . . . . . . . . . . . 4 58 5.2. Procedures on the IGMP/MLD Host . . . . . . . . . . . . . 5 59 6. Message encodings . . . . . . . . . . . . . . . . . . . . . . 6 60 6.1. Feedback message . . . . . . . . . . . . . . . . . . . . . 6 61 6.2. Error codes . . . . . . . . . . . . . . . . . . . . . . . 9 62 7. Feedback to the application layer . . . . . . . . . . . . . . 9 63 8. Impact on IGMP/MLD proxies and equipments doing IGMP/MLD 64 snooping . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 65 8.1. IGMP/MLD Proxies . . . . . . . . . . . . . . . . . . . . . 11 66 8.2. Equipments doing IGMP/MLD snooping . . . . . . . . . . . . 12 67 9. IGMP/MLD Hosts stacks not implementing the Feedback 68 mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . 12 69 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 70 11. Security Considerations . . . . . . . . . . . . . . . . . . . 12 71 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13 72 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 73 13.1. Normative References . . . . . . . . . . . . . . . . . . . 13 74 13.2. Informative References . . . . . . . . . . . . . . . . . . 14 75 Appendix A. Protocol to carry error feedback messages . . . . . . 15 76 A.1. ICMP . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 77 A.2. IGMP/MLD . . . . . . . . . . . . . . . . . . . . . . . . . 15 78 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16 79 Intellectual Property and Copyright Statements . . . . . . . . . . 17 81 1. Introduction 83 Requirements have been formulated for means to provide multicast 84 receivers with error feedback when the IGMP/MLD Querier did not or 85 could not process an IGMP/MLD Membership Report message 86 ([I-D.ietf-mboned-maccnt-req], section 4). Operator's experience 87 with IPTV deployments show that introducing such a feedback in IGMP 88 exchanges between multicast receivers and multicast routing 89 equipments would help provide a better service (e.g. a liaison 90 between the IETF mboned working group and the DSLForum was made in 91 December 2005 to discuss this issue, but didn't lead to a 92 standardized solution). 94 An examples case is when an IGMP Querier refuses to take into account 95 an IGMP Membership Report because the number of multicast channels 96 would surpass the allowed threshold for the service. Many other 97 examples of the case where an IGMP error feedback channel would be 98 useful are presented in Section 6.2. 100 This document describes new message encodings and the associated 101 procedures, all of which being optional and preserving full backward 102 and forward compatibility, and details the impact on the host API for 103 multicast subscriptions. 105 This document doesn't state yet whether the messages should be 106 carried over IGMP, ICMP or another protocol, but tries to document 107 the pros and cons of the different alternatives, to guide the 108 decision process. 110 2. Terminology 112 The terminology in this document is the terminology used in [RFC3376] 113 and [RFC3810]. 115 For readability, "Querier" and "Host(s)" will be used throughout this 116 document, in place of "IGMP or MLD Querier" and "IGMP or MLD 117 Host(s)". 119 3. History and problem statement 121 The DSLForum expressed interest for such a feature, which was 122 discussed [magma-archive] in a liaison with the Magma IETF Working 123 group. The specifications described in this document try to address 124 the comments exchanged on the magma WG mailing-list. 126 4. Principle 128 The procedures described in this memo are fully optional : their only 129 intent is to carry informative data from the Querier to the Hosts. 131 Most specifically, the intent is that: 133 o the procedures don't change the state machine of the Querier or 134 Host, the information carried is only meant to provide information 135 to the application subscribed to multicast data 137 o a Host implementing these specifications will behave correctly in 138 the absence of these informations. 140 o the behavior of a Querier implementing these specifications is 141 unchanged whether or not the hosts implement these specs. 143 Last, these specifications are not meant to carry information about 144 transient errors that the network is supposed to recover from, like 145 network outages. 147 5. Procedures 149 5.1. Procedures on the IGMP/MLD Querier 151 The following procedures introduce a new type of message : the 152 Feedback message. See section Section 6 for details about message 153 encodings. 155 Using these procedures a Querier can OPTIONALLY emmit a Feedback 156 message after receiving an IGMP or MLD Membership Report message that 157 it can not process (see Section 6.2 for example reasons on why a 158 Querier would not process a Membership Report message). 160 The Feedback message carries error type/sub-type field, and 161 information about the group to which the error pertains. Optionally, 162 if IGMPv3/MLDv2 is used, and if the error message pertains to some 163 specific sources, the addresses of the sources to which the error 164 pertains are included in the message. 166 The address to which the Feedback message will be sent is determined 167 as follows: 169 o if IGMPv3/MLDv2 is used (and if the sender IP address is not 170 0.0.0.0 or 0::0), the address of the sender of the Membership 171 Report is used 173 o else, the group address specified in the Membership Report message 174 is used 176 The source address MUST be the same address as the address used for 177 Query messages, and the TTL MUST be set to 1. 179 If IGMPv2/MLDv1 is being used, not more than one Feedback message 180 should be sent for a said Membership Report message. 182 If IGMPv3/MLDv2 is being used, multiple feedback message MAY be sent 183 if the group record of the IGMP/MLD message that triggered the error 184 contained multiple source addresses. 186 In any case the amount of Feedback messages sent on a link MUST be 187 rate-limited, 189 5.2. Procedures on the IGMP/MLD Host 191 When a Host receives an Feedback message, it MAY process it. 193 Processing a Feedback message consists in : 195 o MANDATORY checking that the TTL is set to 1 197 o OPTIONALLY checking that the message source address is the address 198 of a known Querier 200 o parsing the Feedback message 202 o determining the network sockets for which the Feedback message is 203 relevant (G is the group address of the Feedback message) 205 * if no source address is included in the Feedback message, the 206 sockets are the sockets that have some active forwarding state 207 related to G (subscribed to G with a non-null include list) 209 * if some source addresses are indicated in the Feedback message, 210 the sockets are the sockets to which traffic from at least one 211 of these sources, and toward G, would be forwarded 213 o notifying these sockets of the error (see Section 7) 215 o OPTIONALLY logging the error and/or doing any local action 216 depending on policy 218 6. Message encodings 220 6.1. Feedback message 222 The Feedback message is a subtype of IGMP message when used as a 223 feedback to an IGMP message, and a subtype of ICMPv6 when used as a 224 feedback to an MLD message. It contains an error code, the multicast 225 group address in error (optional), and the source addresses in error 226 (optional). 228 The encoding is common to the two types of messages (except the 229 length of fields specifying addresses). 230 1 2 3 231 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 232 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 233 | Type = XXX | Code | Checksum | 234 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 235 | Reserved | Number of Group Records (M) | 236 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 237 | | 238 . . 239 . Group Record [1] . 240 . . 241 | | 242 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 243 | | 244 . . 245 . Group Record [2] . 246 . . 247 | | 248 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 249 | . | 250 . . . 251 | . | 252 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 253 | | 254 . . 255 . Group Record [M] . 256 . . 257 | | 258 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 260 Fields: 262 Type: Identifies this message as a Feedback message. Currently 263 using: 265 * in the case of IPv6/MLD: 0xYY (currently using value 200 as 266 defined in RFC 4443 "private experimentation value", until 267 another value is registered with IANA). 269 * in the case of IPv4/IGMP: 0xZZ (currently using 0xF2, in the 270 "Reserved for experimentation" range, until another value is 271 registered with IANA) 273 Code: One byte, gives additional information about the error that 274 triggered the feedback message. The possible values are described 275 in Section 6.2. 277 Checksum: The standard IGMP checksum. 279 Reserved: Reserved for future use. Set to zero on transmission; 280 ignored upon receipt. 282 Number of Group Records: Indicates the number of group records. 284 The Feedback message MUST at least include one group record. 286 It MUST NOT include more than one group record if the Feedback 287 message is to be sent toward a multicast group address (see section 288 Section 5). 290 o the message that triggered the Feedback message is IGMPv3 or MLDv2 291 and the group record that triggered the error contains no source 292 address 294 o the message that triggered the Feedback message is IGMPv2 or MLDv1 295 and the message contains no source address 297 Group record encoding: 299 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 300 | Multicast Group Address | 301 ~ ~ 302 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 303 | Reserved | Number of Sources (N) | 304 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 305 | Source Address [1] | 306 ~ ~ 307 +--- ---+ 308 | Source Address [2] | 309 ~ ~ 310 +--- ---+ 311 . . . 312 . . . 313 ~ ~ 314 +--- ---+ 315 | Source Address [N] | 316 ~ ~ 317 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 319 Fields: 321 Multicast Group Address: IPv4 multicast group address of the group 322 in error. Possibly set to all zeros. Contains an IPv4 address in 323 the case of IPv4/IGMP, and an IPv6 address in the case of IPv6/ 324 MLD. 326 Reserved: Reserved for future use. Set to zero on transmission; 327 ignored upon receipt. 329 Number of Sources: Indicates the number of sources in error. 330 Possibly set to zero. 332 Source Address [1..n]: Addresses of the multicast sources in error. 333 In the case of IPv4/IGMP, all these fields are 32-bit fields 334 containing IPv4 addresses. In the case of IPv6/MLD, all these 335 fields are 128-bit fields containing IPv6 addresses. 337 The Multicast Group Address field MAY be set to all zeros (for 338 instance, if the error is not specific to a said multicast group). 340 A group record MAY include zero Source Address (it can be the case, 341 for instance, for a feedback that is not specific to particular 342 sources, or that relates to an ASM subscription). It MUST NOT 343 include any source in the following cases: 345 o the message that triggered the Feedback message is IGMPv3 or MLDv2 346 and the group record that triggered the error contains no source 347 address 349 o the message that triggered the Feedback message is IGMPv2 or MLDv1 351 6.2. Error codes 353 This section describes some proposed error codes: 355 o improper message : the Membership Report message is improper (the 356 group address is not in the 224/0 or FF00::/8 range, or specified 357 sources are improper addresses) 359 o IGMP or MLD version is not supported by querier 361 o wildcard on an SSM group : IGMPv2 or IGMPv3/MLDv2 with an Exclude 362 source filter mode was used in the Report, but the group address 363 is not in the SSM range of the Querier 365 o exclude source filter mode not supported by the Querier 367 o group administratively prohibited 369 o source(s) administratively prohibited 371 o resource limit reached 373 o multicast reception is disabled on the link 375 o multicast routing protocol issue 377 [ This section will later be completed to include error code numbers 378 ] 380 Remember that the Feedback message is NOT meant to carry information 381 about transient errors that the network is supposed to recover from, 382 like for instance network outages. 384 7. Feedback to the application layer 386 This section gives an example of how the information from Feedback 387 messages is supplied to applications subscribed to multicast streams, 388 and which expect the reception of multicast datagrams on a socket, 389 based on Linux extensions to the POSIX [posix] network socket API. 391 A first requirement is full backward compatibility with applications 392 not supporting these specifications : an application not supporting 393 these specifications must not be affected by a Feedback message. For 394 instance, a wrong solution would be to return an error on a read() or 395 recv() call. 397 A second requirement is to allow an application to keep receiving 398 data on a socket, even if some error was reported through a Feedback 399 message, for a group or channel joined on this socket. This is 400 needed, for instance, in two cases : when a socket is used to join 401 multiple distinct group or channels and only one of them is subject 402 to an error ; when a socket is used to join only one multicast group, 403 for which the Querier sends a Feedback message, but there are members 404 for this group sending data on a directly connected link. 406 The proposed solution is to rely on the use of the MSG_ERRQUEUE flag 407 of the recvmsg()/recvfrom() POSIX calls. This call allows the socket 408 user to retrieve the network errors queued for the socket. 410 The MLD component receiving an MLD Feedback message containing error 411 condition reports the error to the application via the MSG_ERRQUEUE 412 flag in the recvmsg()/recvfrom() calls. The MSG_ERRQUEUE flag 413 indicates the presence of a sock_extended_err data structure. When 414 the sock_extended_err data structure is passed to the application, 415 the ee_origin field is set to 3 (SO_EE_ORIGIN_ICMP6) in the case of 416 an MLD Feedback message, and XX (SO_EE_ORIGIN_YYYY) in the case of an 417 IGMP Feedback message [XX and YYY is to be determined in compliance 418 with the relevant standard, 4 and SO_EE_ORIGIN_IGMP are proposed as 419 interim values]. The Type and Code fields from the MLD Feedback 420 message are copied into the ee_type and ee_code field of the 421 sock_extended_err data structure. 423 The addresses of the multicast group and sources in error can be 424 retrieved as follows: 426 o in the IPv4 case, the group address and source address are stored, 427 respectively, in the ee_info and ee_data fields, 429 o the group address and source address can be retrieved, in all 430 cases, by calling functions returning a sockaddr pointer and which 431 take into argument a sock_extended_err pointer (similarly as 432 SOCK_EE_OFFENDER) and called SOCK_EE_MCAST_FEEDBACK_GRP and 433 SOCK_EE_MCAST_FEEDBACK_SRC 435 If the Feedback contains multiple sources addresses, a 436 sock_extended_err will be added to the message queue for each such 437 sources. 439 An application receiving a sock_extended_err message from the MLD 440 component MUST NOT terminate the multicast subscription to the group 441 or source/group address in error, except possibly if it can be 442 ascertained that the Feedback message comes from a legitimate Querier 443 (e.g. thanks to a mechanism like SEND [RFC3971]), and if multicast 444 traffic for the said group or channel is not expected from any host 445 attached to a directly-connected link. 447 ( Another proposal would be to allow the setsockopt() and 448 set(ipv4)sourcefilter() calls [RFC3678] to return an error. That 449 would require the local network stack to wait for some time after 450 sending a Membership Report message, before being able to return from 451 the setsockopt()/set(ipv4)sourcefilter() call, and would not easily 452 allow to carry detailed information about the specific group or 453 channel in error. Consequently, this approach doesn't seem a viable 454 one. ) 456 8. Impact on IGMP/MLD proxies and equipments doing IGMP/MLD snooping 458 8.1. IGMP/MLD Proxies 460 To support this Feedback mechanism, an IGMP or MLD proxy [RFC4605] 461 SHOULD send Feedback messages received on its Host side toward its 462 Querier side(s) that have matching multicast memberships. The 463 procedures for sending the Feedback messages are then the same as for 464 a normal Querier, as specified in Section 5: in particular the IGMP/ 465 MLD proxy MUST use its own address as the source address of the 466 Feedback message. 468 A new member of a multicast group already forwarded by the proxy on 469 its Querier side, will have to wait for some time before having a 470 chance to receive a Feedback message : timers will have to trigger 471 before the Querier on the Host side of the proxy sends a Query, 472 causing the proxy to send a Membership Report that may then cause the 473 Querier on the Host side to send a Feedback message, and this 474 Feedback message to be propagated to the new receiver. 476 To quickly provide Feedback messages to receivers on its Querier 477 side, the proxy MAY cache the Feedback messages that it receives on 478 the Host side to later match them with Membership Report messages 479 received on its Querier side, and send relevant Feedback messages in 480 reaction to these. If doing Feedback message caching, the proxy MUST 481 keep only one Feedback message per (S,G) entry or (*,G) entry. It 482 MUST also remove a Feedback message from its cache, if a same 483 Feedback message hasn't been sent in the last <> seconds by the 484 Querier on its Host side. 486 Last, an IGMP/MLD proxy MAY produce its own Feedback messages. In 487 that case it MUST still respect procedures of Section 5. 489 8.2. Equipments doing IGMP/MLD snooping 491 IGMP/MLD snooping equipments are expected to transparently 492 interoperate with the procedures described in this document, given 493 that RFC 4541 section 2.2.1(3) [RFC4541] states that "[a] switch that 494 supports IGMP snooping must flood all unrecognized IGMP messages to 495 all other ports". 497 9. IGMP/MLD Hosts stacks not implementing the Feedback mechanism 499 To allow applications running on an IGMP/MLD Host, whose networking 500 stack or API does not implement the Feedback mechanism described in 501 this spec, it is proposed that IGMP/MLD Querier implementing this 502 specification can, when configured to do so, send each Feedback 503 message twice : once with the encoding described in these 504 specifications, and another time encapsulated in a UDP packet. 506 The UDP message uses port xxx [TBD], with a payload identical to the 507 IGMP or MLD Feedback message, except that the checksum is set to zero 508 (the UDP message having its own checksum). 510 10. IANA Considerations 512 Request to IANA for IGMP and ICMPv6 type allocation will be needed 513 for the messages defined in this document. 515 [Whether or not it is needed to define a registry for the error codes 516 used in IGMP/MLD Feedback messages will be later determined.] 518 [Note to RFC Editor: this section may be removed on publication as an 519 RFC.] 521 11. Security Considerations 523 Given that the specifications in this document do not change nor the 524 state machine of the IGMP/MDLD Querier and Host stack, nor the 525 datagrams that will be received by an application, they are not 526 expected to introduce security issues not already existing with IGMP/ 527 MLD or the protocol used to carry the Feedback message. 529 A possible issue would be to have wrong Feedback sent toward 530 multicast applications. Such an issue could arise if spoofed 531 Feedback messages are sent and interpreted by multicast receiver 532 hosts. This issue is mitigated by the fact that IGMP/MLD Hosts MUST 533 check that the TTL of the Feedback messages is 1, and MAY also check 534 the source IP of the Feedback message against a list of known 535 Queriers. 537 Another possible issue is denial of service of the Querier function, 538 that would be due to having the IGMP/MLD Querier be overloaded by 539 Feedback messages to send. This is mitigated by allowing the Querier 540 to rate-limit the flow of Feedback messages. On a LAN, such a rate- 541 limiting would possibly result in some receivers not receiving the 542 feedback message that they would have, which is a form of denial of 543 service, but only on the Feedback function by itself, with no impact 544 on the rest of the multicast group membership control protocol 545 infrastructure. This later type of denial of service might be 546 mitigated by doing rate-limiting based on the source address of the 547 receivers (the source address of the Membership Report triggering the 548 Feedback message); but such mechanism may themselves be subject to 549 weaknesses due to Membership Report spoofing. 551 12. Acknowledgements 553 Acknowledgments go to DSLForum contributors who provided an initial 554 proposal, to IETF participants that participated in the discussion on 555 the magma WG list, from which guidance and inspiration was largely 556 taken. Thank you to Bill Fenner for providing detailed information 557 on issues related to ICMP errors in reaction to multicast datagrams. 559 Thanks to Toerless Eckert for his inputs and who offered a suggestion 560 on how to handle application running on hosts not implementing the 561 Feedback mechanism. 563 Message encodings are largely inspired from Report message encodings 564 found in[RFC3376]. 566 13. References 568 13.1. Normative References 570 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 571 Requirement Levels", BCP 14, RFC 2119, March 1997. 573 [RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. 574 Thyagarajan, "Internet Group Management Protocol, Version 575 3", RFC 3376, October 2002. 577 [RFC3678] Thaler, D., Fenner, B., and B. Quinn, "Socket Interface 578 Extensions for Multicast Source Filters", RFC 3678, 579 January 2004. 581 [RFC3810] Vida, R. and L. Costa, "Multicast Listener Discovery 582 Version 2 (MLDv2) for IPv6", RFC 3810, June 2004. 584 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 585 "Considerations for Internet Group Management Protocol 586 (IGMP) and Multicast Listener Discovery (MLD) Snooping 587 Switches", RFC 4541, May 2006. 589 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 590 "Internet Group Management Protocol (IGMP) / Multicast 591 Listener Discovery (MLD)-Based Multicast Forwarding 592 ("IGMP/MLD Proxying")", RFC 4605, August 2006. 594 13.2. Informative References 596 [I-D.ietf-mboned-maccnt-req] 597 He, H., "Requirements for Multicast AAA coordinated 598 between Content Provider(s) and Network Service 599 Provider(s)", draft-ietf-mboned-maccnt-req-05 (work in 600 progress), October 2007. 602 [RFC1122] Braden, R., "Requirements for Internet Hosts - 603 Communication Layers", STD 3, RFC 1122, October 1989. 605 [RFC1812] Baker, F., "Requirements for IP Version 4 Routers", 606 RFC 1812, June 1995. 608 [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure 609 Neighbor Discovery (SEND)", RFC 3971, March 2005. 611 [fenner-icmp-mcast] 612 "ICMP errors in response to multicast", March 1999, 613 . 615 [magma-archive] 616 "IETF Magma WG mailing-list archives", December 2005, . 620 [posix] "ISO/IEC 9945 Information technology, Portable Operating 621 System Interface (POSIX), Part 1: Base Definitions", 2003. 623 Appendix A. Protocol to carry error feedback messages 625 ICMP and IGMP/MLD were possible candidates for carrying the Feedback 626 message. This section exposes the pros/cons of both alternatives, 627 and ought to be removed once a decision is made on one of them. 629 A.1. ICMP 631 The Feedback message could be an ICMP message that would use a new 632 ICMP message type (or possibly reusing existing types and codes). 634 Pros: 636 o ICMP is already used to carry error messages between routers and 637 hosts (e.g.. port unreachable message) 639 o ICMP has an extensible format which could easily be reused for the 640 Feedback function described in this memo 642 o Implementations of network socket APIs already take into account 643 ICMP messages 645 Cons: 647 o ICMP has currently nothing to do with multicast today 649 o some RFC explicitly forbid the sending of ICMP in reaction to 650 receiving multicast packets, and IGMP/MLD Membership Reports are 651 multicast packets ([RFC1122] section 7.2 and 3.2.2, [RFC1812] 652 section 4.3.2.7) (see [fenner-icmp-mcast]) 654 o ICMP messages are (currently) never sent toward multicast 655 addresses, whereas that would be required to send Feedback 656 messages to IGMPv2/MLDv1 hostsSo we may say that the generic 657 argument is that the restriction for ICMP ; this has lead to 658 practical issues to integrate this approach into existing stacks, 659 because of the need to work around sanity checks 661 A.2. IGMP/MLD 663 The Feedback message could be an IGMP or MLD message that would use 664 new IGMP/MLD message types. 666 Pros: 668 o IGMP and MLD are the protocols used for all operations related to 669 multicast subscription 671 Cons: 673 o possibly more work to define the encodings 675 o a new IANA registry might be needed to manage Feedback error codes 677 o definition of how the network socket API will be used to carry the 678 information to the applications has to be defined 680 Authors' Addresses 682 Thomas Morin (editor) 683 France Telecom - Orange Labs 684 2, avenue Pierre Marzin 685 Lannion 22307 686 France 688 Email: thomas.morin@orange-ftgroup.com 690 Brian Haberman 691 The Johns Hopkins University, Applied Physics Laboratory 692 11100 Johns Hopkins Road 693 Laurel, MD 20723-6099 694 US 696 Phone: +1 443 778 1319 697 Email: brian@innovationslab.net 699 Full Copyright Statement 701 Copyright (C) The IETF Trust (2008). 703 This document is subject to the rights, licenses and restrictions 704 contained in BCP 78, and except as set forth therein, the authors 705 retain all their rights. 707 This document and the information contained herein are provided on an 708 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 709 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 710 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 711 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 712 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 713 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 715 Intellectual Property 717 The IETF takes no position regarding the validity or scope of any 718 Intellectual Property Rights or other rights that might be claimed to 719 pertain to the implementation or use of the technology described in 720 this document or the extent to which any license under such rights 721 might or might not be available; nor does it represent that it has 722 made any independent effort to identify any such rights. 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