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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Missing Reference: 'RFC2735' is mentioned on line 428, but not defined == Unused Reference: 'RFC2375' is defined on line 717, but no explicit reference was found in the text == Unused Reference: 'IANA' is defined on line 722, but no explicit reference was found in the text == Outdated reference: draft-vida-mld-v2 has been published as RFC 3810 ** Obsolete normative reference: RFC 2461 (ref. 'NDP') (Obsoleted by RFC 4861) == Outdated reference: draft-ietf-magma-igmp-proxy has been published as RFC 4605 Summary: 8 errors (**), 0 flaws (~~), 9 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group M. Christensen 3 Internet Draft Thrane & Thrane 4 Expiration Date: September 2003 K. Kimball 5 Category: Informational Hewlett-Packard 6 F. Solensky 7 Bluejavelin 8 March 2003 10 Considerations for IGMP and MLD Snooping Switches 11 13 Status of this Memo 15 This document is an Internet-Draft and is in full conformance with 16 all provisions of Section 10 of RFC2026 [RFC2026]. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as Internet- 21 Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six 24 months and may be updated, replaced, or obsoleted by other 25 documents at any time. It is inappropriate to use Internet-Drafts 26 as reference material or to cite them other than as "work in 27 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 Copyright Notice 37 Copyright (C) The Internet Society (2003). All Rights Reserved. 39 Abstract 41 This memo describes the requirements for IGMP- and MLD-snooping 42 switches. These are based on best current practices for IGMPv2, 43 with further considerations for IGMPv3- and MLDv2-snooping. 44 Additional areas of relevance, such as link layer topology changes 45 and Ethernet-specific encapsulation issues, are also considered. 47 Interoperability issues that arise between different versions of 48 IGMP are not the focus of this document. Interested readers are 49 directed to [IGMPv3] for a thorough description of problem areas. 51 1. Introduction 53 When processing a packet whose destination MAC address has the 54 multicast bit (bit 7) set, the switch will forward a copy of the 55 packet into each of the remaining network interfaces that are the 56 forwarding state in accordance with [BRIDGE]. The spanning tree 57 algorithm ensures that the application of this rule at every switch 58 in the network will make the packet accessible to all nodes 59 connected to the network. 61 This approach works well for broadcast packets that are intended to 62 be seen or processed by all connected nodes. In the case of 63 multicast packets, however, this approach could lead to less 64 efficient use of network bandwidth, particularly when the packet is 65 intended for only a small number of nodes. Packets will be flooded 66 into network segments where no node has any interest in receiving 67 the packet. While nodes will rarely incur any processing overhead 68 to filter packets addressed to unrequested group addresses, they 69 are unable to transmit new packets onto the shared media for the 70 period of time that the multicast packet is flooded. In general, 71 significant bandwidth can be wasted by flooding. 73 In recent years, a number of commercial vendors have introduced 74 products described as "IGMP snooping switches" to the market. 75 These devices do not adhere to the conceptual model that provides 76 the strict separation of functionality between different 77 communications layers in the ISO model, and instead utilize 78 information in the upper level protocol headers as factors to be 79 considered in the processing at the lower levels. This is 80 analogous to the manner in which a router can act as a firewall by 81 looking into the transport protocol's header before allowing a 82 packet to be forwarded to its destination address. 84 In the case of multicast traffic, an IGMP snooping switch provides 85 the benefit of conserving bandwidth on those segments of the 86 network where no node has expressed interest in receiving packets 87 addressed to the group address. This is in contrast to normal 88 switch behavior where multicast traffic is typically forwarded on 89 all interfaces. 91 Many switch datasheets state support for IGMP snooping, but no 92 requirements for this exist today. It is the authors' hope that 93 the information presented in this draft will supply this 94 foundation. 96 The requirements presented here are based on the following 97 information sources: The IGMP specifications [RFC1112], [RFC2236] 98 and [IGMPv3], vendor-supplied technical documents [CISCO], bug 99 reports [MSOFT], discussions with people involved in the design of 100 IGMP snooping switches, MAGMA mailing list discussions, and on 101 replies by switch vendors to an implementation questionnaire. 103 The suggestions in this document are based on IGMP, which applies 104 only to IPv4. For IPv6, Multicast Listener Discovery [MLD] must be 105 used instead. Because MLD is based on IGMP, we do not repeat the 106 entire description and requirements for MLD snooping switches. 107 Instead, we point out the few cases where there are differences 108 from IGMP. 110 Note that the IGMP snooping function should apply only to IPv4 111 multicasts. Other multicast packets, such as IPv6, might be 112 suppressed by IGMP snooping if additional care is not taken in the 113 implementation. It is desired not to restrict the flow of non-IPv4 114 multicasts other than to the degree which would happen as a result 115 of regular bridging functions. Likewise, MLD snooping switches are 116 discouraged from using topological information learned from IPv6 117 traffic to alter the forwarding of IPv4 multicast packets. 119 2. IGMP Snooping Requirements 121 The following sections list the requirements for an IGMP snooping 122 switch. The requirement is stated and is supplemented by a 123 description of a possible implementation approach. All 124 implementation discussions are examples only and there may well be 125 other ways to achieve the same functionality. 127 2.1. Forwarding rules 129 The IGMP snooping functionality is here separated into a control 130 section (IGMP forwarding) and a data section (Data forwarding). 132 2.1.1. IGMP Forwarding Rules 134 1) A snooping switch should forward IGMP Membership Reports only 135 to those ports where multicast routers are attached. 136 Alternatively stated: a snooping switch should not forward IGMP 137 Membership Reports to ports on which only hosts are attached. 138 An administrative control may be provided to override this 139 restriction, allowing the report messages to be flooded to 140 other ports. 142 This is the main IGMP snooping functionality. Sending 143 membership reports (as described in IGMP versions 1 and 2) to 144 other hosts can result in unintentionally preventing a host 145 from joining a specific multicast group. This is not a problem 146 in an IGMPv3-only network because there is no message 147 suppression of IGMP Membership reports. 149 The administrative control allows IGMP Membership Report 150 messages to be processed by network monitoring equipment such 151 as packet analyzers or port replicators. 153 The switch supporting IGMP snooping must maintain a list of 154 multicast routers and the ports on which they are attached. 155 This list can be constructed in any combination of the 156 following ways: 158 a) This list should be built by the snooping switch sending 159 Multicast Router Solicitation messages as described in IGMP 160 Multicast Router Discovery [MRDISC]. It may also snoop 161 Multicast Router Advertisement messages sent by and to 162 other nodes. 164 b) The arrival port for IGMP Queries (sent by multicast 165 routers) where the source address is not 0.0.0.0. 167 c) Ports explicitly configured by management to be IGMP- 168 forwarding ports, in addition to or instead of any of the 169 above methods to detect router ports. 171 2) IGMP snooping switches may also implement "proxy-reporting" in 172 which reports received from downstream hosts are summarized and 173 used to build internal membership states as described in 174 [PROXY]. The IGMP proxy-reporting switch would then report its 175 own state in response to upstream queriers. If the switch does 176 not already have an IP address assigned to it, the source 177 address for these reports should be set to all-zeros. 179 An IGMP proxy-reporting switch may act as Querier for the 180 downstream hosts while proxy reporting to the 'real' upstream 181 queriers. 183 It should be noted that there may be multiple IGMP proxy- 184 reporting switches in the network all using the 0.0.0.0 source 185 IP address. In this case the switches can be uniquely 186 identified through their link layer source MAC address. 188 IGMP membership reports must not be rejected by an IGMP 189 snooping switch because of a source IP address of 0.0.0.0. 191 3) The switch that supports IGMP snooping must flood all 192 unrecognized IGMP messages to all other ports and must not 193 attempt to make use of any information beyond the end of the 194 network layer header. 196 In addition, earlier versions of IGMP should interpret IGMP 197 fields as defined for their versions and must not alter these 198 fields when forwarding the message. When generating new 199 messages, a given IGMP version should set fields to the 200 appropriate values for its own version. If any fields are 201 reserved or otherwise undefined for a given IGMP version, the 202 fields should be ignored when parsing the message and must be 203 set to zeroes when new messages are generated by 204 implementations of that IGMP version. 206 4) An IGMP snooping switch should be aware of link layer topology 207 changes. Following a topology change the switch should 208 initiate the transmission of a General Query over the receiving 209 ports in order to reduce network convergence time. 211 a) When a port other than the router port goes down, a Query 212 Request should be directed out the switch's remaining non- 213 router ports for those group addresses which had included 214 the lost port as a destination for flooded packets. The 215 Query may be one of the Group-Specific forms if there are 216 a relatively small number of groups affected and should be 217 a General Query otherwise. The router port should be 218 excluded from receiving these Query Requests since it will 219 usually be the source rather than the receipient of 220 flooded multicast packets and is less likely to be 221 affected by the loss of one of the receiver ports. 223 b) When the router port goes down, Multicast Router Discovery 224 should be used to determine which of the remaining ports 225 is the new router port. An IGMPv3 General Query message 226 should be sent out the remaining ports to refresh the 227 forwarding tables for other groups. 229 c) When a new port comes up, a General Query message should 230 be sent out the new port to determine which groups, if 231 any, have receipients that have become reachable. The new 232 port is designated as a router port in MRD messages are 233 processed. 235 If the switch is not the Querier, it should use the 'all-zeros' 236 IP Source Address in these proxy queries. When such proxy 237 queries are received, they must not be included in the Querier 238 election process. 240 5) An IGMP snooping switch must not make use of information in 241 IGMP packets where the IP or IGMP headers have checksum or 242 integrity errors. The switch should not flood such packets but 243 if it does, it should also take some note of the event (i.e., 244 increment a counter). These errors and their processing are 245 further discussed in [IGMPv3], [MLD] and [MLDv2]. 247 6) The snooping switch must not rely exclusively on the appearance 248 of IGMP Group Leave announcements to determine when entries 249 should be removed from the forwarding table. It should instead 250 implement the router side functionality of the IGMP/MLD 251 protocol as described in [PROXY] on all its non-router ports. 253 2.1.2. Data Forwarding Rules 255 1) Packets with a destination IP (DIP) address in the 224.0.0.X 256 range which are not IGMP must be forwarded on all ports. 258 This requirement is based on fact that many hosts systems do 259 not send Join IP multicast addresses in this range before 260 sending or listening to IP multicast packets. Furthermore 261 since the 224.0.0.X address range is defined as link local (not 262 to be routed) it seems unnecessary to keep state for each 263 address in this range. Additionally, some routers operate in 264 the 224.0.0.X address range without issuing IGMP Joins, and 265 these applications would break if the switch were to prune them 266 due to not their not having seen a Join Group message from the 267 router. 269 2) Packets with a destination IP address outside 224.0.0.X which 270 are not IGMP should be forwarded according to group-based port 271 membership tables and must also be forwarded on router ports. 272 This is the core IGMP snooping requirement for the data path. 273 One approach that an implementation could take would be to 274 maintain separate membership and multicast router tables in 275 software and then "merge" these tables into a forwarding cache. 277 3) If a switch receives a non-IGMP IPv4 multicast packet without 278 having first processed Membership Reports for the group 279 address, it may forward the packet on all ports but it must 280 forward the packet on router ports. A switch may forward an 281 unregistered packet only on router ports, but the switch must 282 have a configuration option that suppresses this restrictive 283 operation and forces flooding of unregistered packets on all 284 ports. 286 In an environment where IGMPv3 hosts are mixed with snooping 287 switches that do not yet support IGMPv3, the switch's failure 288 to flood unregistered streams could prevent v3 hosts from 289 receiving their traffic. Alternatively, in environments where 290 the snooping switch supports all of the IGMP versions that are 291 present, flooding unregistered streams may cause IGMP hosts to 292 be overwhelmed by multicast traffic, even to the point of not 293 receiving Queries and failing to issue new membership reports 294 for their own groups. 296 4) All non-IPv4 multicast packets should continue to be flooded 297 out all remaining ports in the forwarding state as per normal 298 IEEE bridging operations. 300 This requirement is a result of the fact that groups made up of 301 IPv4 hosts and IPv6 hosts are completely separate and distinct 302 groups. As a result, information gleaned from the topology 303 between members of an IPv4 group would not be applicable when 304 forming the topology between members of an IPv6 group. 306 5) IGMP snooping switches may maintain forwarding tables based on 307 either MAC addresses or IP addresses. If a switch supports 308 both types of forwarding tables then the default behavior 309 should be to use IP addresses. If the forwarding table is 310 keyed on the MAC address, the switch should use the destination 311 IP address to break hashing table collisions. 313 6) Switches which rely on information in the IP header should 314 verify that the IP header checksum is correct. If the checksum 315 fails, the information in the packet must not be incorporated 316 into the forwarding table. Further, the packet should be 317 discarded. 319 7) When IGMPv3 "include source" and "exclude source" membership 320 reports are received on shared segments, the switch needs to 321 forward the superset of all received membership reports onto 322 the shared segment. Forwarding of traffic from a particular 323 source S to a group G must happen if at least one host on the 324 shared segment reports an IGMPv3 membership of the type 325 INCLUDE(G, Slist1) or EXCLUDE(G, Slist2) where S is an element 326 of Slist1 and not an element of Slist2. 328 2.2. IGMP snooping related problems 330 A special problem arises in networks consisting of IGMPv3 routers 331 as well as IGMPv2 and IGMPv3 hosts interconnected by an IGMPv2 332 snooping switch. The router will continue to maintain IGMPv3 even 333 in the presence of IGMPv2 hosts, and thus the network will not 334 likely converge on IGMPv2. But it is likely that the IGMPv2 335 snooping switch will not recognize or process the IGMPv3 membership 336 reports. Groups for these unrecognized reports will then either be 337 flooded (with all of the problems that may create for hosts in a 338 network with a heavy multicast load) or pruned by the snooping 339 switch. 341 Therefore it is recommended that in such a network, the multicast 342 router be configured to use IGMPv2. 344 3. IPv6 Considerations 346 In order to avoid confusion, the previous discussions have been 347 based on the IGMP protocol which only applies to IPv4 multicast. 348 In the case of IPv6 most of the above discussions are still valid 349 with a few exceptions which we will describe here. 351 The control and data forwarding rules in the IGMP section can, with 352 a few considerations, also be applied to MLD. This means that the 353 basic functionality of intercepting MLD packets, and building 354 membership lists and multicast router lists, is the same as for 355 IGMP. 357 In IPv6, the data forwarding rules are more straight forward 358 because MLD is mandated for addresses with scope 2 (link-scope) or 359 greater. The only exception is the address FF02::1 which is the 360 all hosts link-scope address for which MLD messages are never sent. 361 Packets with the all hosts link-scope address should be forwarded 362 on all ports. 364 MLD messages are also not sent to packets in the address range 365 FF00::/15 (which encompasses both the reserved FF00::/16 and node- 366 local FF01::/16 IPv6 address spaces). These addresses should never 367 appear in packets on the link. 369 The three major differences between IPv4 and IPv6 in relation to 370 multicast are: 372 - The IPv6 protocol for multicast group maintenance is called 373 Multicast Listener Discovery [MLDv2]. MLDv2 uses ICMPv6 message 374 types instead of IGMP message types. 376 - The RFCs [IPV6-ETHER] and [IPV6-FDDI] describe how 24 of the 128 377 bit DIP address are used to form the 48 bit DMAC addresses for 378 multicast groups, while [IPV6-TOKEN] describes the mapping for 379 token ring DMAC addresses by using three low-order bits. The 380 specification [IPV6-1394] makes use of a 6 bit channel number. 382 - Multicast router discovery is accomplished using Neighbor 383 Discovery Protocol [NDP] for IPv6. NDP uses ICMPv6 message 384 types. 386 The IPv6 packet header does not include a checksum field. 387 Nevertheless, the switch should detect other packet integrity 388 issues. When the snooping switch detects such an error, it must 389 not include information from the corresponding packet in the MLD 390 forwarding table. The forwarding code should instead drop the 391 packet and take further reasonable actions as advocated above. 393 The fact that MLDv2 is using ICMPv6 adds new requirements to a 394 snooping switch because ICMPv6 has multiple uses aside from MLD. 395 This means that it is no longer sufficient to detect that the next- 396 header field of the IP header is ICMPv6 in order to identify 397 packets relevant for MLD snooping. A software-based implemention 398 which treats all ICMPv6 packets as candidates for MLD snooping 399 could easily fill its receive queue and bog down the CPU with 400 irrelevant packets. This would prevent the snooping functionality 401 from performing its intended purpose and the non-MLD packets 402 destined for other hosts could be lost. 404 A solution is either to require that the snooping switch looks 405 further into the packets, or to be able to detect a multicast DMAC 406 address in conjunction with ICMPv6. The first solution is 407 desirable when a configuration option allows the administrator to 408 specify which ICMPv6 message types should trigger a CPU redirect 409 and which should not. The reason is that a hardcoding of message 410 types is inflexible for the introduction of new message types. The 411 second solution introduces the risk that new protocols which use 412 ICMPv6 and multicast DMAC addresses could be incorrectly identified 413 as MLD. It is suggested that solution one is preferred when the 414 administrative switch is provided. If this is not the case, then 415 the implementator should seriously consider making this switch 416 available since Neighbor Discovery messages would be among those 417 that fall into this false positive case and are vital for the 418 operational integrity of IPv6 networks. 420 The mapping from IP multicast addresses to multicast DMAC addresses 421 introduces a potentially enormous overlap. The structure of an 422 IPv6 multicast address is shown in the figure below. As a result, 423 there are 2 ** (112 - (32 - 8)), or more than 7.9e28 unique DIP 424 addresses which map into a single DMAC address in Ethernet and 425 FDDI. This should be compared to 2**5 in the case of IPv4. 427 Initial allocation of IPv6 multicast addresses as described in 428 [RFC2735], however, cover only the lower 24 bits of group ID. 429 While this reduces the problem of address ambiguity to group IDs 430 with different flag and scope values for now, it should be noted 431 that the allocation policy may change in the future. Because of 432 the potential overlap it is recommended that IPv6 address based 433 forwarding is preferred to MAC address based forwarding. 435 | 8 | 4 | 4 | 112 bits | 436 +--------+----+----+---------------------------------------+ 437 |11111111|flgs|scop| group ID | 438 +--------+----+----+---------------------------------------+ 440 4. IGMP Questionnaire 442 As part of this work the following questions were asked both on the 443 MAGMA discussion list and sent to known switch vendors implementing 444 IGMP snooping. The individual contributions have been anonymized 445 upon request and do not necessarily apply to all of the vendors' 446 products. 448 The questions were: 450 Q1 Does your switches perform IGMP Join aggregation? In other 451 words, are IGMP joins intercepted, absorbed by the 452 hardware/software so that only one Join is forwarded to the 453 querier? 455 Q2 Is multicast forwarding based on MAC addresses? Would 456 datagrams addressed to multicast IP addresses 224.1.2.3 and 457 239.129.2.3 be forwarded on the same ports-groups? 459 Q3 Is it possible to forward multicast datagrams based on IP 460 addresses (not routed)? In other words, could 224.1.2.3 and 461 239.129.2.3 be forwarded on different port-groups with 462 unaltered TTL? 464 Q4 Are multicast datagrams within the range 224.0.0.1 to 465 224.0.0.255 forwarded on all ports whether or not IGMP Joins 466 have been sent? 468 Q5 Are multicast frames within the MAC address range 469 01:00:5E:00:00:01 to 01:00:5E:00:00:FF forwarded on all ports 470 whether or not IGMP joins have been sent? 472 Q6 Does your switch support forwarding to ports on which IP 473 multicast routers are attached in addition to the ports where 474 IGMP Joins have been received? 476 Q7 Is your IGMP snooping functionality fully implemented in 477 hardware? 479 Q8 Is your IGMP snooping functionality partly software 480 implemented? 482 Q9 Can topology changes (for example spanning tree configuration 483 changes) be detected by the IGMP snooping functionality so that 484 for example new queries can be sent or tables can be updated to 485 ensure robustness? 487 The answers were: 489 ---------------------------+-----------------------+ 490 | Switch Vendor | 491 ---------------------------+---+---+---+---+---+---+ 492 | 1 | 2 | 3 | 4 | 5 | 6 | 493 ---------------------------+---+---+---+---+---+---+ 494 Q1 Join aggregation | x | x | x | | x | x | 495 Q2 Layer-2 forwarding | x | x | x | x |(1)| | 496 Q3 Layer-3 forwarding |(1)| |(1)| |(1)| x | 497 Q4 224.0.0.X aware |(1)| x |(1)|(2)| x | x | 498 Q5 01:00:5e:00:00:XX aware | x | x | x |(2)| x | x | 499 Q6 Mcast router list | x | x | x | x | x | x | 500 Q7 Hardware implemented | | | | | | | 501 Q8 Software assisted | x | x | x | x | x | x | 502 Q9 Topology change aware | x | x | x | x | |(2)| 503 ---------------------------+---+---+---+---+---+---+ 504 x Means that the answer was Yes. 505 (1) In some products (typically high-end) Yes; in others No. 506 (2) Not at the time that the questionnaire was received 507 but expected in the near future. 509 Revision History 511 This section, while incomplete, is provided as a convenience to the 512 working group members. It will be removed when the document is 513 released in its final form. 515 draft-ietf-magma-snoop-06.txt: March 2003 517 Changes in response to comments made during WG last call and 518 assessment by the WG chairs: 520 Substantial comments 521 Clarification in IGMP forwarding seciton on the 522 acceptance of membership reports with source IP address 523 0.0.0.0 as being a switch requirement. 525 Section 2.1.1.(4): Allow the router port to be excluded 526 from the General Query messages 528 Section 2.1.1.(6): Replace description of timing out 529 older entries with a reference to IGMP/MLD Proxying. 531 Section 2.1.2.(3): Replaced description of timeout 532 mechanism with a reference to IGMP/MLD. 534 Section 2.1.2.(4) Expanded rationale to discourage 535 leaking info between IPv4 and IPv6 groups. 537 Section 3: more strongly encourage the use of a 538 configuration option for selection of ICMPv6 message 539 types. 541 Editorial comments. 543 Hyphenation problem resolved for groff by setting then ms 544 HY register to zero, disabling all forms for the entire 545 document 546 (".hy 0" and ".nr" worked only as far as the following 547 ms macro). 549 Sections moved around - again - to comply with 550 rfc2223bis-03 draft. Added copyright notice after memo 551 status. Removed table of contents as the draft is fairly 552 short. Corrected a reference typo. 554 Section 2.1.2.(3): Requirement and rationale broken into 555 separate paragraphs. 557 Added references to other IPv6 encapsulation documents, 559 Corrected estimates for MAC address collisions for 560 Ethernet and FDDI: both specification take the low-order 561 four (not six) bytes from the IPv6 group addresses. 563 draft-ietf-magma-snoop-05.txt: January 2003 565 Changes in wording of IGMP forwarding rule 6) and Data 566 forwarding rule 7). Corrections in the references section. 568 Apart from above, no substantial changes has occured in the 569 document. Several editorial changes, however, have been made 570 to comply with the rfc editors requirements: 572 References splitted in normative and informative sections, 573 other related references added. 575 Abstract shortened. 577 Changed all occurances of MUST, MAY etc. to lowercase to 578 reflect that this is not a standards track document. 580 Sections moved around so they appear in the required order. 582 draft-ietf-magma-snoop-04.txt: November 2002 Editorial changes 583 only. 585 draft-ietf-magma-snoop-03.txt: October 2002 587 IGMP Forwarding rules: 588 Add references to and become consistant with the current IGMP 589 proxy draft, 591 Unrecognized IGMP packets should not be ignored because "mbz" 592 fields are not zero since packets from future versions are 593 expected to maintain consistency. 595 Corrections related to IGMP Querier election process. 597 Add clarification to how lists of router ports may be 598 assembled. 600 Data Forwarding rules: 601 Added discussion of the problems for different IGMP 602 environments in choosing whether to flood or to prune 603 unregistered multicasts. 605 Added refinements for how to handle NON-IPv4 multicasts, to 606 keep IGMP-snooping functionality from interfering with IPv6 607 and other multicast traffic. Any filtering for non-IPv4 608 multicasts should be based on bridge behavior and not IGMP 609 snooping behavior. 611 IGMP snooping related problems: 612 Fixed description of interoperability issues in environments 613 with v3 routers and hosts, and v2 snooping switches. 615 Added discussion of the IGMPv3 "include source" and "exclude 616 source" options, and the inability to support them on shared 617 segments. 619 IPv6 Considerations: 620 Clarifications regarding address ranges FF00::, FF01:: and all 621 hosts FF02::1 in relation to data forwarding. 623 draft-ietf-magma-snoop-02.txt: June 2002 625 Status section removes document history; moved into this 626 section instead. 628 Introduction restores text from the -00 revision that 629 describes snooping and its goals 631 IGMP flooding rules eased, allowing management option to 632 broaden beyond "routers only". 634 Removed a should/MAY inconsistancy between IPv4 Forwarding and 635 IPv6 processing of checksums. 637 IGMP Forwarding Rules: clarify text describing processing of 638 non-zero reserved fields. 640 Data Forwarding Rules, item 3 is changed from "MUST forward to 641 all ports" to "MAY"; item 4 default changes from "MUST" to 642 "should use network addresses". 644 Added two sets of additional responses to the questionnaire 645 and text indicating that responses don't cover all products. 647 Removed (commented out) description of IPR issues: IESG is 648 aware of them. 650 draft-ietf-magma-snoop-01.txt: January 2002 652 Extensive restructuring of the original text. 654 draft-ietf-idmr-snoop-01.txt: 2001 656 Added several descriptions of cases where IGMP snooping 657 implementations face problems. Also added several network 658 topology figures. 660 draft-ietf-idmr-snoop-00.txt: 2001 662 Initial snooping draft. An overview of IGMP snooping and the 663 problems to be solved. 665 5. References 667 5.1. Normative References 669 [BRIDGE] IEEE 802.1D, "Media Access Control (MAC) Bridges" 671 [IGMPv3] Cain, B., "Internet Group Management Protocol, 672 Version 3", RFC3376, October 2002. 674 [IPV6-1394] Fujisawa, K. and Onoe, A., "Transmission of IPv6 675 Packets over IEEE 1394 Networks", RFC3146, 676 October 2001. 678 [IPV6-ETHER] Crawford, M., "Transmission of IPv6 Packets over 679 Ethernet Networks", RFC2464, December 1998. 681 [IPV6-FDDI] Crawford, M., "Transmission of IPv6 Packets over 682 FDDI Networks", RFC2467, December 1998. 684 [IPV6-TOKEN] Crawford, M., Narten, T. and Thomas, S., 685 "Transmission of IPv6 Packets over Token Ring 686 Networks", RFC2470, December 1998. 688 [MLD] Deering, S., Fenner, B. and Haberman, B. 689 "Multicast Listener Discovery (MLD) for IPv6", 690 RFC2710, October 1999. 692 [MLDv2] Vida, R. and Costa, L., "Multicast Listener 693 Discovery Version 2 (MLDv2) for IPv6", draft- 694 vida-mld-v2-06.txt, November 2002. 696 [MRDISC] Biswas, S., Cain, B. and Haberman, B., "Multicast 697 Router Discovery", draft-ietf-idmr-igmp- 698 mrdisc-10.txt, January 2003. 700 [NDP] Narten, T., Nordmark, E. and Simpson, W., 701 "Neighbor Discovery for IP Version 6 {IPv6)", 702 RFC2461, December 1998. 704 [PROXY] Fenner, B. et al, "IGMP/MLD-based Multicast 705 Forwarding (IGMP/MLD Proxying)", draft-ietf- 706 magma-igmp-proxy-01.txt, November 2002. 708 [RFC1112] Deering, S., "Host Extensions for IP 709 Multicasting", RFC1112, August 1989. 711 [RFC2026] Bradner, S. "The Internet Standards Process -- 712 Revision 3", RFC2026, October 1996. 714 [RFC2236] Fenner, W., "Internet Group Management Protocol, 715 Version 2", RFC2236, November 1997. 717 [RFC2375] Hinden, R. "IPv6 Multicast Address Assignments", 718 RFC2375, July 1998. 720 5.2. Informative References 722 [IANA] Internet Assigned Numbers Authority, "Internet 723 Multicast Addresses", http://www.isi.edu/in- 724 notes/iana/assignments/multicast-addresses 726 [CISCO] Cisco Tech Notes, "Multicast In a Campus Network: 727 CGMP and IGMP snooping", 728 http://www.cisco.com/warp/public/473/22.html 730 [MSOFT] Microsoft support article Q223136, "Some LAN 731 Switches with IGMP Snooping Stop Forwarding 732 Multicast Packets on RRAS Startup", 733 http://support.microsoft.com/support/kb/articles/ 734 Q223/1/36.ASP 736 6. Security Considerations 738 Security considerations for IGMPv3 are accounted for in 739 [IGMPv3]. The introduction of IGMP snooping switches adds the 740 following considerations with regard to IP multicast. 742 - The exclude source failure, which could cause traffic from 743 sources that are 'black listed' to reach hosts that have 744 requested otherwise. This can also occur in certain 745 network topologies without IGMP snooping. 747 - It is possible to generate packets which make the switch 748 wrongly believe that there is a multicast router on the 749 segment on which the source is attached. This will 750 potentially lead to excessive flooding on that segment. 751 The authentication methods discussed in [IGMPv3] will also 752 provide protection in this case. 754 - IGMP snooping switches which rely on the IP header of a 755 packet for their operation and which do not validate the 756 header checksum potentially will forward packets on the 757 wrong ports. Even though the IP headers are protected by 758 the Ethernet checksum this is a potential vulnerability. 760 - In IGMP, there is no mechanism for denying recipients 761 access to groups (i.e. no "exclude receiver" 762 functionality). Hence, apart from IP-level security 763 configuration outside the scope of IGMP, any multicast 764 stream may be received by any host without restriction. 766 Generally, IGMP snooping must be considered insecure due to 767 the issues above. However, none of the these issues are any 768 worse for IGMP snooping than for IGMP implementations in 769 general. 771 7. Acknowledgements 773 We would like to thank Martin Bak, Les Bell, Yiqun Cai, Ben 774 Carter, Paul Congdon, Toerless Eckert, Bill Fenner, Brian 775 Haberman, Edward Hilquist, Hugh Holbrook, Kevin Humphries, 776 Pekka Savola, Suzuki Shinsuke, Jaff Thomas, and Rolland Vida 777 for comments and suggestions on this document. 779 Furthermore, the following companies are acknowledged for 780 their contributions: 3Com, Alcatel, Cisco Systems, Enterasys 781 Networks, Hewlett-Packard, Vitesse Semiconductor Corporation. 782 The ordering of these names do not necessarily correspond to 783 the column numbers in the response table. 785 8. Authors' Addresses 787 Morten Jagd Christensen 788 Thrane & Thrane 789 Lundtoftegaardsvej 93 D 790 2800 Lyngby 791 email: mjc@tt.dk 793 Karen Kimball 794 Hewlett-Packard 795 8000 Foothills Blvd. 796 Roseville, CA 95747 797 email: karen.kimball@hp.com 799 Frank Solensky 800 Bluejavelin, Inc. 801 3 Dundee Park 802 Andover, MA 01810 803 email: fsolensky@bluejavelin.net 805 9. IETF IPR Statement 807 "The IETF takes no position regarding the validity or scope of 808 any intellectual property or other rights that might be 809 claimed to pertain to the implementation or use of the 810 technology described in this document or the extent to which 811 any license under such rights might or might not be available; 812 neither does it represent that it has made any effort to 813 identify any such rights. 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