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Miscellaneous warnings: ---------------------------------------------------------------------------- == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'SHOULD not' in this paragraph: The packets with source-specific addresses SHOULD not be forwarded to interfaces with IGMPv2 or IGMPv1 subscriptions for these addresses. -- 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. 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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force Bill Fenner, AT&T Research 3 INTERNET-DRAFT Haixiang He, Nortel Networks 4 draft-ietf-idmr-igmp-proxy-01.txt Brian Haberman, Nortel Networks 5 Hal Sandick, Nortel Networks 6 Expire: January, 2002 July, 2001 8 IGMP-based Multicast Forwarding ("IGMP Proxying") 10 Status of this Memo 12 This document is an Internet-Draft and is in full conformance with 13 all provisions of Section 10 of RFC 2026. 15 Internet Drafts are working documents of the Internet Engineering 16 Task Force (IETF), its areas, and its working groups. Note that other 17 groups may also distribute working documents as Internet-Drafts. 19 Internet-Drafts are draft documents valid for a maximum of six months 20 and may be updated, replaced, or obsoleted by other documents at any 21 time. It is inappropriate to use Internet-Drafts as reference 22 material or to cite them other than as "work in progress." 24 The list of current Internet-Drafts can be accessed at 25 http://www.ietf.org/ietf/1id-abstracts.txt. 27 The list of Internet-Draft Shadow Directories can be accessed at 28 http://www.ietf.org/shadow.html. 30 Abstract 32 In certain topologies, it is not necessary to run a multicast routing 33 protocol. It is sufficient to learn and proxy group membership 34 information and simply forward based upon that information. This 35 draft describes a mechanism for forwarding based solely upon IGMP 36 membership information. 38 This document is a product of the IDMR working group within the 39 Internet Engineering Task Force. Comments are solicited and should 40 be addressed to the working group's mailing list at idmr@cs.ucl.ac.uk 41 and/or the authors. 43 1. Introduction 45 This document applies spanning tree multicast routing[Deering91] to 46 an IGMP-only environment. The topology is limited to a tree, since 47 we specify no protocol to build a spanning tree over a more complex 48 topology. The root of the tree is assumed to be connected to a wider 49 multicast infrastructure. 51 1.1. Conventions 53 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 54 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 55 document are to be interpreted as described in RFC 2119 [Bradner97]. 57 2. Definitions 59 2.1. Upstream Interface 61 A router's interface in the direction of the root of the tree. Also 62 called the "Host interface". 64 2.2. Downstream Interface 66 Each of a router's interfaces that is not in the direction of the 67 root of the tree. Also called the "Router interfaces". 69 2.3. Group Mode 71 For each multicast group, a group is in IGMPv1 mode if an IGMPv1 72 report is heard. A group is in IGMPv2 mode if an IGMPv2 report is 73 heard but no IGMPv1 report is heard. A group is in IGMPv3 mode if an 74 IGMPv3 is heard but no IGMPv1 or IGMPv2 report is heard. 76 2.4. Subscription 78 When a group is in IGMPv1 or IGMPv2 mode, the subscription is a group 79 membership on an interface. When a group is in IGMPv3 mode, the 80 subscription is an IGMPv3 state entry (i.e. a (multicast address, 81 group timer, filter-mode, source-element list) tuple) on an 82 interface. 84 2.5. Membership Database 86 The database maintained at each router into which the membership 87 information of each of its downstream interfaces is merged. 89 3. Abstract protocol definition 91 A router performing IGMP-based forwarding has a single upstream 92 interface and one or more downstream interfaces. These designations 93 are explicitly configured; there is no protocol to determine what 94 type each interface is. It performs the router portion of the 95 IGMP[Deering89, Fenner97, CDFKT01] protocol on its downstream 96 interfaces, and the host portion of IGMP on its upstream interface. 97 The router MUST NOT perform the router portion of IGMP on its 98 upstream interface. 100 The router maintains a database consisting of the merger of all 101 subscriptions on any downstream interface. Refer to section 4 for the 102 details about the construction and maintenance of the membership 103 database. 105 The router sends IGMP membership reports on the upstream interface 106 when queried, and sends unsolicited reports or leaves when the 107 database changes. 109 When the router receives a packet destined for a multicast group, it 110 uses a list consisting of the upstream interface and any downstream 111 interface which has a subscription pertaining to this packet and on 112 which it is the IGMP Querier. This list may be built dynamically or 113 cached. It removes the interface on which this packet arrived from 114 the list and forwards the packet to the remaining interfaces. 116 Note that the rule that a router must be the querier in order to 117 forward packets restricts the IP addressing scheme used; in 118 particular, the IGMP-based forwarding routers must be given the 119 lowest IP addresses of any potential IGMP Queriers on the link, in 120 order to win the IGMP Querier election. If another device wins the 121 IGMP Querier election, no packets will flow. 123 Forwarder election is necessary for links which are considered to be 124 downstream links by multiple IGMP-based forwarders. This rule 125 "piggy-backs" forwarder election on IGMP Querier election. On a link 126 with only one IGMP-based forwarding router, this rule MAY be disabled 127 (i.e. the router MAY be configured to forward packets to an interface 128 on which it is not the querier). However, the default configuration 129 MUST include the querier rule. 131 Note that this does not protect against an "upstream loop". For 132 example, as shown in the figure below: 134 LAN 1 ------------------------------------- 135 Upstream | | Downstream 136 A B 137 Downstream | | Upstream 138 LAN 2 ------------------------------------- 140 B will unconditionally forward packets from LAN 1 to LAN 2, and A 141 will unconditionally forward packets from LAN 2 to LAN 1. This will 142 cause an upstream loop. A multicast routing protocol which employs a 143 tree building algorithm is requried to resolve loops like this. 145 4. Router Behavior 147 This section describes an IGMP-based multicast forwarding router's 148 actions in more detail. 150 4.1. Membership Database 152 The router performs the router portion of the IGMP protocol on each 153 downstream interface. For each interface, the version of IGMP used 154 is explicitly configured and default to the highest version supported 155 by the system. 157 The output of this protocol is a set of subscriptions; this set is 158 maintained separately on each downstream interface. In addition, the 159 subscriptions on each downstream interface are merged into the 160 membership database. 162 The membership database is a set of membership records of the form: 164 (multicast-address, filter-mode, source-list) 166 Each record is the result of the merge of all subscriptions for that 167 record's multicast-address on downstream interfaces. If some 168 subscriptions are IGMPv1 or IGMPv2 subscriptions, these subscriptions 169 are converted to IGMPv3 subscriptions. The IGMPv3 subscriptions and 170 the converted subscriptions are merged using the merging rules for 171 multiple memberships on a single interface specified in the IGMPv3 172 specification[CDFKT01] to create the membership record. For example, 173 there are two downstream interfaces I1 and I2 that have subscriptions 174 for multicast address G. I1 has an IGMPv2 subscription that is (G). 175 I2 has an IGMPv3 subscription that is (G, INCLUDE, (S1, S2)). The 176 I1's subscription is converted to (G, EXCLUDE, NULL). Then the 177 subscriptions are merged and final membership record is (G, EXCLUDE, 178 NULL). 180 The router performs the host portion of the IGMP protocol on upstream 181 interface. If there is an IGMPv1 or IGMPv2 querier on upstream 182 network, then the router will perform IGMPv1 or IGMPv2 on upstream 183 interface accordingly. Otherwise, it will perform IGMPv3. 185 If the router performs IGMPv3 on upstream interface, then when the 186 composition of the membership database changes, the change in the 187 database is reported on the upstream interface as though this router 188 were a host performing the action. If the router performs IGMPv1 or 189 IGMPv2 on upstream interface, then when the membership records are 190 created or deleted, the changes are reported on the upstream 191 interface. All other changes are ignored. When the router reports 192 using IGMPv1 or IGMPv2, only the multicast address field in the 193 membership record is used. 195 4.2. Forwarding Packets 197 A router forwards packets received on its upstream interface to each 198 downstream interface based upon the downstream interface's 199 subscriptions and whether or not this router is the IGMP Querier on 200 each interface. A router forwards packets received on any downstream 201 interface to the upstream interface, and to each downstream interface 202 other than the incoming interface based upon the downstream 203 interfaces' subscriptions and whether or not this router is the IGMP 204 Querier on each interface. A router MAY use a forwarding cache in 205 order not to make this decision for each packet, but MUST update the 206 cache using these rules any time any of the information used to build 207 it changes. 209 4.3. SSM Considerations 211 To support Source-Specific Multicast (SSM), the router should be 212 compliant with the specification about using IGMPv3 for SSM [HC01]. 213 Note that the router should be compliant with both the IGMP Host 214 Requirement and the IGMP Router Requirement for SSM since it performs 215 IGMP Host Portion on upstream interface and IGMP Router Portion on 216 each downstream interface. 218 The packets with source-specific addresses SHOULD not be forwarded to 219 interfaces with IGMPv2 or IGMPv1 subscriptions for these addresses. 221 5. Security Considerations 223 Since only the Querier forwards packets, the IGMP Querier election 224 process may lead to black holes if a non-forwarder is elected 225 Querier. An attacker on a downstream LAN can cause itself to get 226 elected Querier resulting in no packets being forwarded. 228 References 230 Bradner97 Bradner, S., "Key words for use in RFCs to Indicate 231 Requirement Levels", RFC 2119/BCP 14, Harvard 232 University, March 1997. 234 CDFKT01 Cain, B., S. Deering, B. Fenner, I. Kouvelas and A. 235 Thyagarajan, "Internet Group Management Protocol, 236 Version 3", Work in progress. (draft-ietf-idmr-igmp- 237 v3-07.txt) 239 Deering91 Deering, S., "Multicast Routing in a Datagram 240 Internetwork", Ph.D. Thesis, Stanford University, 241 December 1991. 243 Fenner97 Fenner, W., "Internet Group Management Protocol, 244 Version 2", RFC 2236, Xerox PARC, November 1997. 246 Deering89 Deering, S., "Host Extensions for IP Multicasting", 247 RFC 1112, August 1989. 249 HC01 Holbrook, H., and Cain, B., "Using IGMPv3 For Source- 250 Specific Multicast", draft-holbrook-idmr-igmpv3- 251 ssm-01.txt, March 2001. 253 Author's Address: 255 William C. Fenner 256 AT&T Labs - Research 257 75 Willow Rd 258 Menlo Park, CA 94025 259 Phone: +1 650 330 7893 260 Email: fenner@research.att.com 262 Haixiang He 263 Nortel Networks 264 600 Technology Park Drive 265 Billerica, MA 01821 266 Phone: 978-288-7482 267 Email: haixiang@nortelnetworks.com 268 Brian Haberman 269 Nortel Networks 270 300 Perimter Park 271 Morrisvile, NC 27560 272 Email: haberman@nortelnetworks.com 274 Hal Sandick 275 Nortel Networks 276 300 Perimter Park 277 Morrisvile, NC 27560 278 Email: hsandick@nortelnetworks.com