INTERNET-DRAFT IGMPv3/MLDv2 for SSM H. Holbrook Expires May 3, 2003 Cisco Systems B. Cain Cereva Networks B. Haberman Caspian Networks Nov 3, 2002 Using IGMPv3 and MLDv2 For Source-Specific Multicast Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC 2119]. Holbrook/Cain/Haberman [Page 1] INTERNET-DRAFT IGMPv3/MLDv2 for SSM 3 Nov 2002 Abstract This document describes changes to the Internet Group Management Protocol Version 3 (IGMPv3) [IGMPv3] and the Multicast Listener Discovery Protocol Version 2 (MLDv2) [MLDv2] to support source-specific multicast (SSM) [SSM]. 1. Overview and Rationale The Internet Group Management Protocol (IGMP) [RFC1112,IGMPv2,IGMPv3], is the standard mechanism for communicating IP multicast group membership requests from a host to its locally attached routers in IPv4. IGMP version 3 (IGMPv3) [IGMPv3] provides the ability for a host to selectively request or filter traffic from individual sources within a multicast group. The Multicast Listener Discovery Protocol (MLD) [RFC2710, MLDv2] offers similar functionality for IPv6. Specifically, MLD version 2 (MLDv2) performs the same functionality as IGMPv3. Due to the commonality of function, the term "Group Management Protocol" or "GMP" will be used to refer to both IGMP and MLD. The term "Source Filtering GMP", or "SFGMP" will be used to reference IGMPv3 and MLDv2 capable group management protocols. The SFGMP algorithms and message processing rules require small changes to support the source-specific multicast model. This document defines the modifications required to the host and router portions of IGMPv3 and MLDv2 to support source-specific multicast. 2. GMP Host Requirements for Source-Specific Multicast This document does not strictly require the IP layer or GMP module of an SFGMP-enabled host to treat SSM destination addresses specially. To ensure that the routers apply SSM semantics for SSM addresses, however, a host application must - know the range of destination addresses that have SSM semantics - use ONLY source-specific APIs to request delivery of packets sent to SSM destination addresses The 232/8 address range is currently allocated for SSM by IANA [IANA- ALLOCATION] for IPv4. In IPv6, the range is FF3x::/32 [RFC3306] (where 'x' is a valid IPv6 multicast scope value). Hosts and routers may be configured to apply SSM semantics to other addresses as well. A GMP module on a host or router SHOULD have a configuration mechanism Holbrook/Cain/Haberman [Page 2] INTERNET-DRAFT IGMPv3/MLDv2 for SSM 3 Nov 2002 to set the SSM address range(s). If this configuration option exists, it MUST default to the IANA-allocated SSM range. The mechanism for setting this configuration option MUST at least allow for manual configuration. Protocol mechanisms to set this option may be defined in the future. If a host does not have this option, applications on that host may be denied SSM service by other non-compliant applications on the same host or by other non-compliant hosts on the same network, as described below. It is strongly recommended that the multicast source filtering (MSF) APIs of [MSFAPI] be used to implement SSM. If the host IP module receives a non source-specific request for an SSM destination address, it SHOULD return an error to the application. If the host IP module is not configured with the SSM address range, the non-source-specific (RFC 1112) APIs will not return an error when passed an SSM destination addresses. On these hosts, applications that mistakenly use the wrong APIs (e.g., "join(G)", "IPMulticastListen(G,EXCLUDE(S1))" for IGMPv3, or IPv6MulticastListen(G,EXCLUDE(S2))" for MLDv2) to request delivery of packets sent to an SSM address will not receive the requested service, as routers will refuse to process any such request, as per section 3.5 of this document. This section documents the behavior of hosts with respect to sending and receiving the following GMP message types: - IGMPv1/v2 and MLDv1 Reports - IGMPv3 and MLDv2 Reports - IGMPv1/v2 and MLDv1 Queries - IGMPv2 Leave and MLDv1 Done - IGMPv2 and MLDv1 Group Specific Query - IGMPv3 and MLDv2 Group Specific Query - IGMPv3 and MLDv2 Group-and-Source Specific Query 2.1. IGMPv1/v2 and MLDv1 Reports A host SHOULD NOT send IGMPv1, IGMPv2, or MLDv1 host reports for SSM addresses. If an SSM-unaware SFGMP-enabled host receives an IGMPv1, IGMPv2, or MLDv1 host report for SSM destination address G, its GMP module will revert to IGMPv1/v2 or MLDv1 compatibility mode for address G. This will prevent the host from sending source-specific joins, and consequently the SSM service model will not be provided for destination address G to hosts on that LAN. Therefore, it is important that the SSM address range be used only in conjunction with the SSM APIs. Holbrook/Cain/Haberman [Page 3] INTERNET-DRAFT IGMPv3/MLDv2 for SSM 3 Nov 2002 2.2. IGMPv3 and MLDv2 Reports Source-specific multicast destination-and-source pairs (channels) are reported using IGMPv3 or MLDv2 with the SFGMP INCLUDE report. A host implementation MAY report either one or multiple channels in a single report. When source-specific channels are reported in an SFGMP Report, the report may contain one or more group records of the following types: - MODE_IS_INCLUDE as part of a Current-State Record - ALLOW_NEW_SOURCES as part of a State-Change Record - BLOCK_OLD_SOURCES as part of a State-Change Record The source list for any individual Group Record may be of length one or more than one. If a host implementation so chooses, it may report both SSM destination addresses and RFC 1112 multicast (henceforth termed Any- Source Multicast or ASM as in [SSM]) destination addresses in the same message. A host that is configured with the SSM address range would not normally send either of the following record types for an SSM address. - MODE_IS_EXCLUDE as part of a Current-State Record - CHANGE_TO_INCLUDE_MODE as part of a Filter-Mode-Change Record - CHANGE_TO_EXCLUDE_MODE as part of a Filter-Mode-Change Record EXCLUDE mode does not apply to SSM addresses, and the filter mode used for an SSM address should never change to or from EXCLUDE mode under correct application behavior. If all applications on a host use SSM- aware APIs to express interest in SSM addresses, then the host OS would not normally send any of the above record types for addresses in the source-specific range. 2.3. IGMPv1/IGMPv2 and MLDv1 Queries If an IGMPv1, IGMPv2, or MLDv1 query is received, the SFGMP protocol specifications require the host to revert to the older (IGMPv1, IGMPv2, or MLDv1) mode of operation for that destination address. If this occurs, the host will stop reporting source-specific subscriptions for that destination address and start using IGMPv1, IGMPv2, or MLDv1 to report interest in the SSM destination address, unqualified by a source Holbrook/Cain/Haberman [Page 4] INTERNET-DRAFT IGMPv3/MLDv2 for SSM 3 Nov 2002 address. If this occurs, SSM semantics will no longer be applied to G by the router. A router compliant with this document would never generate an IGMPv1, IGMPv2, or MLDv1 query for an address in the SSM range -- this situation only occurs if either the router is not compliant with this document or if the host and the router disagree about the SSM address range. A host SHOULD log an error if this occurs. In order to reduce this problem, it MUST be administratively assured that all routers on a given shared-medium network are compliant with this document and are in agreement about the SSM address range. 2.4. IGMPv2 Leave and MLDv1 Done IGMP Leave/Done messages are not processed by hosts. IGMPv2 Leave and MLDv1 Done messages are not sent for SSM addresses. 2.5. IGMPv2 and MLDv1 Group Specific Query If a host receives an IGMPv2 or MLDv1 Group Specific Query for an address in any configured source-specific range, it SHOULD process the query normally according to [IGMPv3][MLDv2], even if the group queried is a source-specific destination address. The transmission of such a query indicates that the sending router is either not compliant with this document or that is not configured with the same SSM address range(s) as the receiving host. A host SHOULD log an error in this case. 2.6. IGMPv3 and MLDv1 Group Specific Query If a host receives an SFGMP Group-Specific Query in its configured source-specific range, it MUST respond with a report if the group matches the source-specific destination address of any of its subscribed source-specific groups. Although in the current IGMPv3 and MLDv2 protocol specifications, routers would have no reason to send one, the semantics of such a query are well-defined in this range and future implementations may have reason to send such a query. Be liberal in what you accept. Holbrook/Cain/Haberman [Page 5] INTERNET-DRAFT IGMPv3/MLDv2 for SSM 3 Nov 2002 2.7. IGMPv3 and MLDv2 Group-and-Source Specific Query An SFGMP router will query a source-specific channel that a host has requested to leave (via a BLOCK_OLD_SOURCES record) with a group-and- source specific query. A host MUST respond to a group-and-source specific query for which the group and source in the query match match any channel for which the host has a subscription. Hosts MUST be able to process a query with multiple sources listed per group. 3. Router Requirements for Support Source-Specific Multicast Routers must be aware of the SSM address range. The 232/8 and FF3x::/32 address ranges are currently allocated for SSM by IANA [IANA- ALLOCATION][RFC3306]. However, an SSM router may have a configuration option to apply SSM semantics to other addresses as well. If this configuration option exists, it MUST default to the IANA-allocated range. This section documents the behavior of routers with respect to the following types of SFGMP messages for source-specific destination addresses: - IGMPv3 and MLDv2 Reports - IGMPv3 and MLDv2 General Query - IGMPv3 and MLDv2 Group-Specific Query - IGMPv3 and MLDv2 Group-and-Source Specific Query - IGMPv1/v2 and MLDv1 Reports - IGMPv1/v2 and MLDv1 Queries - IGMPv2 Leave and MLDv1 Done 3.1. IGMPv3 and MLDv2 Reports SFGMP Reports are used to report source-specific subscriptions in the SSM address range. If a router receives an SFGMP report that contains a group record for a destination address in source-specific range that matches one of the types listed below, then it MUST ignore that group record, however, it MUST process other group records within that same report. - Any Current-State Record with MODE_IS_EXCLUDE - A CHANGE_TO_EXCLUDE_MODE Filter-Mode-Change Record Holbrook/Cain/Haberman [Page 6] INTERNET-DRAFT IGMPv3/MLDv2 for SSM 3 Nov 2002 In order to be maximally tolerant of host implementations that are not compliant with this specification, a router MUST process CHANGE_TO_INCLUDE_MODE Filter-Mode-Change Group Records for groups in the SSM range. 3.2. IGMPv3 and MLDv2 General Queries SFGMP General Queries are used to periodically build the total desired membership state on a subnet. These queries are used for the same purpose in the source-specific address range -- no change in behavior is required. An SSM router sends periodic SFGMP General Queries as per the IGMPv3 and MLDv2 specifications. 3.3. IGMPv3 and MLDv2 Group Specific Queries SFGMP routers that support source-specific multicast MAY send group- specific queries for addresses in the source-specific range. This specification does not explicitly prohibit such a message, although, at the time of writing, a router conformant to [IGMPv3][MLDv2] would never send one. 3.4. IGMPv3 and MLDv2 Group-and-Source Specific Queries SFGMP Group-and-Source Specific Queries are used when a receiver has indicated that it is no longer interested in receiving traffic from a particular (S,G) pair to determine if there are any remaining directly- attached hosts with interest in that (S,G) pair. Group-and-Source Specific Queries are used within the source-specific address range when a router receives a BLOCK_OLD_SOURCES Record for one or more source- specific groups. These queries are sent normally, as per [IGMPv3][MLDv2]. 3.5. IGMPv1/v2 and MLDv1 Reports An IGMPv1/v2 or MLDv1 report for an address in the source-specific range could be sent by a host that does not support the source-specific model. A router MUST ignore all such reports in the source-specific address range and specifically MUST NOT use them to establish IP forwarding state. A router MAY log an error if it receives such a report. 3.6. IGMPv1/v2 and MLDv1 Queries The GMP querier on a shared-medium network is elected to be the one with lowest source IP address. Therefore, an IGMPv3 or MLDv2 router will Holbrook/Cain/Haberman [Page 7] INTERNET-DRAFT IGMPv3/MLDv2 for SSM 3 Nov 2002 yield to an IGMPv1, IGMPv2, or MLDv1 querier with a lower IP address. SFGMP routers that lose the querier election to a lower version router MUST log an error, as per the IGMPv3 and MLDv2 specifications. An SFGMP router MAY have a configuration option that prevents it from reverting to previous version compatibility mode for source-specific addresses. When this configuration option is enabled, an SFGMP router that loses the querier election to an older version querier SHOULD continue to process source-specific reports in the source-specific address range. This may be useful as a transition mechanism, when used in conjunction with the host configuration option of Section 2.3. 3.7. IGMPv2 Leave and MLDv1 Done An IGMPv2 Leave or MLDv1 Done message may be received for a source- specific address from a host that does not support the source-specific model. A router MUST ignore all such messages in the source-specific address range. 4. Notes [To be removed before going to the IESG.] 4.1. Major changes in this revision There were two major changes in this revision (-03): the inclusion of IPv6, and the removal of the explicit text stating that a host MAY choose to ignore IGMPv1/v2 (MLDv1) queries in the SSM address range. The document was internally inconsistent on this point (it said two different things in two different sections), and the statement conflicted with the existing IGMPv3 specifications. This situation indicates a serious configuration error and if the querying router has already reverted to IGMPv2 mode for a group, then a host can not receive proper SSM service for that group in any case. Hence the authors decided that it was better to remove this statement. 4.2. A note on EXCLUDE mode The IGMPv3 and MLDv2 protocol specifications explicitly state that a host MUST NOT transition to EXCLUDE mode as a result of running out of resources -- hence when a host runs out of resources, it will not fail to provide SSM service. 5. Acknowledgments The authors would like to thank Vince Laviano, Nidhi Bhaskar, and Steve Deering and for their input and careful review. Holbrook/Cain/Haberman [Page 8] INTERNET-DRAFT IGMPv3/MLDv2 for SSM 3 Nov 2002 6. References [IGMPv3] Cain, B., Deering, S., and A. Thyagarajan, "Internet Group Management Protocol, Version 3," RFC 3376, October 2002. [RFC1112] Deering, S., "Host Extensions for IP Multicasting," RFC 1112, August 1989. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels," RFC 2119, March 1997. [IANA-ALLOCATION] Internet Assigned Numbers Authority, http://www.isi.edu/in-notes/iana/assignments/multicast-addresses. [IGMPv2] Fenner, W., "Internet Group Management Protocol, Version 2," RFC 2236, November 1997. [MSFAPI] Thaler, D., Fenner, B., and Quinn, B. "Socket Interface Extensions for Multicast Source Filters." Work in Progress. [SSM] Holbrook, H., and Cain, B., "Source-Specific Multicast for IP", Work in Progress. [RFC2710] Deering, S., Fenner, B., and Haberman, B., "Multicast Listener Discovery (MLD) for IPv6", RFC 2710, October 1999. [RFC3306] Haberman, B., and Thaler, D., "Unicast-prefix-based IPv6 Multicast Addresses", RFC 3306, August 2002. [MLDv2] Vida, R., et. al., "Multicast Listener Discovery Version 2 (MLDv2) for IPv6", Work in Progress. 7. Author's Address Hugh Holbrook Cisco Systems 170 W. Tasman Drive. San Jose, CA 95134 holbrook@cisco.com Brad Cain Cereva Networks 3 Network Drive Marlborough, MA 01752 bcain99@yahoo.com Holbrook/Cain/Haberman [Page 9] INTERNET-DRAFT IGMPv3/MLDv2 for SSM 3 Nov 2002 Brian Haberman Caspian Networks bkhabs@nc.rr.com This document expires May 3, 2003. Holbrook/Cain/Haberman [Page 10]