Internet Engineering Task Force MAGMA WG INTERNET-DRAFT Isidor Kouvelas/Cisco draft-ietf-magma-mrdssm-03.txt 17 June 2003 Expires: December 2003 Multicast Router Discovery SSM Range Option Status of this Document 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. This document is a product of the IETF MAGMA WG. Comments should be addressed to the authors, or the WG's mailing list at magma@ietf.org. Abstract This document defines the Multicast Router Discovery protocol option for advertising the configured IPv4 Source Specific Multicast destination address range. Kouvelas [Page 1]
INTERNET-DRAFT Expires: December 2003 June 2003 1. Introduction With current multicast deployment in the Internet, different multicast routing protocols coexist and operate under separate parts of the multicast address space [1]. Multicast routers are consistently configured with information that maps specific multicast destination address ranges to multicast routing protocols. Part of this configuration describes the subset of the address space that is used by source-specific multicast (SSM) [3]. Under current deployment, the ability to extend the IPv4 SSM destination address range is used to define SSM destination addresses that operate within administratively scoped boundaries. Note that the SSM range for IPv6 is well defined for all valid scopes [4] and a mechanism to allow additional ranges to operate in SSM mode on a per-link bases is not required. There are currently two requirements for a router to advertise its configured SSM range on its attached links: o On links with multiple multicast routers, advertisement of the configured SSM range by each router can be used to discover misconfigurations. o IP systems with multicast sources or receivers can use the advertisements to learn the SSM group range with which the network is configured. This document defines an optional extension for the IPv4 Multicast Router Discovery protocol [2] that can be used by a router to advertise the configured SSM address range. 2. SSM Range Discovery Option Format The SSM Range Discovery option SHOULD be included in all Multicast Router Advertisement messages [2]. It contains the list of multicast destination address ranges that are configured to operate under Source Specific Multicast on this router. The format of the option is as follows: Kouvelas Section 2. [Page 2]
INTERNET-DRAFT Expires: December 2003 June 2003 0 1 2 3 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type=X | Length=var | Mask-Len-1 | Prefix-1 ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Mask-Len-2 | Prefix-2 ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | Type The type value of the Multicast Router Advertisement SSM Range Discovery option is X (TBD by IANA). Length The length of the option in octets excluding the type and length fields. The length of the SSM Range Discovery option is variable and depends on the number of destination ranges present in the option as well as the sizes of the ranges. Mask-Len-n The mask length in bits for the nth address range. Prefix-n The multicast destination address prefix for the nth range present in this option. The size of the prefix field is variable and depends on the number of significant bits in the prefix (specified in the corresponding Mask-Len field). The field is padded by enough trailing bits to make the end of the field fall on an octet boundary. The value of the trailing bits must be sent as zero and ignored on receipt. For example a prefix with a mask length field holding the value 16 would have a prefix field that takes up two octets and requires no padding. A prefix with a mask length of 17 would have a prefix field that takes up three octets and includes 7 trailing padding bits. 3. Notes on Option Processing Routers originating Multicast Router Advertisement messages SHOULD NOT include more than one SSM Range Discovery option in each message. Systems with a multicast capable IP host stack that receive a Multicast Router Advertisement message with more than one SSM Range Discovery options MUST only use the prefixes from the last SSM Range Discovery option in the message as the active SSM range. Kouvelas Section 3. [Page 3]
INTERNET-DRAFT Expires: December 2003 June 2003 The SSM range specified by routers originating Multicast Router Advertisement messages with the SSM Range Discovery option MUST not include any part of the link-local multicast range 224.0.0/24. Systems with a multicast capable IP host stack that receive a Multicast Router Advertisement message with a SSM Range Discovery option that includes destination addresses in the link-local multicast range 224.0.0/24 MUST use as the active SSM range the contents of the option excluding any addresses in the range 224.0.0/24. A router receiving a Multicast Router Advertisement message with an SSM Range Discovery option MUST compare the contents of the option with the multicast address ranges in the local SSM configuration and signal any differences to the administrator in a rate-limited manner. Signaling of range differences may be accomplished by a mechanism as simple as an entry in the router log containing the address of the router with the mismatch in configuration. 4. Security Considerations Multicast Router Advertisement messages are IGMP messages sent to the All-Systems multicast group (224.0.0.1) which is not forwarded by routers. Only rogue systems on a connected link can masquerade as multicast routers. Such rogue systems can include the SSM Range Discovery option in their messages and cause the SSM range mapping to be incorrectly set by hosts on the link. The next Multicast Router Advertisement from a real valid router on the link will restore the correct mapping. This spec mandates that routers log the reception of inconsistent range advertisements which makes it easier to detect rogue systems. 5. IANA Considerations This document introduces the new SSM Range Discovery option for the Multicast Router Discovery protocol. This option requires a new MRD type value to be assigned by IANA. 6. Acknowledgments The author would like to thank Bill Fenner and Dave Thaler for their contribution to this document. Kouvelas Section 7. [Page 4]
INTERNET-DRAFT Expires: December 2003 June 2003 7. Authors' Addresses Isidor Kouvelas Cisco Systems 170 W. Tasman Drive San Jose, CA 95134 kouvelas@cisco.com 8. Normative References [1] Z. Albanna, K. Almeroth, D. Meyer, M. Schipper, "IANA Guidelines for IPv4 Multicast Address Assignments", RFC 3171 (BCP 51), August 2001. [2] S. Biswas, B. Haberman, "IGMP Multicast Router Discovery", Work In Progress, <draft-ietf-idmr-igmp-mrdisc-??.txt>, 2002. 9. Informative References [3] H. Holbrook, B. Cain, "Source-Specific Multicast for IP", work in progress, <draft-ietf-ssm-arch-00.txt>, 21 November 2001. [4] B. Haberman, D. Thaler, "Unicast-Prefix-based IPv6 Multicast Addresses", RFC 3306, August 2002. Kouvelas Section 9. [Page 5]
INTERNET-DRAFT Expires: December 2003 June 2003 Kouvelas Section 9. [Page 6]
