IPNGWG Working Group B. Haberman Internet Draft Nortel Networks draft-ietf-ipngwg-uni-based-mcast-00.txt D. Thaler August 2000 Microsoft Expires February 2001 Unicast-Prefix-based IPv6 Multicast Addresses Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026 [RFC 2026]. 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. Abstract This specification defines an extension to the multicast addressing architecture of the IP Version 6 protocol. The extension presented in this document allows for unicast-prefix-based allocation of multicast addresses. 1. Introduction This document specifies an extension to the multicast portion of the IPv6 addressing architecture [RFC 2373]. The current architecture does not contain any built-in support for dynamic address allocation. This proposal introduces encoded information in the multicast address to allow for dynamic, network prefix-based allocation of IPv6 multicast addresses, as well as allocation of source-specific multicast addresses. 2. Multicast Address Format Section 2.7.2 of RFC 2373 defines the following operational format of IPv6 multicast addresses: Haberman, Thaler 1 Internet Draft Unicast Prefix-based IPv6 Multicast August 2000 | 8 | 4 | 4 | 80 | 32 | +--------+----+----+--------------------------------+------------+ |11111111|flgs|scop| reserved must be zero | group ID | +--------+----+----+--------------------------------+------------+ This document introduces a new format that incorporates unicast prefix information in the multicast address. The following illustrates the new format: | 8 | 4 | 4 | 8 | plen |72 - plen | 32 | +--------+----+----+------+----------------+----------+----------+ |11111111|flgs|scop| plen | network prefix | reserved | group ID | +--------+----+----+------+----------------+----------+----------+ +-+-+-+-+ flgs is a set of 4 flags: |0|0|P|T| +-+-+-+-+ o P = 0 indicates a multicast address that is not assigned based on the network prefix. o P = 1 indicates a multicast address that is assigned based on the network prefix. o The setting of the T bit is defined in Section 2.7 of RFC 2373 plen indicates the length of the network prefix portion of the address when P = 1. This field is required in order to determine the number of bits to include as part of the unicast prefix. network prefix identifies the network prefix of the unicast subnet owning the multicast address. If P = 1, this field contains the unicast network prefix defined in [RFC 2374] and assigned to the domain owning the multicast address. The reserved field MUST be zero. While this limits the number of unicast prefix-based IPv6 multicast groups to 2^32 per prefix, this is unlikely to be a limitation in the future. If it becomes necessary to exceed this limit in the future, multicast will still work but the processing will be slightly slower. With the network prefix-based architecture and the current unicast address architecture [RFC 2374], the network prefix portion of the multicast address will be at most 64 bits. This allows for the group ID field to be at least 40 bits. Haberman, Thaler 2 Internet Draft Unicast Prefix-based IPv6 Multicast August 2000 3. Source-Specific Multicast Addresses The network prefix-based IPv6 multicast address format supports Source-specific multicast addresses, as defined by [IANA]. This is accomplished by: o Setting P = 1 o Setting plen = 0 o Setting network prefix = 0 4. Security Considerations Using unicast network-prefix based multicast addresses can sometimes aid in identifying the allocation domain of a given multicast address, although no guarantee is provided. Using source-specific multicast addresses can sometimes aid in the prevention of denial-of-service attacks by arbitrary sources, although no guarantee is provided. 5. References [RFC 2026] S. Bradner, "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996. [RFC 2460] S. Deering and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998. [RFC 2373] R. Hinden and S. Deering, "IP Version 6 Addressing Architecture", RFC 2373, July 1998. [RFC 2119] S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, BCP14, March 1999. [RFC 2374] R. Hinden, M. O'Dell, and S. Deering, "An IPv6 Aggregatable Global Unicast Address Format", RFC 2374, July 1998. [RFC 2464] M. Crawford, "Transmission of IPv6 Packets over Ethernet Networks", RFC 2464, December 1998. [RFC 2470] M. Crawford, T. Narten, and S. Thomas, "Transmission of IPv6 Packets over Token Ring Networks", RFC 2470, December 1998. [RFC 2375] R. Hinden and S. Deering, "IPv6 Multicast Address Assignments", RFC 2375, July 1998. Haberman, Thaler 3 Internet Draft Unicast Prefix-based IPv6 Multicast August 2000 [RFC 2365] D. Meyer, "Administratively Scoped IP Multicast", BCP 23, RFC 2365, July 1998. [IANA] D. Cheriton, "Single-source IP Multicast Address Range", http://www.isi.edu/in-notes/iana/assignments/single- source-multicast, October 1998. Haberman, Thaler 4 Author's Address Brian Haberman Nortel Networks 4309 Emperor Blvd. Suite 200 Durham, NC 27703 1-919-992-4439 Email : haberman@nortelnetworks.com Dave Thaler Microsoft Corporation One Microsoft Way Redmond, WA 48105-6399 1-425-703-8835 Email: dthaler@microsoft.com Haberman, Thaler 5