MALLOC Working Group B. Haberman Internet Draft Nortel Networks draft-ietf-malloc-ipv6-guide-01.txt July 2000 Expires January 2001 Dynamic Allocation Guidelines for 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 document specifies guidelines to be used when allocating IPv6 multicast addresses. The purpose of these guidelines is to reduce the probability of IPv6 multicast address collision, not only at the IPv6 layer, but also at the MAC layer of media that utilizes IEEE 802 addressing. 1. Terminology 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]. 2. Introduction This document specifies guidelines to be used when allocating IPv6 multicast addresses. The purpose of these guidelines is to reduce Haberman 1 Internet Draft IPv6 Multicast Address Guidelines July 2000 the probability of IPv6 multicast address collision, not only at the IPv6 layer, but also at the MAC layer of media that utilizes IEEE 802 addressing. With the current IPv6 multicast address architecture [RFC 2373] and the proposed extension to that architecture specified in [NEW ARCH], a set of guidelines is needed for multicast address allocation servers [MALLOC] to use in assigning IPv6 multicast addresses. These guidelines specify how the lowest 32 bits of the IPv6 multicast address are chosen and assigned. The guidelines specify several mechanisms that can be used to determine the lowest 32 bits of the multicast address. By supporting several mechanisms, these guidelines can accommodate the varying capabilities of multicast address allocation servers. 3. Assignment of New IPv6 Multicast Addresses The current approach [RFC 2464] to map IPv6 multicast addresses into IEEE 802 MAC addresses takes the low order 32 bits of the IPv6 multicast address and uses it to create a MAC address. Group IDs less than or equal to 32 bits long will generate unique MAC addresses within a given multicast scope. The goal of this document is to present several mechanisms implementers and operators can use to select the group ID portion of the address so that the possibility of collisions at the IP layer and at the IEEE 802 layer is reduced. The following section presents several different mechanisms of varying complexity that can be used to select an appropriate group ID. 4. Group ID Selection Guidelines The following guidelines assume that the upper 96 bits of the IPv6 multicast address have been initialized according to [RFC 2373] and [NEW ARCH]. The T flag of each dynamically allocated multicast address MUST be set to '1'. Permanent addresses MUST NOT be allocated using the multicast address allocation architecture. The group ID portion of the address is set using either a pseudo- random 32-bit number or a 32-bit number created using the guidelines in [RFC 1750]. Possible approaches to creating a pseudo-random number include using an MD5 message-digest [RFC 1321] or portions of an NTP [RFC 1305] timestamp. The high-order bit of the Group ID MUST be set to '1'. This will distinguish the dynamically allocated addresses from the permanently Haberman 2 Internet Draft IPv6 Multicast Address Guidelines July 2000 assigned multicast addresses defined in [RFC 2375] at the MAC layer on any media that utilizes IEEE 802 addressing. A request for multiple multicast addresses SHOULD be handled atomically. One possible approach is to use the initial group ID, created using the guidelines above, as the base address in a contiguous block of multicast addresses. Another approach is to create multiple group IDs and generate the appropriate multicast addresses. 5. Multicast Address Lifetime The lifetime of the assignment of unicast prefix-based multicast addresses MUST be less than or equal to the Valid Lifetime field in the Prefix Information option contained in the Neighbor Discovery Router Advertisement message [RFC 2461]. 6. Security Considerations This document does not have any known impact on Internet infrastructure security. 7. Acknowledgements The author would like to thank Dave Thaler and Steve Deering for their thorough review of this document. 8. References [RFC 2026] Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996. [NEW ARCH] Haberman, B., Thaler, D., "Unicast Prefix-based IPv6 Multicast Addresses", Work in Progress, July 2000. [RFC 2373] Hinden, R., Deering, S., "IP Version 6 Addressing Architecture", RFC 2373, July 1998. [MALLOC] Thaler, D., Handley, M., and Estrin, D., "The Internet Multicast Address Allocation Architecture", draft-ietf-malloc-arch-04.txt, January 2000. [RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, BCP14, March 1999. [RFC 2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet Networks", RFC 2464, December 1998. Haberman 3 Internet Draft IPv6 Multicast Address Guidelines July 2000 [RFC 1305] Mills, D., "Network Time Protocol (Version 3) Specification, Implementation", RFC 1305, March 1992. [RFC 1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, April 1992. [RFC 1750] Eastlake, D., Crocker, S., Schiller, J., "Randomness Recommendations for Security", RFC 1750, December 1994. [RFC 2375] Hinden, R., Deering, S., "IPv6 Multicast Address Assignments", RFC 2375, July 1998. [RFC 2461] Narten, T., Nordmark, E., Simpson, W., "Neighbor Discovery for IP Version 6 (IPv6)", RFC 2461, December 1998. Haberman 4 Author's Address Brian Haberman Nortel Networks 4309 Emperor Blvd. Suite 200 Durham, NC 27703 1-919-992-4439 Email : haberman@nortelnetworks.com Haberman 5