MAGMA Working Group B. Haberman
draft-ietf-magma-mld-source-02.txtdraft-ietf-magma-mld-source-03.txt Caspian Networks Expires April 2003 October 2002 Source Address Selection for Multicast Listener Discovery Protocol (RFC 2710) 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. Abstract It has come to light that there is an issue with the selection of a suitable IPv6 source address for Multicast Listener Discovery messages when a node is performing stateless address autoconfiguration. This memo is intended to clarify the rules on selecting an IPv6 address to use for MLD messages. Introduction The original specification of the Multicast Listener Discovery Protocol[RFC 2710] mandated the use of a link-local IPv6 source address for the transmission of MLD messages. In addition, MLD also requires nodes to send MLD Report messages when joining any IPv6 multicast group (except the All-Nodes address and addresses of scope less than 2). These MLD requirements conflict with the use of IPv6 multicast within the Neighbor Discovery Protocol[RFC 2461]. For stateless autoconfiguration, as defined in [RFC 2462], a node is required to join several IPv6 multicast groups in order to perform Duplicate Address Detection prior to its use. Since the only address the node has is tentative, and cannot be used for communication, it does not have a suitable address to utilize as a source address. This document will clarify the IPv6 source address selection rules for use with MLD. 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]. MLD Source Address Selection Guidelines An MLD speaking node is required to choose a suitable IPv6 source address for all MLD messages (Report, Done, and Query). MLD Query messages MUST be sent with a valid link-local address as the IPv6 source address. If a router receives a query message with an IPv6 source address set to the unspecified address (::), it MUST silently discard the message and SHOULD log a warning. MLD Report and Done messages MUST be sent with a valid link-local address as the IPv6 source address. If a valid link-local address is not available, the message MUST be sent with the unspecified address (::) as the IPv6 source address. Source Address Selection Implications In RFC 2710, MLD Report and Done messages are required to have an IPv6 source address that is link-local. This memo augments that rule by allowing these messages to contain the unspecified address (::) as the source address. The behavior of RFC 2710 implementations, when receiving a message with a source address of ::, is dependent upon how the implementation treats the unspecified address. That is, these messages will be dropped if the implementation does not consider the unspecified address to be link-local in scope. As the unspecified address is only used when there is no link-local address, RFC 2710 implementations discarding these packets will have no affect on the packet's sender as the use should only be for joining the link-local solicited-node multicast group [RFC 2462]. There is an implication to senders with respect to joining other multicast groups prior to the activation of a link-local address. The dropping of Reports using the unspecified address as a source address could cause a lack of multicast traffic that is expected by the node. This black hole will be termporary until the node can send a Report with a valid link-local address. Security Considerations SecurityGeneral security issues related to MLD are discussed in [RFC 2710]. The ability to send MLD messages with the unspecified address can lead to on-link abuse that is harder to trace. However, due to the expected behavior of RFC 2710 implementations to drop these messages and the additional rule that Query messages with the unspecified address be dropped, the impact of such messages will not affect multicast capabilities on the link. References Normative References [RFC 2710] Deering, S., Fenner, W., Haberman, B., "Multicast Listener Discovery (MLD) for IPv6", RFC 2710, October 1999. Informative References [RFC 2461] Narten, T., Nordmark, E., Simpson, W., "Neighbor Discovery for IP Version 6 (IPv6)", RFC 2461, December 1998. [RFC 2462] Thomson, S., Narten, T., "IPv6 Stateless Address Autoconfiguration", RFC 2462, December 1998. [RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. Author's Address Brian Haberman Caspian Networks One Park Drive Suite 400 Research Triangle Park, NC 27709 Phone: +1-919-949-4828 EMail: email@example.com Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. 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