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Haberman 3 draft-ietf-magma-mld-source-03.txt Caspian Networks 4 Expires April 2003 October 2002 6 Source Address Selection for Multicast 7 Listener Discovery Protocol (RFC 2710) 9 Status of this Memo 11 This document is an Internet-Draft and is in full conformance with 12 all provisions of Section 10 of RFC2026. 14 Internet-Drafts are working documents of the Internet Engineering 15 Task Force (IETF), its areas, and its working groups. Note that other 16 groups may also distribute working documents as Internet- Drafts. 17 Internet-Drafts are draft documents valid for a maximum of six months 18 and may be updated, replaced, or obsoleted by other documents at any 19 time. It is inappropriate to use Internet- Drafts as reference 20 material or to cite them other than as "work in progress." 22 The list of current Internet-Drafts can be accessed at 23 http://www.ietf.org/ietf/1id-abstracts.txt. 25 The list of Internet-Draft Shadow Directories can be accessed at 26 http://www.ietf.org/shadow.html. 28 Abstract 30 It has come to light that there is an issue with the selection of a 31 suitable IPv6 source address for Multicast Listener Discovery 32 messages when a node is performing stateless address 33 autoconfiguration. This memo is intended to clarify the rules on 34 selecting an IPv6 address to use for MLD messages. 36 Introduction 38 The original specification of the Multicast Listener Discovery 39 Protocol[RFC 2710] mandated the use of a link-local IPv6 source 40 address for the transmission of MLD messages. In addition, MLD also 41 requires nodes to send MLD Report messages when joining any IPv6 42 multicast group (except the All-Nodes address and addresses of scope 43 less than 2). 45 These MLD requirements conflict with the use of IPv6 multicast within 46 the Neighbor Discovery Protocol[RFC 2461]. For stateless 47 autoconfiguration, as defined in [RFC 2462], a node is required to 48 join several IPv6 multicast groups in order to perform Duplicate 49 Address Detection prior to its use. Since the only address the node 50 has is tentative, and cannot be used for communication, it does not 51 have a suitable address to utilize as a source address. 53 This document will clarify the IPv6 source address selection rules 54 for use with MLD. 56 Terminology 58 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 59 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 60 document are to be interpreted as described in [RFC 2119]. 62 MLD Source Address Selection Guidelines 64 An MLD speaking node is required to choose a suitable IPv6 source 65 address for all MLD messages (Report, Done, and Query). 67 MLD Query messages MUST be sent with a valid link-local address as 68 the IPv6 source address. If a router receives a query message with 69 an IPv6 source address set to the unspecified address (::), it MUST 70 silently discard the message and SHOULD log a warning. 72 MLD Report and Done messages MUST be sent with a valid link-local 73 address as the IPv6 source address. If a valid link-local address is 74 not available, the message MUST be sent with the unspecified address 75 (::) as the IPv6 source address. 77 Source Address Selection Implications 79 In RFC 2710, MLD Report and Done messages are required to have an 80 IPv6 source address that is link-local. This memo augments that rule 81 by allowing these messages to contain the unspecified address (::) as 82 the source address. 84 The behavior of RFC 2710 implementations, when receiving a message 85 with a source address of ::, is dependent upon how the implementation 86 treats the unspecified address. That is, these messages will be 87 dropped if the implementation does not consider the unspecified 88 address to be link-local in scope. 90 As the unspecified address is only used when there is no link-local 91 address, RFC 2710 implementations discarding these packets will have 92 no affect on the packet's sender as the use should only be for 93 joining the link-local solicited-node multicast group [RFC 2462]. 95 There is an implication to senders with respect to joining other 96 multicast groups prior to the activation of a link-local address. 97 The dropping of Reports using the unspecified address as a source 98 address could cause a lack of multicast traffic that is expected by 99 the node. This black hole will be termporary until the node can send 100 a Report with a valid link-local address. 102 Security Considerations 104 General security issues related to MLD are discussed in [RFC 2710]. 106 The ability to send MLD messages with the unspecified address can 107 lead to on-link abuse that is harder to trace. However, due to the 108 expected behavior of RFC 2710 implementations to drop these messages 109 and the additional rule that Query messages with the unspecified 110 address be dropped, the impact of such messages will not affect 111 multicast capabilities on the link. 113 References 115 Normative References 117 [RFC 2710] Deering, S., Fenner, W., Haberman, B., "Multicast 118 Listener Discovery (MLD) for IPv6", RFC 2710, October 119 1999. 121 Informative References 123 [RFC 2461] Narten, T., Nordmark, E., Simpson, W., "Neighbor 124 Discovery for IP Version 6 (IPv6)", RFC 2461, December 125 1998. 127 [RFC 2462] Thomson, S., Narten, T., "IPv6 Stateless Address 128 Autoconfiguration", RFC 2462, December 1998. 130 [RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate 131 Requirement Levels", BCP 14, RFC 2119, March 1997. 133 Author's Address 135 Brian Haberman 136 Caspian Networks 137 One Park Drive 138 Suite 400 139 Research Triangle Park, NC 27709 140 Phone: +1-919-949-4828 141 EMail: bkhabs@nc.rr.com 143 Full Copyright Statement 144 Copyright (C) The Internet Society (2002). All Rights Reserved. 146 This document and translations of it may be copied and furnished to 147 others, and derivative works that comment on or otherwise explain it 148 or assist in its implementation may be prepared, copied, published 149 and distributed, in whole or in part, without restriction of any 150 kind, provided that the above copyright notice and this paragraph are 151 included on all such copies and derivative works. However, this 152 document itself may not be modified in any way, such as by removing 153 the copyright notice ore references to the Internet Society or other 154 Internet organizations, except as needed for the purpose of 155 developing Internet standards in which case the procedures for 156 copyrights defined in the Internet Standards process must be 157 followed, or as required to translate it into languages other than 158 English. 160 The limited permissions granted above are perpetual and will not be 161 revoked by the Internet Society or its successors or assigns. 163 This document and the information contained herein is provided on an 164 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 165 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 166 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION 167 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF 168 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.