v6ops WG S. Gundavelli Internet-Draft M. Townsley Intended status: Standards Track O. Troan Expires: August 19, 2010 W. Dec Cisco February 15, 2010 Unicast Transmission of IPv6 Multicast Messages on Link-layer draft-gundavelli-v6ops-l2-unicast-00.txt Abstract When transmitting an IPv6 packet to a multicast group address, the destination address in the link-layer header is typically set to the corresponding mapped address of that multicast group address. However, it is not mandatory that the destination address in the link-layer header is always a mapped multicast equivalent of its IP destination address. There are various deployment scenarios where there a need to transmit an IPv6 multicast message as an unicast message on the link-layer. Unfortunately, the IPv6 specifications do not clearly state this. This document explicitly clarifies this aspect and makes such packet construct and transmission legal and valid. Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. 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 Internet-Draft will expire on August 19, 2010. Gundavelli, et al. Expires August 19, 2010 [Page 1] Internet-Draft Unicast Transmission on Link-layer February 2010 Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 5 3. Sending and Receiving IPv6 Multicast Packets . . . . . . . . . 6 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 5. Security Considerations . . . . . . . . . . . . . . . . . . . 8 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 7.1. Normative References . . . . . . . . . . . . . . . . . . . 10 7.2. Informative References . . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11 Gundavelli, et al. Expires August 19, 2010 [Page 2] Internet-Draft Unicast Transmission on Link-layer February 2010 1. Introduction When transmitting an IPv6 packet to a multicast group address, the destination address in the link-layer header is typically set to the corresponding mapped address of that multicast group address. However, it is not mandatory that the destination address in the link-layer header is always a mapped multicast equivalent of its IP destination address. There are various deployment scenarios where there a need to transmit an IPv6 multicast message as an unicast message on the link-layer. Such a message construct is valid and is used in various protocols, such as in ISATAP [RFC5214] for sending a unicast Router Advertisement message on ISTAP interfaces. Evidentially, some of the IPv6 specifications, such as [RFC4861], or [RFC2464] do not make any assumption on such tight relationship and it does require the receiving IPv6 node to explicitly apply any such checks across protocol layers. However, it is ambiguous from the protocol specification perspective, on the legality of such transmission and any discussions on this subject always resulted in differing opinions. Therefore, it is the intent of this document to make the specification clear on this aspect. There are many deployment scenarios where there is a need to transmit IPv6 multicast Neighbor Discovery packets as unicast packets on the link-layer. For example, an 802.11 wireless access point may be hosting multiple IPv6 subnets and it would need the ability to selectively advertise hosted IPv6 prefixes on a per-node basis. Such segregation can only be possible by ensuring the Router Advertisements received by any IPv6 node includes only those prefixes that are associated with their respective layer-3 subnet. This essentially requires the ability to transmit multicast messages as unicast messages on the link-layer. The function of the link-layer is purely for transmitting the frame to a peer or to a set of peers on a given media. It is inconsequential for the network layer protocols to go across the layers and check the semantics of message delivery in the link-layer header. Any such check is a violation of the principles of protocol layering and does not serve any purpose. Unfortunately, [RFC4861] or [RFC2464] does not explicitly state this. However, we have verified this on many open source and commercial IPv6 implementations on the behavior of the existing IPv6 stacks, firewalls and we could not find any implementation that drops IPv6 packets sent to a multicast IPv6 destination address, but with a unicast destination address in the link-layer header. Case and Point: o Cisco IOS Operating System Gundavelli, et al. Expires August 19, 2010 [Page 3] Internet-Draft Unicast Transmission on Link-layer February 2010 o Linux Operating System with 2.6 Kernel o BSD Variants based on IPv6 KAME implementation o Microsoft Windows Vista As a result of this analysis, it appears to be quite safe to explicitly state that such message construct is valid, so future implementations do not drop packets based on these checks. This document updates [RFC4861] for allowing this change. Gundavelli, et al. Expires August 19, 2010 [Page 4] Internet-Draft Unicast Transmission on Link-layer February 2010 2. Requirements Language In this document, the key words "MAY", "MUST, "MUST NOT", "OPTIONAL", "RECOMMENDED", "SHOULD", and "SHOULD NOT", are to be interpreted as described in [RFC2119]. Gundavelli, et al. Expires August 19, 2010 [Page 5] Internet-Draft Unicast Transmission on Link-layer February 2010 3. Sending and Receiving IPv6 Multicast Packets The following considerations MUST be applied by all IPv6 nodes when sending and receiving IPv6 multicast messages. o An IPv6 node MAY choose to unicast an IPv6 multicast message on the link-layer. In this case, the destination address in the IPv6 header will be a multicast group address, but the destination address in the link-layer header will be an unicast address. It is up to to the system architecture as when to transmit a IPv6 multicast message as an link-layer unicast message, as long as there is no real impact to the multicast communication. o An IPv6 receiver node SHOULD NOT drop a received IPv6 multicast message containing a multicast destination address in the IPv6 header, but with a unicast destination address in the link-layer header, withstanding all other validity considerations as specified in the relevant IPv6 standards specifications. Gundavelli, et al. Expires August 19, 2010 [Page 6] Internet-Draft Unicast Transmission on Link-layer February 2010 4. IANA Considerations This specification does not require any IANA actions. Gundavelli, et al. Expires August 19, 2010 [Page 7] Internet-Draft Unicast Transmission on Link-layer February 2010 5. Security Considerations This document is about a clarification to the construction and processing rules of IPv6 multicast messages. This clarification makes it valid for an IPv6 receiver node to consider a received IPv6 multicast message with a multicast destination address in the IPv6 header, but containing an unicast destination address in the link- layer header, to be valid withstanding all other validity considerations specified in the IPv6 standards specifications. This change follows the principles of protocol layer design more tightly and does not introduce any security vulnerabilities. Network firewalls and Deep Packet inspection tools that perform validity checks on link-layer and IP layer headers may have to modified to allow such packet transmission. However, the authors of this document could not find a single such implementation that rejects packets based on this check. Gundavelli, et al. Expires August 19, 2010 [Page 8] Internet-Draft Unicast Transmission on Link-layer February 2010 6. Acknowledgements The authors would like to acknowledge Hemant Singh, Eric Levy, Pascal Thubert and Eric Voit for all the discussions on this topic. Gundavelli, et al. Expires August 19, 2010 [Page 9] Internet-Draft Unicast Transmission on Link-layer February 2010 7. References 7.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, September 2007. 7.2. Informative References [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet Networks", RFC 2464, December 1998. [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, March 2008. Gundavelli, et al. Expires August 19, 2010 [Page 10] Internet-Draft Unicast Transmission on Link-layer February 2010 Authors' Addresses Sri Gundavelli Cisco 170 West Tasman Drive San Jose, CA 95134 USA Email: sgundave@cisco.com Mark Townsley Cisco Email: townsley@cisco.com Ole Troan Cisco Skoyen Atrium, Drammensveien 145A Oslo, N-0277 Norway Email: otroan@cisco.com Wojciech Dec Cisco Haarlerbergweg 13-19 Amsterdam, Noord-Holland 1101 CH Netherlands Email: wdec@cisco.com Gundavelli, et al. Expires August 19, 2010 [Page 11]