v6ops WG S. Gundavelli Internet-Draft M. Townsley Intended status: Standards Track O. Troan Expires: February 11, 2011 W. Dec Cisco August 10, 2010 Unicast Transmission of IPv6 Multicast Messages on Link-layer draft-gundavelli-v6ops-l2-unicast-02.txt Abstract When transmitting an IPv6 packet to a multicast group, the destination address in the link-layer header is typically set to the corresponding mapped address of the destination address from the IP header. 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 is an opportunity for the sender to transmit the message as an unicast message on the link-layer. Unfortunately, the IPv6 specifications do not clearly state this. This document explicitly clarifies this point and makes such packet construct and transmission legal and valid. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on February 11, 2011. 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 Gundavelli, et al. Expires February 11, 2011 [Page 1] Internet-Draft Unicast Transmission on Link-layer August 2010 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 Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Sending and Receiving IPv6 Multicast Packets . . . . . . . . . 5 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 5. Security Considerations . . . . . . . . . . . . . . . . . . . 7 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 7.1. Normative References . . . . . . . . . . . . . . . . . . . 9 7.2. Informative References . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10 Gundavelli, et al. Expires February 11, 2011 [Page 2] Internet-Draft Unicast Transmission on Link-layer August 2010 1. Introduction This document is about a clarification to the construction and processing rules of IPv6 multicast messages [RFC2464]. When there are multiple link-layer receivers for an IP multicast message on a broadcast LAN, the link layer multicast address corresponding to the IP address is the one to be used. However, if there is only one receiver and its link-layer address is known, as in some cases of sparse mode multicast or certain special cases, it is legal and correct to send the IP multicast to the unicast link-layer address of that system. Senders therefore have that option, and receivers should not refuse the message on that basis. 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. A received multicast message may have been transmitted as a unicast message on the link-layer. The destination address in the link-layer header of that packet will be a unicast address, while the destination address in the IP header can be a multicast address. It is inconsequential for the network layer protocols or the IP stack to go across the layers and check the semantics of message delivery. 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 destination address in the IP header, but with a unicast destination address in the link-layer header. 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. Section 3.0 of this document defines the additional normative considerations for IPv6 sender and receiver nodes for allowing this mode of packet transmission. Gundavelli, et al. Expires February 11, 2011 [Page 3] Internet-Draft Unicast Transmission on Link-layer August 2010 2. Conventions 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 [RFC2119]. Gundavelli, et al. Expires February 11, 2011 [Page 4] Internet-Draft Unicast Transmission on Link-layer August 2010 3. Sending and Receiving IPv6 Multicast Packets The following additional considerations MUST be applied by all IPv6 nodes when sending and receiving IPv6 multicast messages. 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. o An IPv6 sender node in some special cases and specifically when the link-layer address of the target node is known, MAY choose to transmit an IPv6 multicast message as a link-layer unicast message to that node. 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. Gundavelli, et al. Expires February 11, 2011 [Page 5] Internet-Draft Unicast Transmission on Link-layer August 2010 4. IANA Considerations This specification does not require any IANA actions. Gundavelli, et al. Expires February 11, 2011 [Page 6] Internet-Draft Unicast Transmission on Link-layer August 2010 5. Security Considerations This document is about a clarification to the construction and processing rules of IPv6 multicast messages. This clarification makes it legal for an IPv6 sender node to transmit a layer-3 multicast message to the unicast link-layer address of the target node. This change does not introduce any security vulnerabilities. Network firewalls and Deep Packet inspection tools that perform any such improper checks matching the destination address types in IP header and link-layers have to modified to allow such packet transmission. However, the authors of this document could not find a single such implementation that drops IP packets based on this check. Gundavelli, et al. Expires February 11, 2011 [Page 7] Internet-Draft Unicast Transmission on Link-layer August 2010 6. Acknowledgements The authors would like to acknowledge Stig Venaas, Fred Baker, Dave Thaler, Phil Roberts, Mark Smith, Hemant Singh, Wes Beebee, Olaf Bonness, Suresh Krishnan, Behcet Sarikaya, Eric Levy, Pascal Thubert and Eric Voit for all the discussions on this topic. Gundavelli, et al. Expires February 11, 2011 [Page 8] Internet-Draft Unicast Transmission on Link-layer August 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. Gundavelli, et al. Expires February 11, 2011 [Page 9] Internet-Draft Unicast Transmission on Link-layer August 2010 Authors' Addresses Sri Gundavelli Cisco 170 West Tasman Drive San Jose, CA 95134 USA Email: sgundave@cisco.com Mark Townsley Cisco L'Atlantis, 11, Rue Camille Desmoulins ISSY LES MOULINEAUX, ILE DE FRANCE 92782 France 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 February 11, 2011 [Page 10]