v6ops WG S. Gundavelli
Internet-Draft M. Townsley
Updates: 2464 (if approved) O. Troan
Intended status: Standards Track W. Dec
Expires: February 27, 2011 Cisco
August 26, 2010
Unicast Transmission of IPv6 Multicast Messages on Link-layer
draft-gundavelli-v6ops-l2-unicast-04.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 27, 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
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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
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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
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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 it is legal 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. (Example: as in some cases of sparse mode
multicast, or in other intended use-cases such as for supporting
shared links in Proxy Mobile IPv6 [RFC5213], or as proposed in
[I-D.costa-6man-dad-proxy-00], in which a Duplicate Address Detection
Proxy sends layer-2 unicast messages when appropriate to limit VLAN
flooding).
The function of the link-layer is purely for transmitting the frame
to a node or to a set of nodes on a given link. 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, the authors of this document have
verified many open source and commercial IPv6 implementations on the
behavior of the existing IPv6 stacks, firewalls and they 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
of this document defines the additional normative considerations for
IPv6 nodes to allow this mode of packet transmission.
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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].
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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 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.
o An IPv6 receiver node SHOULD NOT drop a received IPv6 multicast
message only for the one specific reason that the received IPv6
message has a multicast destination address in the IPv6 header
while the link-layer header has a unicast address. Such a
validity check comparing the address types in the IP header and
the link-layer header is considered a layer violation.
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4. IANA Considerations
This specification does not require any IANA actions.
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5. Security Considerations
This document is about a clarification to the construction and
processing rules of IPv6 multicast messages. This clarification
explicitly permits an IPv6 node to send an IPv6 multicast message to
the unicast link-layer address of the target node. This change does
not introduce any new security vulnerabilities.
Network firewalls and Deep Packet inspection tools that perform any
such checks, matching the destination address types in the IPv6
header and the link-layers have to modified to allow such packet
transmission. However, the authors of this document could not find a
single existing implementation that performs this check.
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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,
Alain Durand, Jean-Michel Combes, Ron Bonica and Eric Voit for all
the discussions on this topic.
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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
[I-D.costa-6man-dad-proxy-00]
Costa, F., Combes, J-M., Pougnard, X., and H. Li,
"Duplicate Address Detection Proxy",
draft-costa-6man-dad-proxy (work in progress).
[RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet
Networks", RFC 2464, December 1998.
[RFC5213] Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,
and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008.
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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
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