One document matched: draft-gundavelli-v6ops-l2-unicast-00.txt
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.
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This Internet-Draft will expire on August 19, 2010.
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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
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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
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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
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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.
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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].
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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.
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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
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.
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6. Acknowledgements
The authors would like to acknowledge Hemant Singh, Eric Levy, Pascal
Thubert 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
[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.
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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
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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