6man Working Group S. Krishnan
Internet-Draft Ericsson
Intended status: Standards Track j h. woodyatt
Expires: June 20, 2011 Apple
E. Kline
Google
J. Hoagland
Symantec
M. Bhatia
Alcatel-Lucent
December 17, 2010
An uniform format for IPv6 extension headers
draft-ietf-6man-exthdr-01
Abstract
In IPv6, optional internet-layer information is encoded in separate
headers that may be placed between the IPv6 header and the transport
layer header. There are a small number of such extension headers
currently defined. This document defines a format for defining a new
family of IPv6 extension headers.
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 June 20, 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
Provisions Relating to IETF Documents
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(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions used in this document . . . . . . . . . . . . . 3
2. Generic IPv6 Extension Header (GIEH) format . . . . . . . . . . 4
3. Backward Compatibility . . . . . . . . . . . . . . . . . . . . 6
4. Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Future work . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
9. Normative References . . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
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1. Introduction
The base IPv6 standard [RFC2460] defines extension headers as an
expansion mechanism to carry optional internet layer information.
Extension headers, with the exception of the hop-by-hop options
header, are not usually processed on intermediate nodes. However,
some intermediate nodes such as firewalls, may need to look at the
transport layer header fields in order to make a decision to allow or
deny the packet. If new extension headers are defined and the
intermediate node is not aware of them, the intermediate node cannot
proceed further in the header chain since it does not know where the
unknown header ends and the next header begins. The main issue is
that the extension header format is not standardized and hence it is
not possible to skip past the unknown header. This document defines
a standard format for a new family of IPv6 extension headers.
1.1. Conventions used in this document
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 [RFC2119].
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2. Generic IPv6 Extension Header (GIEH) format
This document proposes a new family of IPv6 extension headers that
will be encoded in a consistent format so that it is possible for
intermediate nodes to skip over unknown extension headers and
continue to further process the header chain if they so desire. The
intention of the base IPv6 Specification [RFC2460] that destination
hosts not be permitted to skip unknown extension headers continues to
apply. One key advantage of using such a generic IPv6 extension
header is that it allows nodes to distinguish between unknown
extension headers and unknown upper layer protocols, which was not
possible earlier. Another one is that this generic extension header
conserves values in the IPv4 protocol numbers registry.
This documents requires the allocation of a single IP protocol number
for the Generic IPv6 extension header (GIEH), say TBA1.
Specifications of new extension headers SHOULD use this generic
extension header format whenever feasible. The generic extension
header will be identified by the value TBA1 occuring in the Next
Header field of the preceding extension header. The second octet
contains the length of the extension header. The third octet of the
GIEH contains a specific extension header type (that identifies the
actual extension header). All other data in the GIEH is type-
specific.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | Specific Type | Hdr Options |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Header Specific Data .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Next Header 8-bit selector. Identifies the type of header
immediately following this Extension header.
Uses the same values as the IPv4 Protocol
field.
Hdr Ext Len 8-bit unsigned integer. Length of the
Extension header in 8-octet units, not
including the first 8 octets.
Specific Type 8-bit unsigned integer. The actual IPv6
extension header type. This will be allocated
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from a new IANA registry.
Hdr Options 8-bit selector. The two most significant bits
specify the action that must be taken if the
processing IPv6 node does not recognize the
extension header:
00 - skip over this option and continue
processing the header.
01 - discard the packet.
10 - discard the packet and, regardless of
whether or not the packet's Destination
Address was a multicast address, send
an ICMP Parameter Problem, Code 1, message
to the packet's Source Address, pointing to
the unrecognized value within the original
packet.
11 - discard the packet and, only if the packet's
Destination Address was not a multicast
address, send an ICMP parameter Problem,
Code 1, message to the packet's Source
Address, pointing to the unrecognized value
within the original packet.
The other 6 bits in this field are reserved. They
MUST be set to zero on transmission and SHOULD be
ignored on reception.
Header Specific Variable length. Fields specific to the
Data extension header. This field MUST be padded
as required in order to ensure that the
complete GIEH is a multiple of 8 octets long.
Figure 1: Generic IPv6 Extension Header (GIEH) layout
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3. Backward Compatibility
The scheme proposed in this document is not backward compatible with
all the currently defined IPv6 extension headers. It only applies to
newly defined extension headers. Specifically, the following
extension headers predate this document and do not follow the format
proposed in this document.
o IPv6 Hop-by-Hop Options Header
o IPv6 Routing Header
o IPv6 Fragment Header
o IPv6 Destination Options Header
4. Exceptions
The the Generic IPv6 extension header is generic enough that it is
suitable to use for most applications. However, it is possible that
the GIEH does not satisfy the requirements in all cases where new
extension headers are required. Hence, the existence of this generic
header does not necessarily preclude the definition of new
independent IPv6 extension headers.
5. Future work
This document proposes one step in easing the inspection of extension
headers by middleboxes. There is further work required in this area.
Some issues that are left unresolved beyond this document include
o There can be an arbitrary number of extension headers.
o Extension headers must be processed in the order they appear.
o Extension headers may alter the processing of the payload itself,
and hence the packet may not be processed properly without
knowledge of said header.
6. IANA Considerations
This document requests a single allocation from the IANA for this
generic IPv6 extension header type (TBA1) from the Assigned Internet
Protocol Numbers registry located at
http://www.iana.org/assignments/protocol-numbers.
This document also requests the creation of a new registry for GIEH
sub-types. The allocation policy for these subtypes is Standards
Action.
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7. Security Considerations
This document proposes a standard format for the IPv6 extension
headers so that intermediate nodes that do not understand the
contents of these headers can look past them. Intermediate nodes,
such as firewalls, skipping over unknown headers might end up
allowing the setup of a covert channel from the outside of the
firewall to the inside using the data field(s) of the unknown
extension headers.
8. Acknowledgements
The authors would like to thank Albert Manfredi, Bob Hinden, Brian
Carpenter, Erik Nordmark, Hemant Singh, Lars Westberg, Markku Savela,
Tatuya Jinmei, Thomas Narten, Vishwas Manral, Alfred Hoenes, Joel
Halpern and Ran Atkinson for their reviews and suggestions that made
this document better.
9. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
Authors' Addresses
Suresh Krishnan
Ericsson
8400 Decarie Blvd.
Town of Mount Royal, QC
Canada
Phone: +1 514 345 7900 x42871
Email: suresh.krishnan@ericsson.com
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james woodyatt
Apple Inc.
1 Infinite Loop
Cupertino, CA 95014
US
Email: jhw@apple.com
Erik Kline
Google
604 Arizona Avenue
Santa Monica, CA 90401
US
Phone: +1 310 460 4080
Email: ek@google.com
James Hoagland
Symantec Corporation
350 Ellis St.
Mountain View, CA 94043
US
Email: Jim_Hoagland@symantec.com
URI: http://symantec.com/
Manav Bhatia
Alcatel-Lucent
Bangalore
India
Email: manav.bhatia@alcatel-lucent.com
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