6man Working Group S. Krishnan
Internet-Draft Ericsson
Intended status: Standards Track j h. woodyatt
Expires: September 15, 2011 Apple
E. Kline
Google
J. Hoagland
Symantec
M. Bhatia
Alcatel-Lucent
March 14, 2011
An uniform format for IPv6 extension headers
draft-ietf-6man-exthdr-02
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 new
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 September 15, 2011.
Copyright Notice
Copyright (c) 2011 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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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions used in this document . . . . . . . . . . . . . . . 3
3. Applicability . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Proposed IPv6 Extension Header format . . . . . . . . . . . . . 4
5. Backward Compatibility . . . . . . . . . . . . . . . . . . . . 4
6. Future work . . . . . . . . . . . . . . . . . . . . . . . . . . 4
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
8. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
10. Normative References . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 5
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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 intends
to define a standard format for IPv6 extension headers.
2. 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].
3. Applicability
The base IPv6 standard [RFC2460] allows the use of both extension
headers and destination options in order to encode optional
destination information in an IPv6 packet. The use of destination
options to encode this information, provides more flexible handling
characteristics and better backward compatibility than using
extension headers. Because of this, implementations SHOULD use
destination options as the preferred mechanism for encoding optional
destination information, and use a new extension header only if
destination options do not satisfy their needs. The request for
creation of a new IPv6 extension header MUST be accompanied by an
specific explanation of why destination options could not be used to
convey this information.
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4. Proposed IPv6 Extension Header format
This document proposes that all IPv6 extension headers be encoded in
a consistent TLV format so that it is possible for nodes to skip over
unknown extension headers and continue to further process the header
chain.
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 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
. .
. Header Specific Data .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Next Header 8-bit selector. Identifies the type of header
immediately following the 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.
Header Specific Variable length. Fields specific to the
Data extension header
Figure 1: Extension header layout
5. Backward Compatibility
The scheme proposed in this document is not intended to be backward
compatible with all the currently defined IPv6 extension headers. It
applies only to newly defined extension headers. Specifically, the
fragment header predates this document and does not follow the format
proposed in this document.
6. 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
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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.
7. IANA Considerations
This document does not require any IANA actions.
8. 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.
9. 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.
10. 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.
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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
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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