6man Working Group S. Krishnan
Internet-Draft Ericsson
Intended status: Standards Track j h. woodyatt
Expires: May 3, 2012 Apple
E. Kline
Google
J. Hoagland
Symantec
M. Bhatia
Alcatel-Lucent
October 31, 2011
An uniform format for IPv6 extension headers
draft-ietf-6man-exthdr-05
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 describes the issues that can arise
when defining new extension headers and discusses the alternative
extension mechanisms in IPv6. It also provides a format for defining
new IPv6 extension headers that would allow implementations to
process past unknown 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 May 3, 2012.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
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 used in this document . . . . . . . . . . . . . . . 3
3. Applicability . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Proposed IPv6 Extension Header format . . . . . . . . . . . . . 5
5. Backward Compatibility . . . . . . . . . . . . . . . . . . . . 5
6. Future work . . . . . . . . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
10. Normative References . . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
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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.
Also, Several existing deployed IPv6 routers and several existing
deployed IPv6 firewalls are capable of parsing past or ignoring all
currently defined IPv6 Extension Headers (e.g. to examine transport-
layer header fields) at wire-speed (e.g. by using custom ASICs for
packet processing). Hence, one must also consider that any new IPv6
Extension Header will break IPv6 deployments that use these existing
capabilities.
Any IPv6 header or option that has hop-by-hop behaviour and is
intended for general use in the public IPv6 Internet could be
subverted to create an attack on IPv6 routers processing packets
containing such a header or option. Reports from the field indicate
that some IP routers deployed within the global Internet are
configured either to ignore the presence of headers with hop-by-hop
behaviour or to drop packets containing headers with hop-by-hop
behaviour.
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
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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.
The base IPv6 standard [RFC2460] defines 3 extension headers (i.e.
Routing Header, Destination Options Header, Hop-by-Hop Options
Header) to be used for any new IPv6 options. The same standard only
allows the creation of new Extension Headers in limited circumstances
[RFC2460] Section 4.6.
As noted above, the use of any option with Hop-by-Hop behaviour can
be problematic in the global public Internet. So new IPv6 Extension
Header(s) having hop-by-hop behaviour MUST NOT be created or
specified. Also, new options for the existing Hop-by-Hop Header
SHOULD NOT be created or specified unless no alternative is feasible.
Any proposal to create a new option for the existing Hop-by-Hop
Header MUST include a detailed explanation of why the hop-by-hop
behaviour is absolutely essential in the Internet-Draft proposing the
new option with hop-by-hop behaviour.
The use of IPv6 Destination Options to encode information provides
more flexible handling characteristics and better backward
compatibility than using a new Extension Header. Because of this,
new optional information to be sent SHOULD be encoded in a new option
for the existing IPv6 Destination Options Header.
Mindful of the need for compatibility with existing IPv6 deployments,
new IPv6 extension headers MUST NOT be created or specified, unless
no existing IPv6 Extension Header can be used by specifying a new
option for that existing IPv6 Extension Header. Any proposal to
create or specify a new IPv6 Extension Header MUST include a detailed
technical explanation of why no existing IPv6 Extension Header can be
used in the Internet-Draft proposing the new IPv6 Extension Header.
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4. Proposed IPv6 Extension Header format
If any IPv6 Extension Headers are defined in future, keeping in mind
the restrictions specified in Section 3 and also the restrictions
specified in [RFC2460], they MUST use the consistent format defined
in Figure 1. This enables future IPv6 implementations to skip over
unknown IPv6 Extension Headers and continue to further process the
IPv6 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, Ran Atkinson and Steven Blake 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
Mori Tower 26F
Roppongi 6-10-1
Minato ku
Tokyo 106-6126
Japan
Phone: +81 3-6384-9635
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/
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Manav Bhatia
Alcatel-Lucent
Bangalore
India
Email: manav.bhatia@alcatel-lucent.com
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