6man Working Group S. Krishnan
Internet-Draft J. Halpern
Intended status: Standards Track Ericsson
Expires: April 21, 2011 October 18, 2010
Reserving bits in the IPv6 header for future use
draft-krishnan-6man-header-reserved-bits-00
Abstract
The IPv6 header does not contain any reserved bits for future
expansion. This document sets aside 4 bits from the flow label field
for future expansion.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
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This Internet-Draft will expire on April 21, 2011.
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions used in this document . . . . . . . . . . . . . . . 3
3. New IPv6 header format . . . . . . . . . . . . . . . . . . . . 3
4. Future use of the reserved bits . . . . . . . . . . . . . . . . 4
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
8. Normative References . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 5
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1. Introduction
The IPv6 header does not contain any reserved bits and all bits in
the header are currently accounted for. This means that it is not
possible to develop any future extension mechanisms that require bits
in the IPv6 header. Mechanisms such as ECN were possible in IPv4
because there were bits available in the IPv4 header. e.g. Re-ECN is
a proof of concept mechanism for ConEx that uses an unused bit (Bit
48) in the IPv4 header. It cannot be implemented analogously in the
IPv6 header. This document proposes reducing the size of the flow
label field from 20 bits to 16 bits and setting aside 4 bits for
future use.
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. New IPv6 header format
This document updates Section 3 of [RFC2460] to reduce the length of
the flow label field from 20 bits to 16 bits, and in the process
creating a 4 bit reserved field. All other fields in the IPv6 header
remain unchanged from [RFC2460].
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| Traffic Class | Resvd | Flow Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload Length | Next Header | Hop Limit |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Source Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Destination Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Resvd 4-bit reserved field.
Flow Label 16-bit flow label.
All other fields are same as those defined by [RFC2460]
Figure 1: Modified IPv6 header format
Senders MUST set the bits in the reserved field to zero and receivers
MUST ignore them.
4. Future use of the reserved bits
New mechanisms that require allocation of one or more of the reserved
bits MUST require Standards Action as specified in [RFC5226].
5. Acknowledgements
The authors would like to Pekka Savola, Christian Huitema, and
Ingemar Johansson for the discussions that led to this document.
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6. Security Considerations
This document does not bring up any new security issues.
7. IANA Considerations
This document does not require any IANA action.
8. 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.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
Authors' Addresses
Suresh Krishnan
Ericsson
8400 Blvd Decarie
Town of Mount Royal, Quebec
Canada
Email: suresh.krishnan@ericsson.com
Joel Halpern
Ericsson
Email: joel.halpern@ericsson.com
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