Network Working Group M. Bagnulo
Request for Comments: 4581 UC3M
Updates: 3972 J. Arkko
Category: Standards Track Ericsson
October 2006 Cryptographically Generated Addresses (CGA) Extension Field Format
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright (C) The Internet Society (2006).
This document defines a Type-Length-Value format for
Cryptographically Generated Address (CGA) Extensions. This document
updates RFC 3972.
Table of Contents
1. Introduction ....................................................22. CGA Extension Field Format ......................................23. IANA Considerations .............................................24. Security Considerations .........................................35. Acknowledgements ................................................36. Normative References ............................................3
The Cryptographically Generated Address (CGA) specification 
defines Extension Fields that allow additional information to be
included in the CGA Parameter Data Structure. So far there seems to
be enough interest in including additional data items into the CGA
Parameter Data Structure through these Extension Fields that it seems
reasonable to expect that more than one mechanism will require its
usage. In order to simplify the addition of multiple data items,
this document updates RFC 3972 , and it defines a Type-Length-
Value format for the Extension Fields.
2. CGA Extension Field Format
Data items to be included in Extension Fields of the CGA Parameter
Data Structure MUST be encoded using the following Type-Length-Value
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
| Extension Type | Extension Data Length |
~ Extension Data ~
Extension Type: 16-bit identifier of the type of the Extension Field.
Extension Data Length: 16-bit unsigned integer. Length of the
Extension Data field of this option, in octets.
Extension Data: Variable-length field. Extension-Type-specific data.
3. IANA Considerations
The IANA has created and will maintain a registry entitled, "CGA
Extension Type". The values in this name space are 16-bit unsigned
integers. Initial values for the CGA Extension Type field are given
below; future assignments are to be made through Standards Action
. Assignments consist of a name and the value.
As recommended in , this document makes the following assignments
for experimental and testing use: the value 0xFFFD, with name
Exp_FFFD; the value 0xFFFE, with name Exp_FFFE, and the value 0xFFFF,
with name Exp_FFFF.
4. Security Considerations
No security concerns are raised by the adoption of the CGA Extension
format described in this document. However, proper security analysis
is required when new CGA Extensions are defined in order to make sure
that they introduce no new vulnerabilities to the existing CGA
Comments to this document were provided by Sam Hartman, Allison
Mankin, Pekka Savola, Thomas Narten, Tuomas Aura, Stefan Rommer,
Julien Laganier, and James Kempf.
6. Normative References
 Aura, T., "Cryptographically Generated Addresses (CGA)", RFC
3972, March 2005.
 Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.
 Narten, T., "Assigning Experimental and Testing Numbers
Considered Useful", BCP 82, RFC 3692, January 2004.
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