Network Working Group C. Perkins
Request for Comments: 4636 Nokia Research Center
Category: Standards Track October 2006
Foreign Agent Error Extension for Mobile IPv4
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 specifies a new extension for use by Foreign Agents
operating Mobile IP for IPv4. Currently, a foreign agent cannot
supply status information without destroying the ability for a mobile
node to verify authentication data supplied by the home agent. The
new extension solves this problem by making a better place for the
foreign agent to provide its status information to the mobile node.
Perkins Standards Track [Page 1]RFC 4636 FA Error Extension October 20061. Introduction
This document specifies a new non-skippable extension for use by
Foreign Agents operating Mobile IP for IPv4 . The new extension
option allows a foreign agent to supply an error code without
disturbing the data supplied by the Home Agent within the
Registration Reply message. In this way, the mobile node can verify
that the Registration Reply message was generated by the Home Agent
even in cases where the foreign agent is required by protocol to
insert new status information into the Registration Reply message.
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 . Other
terminology is used as already defined in .
3. FA Error Extension Format
The format of the FA Error Extension conforms to the Short Extension
format specified for Mobile IPv4 . The FA Error Extension is not
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
| Type | Length | Sub-Type | Status |
A status code used by the foreign agent to supply status
information to the mobile node.
Perkins Standards Track [Page 2]RFC 4636 FA Error Extension October 20064. Operation and Use of the FA Error Extension
The FA Error Extension is only valid for use within Mobile IPv4
Registration Reply messages. The FA Error Extension is not
skippable. A mobile node that cannot correctly interpret the
contents of the FA Error Extension MUST NOT use the care-of address
provided in the Registration Reply message, until another
Registration Request message has been sent and a successful
Registration Reply message received.
Status codes allowable for use within the FA Error Extension are
within the range 64-127. The currently specified codes are as
64 reason unspecified
65 administratively prohibited
66 insufficient resources
68 home agent failed authentication
71 poorly formed Reply
77 invalid care-of address
78 registration timeout
as defined in RFC 3344  for use by the Foreign Agent. Status
codes for use with the FA Error extensions must not be differently
defined for use in the Code field of Registration Reply messages.
When a foreign agent appends a FA Error Extension to the Registration
Reply as received from the Home Agent, it has to update the UDP
Length field in the UDP header  to account for the extra 4 bytes
This document updates the Mobile IP base specification  regarding
the procedures followed by the foreign agent in the case that the
home agent fails authentication. Instead of modifying the "status"
field of the Registration Reply to contain the value 68, now the