Subject: [mobile-ip] Issue with 3012

From: Marcello Lioy <[email-masked]>
Date: Thu, 09 Aug 2001 16:35:26 +0100

There is some vague language in 3012 relating to when new challenges can be 
sent and when they should be used by the FA.  Section 3.2. (Foreign Agent 
Processing for Registration Requests) states

     The Foreign Agent MUST NOT accept any Challenge in the Registration
     Request unless it was offered in last successful Registration Reply
     issued to the Mobile Node, or else advertised as one of the last
     CHALLENGE_WINDOW (see section 9) Challenge values inserted into the
     immediately preceding Agent advertisements.

This explicitly states that the FA is NOT supposed to use challenges which 
are sent to mobiles in RRP failures.  However, in Section 3.3. (Foreign 
Agent Processing for Registration Replies) it also states the following:

     The Foreign Agent MAY include a new Challenge extension in any
     Registration Reply, successful or not.

which seems to imply that the mobile could use this challenge to 
authenticate itself.

This has already caused interop problems with the mobile following the 
section 3.2 (i.e. ignoring the challenge in and RRP failure) and the FA 
following 3.3 (expecting the mobile to use a challenge in a failure).

It would be good if this could be clarified to avoid problems in future.
--------------------
Marcello (in London)