Subject: [MOBILE-IP] Challenge/Response

From: Fredrik Johansson <[email-masked]>
Date: Mon, 18 Dec 2000 10:08:52 +0100

Hi,

I have a couple of questions regarding the Challenge/Response RFC.

1) There seems to be some inconsistency in different sections of the RFC,
see below for each section.
    and by the way what's the meaning of sending a new Challenge extension
in a non successful registration reply if it can not be accepted by the
foreign agent?

Section 3.1
"A successful Registration Reply from the Foreign Agent MAY include
   a new Challenge value (see section 3.3).  The Mobile Node MAY use
   either the value found in the latest Advertisement, or the one found
   in the last Registration Reply from the Foreign Agent.  This approach
   enables the Mobile Node to make use of the challenge without having
   to wait for advertisements."

Section 3.2
"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."

Section 3.3
"The Foreign Agent MAY include a new Challenge extension in any
   Registration Reply, successful or not."

2) Say that a foreign agent allow for a Challenge window of 3, i.e. it will
allow registrations to pass which contain one of the last three challenges
that were sent out from the foreign agent. That means that the foreign agent
need to save the last three challenges it sent on that interface. It also
need to store the challenge it receives in registration request in order to
prevent a mobile to use the same challenge twice. This means at least
one/mobile that tries to register. If the foreign agent also chose to send a
Challenge in the registration reply to a mobile, it has to store one extra
Challenge / mobile it sends a reg reply to. Is it reasonable that a foreign
agent should store and process that many challenges?

/Fredrik
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Fredrik Johansson                    W: +46 (0)8 725 5916
Interactive People Unplugged     M: +46 (0)709 684 376
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