Subject: RE: [Mip4] MIP RRQ Doubt

From: "Arunkumar Sivaraman" <[email-masked]>
Date: Fri, 20 Apr 2007 12:52:01 +0530

Reply inline. 

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of
Bjorn Andersson
Sent: Friday, April 20, 2007 12:43 PM
To: Arunkumar Sivaraman
Cc: [email-masked]
Subject: Re: [Mip4] MIP RRQ Doubt

On 4/20/07, Arunkumar Sivaraman <[email-masked]> wrote:
>    I have a doubt on how a HA will behave, under the following
scenario:
>
> a.       MN sends MIP RRQ, requesting dynamic home address, through FA
-
> which forwards it after auth, to HA.
>
> b.       HA, authenticates user, and replies back with RRP with home
> address.
>
> c.       MN generates one more RRQ as in step #a before RRP from step
#b
> arrives.
>
> Assume, this 3 steps keep happening repeatedly. How does the HA react
to
> this?
>
> 1.       It keeps giving the same home address back to the MN.

Since the MN has to include it's NAI in this scenario I would
implement the HA to always return the same IP address for the same NAI
once it has been allocated for it. The HA could even keep it allocated
for some configurable time after the registration has expired so that
the MN even gets the same address, after expiration, if it registers
again within that time.  There is probably no benefit in allocating a
new address from the home network pool, and as you indicate, this
would probably just generate problems.

[Arun]: HA returning the same IP addr for the same NAI, will this be
because of a policy or the general behavior of the HA? 

So, is it also likely that a HA - not implemented on the lines stated
above, can potentially end up assigning a new IP address, to a (rogue)
MN repeatedly. 

Also, is there a reference in handling such scenario in the base rfc
(3344) or in any updates.

> Or
>
> 2.       It gives a new IP address, from probably a local ip address
pool,
> each time a RRQ comes with HoA=0, and thereby, probably, updating its
> binding list for the MN.

  Bjorn

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---

From: "Bjorn Andersson" <[email-masked]>
Date: Fri, 20 Apr 2007 10:41:00 +0300

On 4/20/07, Arunkumar Sivaraman <[email-masked]> wrote:
> HA returning the same IP addr for the same NAI, will this be

Because of policy. I don't believe the RFCs take any stance on this
issue. Both behaviours will work, the other way is just not as
efficient. Well, on second thought, there can actually be a more
serious problem with allocating a new address in case the second reply
gets lost. Then the HA will be bound to the second address and the MN
will use the first, preventing any data to go through:

1. MN sends RRQ1
2. HA receives RRQ1, allocates addr1 and sends RRP1
3. MN sends RRQ2
4. RRP1(addr1) arrives at MN
5. HA receives RRQ2 removes binding to addr1, allocates addr2 and sends RRP2
6. RRP2(addr2) gets lost

This is actually just a problem if nonces are used in the
identification field. According to the RFC nonces are allowed to be
resent unchanged for retransmissions. Timestamps must change for each
retransmission.

> above, can potentially end up assigning a new IP address, to a (rogue)

Yes, as long as the RRQ is authenticated. But then you know who is
causing the problems and can take actions as an
administrator/operator.

> (3344) or in any updates.

Out of my head, I don't think so. Maybe there should be?

  Bjorn