Subject: RE: [Mip4] Current state of 3012bis solicited agent advertisement issue.

From: "Jayshree Bharatia" <[email-masked]>
Date: Wed, 20 Aug 2003 12:01:13 -0500

Hi Henrik,

Please see my response inline.

Regards,
Jayshree

> -----Original Message-----
> From: Henrik Levkowetz [mailto:[email-masked]] 
> Sent: Tuesday, August 19, 2003 6:45 PM
> To: Charles E. Perkins
> Cc: [email-masked]
> Subject: Re: [Mip4] Current state of 3012bis solicited agent 
> advertisement issue.
...

> > > One of the more disadvantageous implementations would be 
> one where a 
> > > solicitation resulted in the generation of a new (multicast) 
> > > challenge, which would take the most recent slot of the 
> > > CHALLENGE_WINDOW remembered challenges. The lifetime of any 
> > > challenge could then be severely reduced by a malicious node 
> > > soliciting with a high frequency.
> > 
> > That would be bad.  In fact, I think it would be reasonable 
> to specify 
> > an upper limit on the frequency of multicast 
> advertisements, not more 
> > than a few each second.
> 
> I could go with that - although I guess my idea of a few 
> might be as many as 50 or so, as a rough guess.
> 
[JB] Currently we have the following text in RFC3344 (section 2.4):
"The rate at which a mobile node sends Solicitations MUST be limited by the
mobile node.  The mobile node MAY send three initial Solicitations at a
maximum rate of one per second while searching for an agent.  After this,
the rate at which Solicitations are sent MUST
be reduced so as to limit the overhead on the local link.  Subsequent
Solicitations MUST be sent using a binary exponential backoff mechanism,
doubling the interval between consecutive Solicitations, up to a maximum
interval.  The maximum interval SHOULD be chosen appropriately based upon
the characteristics of the media over which the mobile node is soliciting.
This maximum interval SHOULD be at least one minute between
Solicitations...."

Are we looking for further restriction apart from this? Also, I would think
that if we specify to use "previously unused challenge" for the multicast
agent advertisement, it will help also since in these cases, the FA is not
allocating new challenges for each solicited requests.

---

From: Henrik Levkowetz <[email-masked]>
Date: Wed, 20 Aug 2003 19:14:09 +0200

Hi Jayshree,

	My thoughts on this below:

Wednesday 20 August 2003, Jayshree wrote:
> 
> > > > One of the more disadvantageous implementations would be one
> > > > where a solicitation resulted in the generation of a new
> > > > (multicast) challenge, which would take the most recent slot of
> > > > the CHALLENGE_WINDOW remembered challenges. The lifetime of any 
> > > That would be bad.  In fact, I think it would be reasonable to
> > > specify an upper limit on the frequency of multicast
> > > advertisements, not more than a few each second.
> > 
> "The rate at which a mobile node sends Solicitations MUST be limited
> by the mobile node.  The mobile node MAY send three initial
> Solicitations at a maximum rate of one per second while searching for
> an agent.  After this, the rate at which Solicitations are sent MUST
> Solicitations MUST be sent using a binary exponential backoff
> mechanism, doubling the interval between consecutive Solicitations, up
> to a maximum interval.  The maximum interval SHOULD be chosen
> appropriately based upon the characteristics of the media over which
> the mobile node is soliciting. This maximum interval SHOULD be at
> least one minute between Solicitations...."
> 
> Are we looking for further restriction apart from this? Also, I would
> think that if we specify to use "previously unused challenge" for the
> multicast agent advertisement, it will help also since in these cases,
> the FA is not allocating new challenges for each solicited requests.

Yes, the paragraph above only restricts the rate at wich a well-behaved
mobile node sends solicitations.  It seems Charlie and I agree on also
putting a limit on how often an FA may send multicast advertisements (in
response to e.g. solicitations) in order to limit the load a hostile
node may put on the FA by sending very frequent solicitations. 

To also specify to use a "previously unused challenge" in multicast
advertisements may also be a good thing, but we still should have the 
rate limitation, as a hostile node may very well otherwise combine 
solicitations and registration requests in order to make each
advertised challenge used as soon as it has been advertised.

	Regards,
		Henrik