Subject: RE: [nemo] Re: looping problem (was: Questions on multiple mobile network prefixes in a BU)

From: "Pascal Thubert \(pthubert\)" <[email-masked]>
Date: Thu, 29 Apr 2004 02:43:30 +0100

Hi Alex, 

You're right, I need to explain more. Actually there's a draft coming up
about that. 
The Question was initially asked at the Nemo Bof in Yokohama by Steve
Deering in person :) 
When MRs attach to each other in order to form a nested NEMO, you may
very well end up making loops unless you take a particular attention.
It's not just a MR attaching to its back but also 
MR1->MR2->MR3->MR1 , which is the point Jari made as well if I remember
correctly.

Like I said, draft coming up!

Pascal

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]] On Behalf Of
Alexandru Petrescu
> Sent: mercredi 28 avril 2004 15:11
> To: Pascal Thubert (pthubert)
> Cc: Tan, Tat Kin; [email-masked]
> Subject: [nemo] Re: looping problem (was: Questions on multiple mobile
network prefixes in a
> BU)
> 
> Pascal Thubert (pthubert) wrote:
> > I guess that RO contradicts that postulate, though it's true for
> > basic. But basic does not know how to avoid loops...
> 
> Loops with basic nemo support have been mentioned here at least twice.
> The earliest mention I know of was autumn last year (J. Arkko) in an
> email to nemo and then in the winter by E. K. Paik in
> draft-cho-nemo-hmra named "RA confliction problem".
> 
> I've looked closely at both concerns and it is still unclear to me how
> the looping problem can be defined and potentially solved.
> 
> In order to reduce the problem scope, I can say that its simplest form
> appears when a single MR is in a visited network and has one egress
and
> one ingress interface, both wireless.  The RA's sent by the ingress
> interface may be received by the egress interface (on the wireless air
> space between the two antennas) and then the egress interface
configures
> a CoA (by the nemo and mip6 specs) that is valid in the internal link;
> thus making a sort of loop.
> 
> Initially, I was thinking that such a problem has little chance to
occur
> in practice with 802.11b because when one configures such a router
s/he
> is forced to determine two different L2 networks for the two
interfaces
> (via essid/enc) and thus the egress interface could not receive the
RA's
> of the ingress interface.
> 
> True, restricting the reasoning to 802.11b exclusively is little
> relevant to an IP solution that shoudl work over several wireless
types.
>   But imposing hte multiplicity of wireless links as a requirement is
> even more advantageous for avoiding the existence of loop problem: if
> egress is CDMA and ingress is WLAN then there is absolutely 0 chance
for
> egress to receive RA from ingress.
> 
> IMHO, that's what I think right now about the looping problem, looking
> for a better definition.
> 
> So, I take advantage of your mentioning of the looping problem to ask:
> how do you Pascal think more exactly the looping problem looks like
with
> nemo basic, thanks,
> Alex