Subject: Re: Comments on the L2 VPN framework and solutions documents

From: "Cheng-Yin Lee" <[email-masked]>
Date: Thu, 01 May 2003 11:48:58 -0400

Eric, Norm,

Norman Finn wrote:
> 
> I second the motion.  :)
> 
> Eric Rosen wrote:
> >
> > (Of  course, all  these problems  can  be eliminated  by making  all the  CE
> > devices be routers, and using an IPLS service instead ;-))

How does IPLS eliminate the problem where a CE router A cannot see B
(and vice-versa), but CE router C can see CE router A and B (and
vice-versa)? [This question has been raised before].
Customer routing protocols would still get an inconsistent view if this
problem is not eliminated.

Thanks
Cheng-Yin

---

From: Eric Rosen <[email-masked]>
Date: Thu, 01 May 2003 14:40:45 -0400

Cheng-Yin> How does  IPLS eliminate the problem  where a CE  router A cannot
Cheng-Yin> see B (and vice-versa), but CE router C can see CE router A and B
Cheng-Yin> (and  vice-versa)?  ...  Customer  routing protocols  would still
Cheng-Yin> get an inconsistent view if this problem is not eliminated.

The precise effects depend on the routing protocol. 

If the protocol is RIP, for example,  then A won't install any routes with B
as the next  hop, and B won't install  any with A as the next  hop.  So it's
possible that a packet that should go from A to B will actually go from A to
C to B.

If  the protocol  is OSPF,  the  analysis is  more complex,  and depends  on
whether A and/or B are trying  to become the designated router.  I think the
worst that can happen is that some of the traffic which is routed across the
emulated LAN won't make it. I don't think loops are possible.