Subject: RE: MPLS/BGP routing question

From: Chris Flores <[email-masked]>
Date: Fri, 29 Sep 2000 11:30:25 -0500

Eric - 

I agree. It is perfectly valid to tunnel packets through the core via MPLS,
thereby avoiding a full IBGP mesh. In the steady state, we agree. I just
wanted to point out that BGP is needed in the core in case MPLS fails for
any reason. If the MPLS LSPs are not available, then the core will need BGP.

c 

-----Original Message-----
From: Eric Rosen [mailto:[email-masked]]
Sent: Friday, September 29, 2000 11:23 AM
To: Chris Flores
Cc: 'Eric Osborne'; 'Javier Antich'; Michel Redondo Ferrero; [email-masked]
Subject: Re: MPLS/BGP routing question 

Chris> My point is  this. BGP (specifically iBGP) is needed  in the core for
Chris> packets not utilizing a MPLS VPN or if MPLS fails. It may be the case
Chris> that there is a full mesh of MPLS LSPs (PE-PE) that serve all traffic
Chris> flows within  the network -  customers, external peers, etc.  What if
Chris> MPLS fails? Yes, VPN customers are  out of luck till the MPLS VPN can
Chris> be re-established.  However, external peer traffic,  etc should still
Chris> route as if the network did not implement MPLS.

I don't  agree.  I think that  even with respect to  public Internet routes,
there are a  number of advantages to NOT distributing all  the routes to all
the core  routers.  I think it  is a perfectly  valid use of MPLS  to tunnel
packets through the core so as to avoid the need for a full IBGP mesh.

---

From: Eric Osborne <[email-masked]>
Date: Fri, 29 Sep 2000 13:58:44 -0400

> any reason. If the MPLS LSPs are not available, then the core will need BGP.

The statement "if MPLS LSPs are not available then forwarding will by
and large not work" is true.  But it's equally true to say ""if BGP
routes not available then forwarding will by and large not work".

This comes down to mainly an exposure issue.  Right now, people are
asking "what do I do if mpls fails and I don't have bgp"?  This is
generally because of either a lack of understanding *or* a desire for
belt-n-suspenders.  As deployments mature and operators get more
experience with them, there will be less need to back up MPLS with IP.

There's also the point (which you may get, but I didn't see you
acknowledge) that there are some MPLS services that are _not_ backed
up by BGP in the core.  If you want to run MPLS-TE, sure, it's nice to
be able to fall back on BGP in the core if things go wrong with
MPLS. Engineering around pathological conditions is up to the
operator, but not an entirely invalid idea.  But if you want to
provide MPLS-VPN services, or circuit transport, or other such fancy
stuff, then you will be unable to fall back to normal IP routing in
the core.

eric