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I-D ACTION:draft-minei-mpls-ldp-external-00.txt (fwd)

  • From: "Vach Kompella" <vach.kompella@alcatel.com>
  • Date: Tue, 11 Nov 2003 08:10:33 -0800
  • Cc: "'jason rusmisel'" <jason.rusmisel@alcatel.com>, <mpls@UU.NET>
  • Importance: Normal
  • Organization: Alcatel USA
  • X-MIME-Autoconverted: from quoted-printable to 8bit by cell.onecall.net id hABGNYn24512
  • X-OriginalArrivalTime: 11 Nov 2003 16:08:24.0757 (UTC) FILETIME=[09030E50:01C3A86E]

There is a technique which avoids external routes altogether.  The basic
technique is to run IBGP between PE routers only, to do your normal
application of policy, costing, route selection, etc. that BGP gives
you.  Once you pick the BGP next hop that is the best route, you
normally turn to your IGP to get to the BGP next hop.  Instead, what you
do is that you figure out the LDP path to that BGP next hop, and tunnel
the IP packet there.  For want of a better term, let's call this the BGP
shortcuts method.

So there are several issues I'd like you to address, with ref to the
IBGP mesh-avoidance technique:

1. is it less costly?
   - your solution requires all external routes in the LDP database
   - the BGP shortcuts method does not

2. is it more "correct"?
   - since your normal approach to dealing with external routes is to
apply BGP route selection, by sending the external route via LDP without
the BGP attributes, you aren't quite doing what you used to, when you
used IBGP.  I'd suggest that there should be an opaque TLV that carries
BGP attributes so the PEs can do similar route selection.

3. does it converge faster?
   - I highly doubt it: you potentially have BGP, IGP and LDP that need
to converge

So, Luca, could you please resurrect your draft, and let's have some
discussions focussed around that solution?

-Vach 

> -----Original Message-----
> From: owner-mpls@UU.NET [mailto:owner-mpls@UU.NET] On Behalf 
> Of Ina Minei
> Sent: Tuesday, November 11, 2003 6:38 AM
> To: Luca Martini
> Cc: jason rusmisel; mpls@UU.NET
> Subject: Re: I-D ACTION:draft-minei-mpls-ldp-external-00.txt (fwd)
> 
> 
> 
> 	There is nothing wrong in that. The mechanism described 
> in the draft is a general mechnism, the vpn scenario is a 
> usage example.
> 
> 				Thank you,
> 
> 					Ina
> 
> On Mon, 10 Nov 2003, Luca Martini wrote:
> 
> > so what is wrong with using the IBGP, and 3 label MPLS 
> stack , while 
> > leaving LDP out of the routing business ?
> >
> > Luca
> >