IS-IS reference

Dave Cooper dcooper at
Wed Sep 15 20:30:16 UTC 1999

Vijay Gill wrote:
> On Tue, 14 Sep 1999, Dave Cooper wrote:
> > 1. if you are going to scale a large national backbone, limit as much
> > as you can in your IGP. the less fluctation in flooding protocols, the
> > better.  and since most backbones run on a single area (on the main 
> > IGP process) or level-2 only, then fluctuations cause headaches for
> > all participating routers. this is especially so when you have a 
> > full layer-2 mesh or a full MPLS mesh.
> A full mpls mesh should not be a problem as instantiated LSP's are
> probably not going to be in your igp.  Running an IGP over an (opaque) LSP
> adds a lot to your complexity without delivering any major benefits. 

agreed.... i don't advocate running igp process on your tunnels. but
is-is does contribute to LS path selection during setup.  but has nothing
to do with the IGP process itself. thanks for the clarity, vijay.

> You can add hierarchy to your topology obviating a need for a full mesh at
> the L2 level.

> Hierarchy can solve almost any scaling issue.  Hierarchy in BGP through
> confederations/RR, hierarchy in your IGP and hierarchy in your physical
> circuit layout.
> /vijay

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