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. 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