>No worries John. It was I who mentioned the devious nature of
>classless and synch as well :)
Always remember that the best ISPs have no class.
>
>Keep in mind that synch was designed for transit networks that have
>transit providing routers which do not run BGP. Back when the
>internet was smaller I expect some designs had the IGP in an AS
>carry the full table, or parts of it and hence it was relevant to
>make sure your BGP and IGP were synchronized to ensure you didn't
>blackhole routes.
Precisely. I don't have the document number in front of me, but the
old RFC on BGP/OSPF interaction, which assumed this model, has been
recategorized as Historic (i.e., nobody does this, don't try it, it
was a blind alley)
>Today, BGP is run fully meshed with all transit providing routers in
>an AS peering with IBGP and hence synch is a complete non issue.
Full mesh, of course, has its scalability issues, and we deal with
iBGP scalability measures such as route reflectors. There is a trend
to have the main BGP at the edge, and to have principally an IGP in
the provider core. The core is stupid, and is traversed by MPLS
tunnels -- the role of the IGP is to establish reachability for these
LSPs, which run between BGP speakers on the edges.
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