couple comments inserted
Howard>
>> It's misleading to think that all ISP routers need to be "core."
>> Arguably, the highest-bandwidth "core" routers inside an ISP may not
>> need to run full BGP, but have more stringent demands on OSPF, ISIS,
>> and/or MPLS. Think of RFC 2547 "P" routers.
>
dre
>IBGP runs in the core with full routes. Are you talking about MP-BGP?
>MPLS-TE doesn't bother with IBGP information directly (i.e. the constraint-
>based routing is for SPF calculations and doesn't factor into the BGP
>decision process or convergence). MPLS-TE and MPLS-VPN are pretty
>separate topics. Yes, you don't have to do MP-BGP in the core, but I am
>sure that since most ISP's use IBGP in the core, it's also MP-BGP (no bgp
>default ipv4-unicast).
I think the 2547 relationship had more to do with the fact that P routers use
significantly less BGP provided information than do PE's. Essentially, it's only the
PE routers than maintain BGP routing info pertinent to the networks (C) which they
interconnect while the P routers use a less inclusive BGP with IGPs and MPLS to
provide transparent transit. I expect Howard was referring to the IGP dependencies
not on their ability to populate traffic engineering databases, but rather for
stability/scalability/convergence times based on the fact that a core of this nature
would depend heavily on these algorithm.
Furthermore, its quite possible, though I haven't seen it done, to create a BGP less
core that simply uses MPLS -with optional TE- to forward between edge BGP devices. In
such a case, the requirements for the "core" routers do not include BGP table capacity
or forwarding performance during instability etc whereas the "edge" router
requirements do.
I think overall, the point that the term "core" lacks precision is very accurate.
Pete
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