[c-nsp] I-BGP/IGP question

Gert Doering gert at greenie.muc.de
Tue Sep 16 03:45:23 EDT 2014


On Tue, Sep 16, 2014 at 12:55:40AM -0400, Wes Smith wrote:
> I've often wondered how large ISPs handle some basic IGP design issues re routing between I-BGP nodes in the network. 

All routers on the path need to have "full information" (not necessarily
full tables, but they need to agree on the set of routes, possibly including
a default route).

So you'd usually ensure that the "core" of your network is either all
speaking BGP (full mesh or BGP route reflectors), or you have an MPLS
core where you tunnel through the core, and the core doesn't need to
know anything, because MPLS P routers won't look at the IP header.

This is really BGP 101, so you want to get a good BGP book, like the
Halabi "Internet Routing Architectures" book - it's old, but BGP hasn't
changed in that regard (there is a v2 edition which I haven't seen yet,
so maybe all the new BGP stuff is in there already).

USENET is *not* the non-clickable part of WWW!
Gert Doering - Munich, Germany                             gert at greenie.muc.de
fax: +49-89-35655025                        gert at net.informatik.tu-muenchen.de
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