Hi Dan,
I thought I would throw my two cents in.
There are a few key reasons why one requires an interior routing protocol (or at worst
case a routing strategy should one use statics) within an AS. First and foremost, you
must consider what iBGP does within the AS. Essentially, it allows interior routers
to build a table linking reachable prefixes and BGP next hop routers. However, these
next hop entries are not the same as a next hop that one would normally encounter in a
routing table. The Next Hop attribute in BGP describes the ip address of EBGP peer
who advertises the prefix or the IBGP peer who first receives the advertisement (in
the case of next-hop-self). This attribute remains constant throughout the entire AS.
What this means is that outside of the router who receives this advertisement
directly, every other router will receive a list of prefixes linked to a next hop that
they have no awareness of whatsoever. For a router to post a route to a routing
table, it must know how to reach the next hop. In BGP thi!
s is generally referred to as Next Hop Resolution. Enabling this Next Hop Resolution
in my mind is one of the key roles that an IGP plays within an AS. A lesser role
involves basic interior routing most notably enabling IBGP routers to peer with their
loopback interfaces.
All in all, you will find that despite the "i" in IBGP, the protocol does not perform
in such a way that would meet the criteria for interior routing.
*********** REPLY SEPARATOR ***********
On 12/18/2000 at 10:50 PM Dan West wrote:
>Is it possible to run IBGP as the ONLY IGP for a
>particular network (AS)??
>
>I know all routers would know about outside networks,
>but how about different internal areas knowing about
>what other networks are advertising
>
>BGP seems so capable that it could almost be done
>without OSPF, EIGRP, etc....
>
>thanks.
>
>=====
>Dan West -- CCNA, CCNP (in progress)
>
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