In relaity iBGP must always be run in conjunction with an IGP - I suppose
that static routing could be used in theory, but in practise an IGP is
something of a neccesity.
Say for instance that you have an AS with a /24 of address space, and that
you have four routers - two route refelctors and two route reflector
clients. What would most likely happen is that the two RRs would originate
the /24 route to the internet, and also to the internal network. Running
OSPF or IS-IS (typically) as the IGP withing the network would provide
internal reachability between the iBGP peers.
I suppose the point here is that although iBGP will advertise the aggregate
route within the network, there will always be more-specific routes for the
internal network blocks (loopbacks, interlinks, host-attached net blocks,
etc.) within the IGP, so the fact that the AS's own network is advertised
within iBGP is ultimately irrelevant.
hope that makes sense
Andy
----- Original Message -----
From: "RAJESH.V.S"
To:
Sent: Wednesday, May 02, 2001 5:26 PM
Subject: BGP Route Reflector Question. [7:2900]
> Hi All,
>
> Got a Doubt on BGP Route Reflectors. BGP uses route reflectors to
simplify
> the IBGP mesh configuration.
> Say a RR reflects an IBGP route announced by RRclient-1 to another RR
> client say, RRClient-2. The RR keeps the next hop of the IBGP network
> announced by RRclient-1 un-altered while announcing to RRclient-2. Now if
> the next hop i.e. RRClient-1 is inaccessible to RRclient-2 , RRClient-2
> will not advertise that route to its peers ( EBGP/IBGP). And IBGP peers
can
> be many hops away ( i.e. not directly connected/in same subnet). As per
BGP
> doc from Cisco , even if you use next-hop-self, only EBGP next hops will
be
> altered, not Reflected IBGP next hops. So in a large IBGP only network
( no
> other IGP ), how will you ensure the connectivity to all the links between
> RRClient nexthops?
>
> Will they use any IGP or static route for this purpose ?. Or you have to
> manipulate the point where you advertise each IBGP networks to contain
> next-hop subnets also ?. Or is there any mistake in my understanding ?.
>
> Please advice,
>
> Thanks in advance
> Regards
> Rajesh
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