From: Jezz Bird (jezzbird@hotmail.com)
Date: Wed Oct 17 2007 - 15:22:27 ART
Hi,
This what I think is happening - as you have aggregate-address 10.1.0.0 /16 on
R1 and as long as you have at least one more specific component route of the
aggregate in your BGP table then R1 will keep the aggregate in it's BGP table
and use that to attempt to get to 10.1.3.0 /24 and not it's default route. As
10.1.3.0 is actually reachable via R3 and is not specifically in R1s routing
table then traffic destined for it will be dropped (sent to Null0). Only when
ALL the component routes of the aggregate have gone will the aggregate be
withdrawn and so R1 would again use it's default route to get to 10.1.3.0 and
connectivity to it from R1 would be restored.
Does anyone else have similar/differing thoughts ? Could you post your configs
as this might help us to work it out ?
Regards,
Jezz. :)
> From: con@spathas.net> To: ccielab@groupstudy.com> Subject: BGP
aggregate-address and null0 route> Date: Wed, 17 Oct 2007 17:29:47 +0100> > I
think I'm missing something here but for the life of me I can't work it>
out...> > When you configure an aggregate-address summary in BGP it adds the
relevant> summary into the routing table pointing to null0.> > Is there any
way to remove this?> > I have a scenario where a router (R1) running BGP is
advertising a summary> to a peer (R2). However another router (R3) is sending
R1 a default-route> via RIP.> > R3 knows how to get to say 10.1.3.0/24 and R1
uses the default route to R3> to get to this subnet. Things work nicely up to
this point. > > However when R1 advertises the 10.1.0.0/16 summary into BGP -
the route to> null0 is matched on R1 and I lose connectivity to 10.1.3.0/24
from R1.> > Thx.> >
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