From: maureen schaar (maureen.schaar@gmail.com)
Date: Sat Mar 31 2007 - 06:12:22 ART
Tthis sounds like normal behaviour to me.
RTR1 receives eBGP from ISP1 and assings localpref 200.
RTR2 receives eBGP from ISP1 and assigns localpref 150.
RTR1 advertises its path via iBGP to RTR2. RTR2 now sees this path is
better than the path it has itself. Since a BGP speaker only
advertises its best path, RTR2 is not going to advertise its own
(worse) prefix via iBGP to RTR1.
Hence you will only see an iBGP and eBGP path on RTR2.
Maureen
On 3/30/07, Peter Gill <Pete.Gill@inxi.com> wrote:
> Group,
>
> I'm trying to fully understand why when I use local preference in BGP to
> influence which ISP I want to go out, my iBGP advertisements disappear on one
> router.
>
> Here are the details:
> 1. I am using a local preference of 200 when routes come in from ISP1 to
> RTR1, and of 150 when coming in through ISP2 - so that ISP1 is preferred when
> going out.
> 2. I am prepending the as-path for advertisements out to ISP2 - so ISP1 is
> preferred coming in.
> 3. I am advertising ISP1's IP block to ISP2 and ISP2's to ISP1 - for
> redundancy.
> 4. I am using an aggregate-address for the networks I am advertising. I am
> using a class C with a /25 SM and advertising a class C with a /24 SM with an
> aggregate.
> 5. RTR1 and RTR2 are peered as iBGP routers.
>
> My issue is that on RTR1 (ISP1) when doing a "show ip bgp x.x.x.x", I see
> "advertised to update-groups" and no internal advertisements from RTR1 (ISP1).
> In other words, I don't see ANY iBGP entries from RTR2 (ISP2), just my eBGP
> entries from ISP1.
>
> When I do a "show ip bgp" on RTR2 (ISP2), I see "not advertised to any peer"
> and I have both internal from RTR1 and external routes from my ISP2.
>
> Is this because the local preference is keeping internal routes from showing
> up in the bgp table on RTR1 since it is the preferred outbound router? If I
> set it all back to LP of 100 it shows up with both iBGP and eBGP routes in the
> bgp table on both routers. Is this the default behavior?
>
> Thanks!
>
> Pete
>
>
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