From: Peter Gill (Pete.Gill@INXi.com)
Date: Fri Mar 30 2007 - 14:17:49 ART
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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