Router doesn't prefer BGP Route

[t-systems]

Hi all,

I've a problem with my backup router. This router have BGP configured and several static routes. My problem is, that facing a peer closing the router choose the static route (with high administrative distance, 210) and when the peer is back the BGP route (AD 20) is nomore preferred even if the BGP route is present.

My platform is a Cisco 2621XM with 12.3.10 - IP Plus.

Follow the output of command "ip bgp summary" and "ip route":

* 10.100.37.0/24 192.168.103.23 0 20608 65211 i

* 192.168.103.22 0 65001 20608 65211 i

*> 192.168.254.64 0 32768 i

sh ip route 10.100.37.0

Routing entry for 10.100.37.0/24

Known via "static", distance 210, metric 0

Advertised by bgp 65001

Routing Descriptor Blocks:

* 192.168.254.64

Route metric is 0, traffic share count is 1

Thanks

[Kevin Dorrell]

I hope this is correct - if not, someone put me right please.

I think the AD of the BGP route is 200 because it is interior BGP. AD=20 is only for exterior BGP routes. This is so that if you are running an interior routing protocol as well as BGP, then the interior protocol takes precedence over iBGP.

But is still doesn't explain why the static AD=210 is winning - that has got me stumped.

Kevin Dorrell

Luxembourg

[Kevin Dorrell]

Looking at it again, maybe I'm wrong - it is eBGP. Is you local AS=65001? And the route came from AS=32768? OK, let's start again ....

I was looking at the rules for BGP path selection, of which there are 11, making it horrifically complicated.

1. If next hop is inaccessible, drop the path.

2. If path is internal and sync enabled, and path not in IGP, then drop the path.

3. onards are all about arbitration between alternate BGP routes, so they not relevant here.

Kevin Dorrell

Luxembourg

[marikakis]

Can you ping the next-hop of the BGP route for prefix 10.100.37.0/24 ?

Do you have a route for 192.168.103.23 ?

M.

[Harold Ritter]

Can you include a "show ip bgp 10.100.37.0/24". This will help in determining why the route is not selected as the best path by BGP.

Thanks,

[t-systems]

I've attached the output of command.

Thanks,

[Harold Ritter]

The best path is actually the locally originated route (probably from the static route), hence the floating static not being replaced. You probably don't need to locally originate the route. This is clearly what is causing the issue.

Hope this helps,

[marikakis]

It seems like router DITass14 is trying to announce the prefix 10.100.37.0/24 via a network command.

When the BGP external route was valid,

the static route was not preferred.

After peer flapped, static route took effect,

and now you announce the network because you have it in your IGP.

Is there a particular reason for you to announce the the prefix 10.100.37.0/24 ?

Anyway,a prefix being announced by 2 different ASs,

is looking for trouble...

M.

[t-systems]

Hi,

the purpose to announce the prefix 10.100.37.0/24 via floating static route is to have ISDN backup...

tks 4 your help

[Harold Ritter]

The issue is not with the floating static itself but rather with the fact that you originate it in BGP using a network statement.

Hope this helps,

[t-systems]

Hi

but erasing the network statement the behaviuor doesn't change...

tks for your effort!

[Harold Ritter]

Really? Do you also have a "redistribute static" command configured under the BGP process.

It would be interesting to see another "sh ip bgp 10.100.37.0" after you remove the network statement.

Hope this helps,

[t-systems]

Sure, I attached the file.

[Harold Ritter]

In the output you provided, the origin changes from IGP to imcomplete. This indicates that after removing your network statement, "redistribute static" continues to originate the route locally. You should either remove the "redistribute static" statement or use a route-map that filters out the floating statics.

Hope this helps,