connected interface getting redistributed via bgp

[Kashish_Patel]

On one of our routers (running bgp and ospf), we are redistributing ospf to bgp. This router has a loopback interface which is advertised in ospf.

Router#sh ip route 10.22.0.24

Routing entry for 10.22.0.24/32

  Known via "connected", distance 0, metric 0 (connected, via interface)

  Redistributing via bgp 64999

  Routing Descriptor Blocks:

  * directly connected, via Loopback11

      Route metric is 0, traffic share count is 1

I am confused about "Redistributing via bgp 64999" part.....Under router bgp, we are redist only ospf and static routes, but using route-maps like this:

redistribute static route-map STATIC2BGP

redistribute ospf 1 route-map OSPF2BGP

Obviously it won't match redistribute static because it is not static, but connected interface...And 10.22.0.24 does not appear in match statement in route-map OSPF2BGP, how is it still shown as "Redistributing via bgp 64999"?

[Ben Anderson]

Do you have any null routes that might be used to encompass a range for loopbacks? I've commonly used null routes for loopback ranges just to ensure advertisement at an aggregation point.

[Harold Ritter]

Hi Kashish,

This prefix is owned by the ospf process. By redistributing ospf into bgp, this prefix would be redistributed in bgp as well. The "Redistributing via bgp 64999" does not take the filtering into account and appears as soon as redistribution is configured. So this message will show up even though this prefix is being filtered out by the OSPF2BGP route-map.

Regards

[Kashish_Patel]

Hi Harold,

Thanks for replying.

Is the prefix actually getting redistributed in bgp here (even though not allowed in route map)?

Thanks.

[Harold Ritter]

Hi Kashish,

The prefix does not get redistributed if the route-map does not allow it.

Regards

[Kashish_Patel]

That's where my confusion comes from.

Why does it still say:

"Redistributing via bgp 64999"?

[Harold Ritter]

Hi Kashish,

As I mentioned before, this message does not take into account whether the prefix is filtered or not but rather whether the protocol, the prefix was learned from, is redistributed or not.

Regards

[Kashish_Patel]

Hi Harold,

I appreciate your response. I will explain my confusion (I may not have been clear before).

On some router A in our network, I see this in the output of "show ip bgp":

Router#sh ip bgp | i 10.22.0.24/32

*> 10.22.0.24/32   10.219.65.217                          0 65000 64999 ?

Above output means that prefix 10.22.0.24/32 is actually redistributed in BGP on some router (say, router B in AS 64999)... Now router B has :

Router#sh ip route 10.22.0.24

Routing entry for 10.22.0.24/32

  Known via "connected", distance 0, metric 0 (connected, via interface)

  Redistributing via bgp 64999

  Routing Descriptor Blocks:

  * directly connected, via Loopback11

      Route metric is 0, traffic share count is 1

and redistribution taking place via Route maps as I mentioned before:

redistribute static route-map STATIC2BGP

redistribute ospf 1 route-map OSPF2BGP

So from where is prefix 10.22.0.24/32 getting redist in BGP table when route-map is not even allowing it?

Thanks.

[Harold Ritter]

Hi Kashish,

Oh, I see. Can you please post route-map OSPF2BGP.

Regards

[Kashish_Patel]

Harold,

Just sent you relevant config as a private message.

Thanks.

[Kashish_Patel]

Hi Harold,

I hope you got the related configuration. Could you tell me the reason for my confusion?

Thanks.

[Harold Ritter]

Hi Kashish,

Could you please post the output of a "show ip bgp 10.22.0.24 255.255.255.255" from the router doing the redistribution.

Regards

[Kashish_Patel]

Just sent you that.

[Harold Ritter · Accepted solution]

Hi Kashish,

It appears that the current router is not the one redistributing the connected prefix into BGP. This prefix is received from one of the BGP peers. It might be worth looking at this peer to see if the redistribution filtering is adequate.

Regards

[Kashish_Patel]

Thanks...That was it!