Filtering OSPF routes from MPBGP to BGP speaker in the same VRF

[jlixfeld]

I'm wondering if anyone has some ideas they an share on this.

Assume the following:

- CE1 is speaking *iBGP and OSPF to PE1 inside vrf foo

- PE1 is mutually redistributing CE1's OSPF table with MPBGP

- PE1 exchanges MPBGP routes with PE2.

- PE2 is mutually redistributing CE2's OSPF table with MPBGP

- CE2 is speaking *iBGP and OSPF to PE2 inside vrf foo

So the problem is that the OSPF routes redistributed into MPBGP from via one CE are being announced to the other CE via the PE-CE BGP process.  Because those routes are already being received by the CE via the PE-CE OSPF process, they are showing up in the CE's BGP table as RIB failures.

Is there any way to filter those out?  I've tried setting and matching tags and communities from within various redistribution points on the PE, but I can't seem to keep them out of the CE's BGP table.

[Olivier ARRIGHI]

Hi

Do you really need both IGP and IBgp  on PE-CE link? Get rid of BGP and you should be OK.

Also, you can try to tweak routing protocols distances to make sure OSPF gets a worse distance than BGP. Then if BGP receive the route with better distance, you wont have a rib failure anymore.

Can you show your setup configs?

[jlixfeld]

Yes, OSPF and iBGP are both required.  There are BGP speaking device behind the CE network that require a full BGP in addition to us providing a backup area 0 link for their OSPF network.  Multiple VRFs are not possible.

[Olivier ARRIGHI]

are you sure you are using iBGP on both sides and not eBGP?

I'm asking because routes learnt by PE1 from CE via iBGP ( meaning same BGP AS number on CE1 and PE1 vrf foo) will not be propagated to CE2, because an iBGP route learned by a BGP speaker in not pushed to another iBGP speaker.

So it means that a show ip bgp neighbor vrf foo advertised routes on PE2 shall  show that no routes from CE1 are being advertised to CE2.

As mentionned earlier, changing BGP admin distance is an option. Let BGP have a better distance on your CEs and this should do the trick :

router bgp xxx

distance bgp 20 20 20

Then after clearing bgp session, the rib failures are gone as OSPF is AD 110 and BGP is now AD 20 ( also remember that BGP does not annouces rib failure routes to other BGP peers)

cheers