bgp-ospf

Unanswered Question
Sep 29th, 2008

Hi,

I have the following scenario:

site A- OSPF distribution routers -----BGP CE---MPLS cloud------BGP CE----OSPF distribution routers- Site B.

BGP is selectively redistributed into OSPF. However, OSPF redistribution into OSPF is NOT allowed.

How do I have full connectivty ?

I can see the BGP routes from both sites, but the OSPF routers can't ping the networks advertised by BGP.

Any suggestions much appreciated.

Thanks,

Paul

I have this problem too.
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Giuseppe Larosa Mon, 09/29/2008 - 08:47

Hello Paul,

first of all you need to understand if the problem lies in the MPLS forwarding plane or in the MPLS signaling /IP routing plane.

Is possible to ping from CE to CE using the links to the PE routers ?

If it is not you are facing an MPLS forwarding plane issue and you have to work with service provider people to have it solved.

If this basic connectivity test works you should move to examine the MPLS signalling / IP routing plane.

Have you provided in BGP networks commands that cover the OSPF router links' IP subnets ?

you need to advertise all the IP subnets of interest of each site.

CE router has to take part both in OSPF domain and to have an eBGP session with PE router.

Your CE routers will be OSPF ASBR for routes imported from BGP to OSPF.

You can use a route-map with an access-list or prefix-list to filter locally known OSPF routes (if you used the network command to advertise OSPF internal routes) when importing BGP routes in OSPF.

take care to have BGP router-id = OSPF router-id on CE routers this help the redistribution.

Advertising router must be reachable in order to have its LSA taken in account.

Can you see in the OSPF database the external LSA that result from BGP redistribution into OSPF?

on internal router R1 do

sh ip ospf database external x.x.x.x

x.x.x.x is prefix imported from BGP from site B

if you don't see anything probably your route filter needs to be changed.

If you see the LSA but the corresponding route is not installed some parameter in the LSA like advertising router of forwarding address is unknown to OSPF internal routers.

A redistribute connected in ospf process in router CE could help for the forwarding address.

As you see there are many possibilities: I would suggest you, if you like, to post a filtered version of your configuration of CE site A, internal router site A, CE site B, internal router site B to get better help.

Hope to help

Giuseppe

Joseph W. Doherty Mon, 09/29/2008 - 10:17

"BGP is selectively redistributed into OSPF. However, OSPF redistribution into OSPF is NOT allowed."

Did you actually mean what your wrote or did you mean to write "OSPF redistribution into BGP is NOT allowed."?

Whatever you're doing, your CE (BGP) router probably doesn't "know" your local LAN routes. How this might be corrected would depend on your local site topology and how your CE router can interact with your local OSPF topology.

Further route redistribution might not be necessary although a router "knowing" both BGP and OSPF routes or a default route might be necessary.

Could you expain further the local OSPF topology?

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