MPLS PE-CE OSPF

[pgyogeshkumar]

In MPLS PE-CE OSPF I have below queries

1. Can OSPF with area 0 can be configured in each different VRFs ?

2. In MPLS environment, CE router will advertise routes towards PE router and OSPF route will be redistributed into BGP and inturn BGP routes will redistributed into ospf so that other CE routes will be imported to OSPF. Does the OSPF route advertised to MPBGP will be again learnt via VPN because of BGP to OSPF redisribution in MPLS environment ?

3. I understand that the ospf routes received by CE routers from PE router will be with type 3 LSAs even if all CE routers are configured with same area ID. If we have different area IDs configured for different CE routers, then what type of LSA will be generated by PE routers to advertise back to CE routers ?

4. Whats the use of DN bit in MPLS OSPF  CE-PE process ?

[Markus Benz]

Hi,

I try to answer your question:

1. yes this is possible. If you run CE based OSPF over an MPLS core you may use Super-Backbone. With this you stretch your Area 0 across the core.

2. No, the redistributed routes should not be redistributed again. They are marked.

3. Following a detailed description of the DN bit:
http://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/118800-configure-ospf-00.html#anc8

It is actually used in the redistribution process to avoid the problem in question 1...

Regards,
Markus

[pgyogeshkumar]

Thanks Markus,

can you please clarify on below query as well

3. I understand that the ospf routes received by CE routers from PE router will be with type 3 LSAs even if all CE routers are configured with same area ID. If we have different area IDs configured for different CE routers, then what type of LSA will be generated by PE routers to advertise back to CE routers ?

[Markus Benz]

In MPLS VPN networks, the OSPF process ID should match. Otherwise, external Type 5 routes are generated.

There is also a good article on the net:
http://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/WAN_and_MAN/L3VPNCon.html#wp320797

Check the "Using OSPF to CE-PE Routing" section

Regards,
Markus