Hi Samir, If the OSPF process id is the same at either end of the provider network, there is an implied domain-id set by IOS but if you are using different process ids to get alignment you need both sides to have a common domain-id only if you want routes to appear as inter-area rather than external routes. If domain-ids are in alignment then routes over the provider network will appear as inter-area (type 3) otherwise routes will appear as external (type 5)
To have routes appearing as intra-area via the provider network shamlinks are required, as they are similar to a virtual-link but can extend any OSPF area, not just area 0 over the provider's network (type 1) - as you have found, the domain-id doesn't matter here. The value of a sham-link is meant to be if you have a backdoor link (not using the provider network) that is in the same area, you aren't going to get into problems where intra-area routes are always preferred over inter-area routes (should the backdoor link be in the same OSPF area) however I think for the backdoor link you're probably going to have to manipulate the link costs to be less preferred than the MPLS network anyway, so you may as well give the backdoor link a different OSPF area - which I think kind of negates the need for a sham-link in the first place :) Cheers, Adam On Tue, Jun 7, 2011 at 9:02 PM, Samir Idris <[email protected]> wrote: > Hey Hey, > > I have lab'ed up a scenario where EIGRP is running as an IGP in the MPLS > core. I am using OSPF as an IGP between PE-CE at both the sites. > > 1)- If I create a sham-link with NO domain-id, the routes appear to be > intra-area. It makes sense as sham-link is like a virtual-link over MPLS. > Please correct me if wrong. > > 2)- If I add domain-id and different ones still the routes appear to be > intra-area. Is it because domain-id doesn't take effect or what? Confused > at this point > > 3)- If I remove the sham-link and simply use same domain-id at both PEs I > get inter-area routes. This one makes sense as the BGP community carries > the domain-id along with it. The PE looks as it and knows how to > manipulate > it. > > I am confused at point 2. Can anyone explain please? Thanks. > > Regards, > Samir Idris. > _______________________________________________ > For more information regarding industry leading CCIE Lab training, please > visit www.ipexpert.com > > Are you a CCNP or CCIE and looking for a job? Check out > www.PlatinumPlacement.com > _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com
