Hi Samir, Well a distribute-list is one way to do it if you want to have selective control, otherwise if the CE-PE and backdoor protocol is OSPF and you want to save the backdoor link for protection only, I would suggest you just set the interfaces on the backdoor link to have a higher ospf cost than the accumulated cost across the provider network.
Cheers, Adam On Tue, Jun 7, 2011 at 11:05 PM, Samir Idris <[email protected]> wrote: > Adam Adam! > > Thanks alot for the explanation. Really appreciated. > > I did put in a backdoor link when lab'ing it up. Certainly route over > backdoor was preferred due to the cost to I manipualted it. > > I lab'ed up similar stuff but with EIGRP as a CE-PE protocol. Here I tried > soo and it worked fine. In all the examples I saw on the web I didn't see > any metric manipulation being done and so the backdoor link was being > preferred. I used distribute list at the CEs connected via backdoor to make > the path preferred over MPLS network. Is it the right way? > > Thanks again. Regards, > Samir Idris. > > On Tue, Jun 7, 2011 at 5:21 PM, Adam Booth <[email protected]> wrote: > >> 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 <http://www.platinumplacement.com/> >>> >> >> > > > -- > 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
