OSPF Acting up!

[funraps]

Hello,

I have an MPLS VPN going through fast 0/0 when OSPF being redistributed by the ISP on both ends, and it works fine most of the time, for backup purposes I have 2 T-1's also coming in to the router and going to the same location, for some strange reason, when I turn the serial ports on, OSPF sends all the traffic across one of the T-1s instead of the MPLS VPN, which goes through a fast ethernet port, Any ideas?

other than static routes :-)

Thanx

[mmolina2 · Accepted solution]

Long story short:

Your MPLS provider needs to create an "OSPF Sham Link". By default, all internal OSPF routes that traverse an MPLS backbone will be propagated as a Type 3 Inter-Area LSA's. OSPF routes for the same networks are being advertised over your non-MPLS Serial link as Intra-Area (native) OSPF routes. Intra-Area routes for the same networks will always be preferred over Inter-Area routes.

By configuring a Sham Link, your provider will override this default OSPF behavior and make the routes that have traversed the MPLS backbone appear as Intra-Area routes. Assuming the provider adjusts the cost for the Sham Link as low as possible, you will probably start to prefer the MPLS cloud as opposed to your T1. Depending on the Media type used for your MPLS access, you may have to adjust the cost on the T1's to help your provider out. Good Luck

[mmolina2]

P.S- Forget the "native" reference. I believe it is a loose term to describe any OSPF route that isn't external. It doesn't really fit where I used it :)