Today we are going to configure an OSPF Virtual Link.
What is it?
Before we answer what it is, take a step back and look at one of the basic requirements of OSPF. That is, all areas must be connected to the backbone area (area 0). A virtual link gives us a way around that requirement.
If for some reason, you are stuck with a topology where you must connect a non-zero area via another non-zero area you can create a virtual link between the ABR in non-connected area to a router in area 0. That will hopefully make a bit more sense in a few minutes.
This is a pretty common scenario. You are running and IGP (in this case, OSPF) on your local network and you connect to another company or ISP via an eBGP link.
Your goal is to leak some of the external routes received via BGP into your IGP, and in turn leak some of your internal routes out via BGP. The constraint is you don’t want everything. Only the routes you decide.
This is a bit of a resource for troubleshooting OSPF but breaking various aspects and see just how it fails.
To begin with, we have a simple OSPF setup with two routers working normally.
This post is about extending your OSPF routing domain through a VRF in a MPLS backbone. If you are unfamiliar with the MPLS side of things check the previous post out. This post only focuses on the PE/CE side of things, it assumes that a working MPLS backbone has been set up.
Then you have the choice of if you plan on using the MPLS link as a primary link or as a backup.