I've got a great question from one of my readers: I have two central sites (primary data center and a disaster recovery data center) and I've inherited a situation where there was a lot of static routing and a default route pointing from the primary campus to the DRC. I've replaced most of the static routing with dynamic routing protocol, but as the documentation is scarce, I am afraid to remove the default static route (which I would need for proper Internet access). Is there a way to figure out whether the default route is still used?
Obviously, there are two types of solutions:
- The deterministic one: inspect the IP routing tables on primary router and DRC router and identify any IP prefix on the DRC router that has no matching or less specific prefix on the primary router.
- The non-deterministic ones: try to figure out if any packet is using the default route
- This is where you can get really creative: how would you figure out if a packet going from the primary data center to the DRC site is using the default route?