Distance Command

And this is why I like to lab.  So I was working on the first of my redistribution scenarios today and I learned some important stuff. First off, if an OSPF ABR injects a default route into a NSSA, the route is not added to the route table by default.  If redistribution brings that default route back to the router through another means, then the route can be injected into the route table as a new route and that will cause a loop to form.  Oh what fun. 

So this scenario is something that I was looking at trying to cause.  I wanted to see how to filter the default route out so that the initiator wouldn't see it and cause a loop.  I tried using the distance command and nothing seemed to work.  I was using an ACL that was matching but the route was always there.  I modified the ACL to include another route and it worked for the other route but not the default route.  I am thinking that since this is a default route, it was basically like, piss off.  You can't touch me.

This caused me to look at another way to kill it.  I went to my all time favorite...distibute-list.  Did a quick prefix-list to deny that route and allow all others coming in the correct interface and BAM, it worked like a charm.  That is something that is definitely good to know. 

So one last mention about this scenario is that I used a triple route-map setup since I had three routing protocols.  This worked on filtering routes correctly but did cause some sub-optimal routing.  May come back to fixing that later but for now this is a test to know that I can do route redistribution with no loops.