Route Redistribution

So today I watched the iPexpert video on route redistribution and came up with a couple of scenarios to lab up on GNS3.  I also made some notes for a problem that has been bugging the crap out of me since my last lab attempt.  I am working on labbing it up as well since there was a problem with redistribution on there that I know caused me an issue.

So scenario one involves a problem that was gone over in the video and I want to make sure that I can find out the answer.  It involves blocking routes when they are distributed in with redistribution.  It has the three major routing protocol (RIPv2, OSPF, and EIGRP) and can cause a major loop but I know how to beat that.  Using route maps will beat that.  The tricky part is when I will inject  default route into an NSSA area.  To beat this I know that I can use distance, ACLs, or distribute lists.  Gonna try to do this with distance.

The second scenario is another triple route injection problem just for me to cement my ability.

The other scenario is what I said earlier.  It is a topology from my last attempt and something I won't talk about much here.  I will have to figure out how to talk about that one without breaking the NDA which may not happen.

So with redistribution, I do like iPexpert's way of handling redistribution.  No matter the task scenario given, always break it up into little pieces.  Configure each protocol first and then worry about redistribution.  It may not give you points until they are all done but so what.  Make life easier for you.  Having seen multiple scenarios, I would suggest following those guidelines as well.  Configure RIP.  Configure OSPF.  Configure EIGRP.  Configure redistribution based on what is asked.  Like I said, this is great way of approaching it.

So how to fix a three way distribution.  The easiest way if you can do it is to route-maps.  Set the tags to the AD of the originating routing protocol.  Block the routes with the tag of the same AD as the destination of the route.  Copy all other tags.  Finally set the tag to the AD of the source protocol.  Do that on every router for each protocol with very little changing and BAM.  What a great and awesome loop free topology.  Well nearly loop free.

Supposedly, and I am still looking at this in scenario 1 from above, a loop can form if a route is injected using a non-normal way of making the route.  Think of injecting a default route in a NSSA area.  Like I said, this is supposedly.  Will hopefully know more tomorrow.

My final gotcha of the night.  When redistributing connected routes using route-maps, be careful to make sure that interfaces are redistributed correctly.  Not including all the correct interfaces can cause full connectivity to fail and fail hard.  Thank goodness for TCL scripts to quickly check this all out.

Well, for now, that is all.  Hopefully I can keep this going.  I am liking it because it is really helping me to cement what I am learning.