Sunday, May 9, 2010


Here's a problem I ran into. I set up a new environment with a different layer 3 infrastructure. And everything seemed to be working. Until I got reports that some people couldn't get to one network in the new environment.

So, traffic going to the range was working great for some people, but for others, it was not -- TCP connections would connect and then fail after a few seconds.

I spent a bunch of time looking at switch ports, and spanning tree, looking to see where the blocking ports were and making sure that there's no loops. So I gave up on that line of inquiry and started tracing back at layer 3.

Sure enough, there were two routes for in one of my core routers - one of which pointed to the right place, and one of which pointed to the wrong place.

I deleted the wrong route, and things worked again.


  1. Out of curiosity, what generated the incorrect route?

  2. Me!
    Regis sits in the corner with the dunce hat on

    More specifically, the new environment was actually a data center move that included some topology changes. And one of the topology changes was a change in that route -- I'd remembered to add the new route, but forgot to delete the old one.



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Regis has worked as a network engineer since 1994 for small companies and for large companies.