Cisco has introduced Tunnel Route Selection, another “somewhat” underdocumented feature in IOS release 12.4(11)T (reading the sparse documentation, it appears to be a half-baked kludge implemented for a specific customer). I was wondering for a long time why I would ever want to use this feature, until Floris Martens asked me a question about a redundant DMVPN network using two ISPs, and all of a sudden it all made a perfect sense.

Building redundant DMVPN networks with multiple ISPs is a pretty common scenario, so I’ve included it in the DMVPN – From Basics To Scalable Networks. However, when I tried to build a test lab, I could not get tunnel route-via to work in a protected DMVPN network. After a few hours, I had to conclude there’s no way to make tunnel route-via work with tunnel protection (you could probably make it work in combination with crypto maps in Phase I DMVPN configuration, but I definitely didn’t want to go down that route).

To add insult to injury, somehow Cisco’s programmers managed to lose the “tunnel route-via feature is on” part of the show interface printout when merging various IOS trains to produce 15.0(1)M. The feature works in 15.0(1)M, but there’s no way to check with a show printout whether it’s enabled or not.