A while ago I wrote about the Tunnel Route Selection feature of Cisco IOS and how it could be used to solve the redundantly-connected spoke site issue. Here’s the basic design: you have two uplinks to two ISPs, two DMVPN tunnel interfaces, each one sourced from one of the uplinks and two default routes. Everything works great until one of the ISPs enables RPF checks ... and then the all hell breaks loose. More in a short clip made from a recording of my DMVPN – From Basics To Scalable Networks webinar.
Ivan Pepelnjak, CCIE#1354, is the chief technology advisor for NIL Data Communications. He has been designing and implementing large-scale data communications networks as well as teaching and writing books about advanced technologies since 1990. See his full profile, contact him or follow @ioshints on Twitter.