DMVPN Phase 1 Fundamentals

The following video explains the DMVPN Phase 1 fundamentals and spoke router configuration guidelines (here’s why I started this series of posts):

Let's summarize:

  • Phase 1 DMVPN uses point-to-point GRE tunnel on spoke routers and multipoint GRE tunnel on the hub router.
  • All the DMVPN traffic (including the traffic between the spokes) flows through the hub router.
  • On the spoke routers, the hub router must be the IP next-hop for all destinations reachable through the DMVPN subnet (including other spokes).
  • Multicast packets (including routing protocol hello packets and routing updates) are exchanged only between the hub and the spoke routers.

More information

The Phase 1 DMVPN section of the DMVPN: from Basics to Scalable Networks webinar (register here or buy a recording) also includes the following topics:

  • Basic hub router configuration;
  • Explanation of GRE tunnel key concept and its potential performance implications;
  • NHRP configuration of the hub and spoke routers;
  • Non-unique NHRP registrations;
  • Multicast over mGRE principles;
  • DMVPN redundancy;
  • IPSec configuration with shared keys and certificates;
  • Monitoring and troubleshooting guidelines.

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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.