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.