If you’re building a DMVPN network with large spoke-to-hub ratio, BGP is one of the better options – it has no scalability limitations associated with multicast flooding; the only parameter you have to consider is the number of BGP sessions the hub router can handle (and according to this presentation, ASR can handle 2000+ spokes).
Here’s a brief summary; to learn more, watch a (free) step-by-step explanation of BGP-over-Phase 1 DMVPN configuration guidelines video:
- Use EBGP between the hub and the spoke routers to eliminate potential IBGP next-hop issues (unless your hub router can change BGP next hops on reflected routes)
- You should filter outbound routing updates on the hub router to minimize the amount of routing information and the load placed on the hub router;
- When using outbound filter in the hub router, advertise the default route to the spokes;
- Use BGP session templates and policy templates to minimize the hub router’s BGP configuration.