Cisco – Configuring Dynamic Multipoint Virtual Private Networks DMVPN
KB ID 0000954 Problem A while back I uploaded a run through on how to deploy GRE tunnels and protect those tunnels with IPsec. That point-to-point GRE tunnel is a good solution, but if you have a lot of sites it’s not a solution that scales very well. Yes you can have 2147483647 tunnel interfaces, but good luck manually configuring all those tunnels and even if you did, if you want each of your remote sites to talk to each other...