DMVPN - using a default route
When deploying a DMVPN topology, the hub router of the topology often uses a statically defined default route. This default route can be used to route traffic to the spokes, and can be redistributed into the routing protocol being used such as RIP or OSPF. This is often done in a lab environment.
However, in a real world scenario, you are probably already using a default route for traffic destined for the Internet. In this case, you should use a summary route that matches the networks behind the spoke routers instead of a default route.
For example, let’s say we have a single Hub that uses a default route to connect to the Internet. Let’s assume that we have three spokes, and behind each spoke we have the following subnets:
- Spoke 1: 192.168.4.0/24
- Spoke 2: 192.168.5.0/24
- Spoke 3: 192.168.6.0/24
We want to create a summary route that includes all of these networks. In the lesson, Rene used a default route like so:
Hub(config-if)#ip summary-address rip 0.0.0.0 0.0.0.0
But this won’t work since our default route is used to connect to the Internet. We need a summary route that will include all of the subnets of the spoke routers. We can do the following, assuming we are using RIP as the routing protocol:
Hub(config-if)#ip summary-address rip 192.168.4.0 255.255.252.0
This network and subnet mask combination includes all the subnets on all spokes.