Why there is a need to increase the tunnel interface bandwidth when running EIGRP with DMVPN?
The default value is 9. The recommend bandwidth value is 1000 or greater. Setting the bandwidth value to at least 1000 is critical if EIGRP is used over the tunnel interface. Higher bandwidth values may be necessary depending on the number of spokes supported by a hub. The bandwidth setting for the spoke does not need to equal the bandwidth setting for the DMVPN hub. It is usually easier if all of the spokes use the same or similar value.