The router at the Head Quarter undertakes the role of a Hub while branch routers take the role of Spokes. In this Hub-and-Spoke topology, each Branch can access some resources on the HeadQuarter. But there are some disadvantages with this topology:
+ When a spoke wants to communicate with another Spoke, it must go through the Hub which increases the traffic passing through the Hub, increase CPU and memory usage on Hub and can create bottle-neck problem. This also increases latency for time-sensitive applications such as VoIP, video conference…
+ Each site requires a static public IP address if the environment between them are public (like the Internet).
+ The configuration is complex, especially with large network. When a new Spoke is added, additional configuration is required on Hub
Dynamic Multipoint VPN (DMVPN) is a solution of Cisco that can be used to overcome these disadvantages. DMVPN provides the following advantages:
+ Provides full meshed connectivity with simple Hub-and-Spoke topology. The spokes can communicate between each other without going through Hub
+ Only one static public IP address is required on Hub. Spokes can use dynamic (unknown) public IP addresses
+ The configuration is simple even in large network. No additional configuration is required on Hub when new Spokes are added.