Chapter 11 IPsec VPN for FortiOS 5.0 : IPsec VPN in the web-based manager : Concentrator
  
Concentrator
In a hub-and-spoke configuration, policy-based VPN connections to a number of remote peers radiate from a single, central FortiGate unit. Site-to-site connections between the remote peers do not exist; however, you can establish VPN tunnels between any two of the remote peers through the FortiGate unit’s “hub”.
In a hub-and-spoke network, all VPN tunnels terminate at the hub. The peers that connect to the hub are known as “spokes”. The hub functions as a concentrator on the network, managing all VPN connections between the spokes. VPN traffic passes from one tunnel to the other through the hub.
You define a concentrator to include spokes in the hub-and-spoke configuration. You create the concentrator in VPN > IPSec > Concentrator and select Create New. A concentrator configuration specifies which spokes to include in an IPsec hub-and-spoke configuration.
Concentrator Name
Type a name for the concentrator.
Available Tunnels
A list of defined IPsec VPN tunnels. Select a tunnel from the list and then select the right arrow.
Members
A list of tunnels that are members of the concentrator. To remove a tunnel from the concentrator, select the tunnel and select the left arrow.