Chapter 11 IPsec VPN for FortiOS 5.0 : Defining VPN security policies : Defining VPN security policies : Defining an IPsec security policy for a policy-based VPN : Allow traffic to be initiated from the remote site
  
Allow traffic to be initiated from the remote site
In addition to these operations, security policies specify which IP addresses can initiate a tunnel. by default, traffic from the local private network initiates the tunnel. When the Allow traffic to be initiated form the remote site option is selected, traffic from a dialup client or computers on the remote network initiates the tunnel. Both can be enabled at the same time for bi-directional initiation of the tunnel.