Chapter 9 High Availability for FortiOS 5.0 : HA and failover protection : Session failover (session pick-up) : IPsec VPN session failover
  
IPsec VPN session failover
Session failover is supported for all IPsec VPN tunnels. To support IPsec VPN tunnel failover, when an IPsec VPN tunnel starts, the FGCP distributes the SA and related IPsec VPN tunnel data to all cluster units.