Chapter 9 High Availability for FortiOS 5.0 : HA and failover protection : Session failover (session pick-up) : PPTP and L2TP VPN sessions
  
PPTP and L2TP VPN sessions
PPTP and L2TP VPNs are supported in HA mode. For a cluster you can configure PPTP and L2TP settings and you can also add security policies to allow PPTP and L2TP pass through. However, the FGCP does not provide session failover for PPTP or L2TP. After a failover, all active PPTP and L2TP sessions are lost and must be restarted.