Chapter 11 IPsec VPN for FortiOS 5.0 : IPv6 Features : IPv6 Network Address Translation : NAT64 and NAT66 session failover
  
NAT64 and NAT66 session failover
The FortiGate Clustering Protocol (FGCP) supports IPv6, NAT64, and NAT66 session failover. If session pickup is enabled, these sessions are synchronized between cluster members and, after an HA failover, the sessions will resume with only minimal interruption.