Chapter 11 IPsec VPN for FortiOS 5.0 : IPv6 IPsec VPNs : Configuring IPv6 IPsec VPNs : Phase 1 configuration
  
Phase 1 configuration
In the web-based manager, you define the Phase 1 as IPv6 in the Advanced settings. Enable the IPv6 Version check box. You can then enter an IPv6 address for the remote gateway.
In the CLI, you define an IPsec phase 1 configuration as IPv6 by setting ip‑version to 6. Its default value is 4. Then, the local-gw and remote-gw keywords are hidden and the corresponding local-gw6 and remote-gw6 keywords are available. The values for local-gw6 and remote-gw6 must be IPv6 addresses. For example:
config vpn ipsec phase1-interface
edit tunnel6
set ip-version 6
set remote-gw6 0:123:4567::1234
set interface port3
set proposal 3des-md5
end