Chapter 1 What’s New for FortiOS 5.2.1 : IPsec VPN : Internet Key Exchange (IKE) : Assign Client IP Addresses Using DHCP Proxy
  
Assign Client IP Addresses Using DHCP Proxy
IKE can now use the system DHCP proxy to assign client IP addresses. To use this feature, the DHCP proxy must be enabled and a IP range selected. Up to 8 addresses can be selected for either IPv4 or IPv6. After the DHCP proxy has been configured, the assign-up-from command is used to select assign IP address via DHCP.
Syntax
system settings
set dhcp-proxy enable
set dhcp-server-ip <range>
set dhcp6-server-ip <range>
end
 
config vpn ipsec phase1
set assign-ip-from dhcp
end
 
IP assignment can also come from a locally defined range or via the user group.