DHCP relaying

Hi, I would like to ask how we can direct FR dhcp server (using an ldap backend) to relay to another dhcp server. The idea is that we have a db of known MAC addresses which have an associated VLAN (assigned during MAC Auth) and a static IP address (assigned through FR dhcp server). If a MAC address is unknown, we would like to be able to relay to another dhcp server which will be responsible for dynamic IP address allocation (because, as I understand, FR does not support dynamic IP address allocation) on a private IP address range, with limited access. What will be the "command" to use for relaying? Thanks in advance, Nick