pfSense can only be configured as a DHCP relay if the DHCP server has been disabled on all interfaces. If necessary, disable the DHCP server first. To disable the DHCP server, do the following:

1. Navigate to Services | DHCP Server.
2. Click on the tab for the interface on which the DHCP server is enabled (for example, LAN).
3. Uncheck the Enable DHCP Server on the interface checkbox.
4. Click on the Save button.
5. Repeat Steps 2 through 4 for each interface on which the DHCP server is enabled.