pfSense

Certain DHCP server relay scenarios can benefit from using RFC 3527 behavior for the gateway IP address in a relayed DHCP packet.

This option is supported with the -U <interface> parameter with the current DHCP relay software, but is likely also supported on others.

The option replaces the gateway IP address in the DHCP packet with that interface address, and encodes the original gateway address in suboption 5.

A DHCP server running Kea understands this suboption natively and automatically chooses an appropriate subnet.

Unlike upstream interfaces, -U can only be specified once, so it would make sense to have a separate drop-down selector for this, defaulting to None/Disabled.

See also: https://kb.isc.org/docs/isc-dhcp-44-manual-pages-dhcrelay