DHCP Relay Server

[HankG]

Hello!

I have problems with DHCP relay. We have two sites, A and B, both have an OPNSense firewall, connected by a direct link. I want the opnsense on A to be the dhcp server for *both* sites. I understand that I can tell B to forward DHCP requests to A, but how do I configure *A* so that it specifically answers these DHCP requests with a specific subnet? We're still on ISC dhcpv4, I need to create some sort of interface for this, but I don't understand how and which. To my understanding, normally the circuit-ID that is sent with the dhcp relay might be used to determine which dhcp replies to serve, but I can't find any place to use that in the dhcp configuration web ui.

I'd be glad about any help on how to correctly set this up!
Greetings, Hank