Under my OpenBSD machine, it's smart enough without further configuration. That is, I have two networks beyond my Internet connection, I bind dhcpd to the two internal interfaces by setting them on the command line, and I have network-specific configurations in my dhcpd.conf without any mention of the interfaces. I assume that it figures it out based on the IP address and netmask of the interfaces, but, honestly, it never occurred to me that it wouldn't work. I set it up in the most obvious manner possible the first time out, and it worked like a champ. (Except for my Windows 2K box's client, which somehow notices that the DHCP server has gone down when I reboot it for upgrades, and releases the lease, despite having ten hours remaining. What a PoS. )