Note: This document replaces an old, deprecated technique for accomplishing the same goal. This way is much better, but I'm leaving the old page online for posterity's sake.
The Problem
You have devices or computers on your network which require a more complicated DHCP configuration than the Apple Airport can provide. Perhaps it's a Cisco phone that wants to know where the tftp server is, or it's desktop computers that need to know about your LDAP server in order to support network logins. Whatever the dilemma, the consumer-oriented firmware in the Apple product just isn't going to get you there.
And yet, for some reason you still want to use the Airport to do NAT translation for your private IP space so that all your devices can still talk to the Internet. But, to your dismay, you discover that it's "all or nothing" with Apple. If you disable DHCP it shuts off NAT as well. There's not a way to independently control both settings.
The Answer
It's brutally simple, actually. Just leave DHCP enabled on the Airport, but restrict the available IP range to just a single IP. Then use a DHCP Reservation to bind that IP to a MAC address that doesn't actually exist. The Airport will silently refuse to respond to DHCP requests since it thinks that it is out of addresses that can be assigned. This lets you bring up a "real" DHCP server on another computer which can provide the more complicated DHCP settings you need.
© Copyright 1995-2012 David McNett. All Rights Reserved.
