David McNett :: Custom Configuration of Airport Extreme Base Station

Airport Base Station Here at SlackerNOC I use an Apple Airport Extreme Base Station (Extreme) for 802.11b and 802.11g wireless networking. I've got it located in closet upstairs at my house and I get pretty good coverage throughout the house and even into the back yard. I love it, because it lets me roam the house with my powerbook choosing a spot to sit and work to suit my mood.

I chose the Apple base station over cheaper, more flexible third party solutions because I was most interested in ensuring that iChat AV audio and video chat would be able to successfully pierce the NAT layer of my network for wireless and other NAT hosts. At my apartment I was using my old Cayman DSL router to do NAT and its NAT implementation didn't support the UPnP NAT Traversal gook which iChat requires to make the connections for AV chatting. I knew that if I went with the Apple solution I'd be covered. I was also interested in a device which could act as a dialup internet router to give me network connectivity at the house until my DSL was live.

The router has done what I've needed it to do, with two disappointing exceptions.

The configuration tool is simplified and lacks the ability to provide NAT without also providing DHCP address assignment.
The NAT configuration is limited and doesn't allow much flexibility for the network settings

So there's no way to independently control these two services -- disabling "Distribute IP Addresses" greys out the NAT configuration and effectively disables the ability of the base station to do address translation. Plus, there's also no provision for NAT to handle hosts which are outside of the range of DHCP assigned addresses.

My preference is to do DHCP from my FreeBSD server in order to benefit from the greater logging and flexibility it provides. Using dhcpd on a Unix box lets me customize the address assignment based on whether or not the MAC address is known or unknown. It allows me to ensure that my Powerbook always gets the same address. It lets me do host-updated Dynamic DNS so that roaming clients have useful hostnames. Plus it also lets me easily log and monitor active DHCP leases. In all, it's a superior solution for my needs.

The Apple hardware is perfectly capable of working they way I prefer, it's merely the configuration tool which thwarts me.

What I do now is to configure the base station using the Apple tools, enabling DHCP and NAT. When I save the configuration, the base station restarts and for a few minutes I've got the confusing situation of having two DHCP servers on the network.

Then I fire up Jonathan Sevy's Java Base Station Configurator which is a Java based configuration tool for these units. With it, I'm able to disable just the DHCP server in the base station while leaving NAT enabled. I'm also then able to configure NAT to a more flexible setting which allows my non-DHCP-assigned internal hosts to also access the internet through the NAT functions of the base station.

It's that non-standard network configuration of 10.0.0.1/23 that's not possible to do with the Apple tools. My DHCP server is responsible for the addresses in 10.0.1.0/24 and I manually assign the addresses in 10.0.0.0/24. With the /23 netmask, the base station's NAT will handle both groups of addresses.