Disabling DHCP on an Airport Extreme Router

I’ve been looking at the Apple Airport Extreme.

Disabling DHCP on an Airport Extreme Router

I’ve been testing an Airport Extreme Router and found that I couldn’t disable using it as a DHCP server. Well, actually if it’s in bridge mode it won’t be a DHCP server but I wanted it as a router, not a bridge.

I’m using what are the current Airport Extreme and Airport Utility. The Airport Utility version is 6.3.2 (632.3). The Airport Extreme shows a version of 7.7.3 (which I assume is the firmware but it just says version) and the part number is ME918LL/A. It is the current model at the time of this post (July 2014).

The three router modes are:

Available router modes
Available router modes

I wanted to use it as a NAT router but without DHCP. I already have a DHCP server I want to keep (my Synology NAS). I couldn’t really turn off DHCP but there was an easy enough way to get around this limitiation.

The short instructions are summarized in the screenshot below (details later).
Configuration to prevent DHCP addresses
1. Set a small DHCP range using IP addresses that aren’t used by the real DHCP server or any other device on the network. (Actually, it can probably duplicate another device but this is cleaner.) In the screenshot I used 192.168.1.253 to 192.168.1.254. I had to use two addresses, the same beginning and ending addresses weren’t allowed.
2. Create dummy DHCP reservations for each of the IP addresses. The MAC addresses don’t have to be real.

Detailed Instructions

  1. Open the Airport Extreme Utility and go to the Network tab and click the Network Options button.
    Airport Extreme network tab
  2. Set a DHCP range that’s appropriate for your network. Use addresses that aren’t used by any of your computers or other DHCP ranges. (In theory none of these addresses should be used, but keeping things valid will avoid problems.) Save the screen and you’ll be back on the network tab.
    DHCP range
  3. Click the “+” sign under “DHCP Reservations.
    Click the + to add the DHCP reservations
  4. Type in a description, make sure “MAC Address” is selected for “Reserve Address By” and type an dummy Mac address. I just type the number “1” (or 2) until it stops me. Then save the information.
    Screenshot of the DHCP reservation
  5. Repeat step 4 for all IPs in the DHCP range. The Airport Utility will prefill an unreserved IP in the range so you don’t need to keep track.
  6. Save everything all the way out and your Airport Extreme will restart.

In the end the Airport Extreme is still running a DHCP server, except it doesn’t have any IP addresses to hand out so the “real” DHCP will be the only one to respond.