Home Forums Networks & Cross-Platform Networking Airport Utility IP address limit

I have been attempting to configure a new 3TB Time Capsule for my son. However, he has a high speed cable internet connection that requires the connecting device, in this case the Time Capsule, to have a fixed IP address. The TC creates a LAN, just as it should, and the drive works perfectly. When I connect the TC to his backup DSL connection everything works perfectly.

The problem occurs when I attempt to configure the WAN with a fixed IP in the form: Airport Utility refuses to accept the third digit in the final triad. In other words I can only enter the first 13 of the required 14 characters (with a possible maximum of 15). So far I have:

• Verfied I am using the latest revision of Airport Utility 5.5.3
• Resset the Time Capsule several times using Airport Utility and the hardware reset button on the TC itself
• Tried using another copy of Airport Utility on another computer (also running OS X 10.7.1)
• Attempted to set another Airport Extreme to the same IP address and run into the same 13 character limit in the IP address field

I am pretty well convinced at this point the problem is due to an error in Airport Utility 5.5.3 but not even Google has been able to uncover a reference to this problem which makes me wonder why someone else has not encountered it before.

So before I give up and call Apple, does anyone have any ideas what I may be missing or suggestions for solving the problem?

The limit on each "triad" is a range of values, not a number of digits. The actual range depends on your netmask, but in the common case where your netmask is 255.255.255.0, the final byte of your WAN address must be in the range 1-254. (0 is reserved to refer to the subnet itself, and 255 is reserved as the broadcast address.) Moreover, leading zeroes are commonly prohibited, to avoid confusing software that might interpret the value as octal.

More than once I've needed to set things up in very specific ways on my airport, and Apple has left me with a very nifty way to do it. Use the airport utility to save a backup of your configuration. Open the file.

Surprise, surprise, it's XML. Piece of cake to edit however you like. You can do things not possible with the airport utility, like specifying router IP address independent from DHCP pool range.

Then when you're done, just restore the configuration file.

Unfortunately these forums do not have a "dope-slap" smiley and I need one now. Interestingly enough I got the settings from the setup letter sent by the ISP and the last group is most definitely out of the allowable range of values. I should have caught that, but I don't feel quite so bad knowing the ISP made the same mistake.


That is a handy dandy little piece of information to add to my knowledge base. I have a feeling I will have need of it — possibly in the very near future.


Thanks to both of you!