The following article discusses the source of the 169.254.x.x address seen on AirPort clients attempting to connect to the AirPort Base Station.

The 169.254.x.x address is typically seen on computers set to connect to the network via Ethernet or AirPort using a DHCP server. If a DHCP (Dynamic Host Configuration Protocol) server is not found by the computer, a valid and unique address in the range of 169.254.0.0 to 169.254.254.255 inclusive and a subnet mask of 255.255.0.0 will be assigned. This feature has been built-in to every version of Open Transport since Mac OS 8.5. It is also built-in to all Microsoft Windows-based computers using Windows 95, Windows 98, or Windows 2000.

If you have been unsuccessful in trying to connect your AirPort equipped-computer to an AirPort Base Station, then you probably have seen this 169.254.x.x address. The most common reason for getting it is not associating with a base station before trying to use an application that uses TCP/IP such as a Web browser.

It may also indicate that the IP address of the base station is on a different subnet than the connecting computer. In this situation, you will need to manually assign the client computer an address that is on the same subnet before attempting to access the base station.

Remember that if you have the base station set to bridge to an existing local area network (LAN) providing IP addresses from a DHCP server, a wireless client can still obtain a 169.254.x.x address if a server is not found.

Why the 169.254.x.x address?

This 169.254.x.x address, although not an officially private address (as 10.0.0.0 would be), poses little if any chance for conflict with other addresses on the Internet. Open Transport will choose a number randomly in a range of 169.254.0.0 to 169.254.254.255 - a range of over 64,000 possible addresses.

The result of this auto configuration of addresses allows communication automatically with other 169.254.0.0 network addresses on the same LAN without a DHCP server. In other words, Macintosh and Windows-based computers with their default networking configurations installed can communicate with each other on the same LAN automatically.

The auto-configuration of IP addresses is beneficial for workgroups without a professional network administrator, as well as any LAN when its DHCP server is not available or when it has simply stopped working.

It is also very useful when using AirPort equipped-computers on an ad-hoc or computer-to-computer network.

Additional information is available in article 58619: " AirPort Base Station: Reason for 192.42.249.12 IP Address ".

Note: Wireless Internet access requires AirPort Card, AirPort Base Station, and Internet Access (fees may apply). Some ISPs are not currently compatible with AirPort, including America Online. Range may vary with site conditions.