The Internet Assigned Numbers Authority( IANA) has made the addressing range from 169.254.1.0 to 169.254.254.255 available for the automatic generation of private IP addresses. The service for automatic IP addressing is called Internet Protocol Automatic Configuration (IPAC) and on Windows Automatic Private IP Addressing (APIPA). It is also referred to as Zero Configuration Networking (Zeroconf).
The APIPA protocol supports simple network operation in which the network interfaces connected to a network are automatically configured with the IP protocol by the operating system and the connected devices can communicate via the IP protocol. The connected computers scan the network for a DHCP server at regular intervals. As soon as a computer has found a DHCP server, it discards the automatically generated IP address and uses the new one provided by the DHCP server. The user can use the "ipconfig" command to determine which IP address has been assigned to the computer.
If no DHCP server is available, the DHCP clients can be provided with IP addresses and subnet masks using APIPA. In this case, Windows generates an appropriate IP address during APIPA operation. IP addresses can also be assigned dynamically via a DHCP server and the DHCP protocol. The address space 169.254.x.x is available for the IP addresses, the subnet mask is set to 255.255.0.0 and the gateway is set to the IP address 0.0.0.0.
APIPA is enabled by default and can be disabled in the computer. If the APIPA protocol is disabled, the computer uses a default IP address, but this can be easily changed. It is not available for Windows NT and Windows 95operating systems.