Automatic Private IP Addressing (APIPA)

If a computer running Microsoft Windows 98 or a later version of Windows does not have a static IP address configured and cannot obtain an IP address from a Dynamic Host Configuration Protocol (DHCP) server, it will use Automatic Private IP Addressing (APIPA) to assign a random IP address from the link-local address range 169.254.1.0 to 169.254.254.255.

APIPA, also known as IPv4 Link-Local (IPv4LL), Zero Configuration Networking, or Zeroconf, is described in RFC 3330 (available at RFC 3330 - Special-Use IPv4 Addresses) and RFC 3927 (available at RFC 3927 - Dynamic Configuration of IPv4 Link-Local Addresses).

APIPA allows computers to communicate on a Local Area Network (LAN), such as an ad-hoc wireless network, without a DHCP server or static IP address configuration. If a computer has an APIPA IP address on a network that has a DHCP server, it means that the computer could not contact the DHCP server. Either the computer is not properly connected to the network, or the DHCP server was offline.

Computers with APIPA IP addresses will regularly attempt to contact a DHCP server in case a DHCP server is brought online after the client computer starts.