APIPA stands for Automatic Private Internet Protocol Addressing.

APIPA is in every version of Windows since NT and all versions of Mac OS X.

APIPA is a DHCP mechanism that provides DHCP clients with self-assigned IP addresses when DHCP servers are not available. When there isn’t a DHCP server available, APIPA assigns IPs from 169.254.0.1 to 169.254.255.254 with a default mask of 255.255.0.0.

Clients leverage ARP ( Address Resolution Protocol )to verify their address doesn’t conflict with another on the network. APIPA is enabled on all interfaces of all DHCP clients in pretty much all modern operating systems.