APIPA stands for Automatic Private IP Addressing. It is a feature of Windows-based operating systems that enables a Dynamic Host Configuration Protocol (DHCP) client to automatically assign an IP address to itself when theres no DHCP server available to perform that function. APIPA serves as a DHCP server failover mechanism and makes it easier to configure and support small LANs. If a DHCP client is unable to communicate with a DHCP server, it selects an IP address from a range of predefined addresses -- 169.254.0.0 to 169.254.255.255 -- and automatically assigns that address to itself. The Internet Assigned Numbers Authority (IANA) reserves these addresses specifically for APIPA use cases to ensure they dont conflict with DHCP routable addresses. As part of the APIPA assignment process, the DHCP client uses the Address Resolution Protocol (ARP) to ensure the chosen address isnt being used by another network computer. Once the client has assigned itself an IP address, it can communicate over TCP/IP with other computers on the LAN that are either configured for APIPA or manually set to the correct address range and using a subnet mask of 255.255.0.0.