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Automatic Private IP Addressing (APIPA) is the Microsoft Windows term for fallback to the "link local" addresses as prescribed in RFC 3330. It provides a recovery capability for DHCP clients that can neither contact nor obtain addresses from their designated server. APIPA effectively places clients on a peer-to-peer network until such a time as the server can be contacted for IP distribution.
Automatic Private IP Addressing (APIPA) is appropriate for simple networks that have only one subnet. With APIPA, if no DHCP server is available, the computer automatically assigns itself a private IP address. If a DHCP server later becomes available, the computer changes its IP address to one obtained from a DHCP server. Computers using APIPA addresses can communicate only with other computers using APIPA addresses, on the same subnet. They are not directly reachable from the Internet.
APIPA is used when there is no DHCP server detected and static IP address configurations are not used.
