What is automatic private IP addressing?
Automatic private IP addressing (APIPA) is Microsoft's terminology for automatic address configuration in the Windows 98, ME, 2000 and XP operating systems. APIPA allows a computer on a local area network (LAN) to assign itself a unique IP address when Dynamic Host Configuration Protocol (DHCP) is not available. APIPA is sometimes referred to as Auto-IP.
Networked computers differ in their individually assigned IP addresses. The address is referred to as the link-local address. This is an IP address that is used for local communication with other LAN computers.
Stateless address automatic configuration techniques use two protocols to assign IP addresses to computers connected to the Internet: Internet Protocol Version 4 (IPv4) and Version 6 (IPv6). These protocols are used in the absence of a DHCP server or some other automatic method of assigning unique IP addresses. Automatic IP addressing can also be used in the event of a server failure with an IP address assignment function.
IPv4 link local addressing uses an address block that is reserved by the Internet Engineering Task Force (IETF). This address block range is 169.254.1.0 to 169.254.254.255.
The IPv6 protocol requires an operating system to assign a link-local address to the network interfaces and to use the prefix 'fe80 :: / 10'. It also uses more than one IPv6 address for each computer's network interface. A media access control (MAC) address-based methodology and duplicate address algorithms guarantee the uniqueness of IP addresses.