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APIPA
Last modified: Thursday, September 18, 2003
Short for Automatic Private IPAddressing, a feature of later Windows operating systems. With APIPA, DHCPclients can automatically self-configure an IP address and subnet mask when a DHCP server isn't available. When a DHCP client boots up, it first looks for a DHCP server in order to obtain an IP address and subnet mask. If the client is unable to find the information, it uses APIPA to automatically configure itself with an IP address from a range that has been reserved especially for Microsoft. The IP address range is 169.254.0.1 through 169.254.255.254. The client also configures itself with a default class B subnet mask of 255.255.0.0. A client uses the self-configured IP address until a DHCP server becomes available.
The APIPA service also checks regularly for the presence of a DHCP server (every five minutes, according to Microsoft). If it detects a DHCP server on the network, APIPA stops, and the DHCP server replaces the APIPA networking addresses with dynamically assigned addresses.
APIPA is meant for nonrouted small business environments, usually less than 25 clients.
APIPA in Windows Millennium Edition This article provides a description of the Automatic Private IP Addressing feature in Windows Millennium Edition (Me).
APIPA Tutorial This Knowledge Labs tutorial walks the user through the APIPA set up.
