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I have seen a term APIPA many times i all the windows system except NT. And have seen it starting with 169. To be frank i don't know what exactly APIPA is and why is it required? Now as i come across it many times, i need to know what is meant by APIPA ? Could you guys please help me out for the same ? Thanks in advance.
APIPA stands for Automatic Private IP Addressing. It is one of the feature of Microsoft Windows which is a DHCP failover mechanism.With APIPA, DHCP clients can automatically self-configure an IP address and subnet mask when a DHCP server isn't available. A Windows-based computer that is configured to use DHCP can automatically assign itself an Internet Protocol (IP) address if a DHCP server is not available. This occurs when the TCP/IP protocol is installed, set to obtain it's IP address automatically from a Dynamic Host Configuration Protocol server, and when there is no DHCP server present or the DHCP server is not available.The device chooses its own IP address in the range 169.254.1.0 through to 169.254.254.255.
When a DHCP client boots up, it first looks for a DHCP server in order to obtain an IP address and subnet mask.It also allows household users and small business users to create a functional single subnet TCP/IP network without manually configuring the TCP/IP protocol or setting up a DHCP server.This is a dynamic service that means this service is related with DHCP.When a DHCP server fails, APIPA allocates addresses in the private range 169.254.0.1 to 169.254.255.254.
In APIPA, all devices use the default network mask 255.255.0.0 and all reside on the same subnet.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. This feature makes configuring and supporting a small Local Area Network (LAN) running TCP/IP less difficult.The subnet mask is automatically set to 255.255.0.0 and the gateway address is set to 0.0.0.0.The APIPA service also checks regularly for the presence of a DHCP server and APIPA protocol is enabled by default.