Thursday, April 14, 2011

APIPA Automatic Private Internet Protocol Addressing

  • APIPA (Automatic Private Internet Protocol Addressing) is alternatively known as zero configuration networking or address autoconfiguration.
  • It is a TCP/IP standard designed by Microsoft as substitute to DHCP (Dynamic Host Configuration Protocol).
    • It is used to automatically configure IP-based hosts when a DHCP Server is unavailable.
    • APIPA is a useful solution for computer connected to a small local network (LAN) where all devices are connected on a single physical link.
  • Computers that have been configured by APIPA have an IP address that is in the range and have a subnet mask of
  • IETF's formal standard for APIPA functionality is RFC 3927 (Dynamic Configuration of IPv4 Link-Local Addresses.
  • APIPA is useful in cases where there is no DHCP server and and there is either no previous IP address or the IP address's lease has expired.
    • A Windows computer will retain the previous IP address as long as the default gateway replies, but if not, will automatically configure itself a new one.
    • A discover message is sent every 3 minutes in an attempt to re-establish communications with the DHCP server.

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