Apipa - Automatic Private Ip Addressing - Apache Labs ANAN-100/D Manual

Apache Labs ANAN-100/D

APIPA - Automatic Private IP Addressing

Definition: A feature of Microsoft Windows, APIPA is a DHCP failover mechanism for
local networks. With APIPA, DHCP clients can obtain IP addresses when DHCP servers are
non-functional. APIPA exists in all modern versions of Windows except Windows NT.
When a DHCP server fails, APIPA allocates IP addresses in the private range 169.254.0.1
to 169.254.255.254. Clients verify their address is unique on the network using ARP. When
the DHCP server is again able to service requests, clients update their addresses
automatically.
In APIPA, all devices use the default network mask 255.255.0.0 and all reside on the same
subnet.
APIPA is enabled on all DHCP clients in Windows unless the computer's Registry is
modified to disable it. APIPA can be enabled on individual network adapters.
Also Known As: Automatic Private IP Addressing; AutoNet
Examples:
Because APIPA uses IP addresses in the private Class B space, APIPA is a feature generally
only useful on home or other small intranet LANs.
Reference:
http://en.wikipedia.org/wiki/APIPA
Revision v1.8 April 23, 2013 67 of 70 authors N9VV and KC9XG