Automatic Private IP Addressing (APIPA):
Short for Automatic Private IP Addressing, a feature of later Windows operating systems.
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
If a network client fails to get an IP address using DHCP, it can discover an address on its own using APIPA.
To get an IPv4 address, the client will select an address at random in the range 169.254.1.0 to 169.254.254.255 (inclusive), with a netmask of 255.255.0.0. The client will then send an ARP packet asking for the MAC address that corresponds to the randomly-generated IPv4 address. If any other machine is using that address, the client will generate another random address and try again.
The entire address range 169.254.0.0/16 has been set aside for "link-local" addresses (the first and last 256 addresses have been reserved for future use). They should not be manually assigned or assigned using DHCP. See RFC 3330, which describes various special-use IPv4 addresses and address ranges, including the link-local range.
Short for Automatic Private IP Addressing, a feature of later Windows operating systems.
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
If a network client fails to get an IP address using DHCP, it can discover an address on its own using APIPA.
To get an IPv4 address, the client will select an address at random in the range 169.254.1.0 to 169.254.254.255 (inclusive), with a netmask of 255.255.0.0. The client will then send an ARP packet asking for the MAC address that corresponds to the randomly-generated IPv4 address. If any other machine is using that address, the client will generate another random address and try again.
The entire address range 169.254.0.0/16 has been set aside for "link-local" addresses (the first and last 256 addresses have been reserved for future use). They should not be manually assigned or assigned using DHCP. See RFC 3330, which describes various special-use IPv4 addresses and address ranges, including the link-local range.
For Example APIPA :
In many cases the presence of a "link-local" address indicates a loss of network connectivity, or that a DHCP server is down.
APIPA is implemented in Windows 98 and later, and is used only if DHCP is activated. It can be disabled by following the directions in Microsoft KB article 244268.
APIPA is available in Mac OS 8.5 and later, including Mac OS X.
APIPA is part of Zeroconf. See the Dynamic Configuration of IPv4 Link-Local Addresses Internet-Draft for more information.
The IPv6 specification includes self-assigned link-local addressing.
You can also determine whether your computer is using APIPA by using the Winipcfg tool in Windows Millennium Edition, Windows 98, or Windows 98 Second Edition:
Click Start, click Run, type "winipcfg" (without the quotation marks), and then click OK. Click More Info. If the IP Autoconfiguration Address box contains an IP address within the 169.254.x.x range, Automatic Private IP Addressing is enabled. If the IP Address box exists, automatic private IP addressing is not currently enabled.
Windows 2000/XP/2003
For Windows 2000, Windows XP, or Windows Server 2003, you can determine whether your computer is using APIPA by using the IPconfig command at a command prompt:
Click Start, click Run, type "cmd" (without the quotation marks), and then click OK to open a MS-DOS command line window. Type "ipconfig /all" (without the quotation marks), and then hit the ENTER key. If the 'Autoconfiguration Enabled' line says "Yes", and the 'Autoconfiguration IP Address' is 169.254.x.y (where x.y is the client's unique identifier), then the computer is using APIPA. If the 'Autoconfiguration Enabled' line says "No", then the computer is not currently using APIPA.
In many cases the presence of a "link-local" address indicates a loss of network connectivity, or that a DHCP server is down.
APIPA is implemented in Windows 98 and later, and is used only if DHCP is activated. It can be disabled by following the directions in Microsoft KB article 244268.
APIPA is available in Mac OS 8.5 and later, including Mac OS X.
APIPA is part of Zeroconf. See the Dynamic Configuration of IPv4 Link-Local Addresses Internet-Draft for more information.
The IPv6 specification includes self-assigned link-local addressing.
Is my computer using APIPA now?
Windows 98/MEYou can also determine whether your computer is using APIPA by using the Winipcfg tool in Windows Millennium Edition, Windows 98, or Windows 98 Second Edition:
Click Start, click Run, type "winipcfg" (without the quotation marks), and then click OK. Click More Info. If the IP Autoconfiguration Address box contains an IP address within the 169.254.x.x range, Automatic Private IP Addressing is enabled. If the IP Address box exists, automatic private IP addressing is not currently enabled.
Windows 2000/XP/2003
For Windows 2000, Windows XP, or Windows Server 2003, you can determine whether your computer is using APIPA by using the IPconfig command at a command prompt:
Click Start, click Run, type "cmd" (without the quotation marks), and then click OK to open a MS-DOS command line window. Type "ipconfig /all" (without the quotation marks), and then hit the ENTER key. If the 'Autoconfiguration Enabled' line says "Yes", and the 'Autoconfiguration IP Address' is 169.254.x.y (where x.y is the client's unique identifier), then the computer is using APIPA. If the 'Autoconfiguration Enabled' line says "No", then the computer is not currently using APIPA.
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