Configuring Automatic Private IP Addressing Apipa Problem

You want to enable or disable Automatic Private IP Addressing (APIPA) on a Windows Server 2003 computer.

Solution

To disable APIPA for a particular adapter, create the following Registry value:

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ Tcpip\Parameters\Interfaces\f<Tnterface GUID>}\] "IPAutoConfigurationEnabled"=dword:0

To disable APIPA for all adapters installed in a particular computer, create the following Registry value—no reboot is necessary:

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters] "IPAutoConfigurationEnabled"=dword:0

■Note If either of these Registry entries is not present, the operating system assumes a default value of 1. This means that APIPA is turned on and enabled on all Windows Server 2003 adapters by default.

How It Works

Similar to Windows 2000, Windows Server 2003 offers you the ability to configure an alternate IP configuration for a DHCP-enabled computer that is unable to contact a DHCP server. When your Windows Server 2003 computer is unable to obtain or renew a DHCP lease, it will configure itself with an IP address in the 169.254.0.0 Class B network. This can be used to enable temporary (albeit restricted) network access if your DHCP server becomes unavailable, or to provide a primary access solution for a small office with limited connectivity needs that does not have a DHCP server available.

By default, a computer that has received its IP address through APIPA will attempt to contact a DHCP server every five minutes in an attempt to obtain a valid IP address. (To prevent address collision on a network where multiple computers might be using APIPA, each workstation will perform its own collision detection to ensure that the IP address it is assigning itself is not already active on the APIPA subnet.)

APIPA addresses have a few limitations, including the following:

• 169.254.0.0 is a private network, which means that any traffic from an APIPA-enabled computer will not be transmitted by a router—this limits APIPA traffic to a single subnet.

• APIPA address information does not include a default gateway, further restricting traffic to the local subnet only.

• APIPA addresses do not allow for DHCP configuration options such as DNS and WINS server information.

To prevent APIPA from creating unnecessary confusion for the users of a Windows Server 2003 computer or network, you can choose to disable APIPA addressing. You can disable APIPA for a single installed NIC, or globally for all NICs installed in a computer.

See Also

• Recipe 1-7 for more on configuring an alternate IP configuration

• Microsoft KB 220874: "How to Use Automatic TCP/IP Addressing Without a DHCP Server"

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