New DHCP Parameter for Switched Networks

The Dynamic Host Configuration Protocol (DHCP) server service in Windows NT 4.0 Service Pack 2 has a new parameter that will allow the client's default gateway to be set to its own IP address.

WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

If you configure the SwitchedNetworkFlag parameter with Registry Editor, a DHCP client obtains a default gateway address equal to the IP address that the client receives. This causes the client to use the Address Resolution Protocol (ARP) for all IP addresses on the local subnet, and is useful for routerless switched networks.

NOTE: If routers exist on your network and you set the SwitchedNetworkFlag parameter, your clients may not connect to hosts on other networks. Only a proxy ARP device allows this type of connectivity configuration. Make sure that all routers within the network can proxy ARP and that you do not want any outside connectivity.

To turn on this feature for all clients in a scope, add the following value to the registry on the DHCP Server:

1. Start Registry Editor (Regedt32.exe) and locate the following subkey:
   
   For Windows NT 4.0:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\DHCPServer\Configuration\Subnets\a.b.c.d\
   For Windows 2000:
   HKEY_LOCAL_MACHINE\Software\Microsoft\DhcpServer\Configuration\Subnets\a.b.c.d
   Where a.b.c.d is the IP address of the DHCP subnet.
2. From the Edit menu, click Add Value and use the following entry:
   Value Name: SwitchedNetworkFlag
   Data Type: REG_DWORD
   Value: 1 or 0 (default=0)
   
   1 enables the DHCP server to send the client's IP address as the default gateway.

NOTE: The Readme.txt file that ships with Windows NT Service Packs 2 and 3 incorrectly states the registry path as the following: This path is incorrect and will not work.

NOTE: After you add the SwitchedNetworkFlag parameter and set it to the value 1, restart the DHCP service for this change to take effect.

To restart the DHCP service, run the following commands (press ENTER after each command):