KB167686 - New DHCP Parameter for Switched Networks

Article ID: 167686

Article Last Modified on 2/27/2007

Microsoft Windows 2000 Server
Microsoft Windows 2000 Advanced Server
Microsoft Windows 2000 Datacenter Server
Microsoft Windows NT Server 4.0 Standard Edition

This article was previously published under Q167686

IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:

256986 Description of the Microsoft Windows Registry

SUMMARY

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.

MORE INFORMATION

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:

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.
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:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\DHCPServer\Subnets\a.b.c.d\SwitchedNetworkFlag=1 (REG_DWORD)

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):

NET STOP dhcpserver

NET START dhcpserver

Keywords: kbinfo kbnetwork KB167686