New DHCP Parameter for Switched Networks

Last reviewed: January 8, 1998
Article ID: Q167686

The information in this article applies to:

Microsoft Windows NT Server version 4.0

IMPORTANT: This article contains information about editing the registry. Before you edit the registry, make sure you understand how to restore it if a problem occurs. For information about how to do this, view the "Restoring the Registry" Help topic in Regedit.exe or the "Restoring a Registry Key" Help topic in Regedt32.exe.

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

The new parameter "SwitchedNetworkFlag" is configured through Registry Editor. When enabled, this causes a DHCP client to obtain 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: In the event that routers do exist on your network, setting the SwitchedNetworkFlag will normally cause failure of your clients to connect to hosts on other networks. Only a proxy ARP device will enable this type connectivity configuration. Care must be taken to ensure that any and all routers within the network can proxy ARP and that no outside connectivity is desired.

WARNING: Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk.

For information about how to edit the registry, view the "Changing Keys And Values" Help topic in Registry Editor (Regedit.exe) or the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe. Not that you should back up the registry before you edit it.

To enable 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:
```
      HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\DHCPServer\
      Configuration\Subnets\a.b.c.d\
```
NOTE: The above registry key is one path; it has been wrapped for readability.
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 their default gateway.

NOTE: The README.TXT file that ships with Windows NT Service Packs 2 and 3 incorrectly state the registry path as the following:

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

The above path is incorrect and hence will not work.

Keywords          : nthowto ntnetserv NTPROTOCOL ntregistry NTSrv nttcp kbnetwork
Version           : WinNT:4.0
Platform          : winnt
Issue type        : kbinfo
Solution Type     : Info_Provided

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Last reviewed: January 8, 1998
© 1998 Microsoft Corporation. All rights reserved. Terms of Use.