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Q167686: New DHCP Parameter for Switched Networks

Article: Q167686
Product(s): Microsoft Windows NT
Version(s): 2000,4.0
Operating System(s): 
Keyword(s): kbnetwork
Last Modified: 06-AUG-2002

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The information in this article applies to:

- Microsoft Windows NT Server version 4.0 
- Microsoft Windows 2000 Server 
- Microsoft Windows 2000 Advanced Server 
- Microsoft Windows 2000 Datacenter Server 
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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:

  Q256986 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:

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:

  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" (without the quotation marks)

  "NET START dhcpserver" (without the quotation marks)


Additional query words:

======================================================================
Keywords          : kbnetwork 
Technology        : kbWinNTsearch kbWinNT400search kbwin2000AdvServ kbwin2000AdvServSearch kbwin2000DataServ kbwin2000DataServSearch kbwin2000Serv kbWinNTSsearch kbWinNTS400search kbWinNTS400 kbwin2000ServSearch kbwin2000Search kbWinAdvServSearch kbWinDataServSearch
Version           : :2000,4.0
Issue type        : kbinfo

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