Dead Gateway Detection in TCP/IP for Windows NT (128978)
The information in this article applies to:
- Microsoft Windows NT Workstation 3.5
- Microsoft Windows NT Workstation 3.51
- Microsoft Windows NT Workstation 4.0
- Microsoft Windows NT Server 3.5
- Microsoft Windows NT Server 3.51
- Microsoft Windows NT Server 4.0
This article was previously published under Q128978 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
Microsoft TCP/IP for Windows NT provides a method of detecting whether or
not the default gateway is still functioning. Dead gateway detection is
enabled by default (on NT 3.51, 4.0 and above) when you install the TCP/IP
protocol. However, Microsoft TCP/IP does not provide a method to detect
when the default gateway returns to operation.
MORE INFORMATIONWARNING: 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.
For the dead gateway detection to work correctly, you must specify more
than one default gateway address in the Advanced Options of the TCP/IP
configuration dialog box in the Network portion of Control Panel. If the
default gateway fails to respond to TCP requests after several tries, IP
will direct packets to the address specified for a backup gateway.
Here is an example of how Windows NT will behave when the current default
gateway is unavailable, and you have more than one default gateway
configured:
Windows NT will switch to the next default gateway on the list. When the
original default gateway comes back up, it broadcasts its routes to other
intelligent routers.
When Windows NT tries to access a network through the current default
gateway, it will be informed of a better route (the original default
gateway). Windows NT will add a host route to it's routing table, but will
NOT switch back to the original default gateway. To switch back to using
the original default gateway you will need to reboot the Windows NT Server.
Note: If the second default gateway becomes unavailable, it will switch to
the next default gateway configured on the list. When the end of the list
of default gateways is reached, the search returns to the beginning again.
For information about obtaining a RFC document, please see the following
article in the Microsoft Knowledge Base:
185262: How to Obtain Request for Comments Documents from the Internet
The registry setting that enables dead gateway detection can be found in
the following location of the Windows NT 3.5 Registry:
Key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
Value Name: EnableDeadGWDetect
Value Type: REG_DWORD
Value Range: 0 or 1 (False, True)
Default setting is 1 (True)
Note: Dead gateway detection is enabled by default on Windows NT 3.51, 4.0
and above. This registry change applies to Windows NT 3.5 only. For additional information about dead gateway detection in Windows NT, click the article number below
to view the article in the Microsoft Knowledge Base:
171564 TCP/IP Dead Gateway Detection Algorithm Updated for Windows NT
REFERENCES
"Inter-Networking with Microsoft TCP/IP Using Microsoft Windows NT",
Participant's Workbook, Microsoft WWT, 1993, pg. 72; Appendix A, pg. 217.
| Modification Type: | Major | Last Reviewed: | 5/6/2003 |
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| Keywords: | kbinfo kbnetwork KB128978 |
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