Default Settings and Behavior or NbtKeepAlive and TcpKeepCnt (110136)

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According to the Windows NT Resource Kit Volume 1, the following are default values for keepalive parameters:

   NbtKeepAlive = 0 (disabled)
   TcpKeepCnt = 120 seconds
				

However, the actual defaults are the following:

   NbtKeepAlive = 60 seconds
   TcpKeepCnt = 120 seconds
				

Any frame sent by NBT (including a NetBIOS keep-alive) is considered to be data by TCP. Because the NbtKeepAlive parameter is set lower than TcpKeepCnt, on an idle NetBIOS session there will be one NBT keep-alive sent per minute, and no TCP keep-alives sent. On an idle non-NetBIOS TCP session, such as that used by a Windows Sockets program, TCP keep-alives will be sent, with their frequency controlled by the TcpKeepCnt parameter.



As documented in the Windows Resource Kit, these parameters can be modified to produce different behavior. To change these parameters, use the following procedure:

WARNING: Using the Registry Editor incorrectly can cause serious, system- wide problems that may require you to reinstall Windows NT to correct them. Microsoft cannot guarantee that any problems resulting from the use of Registry Editor can be solved. Use this tool at your own risk.

1. Open the Registry Editor (REGEDT32.EXE).
2. For NbtKeepAlive, use the following path:
   
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Nbt\Parameters
3. Add a value for the NbtKeepAlive parameter as a REG_DWORD with the desired value in seconds. "0" disables NBT keepalives.
4. For TcpKeepCnt use the following path:
   
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
5. Add a value for the TcpKeepCnt parameter as a REG_DWORD with the desired value in seconds. "0" disables TCP keepalives.

For example, if you want to send one TCP keep-alive every five minutes, and no NetBIOS keep-alives, use the following values:

   NbtKeepAlive = 0
   TcpKeepCnt = 300