#NOFNR Flag in LMHosts to Communicate Across Routers

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When you are communicating with a server across a router in a IP routed environment, the LMHosts file is used to resolve Workstation name-to-IP address mapping. The LMHosts entry for a remote machine name provides the IP address for the remote machine. In Lan Manager 2.x, providing the LMHosts entry eliminates the need to do a Name Query broadcast to the local domain and instead a TCP session is established with the remote machine. Windows NT performs the same function in a different way.

When an LMHosts entry exists for a remote server, Windows NT will not send a Name Query broadcast to the local subnet and instead send a directed Name Query to the remote server. If the remote server does not respond to the Name Query, further communications (TCP SYN, and so on) will not take place. This was done to eliminate the performance issues when trying to connect to a remote machine when it was not available (down).

Some of the older LAN Manager for UNIX and DEC Pathworks servers do not respond to directed Name Queries sent by Windows NT. In that case, the users will see an error 53 (Path not found), even though they have specified the LMHosts entries correctly. A new LMHosts flag #NOFNR was added to solve this problem. By specifying the #NOFNR flag on the same line where the name resolution information for the server is provided, the directed Name Query can be avoided. For example:

   130.20.1.1   mylmxserver   #PRE  #NOFNR
				

Note that this will only apply to mylmxserver and not to any other entries in the LMHosts file. To set a global flag, an entry could be added in the registry. To completely remove any directed Name Queries sent from a Windows NT machine, create the following value in HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Nbt\Parameters:

   NoDirectedFNR   REG_DWORD   1
				

This will cause the directed Name Queries to not go out for any remote machines.