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Using NAT with Windows NT

Article Number: I009
Article Type: Info
Modified: December 3, 1998

SUMMARY

If your organization is like many, you have remote offices that may need access to a local NT-based server through their Internet connection. The question becomes, what is involved?

This article presents some of the issues related to this application and how to deal with these issues with an Orbitor solution.

MORE INFORMATION

Network Address Translation (NAT)

If the server location (or either end of the Internet connection) is currently using NAT to perform IP Address mapping, you will have to "export" Port 139, a key Windows NT port, on the server-side router. This allows NT-destined traffic to be directed to the server through the router.

With an Orbitor router at the server location, a NAT Exports entry must be configured. In the NAT Exports menu you would specify NAT Port '8B' (without quotes), and the IP Address of the NT Server. '8B' is the hexidecimal notation for 139. This informs the Orbitor to direct any data destined for this port to the NT Server.

There is no special configuration required on the client (or remote) side if there isn't a server located there.

LMHOSTS

In this example, it is mandatory that the LMHOSTS file be used. This is due in whole to the isolation of Window's Name Bindery information from the remote LAN.

Normally, each Windows stations (NT or 95/98) broadcasts its existence onto the LAN at regular intervals. These broadcasts remain local to the LAN segment and would not be propogated over the Internet to the remote server, or vice versa. As such, the mapping that would normally occur between server (or workstation) name to IP Address has to be accomplished in other manners. This is where the LMHOST file comes in.

Located in the Windows directory of every workstation is a file called LMHOSTS.SAM. This file presents a sample configuration of a properly configured LMHOST file. Essentially, this file maps a workstation/server name to an IP address.

On the client workstations, the LMHOST file would require an entry for the name of the server and the IP Address used to reach it. Remember, if NAT is being used, the IP Address entered here will be the address of the server-side router.

For additional details configuring the LMHOST file, the Microsoft Support web site is a valuable source of information. One article available on their web site is "How to Write an LMHOSTS file for Domain Validation".

REFERENCES

Please consult the Orbitor Reference manual for additional information on using NAT Exports. Also, review the LMHOSTS.SAM file located in WINDOWS directory of the workstation. Lastly, searching Microsoft's Knowledge Base is an excellent source for Windows Networking information. §

Copyright © 1998 Develcon Electronics Ltd.  All Rights Reserved.