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Q166371: WindowsNT 4.0 Not Filtering Ports Destined for Remote Segments

Article: Q166371
Product(s): Microsoft Windows NT
Version(s): winnt:4.0
Operating System(s): 
Keyword(s): 
Last Modified: 09-AUG-2001

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The information in this article applies to:

- Microsoft Windows NT Workstation version 4.0 
- Microsoft Windows NT Server version 4.0 
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SUMMARY
=======

Windows NT 4.0 Transmission Control Protocol/Internet Protocol (TCP/IP) advanced
security does not allow for the creation of a firewall.

MORE INFORMATION
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Although Windows NT 4.0 offers TCP/IP port filtering, port filtering only
filters ports destined for the local computer that is entering the card that has
restricted ports. If Internet Protocol (IP) Forwarding is enabled, the TCP/IP
packets are forwarded as needed, and then filtered (if enabled) at the receiving
end.

For example:

Assume you have 3 computers, A, B, and C, running FTP Server and computer B is
multihomed, connecting the other 2 machines.

If computer B is configured to permit only ports TCP 139, and UDP 137 & 138
(NetBIOS), then it would seem that none of the clients could FTP to each other.
However, in this example, A and C can FTP to each other, but neither computer
can FTP to B. Windows NT by itself is not designed to be used as a firewall,
however, additional software (from Microsoft and other vendors) can be used to
add this functionality.


Additional query words: howto prodnt router route forward pass thru through proxy

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Keywords          :  
Technology        : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT400search kbWinNTSsearch kbWinNTS400search kbWinNTS400
Version           : winnt:4.0
Issue type        : kbinfo

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