FAQ: Disable Port 137, 138 and 139

"There’s No Such Thing As A Silly Question" -- does the cliche sound familiar? In this part of pimp-my-rig reloaded, technical questions are answered. Mail them to me and I will post the answers here. If you have a better answer, by all means share it with us.

In one of our FAQ entries, the disabling of port 135 was outlined. And it successfully shutdown port TCP/135. Now one of the questions asked was how to disable netbios ports UDP/137 (netbios-ns), UCP/138 (netbios-dgm) and TCP/139 (netbios-ssn). This procedure disables all three ports and the procedure is as follows.

[1] Right-click "My Network Places" and select "Properties" from the ensuing menu that opens.

[2] Executing the previous step opens a window showing the available network connections in the machine. Right-click on "Local Area Connection" and select "Properties". This step is almost similar to the previous.

[3] Scroll down to "Internet Protocol (TCP/IP)". Select it (to highlight it) and click "Properties". You will be opening another window similar to the one below.



[4] From the "Internet Protocol (TCP/IP) Properties" Window, click on "Advanced.." (toward the lower right). Then go to the "WINS" tab (like the screenshot below).



[5] Under "NetBIOS setting", tick "Disable NetBIOS over TCP/IP" and click OK to accept the change. Click OK to the other windows previously opened prior to this properties window.

The ports 137, 138 and 139 will have closed on the machine. If the machine has multiple network interface connections (or NICs), repeat the above for every connection.

Closing down the above ports for a Windows XP Pro machine has so far not impacted any application on my end. If it should impact an application you are running, please let me know so I can post them here for the information of others.

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