File and Printer Sharing Ports



I noticed that opening either TCP Port 139 or 445 will allow me to provide
file sharing. So, what is the difference between the two ports? Why does
Windows Firewall exception for File and Printer Sharing open both ports (as
well as UDP Ports 137 and 138)? What is each of these ports typically used
for in Windows?



Thanks for your reply, Juan. I've actually gone to that web site previously
and am unclear on the difference between the function of port 139 and port
445. Basically, I am trying to open as few ports as possible and would like
to know when 139 would be used and when 445 would be used.



Hi John:

I suppose it's the same as with other programs;
they use one port for outgoing data and another for incomming.
one example is Outlook Express; for outgoing Hotmail messages
it uses port 25... and port 995 for incomming.
The only sure way to know which ports a specific program uses,
is with the use of specialized software like the one in the following link.

The Software Publisher's Description reads:

From the developer: "Active Ports - easy to use tool for Windows
NT/2000/XP that enables you to monitor all open TCP/IP and UDP ports on the
local computer. Active Ports maps ports to the owning application so you can
watch which process has opened which port. It also displays a local and
remote IP address for each connection and allows you to terminate the owning
process. Active Ports can help you to detect trojans and other malicious

Download Active Ports 1.4 from;

Publisher's website.

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