PS The trick to effective firewalling is to learn what TCP/UDP port numbers your applications require, and to open those; firewalls cannot recognize this automatically. For those who want to try configuring a router or firewall, find out which TCP/UDP port numbers your applications require. In Windows you find this out by opening the following the folder: root-partition(usually c:)\winnt\system32\drivers\etc in that folder open the file: services (no extension) You can use your favorite text program to open the file, as your favorite text program does not require extensions. This file contains the list of applications currently installed on your machine and what port numbers they reserve for networking functions. Make a note of the ports, but do not change anything in the file (if you do, the associated apps won't work properly anymore on the network). Those are the ports to open in your firewall or router access list. The list shows you which ports are required by applications in general, but not which ports are being used at any given moment. To see THAT, open a DOS window and type: netstat -a. That shows you which ports/appls are actually online at any given moment. FYI, attached is a copy of RFC1700, which lists common applications and their port numbers.Attachment: RFC 1700.pdf
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