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firewalling



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
Description: Adobe PDF document