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Firewalls should be the first line of defense
in any network connected to the Internet. In general, the best
solution is a hardware-based or dedicated firewall at the gateway
that protects the entire network. The second-best solution is a
local firewall, such as ZoneAlarm or Tiny Firewall.

But even with a gateway firewall in place, you
might want to limit the traffic coming into your computer. For
example, you may be concerned about locally generated traffic as
well as Internet traffic. Blocking that local traffic is as easy as
setting up filters on your computer.

Windows 2000 offers the capability to specify
the ports on which Windows will allow traffic to your computer. For
example, you might limit the traffic to port 80 (HTTP), port 110
(POP3), and port 25 (SMTP) and exclude all others.

To configure filters on your computer, follow
these steps:

  1. In Control Panel, open the Network And
    Dial-Up Connections folder, right-click the network interface, and
    choose Properties.
  2. Click TCP/IP, choose Properties, and click
  3. On the Options tab, select TCP/IP Filter, and
    click Properties.
  4. In the TCP/IP Filtering dialog box, select
    Enable TCP/IP Filtering.
  5. In the TCP Ports, UDP Ports, and IP Protocols
    sections, add the ports that you want to allow, and click OK.
  6. Close all dialog boxes.