blocking ports

[Sam]

I'm thinking about blocking ports, but have a 3 PC
network via a router sharing a cable connection. I know
that some firewall software can block ports, but I'd
rather not use one since they're becoming illegal in some
states. This was what I read here.

http://www.theinquirer.net/?article=8595

What about TCP/IP filtering? I've read that you can
enable TCP/IP filtering and enable the ports I want to
opened. The common ports are

HTTP - 80
SMTP - 25
IMAP - 143
POP3 - 110
TELNET - 23
FTP - 20,21

Does this work and does it block what I don't specify?
What other ports should I open? I do not want to block
file and printer sharing over the network, and I use the
Windows Update for alot of things. I also use Norton to
automatically get for live updates and things too.

 

[David Jones]

I wouldn't worry about the article you mention. If
firewall devices become illegal, lets just say that it
would be impossible to enforce, and I'm sure the law
would be challenged in court.

Most home router devices use what is called Network
Address Translation, and as a side effect of this, they
block all incoming traffic (all incoming ports) unless
you specifically allow it (by forwarding ports in the
router, or putting a computer in the DMZ).

You're basically doing all the right things - if you're
worried about outbound traffic you can install something
like Zone Alarm or Norton/McAfee firewalls that look at
outgoing traffic as well.

 

[Sam]

So the TCP/IP filtering only effects incoming traffic?
What ports do file and printer sharing use? In the TCP/IP
filtering thing, there is three columns: UDP, TCP, IP if
I remember correctly.

 

[David Jones]

TCP/IP filtering is way overkill for your situation. It
cannot be used for filtering outgoing traffic in the way
you seem to want to.

Windows file sharing traditionally uses ports 135-139 and
445. However, what is your concern? Your router is
already blocking all incoming traffic from the Internet,
unless you configure it to allow stuff.

 

[Skip Knoble]

Sam, Just a suggestion.

If you have a router, it should have a Web interface. Look at the
PDF documentation files on the manufacturer's web page for how to
access this Web interface. Then you can limit traffic on the 3PC network
by MAC Addresses (of the 3 PC's) using the Router's built-in firewall.
At that point, the router's firewall will block all access to the network
by any PC with any other MAC address. Then, if you want to block
specific ports within the network you can also do this.

In the mean time you should also use a Spyware scanner to eliminate
the possibility that you already have spyware on your systems.
A free one is available from Lavasoft:
http://www.lavasoft.de/software/adaware/.

Skip Knoble, Penn State