Firewall rules

[Giorgos Keramidas]

On 2004-06-15 20:54, Robert Downes <nullentropy at lineone.net> wrote:
> I'm obviously missing something...
>
> su-2.05b# ipfw -a list
> 00100  16  1144 divert 8668 ip from any to any in via rl0
> 00200  17   964 divert 8668 ip from any to any out via rl0
> 00300   0     0 check-state
> 00400  32  3296 allow ip from me to me
> 00500  21  1268 allow ip from 192.168.0.0/24 to any keep-state
> 00600 274 25875 allow ip from 192.168.1.0/24 to any keep-state
> 00700   2    96 deny log ip from any to any
> 65535   4   429 deny ip from any to any
>
> Now, having seen plenty of examples of huge lists of rules, I'm
> obviously not seeing something that is apparent to others.

Perhaps.  This depends on what you mean to achieve.

> I've tested my network using the grc.com ShieldsUp! port probing
> system.  It informs me that every one of the first 1056 ports is
> stealthed (i.e.  does not even reply to probes).

That's because the canonical behavior of a host that doesn't listen on a
TCP port is to return RST replies when connection attempts are seen.
You'd need something like this added to your ruleset:

	add 301 deny tcp from any to any established
	add 601 reset tcp from any to any

> In fact, the only thing it complains about is the fact that my IP
> replies to ICPM ping requests (though I don't understand how).

I think rule 65535 should catch these, but I haven't used ipfw in a very
long time and I might be mistaken.  Anyway, if you are limiting ICMP
replies through the net.inet.icmp.icmplim sysctl pings shouldn't be a
source of trouble.

> And my /var/log/security file shows that dozens of random connections
> to ports 135 and 445 have been dropped.  So, what am I missing?

You're missing a lot of Windows viruses.  Ports 135 and 445 are used by
Microsoft-specific protocols (Location Service and Directory Services,
respectively).  What you're seeing is a lot of attempts by trojans and
other viral programs trying to break into your "Windows" machine.

- Giorgos