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On Saturday 22 November 2003 15:33, Jorge Almeida wrote:
>  I have in my home box a iptables firewall configured via shorewall with
> the "standalone machine" standard configuration (no services whatsoever to
> the outside world). Just for good measure, I tryed portscanning from a
> computer at work: (my dynamic IP number edited)
> $ nmap -vv <IP number>
>
> Starting nmap V. 3.00 ( www.insecure.org/nmap/ )

> (The 1597 ports scanned but not shown below are in state: closed)
> Port       State       Service
> 6/tcp      filtered    unknown
> 25/tcp     filtered    smtp
> 80/tcp     open        http
> 135/tcp    filtered    loc-srv

> The scanning from the home box itself gives a more reassuring outcome:
>
> $ nmap -vv localhost

> Interesting ports on localhost (127.0.0.1):
> (The 1621 ports scanned but not shown below are in state: closed)
> Port       State       Service
> 6000/tcp   open        X11
> 10000/tcp  open        snet-sensor-mgmt

> Now, why should nmap at the remote machine report that port 80 is open? I
> assume that this happens because nmap is not supposed to be used when the
> target has a firewall. Can I be right? And, if so, how can I check whether
> the firewall is really working as expected?

You are right not to question ports 6, 25, and 135, they will be some sort of 
firewall/router in your path home.
Port 80 will almost certainly be open because someone along the line is 
trapping port 80 traffic, probably to send it off to a proxy. I do this 
myself on my home network, and have seen that same behaviour with an ISP I 
was on.

- -- 
Mike Williams
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