Re: how nmap can know my firewalled servers ?

["Alice Bryson" <abryson () bytefocus com>]

Yes, i agree that.
How about UDP, if an udp port firewalled, how does NMAP know it?

2006/4/13, Nathaniel Hall <nathaniel.d.hall () gmail com>:
> I am assuming you are using a DROP rule on your firewall.  NMAP knows
> that if it does not receive a response for a TCP connection then it is
> firewalled.  Dropping traffic at a firewall violates RFC and makes it
> much easier to know when there is a firewall between the scanner and the
> end host.  I recommend using REJECT
>
> -A INPUT -j REJECT --reject-with icmp-host-unreachable
>
> That will conform to RFC (I'm pretty sure) and will make it harder to
> detect a firewall with NMAP.
>
> Alexey Eremenko wrote:
>
> > Hi all !
> >
> > I know that "nmap" can show open ports. But nmap also shows my
> > firewalled ports !
> > How?
> >
> > Since some servers (like apache) are firewalled with iptables, how can
> > nmap know wherever
> > my system run the service with open port, filtered port or doesn't run
> > it at all ?
> --
> Nathaniel Hall, GSEC GCFW GCIA
>
>
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