RE: how nmap can know my firewalled servers ?

["David Gillett" <gillettdavid () fhda edu>]

  Some kinds of firewalls may respond to a blocked connection
attempt with:

a) an RST packet (some hosts do this too), or

b) an ICMP prohibited/unreachable packet.

  Some firewalls offer you a choice between "block" (send such
a response) and "drop" (no response) actions.

David Gillett
 

> -----Original Message-----
> From: Alexey Eremenko [mailto:al4321 () gmail com] 
> Sent: Wednesday, April 12, 2006 11:24 AM
> To: security-basics () securityfocus com
> Subject: how nmap can know my firewalled servers ?
>
> 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 ?


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