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Network Security Security-Basics
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RE: how nmap can know my firewalled servers ?

Subject: RE: how nmap can know my firewalled servers ?
Date: Wed, 12 Apr 2006 15:11:16 -0700
  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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