From: Frank Knobbe (
Date: 10/04/01

Message-ID: <>
From: Frank Knobbe <>
To: 'Rosenau' <>,
Subject: RE: DENY x REJECT
Date: Thu, 4 Oct 2001 14:44:03 -0500 

Hash: SHA1

> -----Original Message-----
> From: Rosenau []
> Sent: Wednesday, October 03, 2001 10:53 AM
> Does anybody know a port scanner that could distinguish a
> "deny" filtered
> tcp port (firewall drops packets for the port) from a
> "reject" filtered tcp
> port (firewall returns an ICMP - port unreachable)?.
> Nmap seems to report boths cases simply as "filtered".
> Actually, both cases
> are filtered, but when you receive a ICMP, you can be sure
> that the port is
> really filtered. If you do not receive nothing, the port
> could be filtered,
> or packets could have been lost...

I always run a tcpdump session along with scans to watch for
interesting stuff like that. Also, variations in the responding TTL
will give clues where system are located during sweep scans.

tcpdump is your friend ;)


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