Wrong.

1) If you don't receive "destination unreachable" packet, you know
nothing about the target host yet. This is not perfect-network world.
There can be other fw/router anywhere in the way, killing this type of
icmp traffic.

2) It slows scans a lot. You can of course do scannig in parallel, but
don't be surprised, when you find yourself killed with no mercy by IDS,
after matching SYN threshold. 1000+ syns/sec form IP adress to monitored
system is sure ban.

Daniel Privratsky



Oliver Schad wrote:

> Am Mittwoch, 7. Januar 2004 23:05 schrieb mir Mark Hurst:
> 
>>It's much better to have a firewall than just have ports not open. Even
>>though a port is not open it can reveal the presence of your machine by
>>the manner in which the IP stack responds to a connection attempt.
>>Using a firewall you can drop those packets, making all your closed
>>ports invisible.
> 
> 
> If you want to invisible, the next router to you have to send an ICMP 
> packet with "host unreachable". If you say nothing anybody with some 
> brain between his ears knows there is a very intelligent guy that want to 
> be invisible.
> 
> mfg
> Oli
> 
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> gentoo-security@g.o mailing list
> 
> 




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