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Re: NMAP Accuracy vs. Speed
From: Eric Hagen <eric () sandpile net>
Date: Wed, 31 Mar 2004 17:43:09 -0600

Sorry for a late reply, but I remember noting that at SYN scan is much faster than a full-TCP-connect scan and does not time out as easily on faster settings. Try -sS and -t4. That might do it for you.

Eric Hagen

jburzenski () americanhm com wrote:

I'm looking for any recommended settings for scripting nmap to accurately
scan several large logically disperse networks.  My target list consists of
about 5 c-class networks that do not respond to ICMP and about 40 single Ips
that either do or do not respond to ICMP.
I would prefer accuracy over speed if the scan times are reasonable.  I have
been -P0 on all scans since I can't reliably detect 100% of online hosts
(which generates about 1.5MB of output in -oG format due to all of the
filtered ports reported on).  Scans with -T 3 currently take about 8 days.
Scans on -T 4 take about 1 day.  T 3 are noticeably more accurate and some
networks report as no hosts online or ports open under T 4.
Here is my current scanning command:

nmap -T 4 -iL targetlist.txt -sT -P0 -oG output.log

My goal is to maintain an updated list of target networks and use nmap to
detect all open ports across the span monthly.  Then, another script will
diff the outputs and report on any changes.  Eventually, I'll get a udp
audit going as well. Any help would be appreciated.


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Ethical Hacking at the InfoSec Institute. Mention this ad and get $545 off any course! All of our class sizes are guaranteed to be 10 students or less to facilitate one-on-one interaction with one of our expert instructors. Attend a course taught by an expert instructor with years of in-the-field pen testing experience in our state of the art hacking lab. Master the skills of an Ethical Hacker to better assess the security of your organization. Visit us at: http://www.infosecinstitute.com/courses/ethical_hacking_training.html
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