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Re: Nmap probes per port
From: Paul Johnston <paul () westpoint ltd uk>
Date: Fri, 19 Mar 2004 10:29:20 +0000


I guess you're using a connect() scan? The large number of retries occurs because the kernel retries sending the SYN several times for each connect, while nmap also retries calling connect. Using SYN scan will reduce the number of retries to 6, which I believe is around the right number. However I've found the timing of SYN and connect scan to be almost identical. You may want to consider using a fixed rate port scanner, such as scanrand.


Nmap-3.50 sends approx 16 TCP SYNs for a filtered port.
My aim is to reduce the time taken to do a full port scan
and by sending less probes per port be slightly more
stealthy. Ideally I'd like one probe per port sent, I know
this may affect the reliability of the results.

Paul Johnston
Internet Security Specialist
Westpoint Limited
Albion Wharf, 19 Albion Street,
Manchester, M1 5LN
Tel: +44 (0)161 237 1028
Fax: +44 (0)161 237 1031
email: paul () westpoint ltd uk
web: www.westpoint.ltd.uk

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