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Re: nmap performance -> timeout issue
From: "Maarten Hartsuijker" <m.hartsuijker () wanadoo nl>
Date: Wed, 13 Apr 2005 21:22:06 +0200

One point missing...  version of nmap?  I ran into a problem with some
Latest version (3.81). Tried the RPM as well as a custom compiled version: 
same issues. I just tried setting max_scan_delay to 0. Nmap now no longer 
mentions the need for increasing the send delay, but nevertheless, the 
problems remain.

I also found that nmap would stall some times on a single host, which is 
why I originally wrote my nmap wrapper to run X number of nmap processes in 
parallel.  I think at last count I was scanning more than 180K IPs in less 
than 16 hours, but I had ICMP enabled for all my hosts to/from my 
monitoring host.
I know nmap will probably be able to do better timing if ICMP is enabled, 
but I prefer the the audit machine not to have any special privileges when 
performing scans. I could run more processes in parallel, by wrapping up 
some threads from a script, but I think the min_hostgroup option I'm using 
should achieve more or less the same. Although an improvement of this option 
might be to have it start new hosts after the first one is finished. 
Currently I'm scanning 52 hosts simultaniously. 45 hosts that have no open 
ports perform as they should and finish within the hour. 7 hosts with open 
ports take about 9,5 hour to complete. It would be nice if it were possible 
to instruct nmap to start scanning host 53 as soon as the first one is 
finished, in stead of waiting for all 52 to complete. But this just as a 
side note. I am really curious why some of the hosts take >9 hours to 
complete, even though I set all the possible timeout parameters....

maarten





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