It's "funny" how many questions are related to the purging of idle 
hosts/sessions.

By default, when hosts are idle for n mins (forget the default), it's 
purged/erased/deleted/etc.  GONE!  You can do three things:

1.) Nothing - just accept / understand this is how it works.
2.) Enable "sticky-hosts", read the FAQ / man and be careful.
3.) Tweak the idle timers in the source.  MAYBE only on globals-define.h, but I 
forget exactly.

Let's say I have a network range, /24 - or 254 hosts.  But, lets say there are 
really no hosts on it; zero.  You browse that range in ntop and it's zero.  
Cool right?  Now you run a scan / ping sweep / broadcast ping / etc and an arp 
is issued for every IP on that range.  Even though nothing is there, nTop *MAY* 
show 254 hosts...  I say MAY because it MAY depend on if you're using netflow 
or libpcap to populate ntop - I don't recall which option leads to which 
behavior.  I just recall that with netflow when my "Security" team's "AWESOME" 
AV software (eTrust) would scan my ENTIRE LAN range, I'd end up with 64,000+ 
hosts!  Not good!  See my warning on sticky-hosts...

So no, host count is not cumulative; it's dynamic based on the number of 
"Active" hosts at that period of time.  You can view the Host History reports 
and see the historical data, trends, etc.

HTH

G





-----Original Message-----
From: [email protected] 
[mailto:[email protected]] On Behalf Of Eric Rogers
Sent: Thursday, March 25, 2010 4:53 PM
To: [email protected]
Subject: [Ntop] Total number of local hosts...

Hello all!
  I am trying to ensure that I am seeing all local hosts in the ntop
reports.  I am looking to get a total number of hosts that access the
internet and the numbers appear to be way off.  Any guidance would be
appreciated.  I have gone to Summery | hosts and sorted the list and
found the IP range I was interested in.  But I wonder if hosts are
automatically deleted after X days or if this report should reflect all
hosts from the first date ntop started collecting.

Thanks to all for any direct you can provide!
  -Eric
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