ping sweep and threads

Dear Sir(s),

I'm looking for a quick to scan the local network (/24). I choose to use =
'net-ping' gem, since I'm working under Ruby 1.9 and 'ping' is not =
available by default.
I use the 'external' ping because it's way faster but still very slow. =
It takes like 2 minutes to 'ping' 254 addresses with a 2 hosts 'up'. So =
I decided to make it a bit faster by using threads. Since I have no =
prior experience with Threads, I've read a couple of articles about ruby =
threads and here is the code that I came up with:

------------------------
require 'net/ping'

network =3D '192.168.1.'
list =3D []
host_up =3D []
host_down =3D []
x =3D 1=20
while x < 255
  ip =3D network + x.to_s
  list.push(ip)
  x +=3D 1
end           =20
list.each { |x|
  t =3D Thread.new {
    pt =3D Net::Ping::External.new(x)
    if pt.ping
      host_up.push(x)
    else
      host_down.push(x)
    end
  }
}

puts host_up =20
-------------------------

First thing, do I use Threads the right way?=20

Second, Trying to find out whats going on from 'lsof -i', I counted 155 =
simultaneous connections but not more. It should be 254 in theory?

Third, do you think that is there any faster way in scanning weather a =
host is up or not? I understand that this is a more general question, =
but tools like 'ettercap' scan a /24 network in less than 10 seconds on =
the same machine same network, which makes me thing that I'm doing =
something wrong. I'm not experienced programmer, neither experienced =
with computer networks at that level, like Alor and Naga (author's of =
ettercap) but then again, why the difference is so big? :-/

Thanks for your time.

Panagiotis Atmatzidis
-----------------------------
Pharmacy Student at VFU, Brno
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The wise man said: "Never argue with an idiot, he brings you down to his =
level and beat you with experience."