From: Robert Klemme <shortcutter@...>
Date: 2011-09-27T21:52:15+09:00
Subject: Re: ping sweep and threads

On Tue, Sep 27, 2011 at 2:11 PM, Panagiotis Atmatzidis
<ml@convalesco.org> wrote:

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

You need to properly synchronize since host_up and host_down are
shared between threads.  But in your case you can get rid of them
completely and just output x if pt.ping returns true.

>    end
>  }
> }
>
> puts host_up
> -------------------------
>
> First thing, do I use Threads the right way?

You should at least wait for all threads to finish (i.e. by joining).

threads = list.map { |x|
 Thread.new {
  # ...
 }
}

threads.each {|th| th.join}


> 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?

Maybe some ulimit getting in the way.  Try

$ ulimit -a

You should probably also do this at the top to see errors:

Thread.abort_on_exception = true

> 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? :-/

Threads should be OK.  What Ruby version are you using?

Kind regards

robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/