From: ptkwt@...1.aracnet.com (Phil Tomson)
Date: 2001-09-03T17:12:06+09:00
Subject: [ruby-talk:20748] dRuby,TCPSocket and blocked ports (Linux question)

This may be more of a Linux question, but maybe someone else here has 
experienced this and has found a way around it...

I was initially playing with the dRuby examples on page 275 of the Pickaxe 
book.  I was using two Linux machines here on my home network - one to run 
the server the other to run the client.  But I kept getting connection 
refused errors on the client machine ... I knew that I had tried this 
exact code months ago at work (on Windows machines).  Then I tried running 
the server on a windows machine on my network and ran the client on the 
Linux machine - it worked, no problem.  then I concluded that my Linux 
boxen are blocking port 9000 (the port address used in the examples), so 
to figure out which ports were available I wrote this script:

#######socket_test.rb##########
require 'socket'
machine = "127.0.0.1"
(0..20000).each { |port|
   begin
      puts "trying: #{port}" if $DEBUG
      soc = TCPSocket.open(machine, port)
      puts "***SUCCESS: port #{port}"
   rescue
      puts "couldn't open port: #{port}" if $DEBUG
   ensure
      soc.close if soc
   end
}
######end####################

I ran it on each Linux box and got the following results:

***SUCCESS: port 9
***SUCCESS: port 13
***SUCCESS: port 21
***SUCCESS: port 22
***SUCCESS: port 37
***SUCCESS: port 80
***SUCCESS: port 111
***SUCCESS: port 515
***SUCCESS: port 6000
***SUCCESS: port 16001

[Side note: Interestingly enough, I also ran this script on Windows98 and 
it doesn't seem to do anything - gets stuck right away at port 1 - since 
all ports seem to be available on Windows, I'm not sure why that is (?)]

Not a lot of available (non-blocked) ports... and these are of course 
being used by other services (checked /etc/services ).  This all makes 
sense from a security standpoint (at least for the firewall) - but it 
makes it hard to use dRuby.

So, does anyone know how to unblock a port, say port 9000, so I can use it 
for dRuby?

Phil