LocalAddr => 'localhost',
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Delete that line, or set the LocalAddr to "0.0.0.0" , which allows binding to ANY available local IP address.

This will enable connections from outside the local 127.0.0.0 network to connect.

Hello NetWallah,

Thank you for your time and effort, reading and replying to my question.

After some experimentation I finally understood that PeerAddr on the server side has to combined with the LocalPort, because is the server port locally and it will use this port for communication with the clients.

The only part that I still can not understand is on the server side, it dose not really matters what king of modification I am applying on the LocalAddr => 'localhost', or LocalAddr => "0.0.0.0", still can not communicate locally. I was under the impression that local communication is different than external.

Last question just in case you know about it. I found on IO::Socket::INET the following part of code:

$sock = IO::Socket::INET->new(
                           PeerPort  => 9999,
                           PeerAddr  => inet_ntoa(INADDR_BROADCAST),
                           Proto     => udp,    
                           LocalAddr => 'localhost',
                           Broadcast => 1 ) 
                       or die "Can't bind : $@\n";
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I was trying to understand the use of PeerAddr  => inet_ntoa(INADDR_BROADCAST),. I was looking online and I found 8.2 The IP address INADDR_BROADCAST where it explains:

If there is a socket that is bound to the address assigned to the interface from which the packet was received, the packet will be delivered to this socket.

I was under the impression that if there is a socket available on the server side, then it can be used for communication but so far I did not found a way to use it. But maybe I did not understand correctly.

Any way thank you again for your time and effort.

Seeking for Perl wisdom...on the process of learning...not there...yet!

I believe you derived your code from http://www.thegeekstuff.com/2010/07/perl-tcp-udp-socket-programming/.

I modified/simplified the code, and this set works fine for me:
SERVER:

#!/usr/bin/perl
#udpserver.pl
use strict;
use warnings;
use IO::Socket::INET;

$| = 1; # flush after every write

my $socket = new IO::Socket::INET (
                        LocalPort => '5000',
                        Proto => 'udp',
                    ) or die "ERROR in Socket Creation : $!\n";

while(1){
    $socket->recv(my $recieved_data,1024);
    my $peer_address = $socket->peerhost();
    my $peer_port = $socket->peerport();
    print "\n($peer_address , $peer_port) said : $recieved_data";
    #send the data to the client at which the read/write operations do
+ne recently.
    $socket->send ("Server received '$recieved_data'. This is the SERV
+ER response\n");
}
$socket->close(); # We will never get here , but good practice to clos
+e
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CLIENT:

#!/usr/bin/perl
#udpclient.pl
use strict;
use warnings;
use IO::Socket::INET;

$| = 1; # flush after every write

my $socket = new IO::Socket::INET (
    PeerAddr   => '127.0.0.1:5000',
    Proto        => 'udp'
  ) or die "ERROR in Socket Creation : $!\n";

$socket->send("data from client");

$socket->recv(my $data,1024);
print "Data received from socket : $data\n";
$socket->close();
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The BROADCAST is a way to send data to all listeners on the subnet. To do that, you use a special broadcast IP addressto SEND data.

I'm not sure I understood your question in this regard.

        "You're only given one little spark of madness. You mustn't lose it."         - Robin Williams