test1.pl:
use IO::Socket::INET;
my $socket = new IO::Socket::INET(Proto => "udp", 
                               LocalAddr => "localhost",
							   LocalPort => 3000,
							   PeerAddr => "localhost", 
							   PeerPort => 3001, 
							   Timeout => 10) 
		|| die "failed";
while (1) {
	my $msg = <$socket>;
	chomp $msg;
	print "got $msg\n";
	print $socket $msg + 1, "\n";
}

test2.pl:
use IO::Socket::INET;
my $socket = new IO::Socket::INET(Proto => "udp", 
                               LocalAddr => "localhost",
							   LocalPort => 3001,
							   PeerAddr => "localhost", 
							   PeerPort => 3000, 
							   Timeout => 10) 
		|| die "failed";
print $socket "1\n";
while (1) {
	my $msg = <$socket>;
	chomp $msg;
	print "got $msg\n";
	print $socket $msg + 1, "\n";
}