Hello,

I am writing a small Perl/TK app, which communicates with other instances of itself on a LAN (think a sort of Instant Messaging application).

This snippet of code works under FreeBSD, but not under Linux:

#!/usr/bin/perl -w

use IO::Socket;
use strict;

my($sock, $server_host, $msg, $port, $ipaddr, $hishost,
    $MAXLEN, $PORTNO, $TIMEOUT);

$MAXLEN  = 1024;
$PORTNO  = 5151;

$server_host = '192.168.0.255';
$msg         = "test";
$sock = IO::Socket::INET->new(Proto     => 'udp',
                              PeerPort  => $PORTNO,
                              PeerAddr  => $server_host)
  or die "Creating socket: $!\n";
$sock->sockopt(SO_BROADCAST, 1);
# $sock->sockopt(SO_DONTROUTE, 1);

$sock->send($msg) or die "send: $!";
[download]

Running under FreeBSD works (as verified with a tcpdump process), running under Linux gives a:

Creating socket: Permission denied

I was given the two options to set on the socket (via 'sockopt') by a C programmer - the 'SO_DONTROUTE' doesn't seem to be necessary. Turning it on does not make it work under Linux. The 'SO_BROADCAST' is 100% necessary for it to work at all under FreeBSD.

Yes, I really want to use UDP broadcasts. Suggestions I use unicast addresses will be cheerfully ignored :-)

Oh, and although it would be totally unsuitable for my application, I did try running it as root. It made no difference.