udp broadcast: doesn't work in Linux

fjonckers has asked for the wisdom of the Perl Monks concerning the following question:

strange... the following script doesn't work under Linux
I get following error:

send: Cannot determine peer address at udp.pl line 24
[download]

in Windows it works fine (activeperl)
anyone has an idea why ?????

#!/usr/bin/perl
#
use strict;
use IO::Socket;


# defaults
my $bcaddr = '192.168.254.255';
my $port = 9870;

# open UDP socket
my $sock = IO::Socket::INET->new(
    Proto=>'udp',
    LocalPort=>$port,
    PeerHost=>$bcaddr,
    PeerPort=>$port)
        or die "new socket:$@";

# 10 udp's on the wire
for (my $i=0;$i < 10;$i++) {
    my $data = 'UDP packet ' . $i;
    # send udp packet
    $sock->send($data) || die "send(): $!";
}
[download]

Comment on udp broadcast: doesn't work in Linux Select or Download Code

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Re: udp broadcast: doesn't work in Linux by fjonckers (Novice) on Oct 12, 2001 at 01:27 UTC
ok guys, found it... The option SO_BROADCAST requests permission to send broadcast datagrams on the socket. Broadcast was a privileged operation in earlier versions of the system. so, I rewrote my snippet: `#!/usr/bin/perl # use strict; use IO::Socket; # defaults my $bcaddr = '192.168.254.255'; my $port = 9870; socket(sock, PF_INET, SOCK_DGRAM, getprotobyname("udp")) or die "socket:$@"; setsockopt(sock, SOL_SOCKET, SO_BROADCAST, 1) or die "setsockopt:$@"; my $dest = sockaddr_in($port,inet_aton($bcaddr)); # 10 udp's on the wire for (my $i=0;$i < 10;$i++) { my $data = 'UDP packet ' . $i; # send udp packet send(sock,$data,0,$dest) \|\| die "send(): $!"; }` [download] doesn't seem to work with IO::Socket::INET->new thanks for the tips! made me look further than Perl (C, kernel)...	[reply] [d/l]
Re: udp broadcast: doesn't work in Linux by cjensen (Sexton) on Oct 11, 2001 at 21:39 UTC
Well, this is tough, because it seems your script isn't at fault. It looks like the call to `getpeername($sock)` is failing for this socket in IO::Socket. Try calling that directly in your script and see if you get the error at that point. Try connecting to another host/port. It's hard to diagnose without knowing more about your network config and the circumstances of this test.	[reply]
Re: Re: udp broadcast: doesn't work in Linux by fjonckers (Novice) on Oct 11, 2001 at 23:34 UTC
thanks cjensen! I added the following just below the socket creation and above the send method: `print "\ngetpeername: " . getpeername($sock) . "\n";` [download] output is: `getpeername: send: Cannot determine peer address at udp.pl line 26` [download] so, no error when calling getpeername... checking the linux kernel road.. woulb be very strange if you cannot send something to a LAN broadcast address tried other port values... nothing (port is random) F.	[reply] [d/l] [select]
Re: Re: Re: udp broadcast: doesn't work in Linux by cjensen (Sexton) on Oct 12, 2001 at 00:39 UTC
I should have been more clear... The error is occurring when the peer name is undefined in IO::Socket. It won't give you an error when it can't determine the peer address, it just returns undef. Then the call to send in IO::Socket croaks when peer name is undefined: croak 'send: Cannot determine peer address' unless($peer); So `getpeername($sock)` returning undef is what I expected would happen, I just didn't explain that well enough. It should return the address of the peer at the remote end of the socket. Try this and vary the $bcaddr in your script: my ($port, $addr) = unpack_sockaddr_in(getpeername($sock)); my $host = gethostbyaddr($addr, AF_INET); print "Host:\t$host\n"; print "Port:\t$port\n";	[reply]
Re: udp broadcast: doesn't work in Linux by perrin (Chancellor) on Oct 11, 2001 at 21:17 UTC
I think it requires support compiled into the kernel. At least it used to. Check on the Linux newsgroups or help sites for configuration info.	[reply]
Re: udp broadcast: doesn't work in Linux by Anonymous Monk on Oct 11, 2001 at 23:07 UTC
yes make sure your udp stuff is set up properly in the kernel http://www.linuxdocs.org/HOWTOs/Multicast-HOWTO.html	[reply]
Re: Re: udp broadcast: doesn't work in Linux by fjonckers (Novice) on Oct 11, 2001 at 23:25 UTC
thanks for your reply Ano! but I'm using an UDP BROADCAST not a Multicast... I want to send a packet to the broadcast address of my local subnet network: 192.168.254.0/24 where the broadcast address is 192.168.254.255 Multicasting is something completely different, broadcast addresses is standard ip stuff... Filip	[reply]