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

Hello
I want to send one UDP packet from a Windows to a port on a Windows and se if the port is open.

I want to print the answer if the port is open or closed.
I can send the packet but how can i read the answer "ICMP udp port portnumber unreachable" if the port is closed?.

use strict;

use IO::Socket::INET;

my $MySocket=new IO::Socket::INET->new(PeerPort=>888,
Proto=>'udp',
PeerAddr=>'192.168.1.10');

my $msg = "x";
$MySocket->send($msg);


// Anders Andersson

Replies are listed 'Best First'.
Re: How read ICMP UDP port unreachable?
by kvale (Monsignor) on Mar 27, 2004 at 00:42 UTC
    If you want ot try an ICMP udp ping, it might be easier to use the Net::Ping module: 
    use Net::Ping;

$p = Net::Ping->new("udp");
print "$host is alive.\n" if $p->ping($host);
$p->close();

    [download]

    -Mark

[reply]
[d/l]
Re: How read ICMP UDP port unreachable?
by castaway (Parson) on Mar 28, 2004 at 09:51 UTC
    I've played around some with NetPacket::ICMP and such. What I think you'd need to do, to test that particular UDP port, would be to listen locally on the ICMP port (which is a protocol like UDP and TCP), and read any incoming packets that occur when you connect via UDP.

    Anyway, this is as far as I got, it doesn't seem to get a ICMP packet type that makes any sense, though, anyone have an idea why? 

    #!/usr/bin/perl -w

use Data::Dumper;
use NetPacket::ICMP;
use IO::Socket;

my $icmps = IO::Socket::INET->new("LocalHost" => "192.168.1.2", 
                                  "Proto" => "icmp") 
    or die "Cant icmp listen ($!)"; 

print "boo\n";

my $udptest = IO::Socket::INET->new("PeerAddr" => "192.168.1.20", 
                                    "PeerPort" => "2222", 
                                    "Proto" => "udp", 
                                    "Timeout" => 20); 

$udptest->print("test"); 

my $y = $icmps->recv($buffer, 1024, 0); 
if($y)
{
    ($xport, $iaddr) = unpack_sockaddr_in($y);
    $remotehost = inet_ntoa($iaddr);
    print("peerhost $remotehost:$xport\n");
}

my $dec = NetPacket::ICMP->decode($buffer); 

print Dumper($dec);

    [download]
    Which outputs: 
    boo
peerhost 192.168.1.20:0
$VAR1 = bless( {
                 '_parent' => undef,
                 'data' => 'c
                             @À¨À¨E Àl@@öùÀ¨À¨®

                                               qtest',
                 'cksum' => 60,
                 'type' => 69,
                 '_frame' => 'EÀ<c
                                  @À¨À¨E Àl@@öùÀ¨À¨®

                                                    qtest',
                 'code' => 192
               }, 'NetPacket::ICMP' );

    [download]
    Where 69 is not any of the possible packet types listed in NetPacket::ICMP.. So, no clue whats going haywire..

    C.

[reply]
[d/l]
[select]
Re: How read ICMP UDP port unreachable?
by neniro (Priest) on Mar 27, 2004 at 10:33 UTC
    Because UDP is stateless (as mentioned above), none reaction is a good reaction, but firewalls will drop your packets silently so it looks like a connection but it isn't. If there are no firewalls you won't get in trouble with this awkward behavior.
[reply]
Re: How read ICMP UDP port unreachable?
by flyingmoose (Priest) on Mar 27, 2004 at 02:40 UTC
    UDP is by definition unreliable, unordered, and sessionless. If you need to know if a port is open, you probably want to initiate a TCP/IP connection to that particular port. if you want to be creative, you could perhaps use nmap for this scanning, as that is well suited for checking a large number of ports over a network very efficiently -- just be careful to ensure you are scanning only computers you own, else you could easily get into trouble with your ISP, or worse...
[reply]
      Note, UDP and TCP ports are completely separate things, thus checking using TCP/IP if a particular port is open will not tell you anything about whether the UDP port with the same number is open, at all.

      C.

[reply]

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