#
# How to get an ICMP host unreachable packet???
#
use IO::Select;
use IO::Socket;

use strict;  use warnings;

my $sock_udp = IO::Socket::INET->new(Proto=>'udp');  
print "created udp=$sock_udp\n";
my $sock_icmp = IO::Socket::INET->new(Proto=>'icmp'); 
print "created icmp=$sock_icmp\n";
my $select = IO::Select->new();
my $host = '192.168.0.4';
my $port = 2;
my $rbits = 0;

my $aton = inet_aton($host);
my $addr = sockaddr_in($port, $aton);

$sock_udp->connect($addr) or die "$!\n";    #Unix socket faq says udp must be "connected" to get icmp msg
print "  udp 'connected' to $host:$port\n"; #http://www.unixprogram.com/socket/socket-faq.html#faq55
$select->add($sock_icmp);
$select->add($sock_udp);
vec($rbits, $sock_icmp->fileno(), 1) = 1;
vec($rbits, $sock_udp->fileno(), 1) = 1;

$sock_udp->send("test", 0) or die "$!\n";
print "  send test msg to $host:$port\n";

# select attempt
my $found = select($rbits, undef, undef, 1);
if ($found > 0)                          
{
    my $msg  = "";
    my $size = 1500;
    my $from_icmp = recv($sock_icmp, $msg, $size, 0) or die "$!\n";
    my $from_udp = recv($sock_icmp, $msg, $size, 0) or die "$!\n";

    my ($from_port, $from_ip) = sockaddr_in($from_icmp);

    # I need to unpack the packet here I think...
}

# io::select attempt
my @found = $select->can_read();
foreach (@found)
{
    print "  got a can_read on socket=$_\n";
    my $msg  = "";
    my $size = 1500;
    #my $from_icmp = recv($sock_icmp, $msg, $size, 0) or die "    $!\n";
    my $from_udp = recv($sock_icmp, $msg, $size, 0) or die "    $!\n";

    my ($from_port, $from_ip) = sockaddr_in($from_udp);

    # I need to unpack the packet here I think...
}

#If you can figure this out, here is another question:
#I want to scan more than 1 machine for a certain open UDP ports
#(for use internally at my business and I want to write it myself and not use the awesome nmap...)
#Should I create a new UDP socket for each host I want to test?
#and then wait in the select loop?
#The reason I ask is that I expect to get stuck on determinig
#what hosts/ports replied back as ICMP unreachable...
#I am not there yet, but expect to get stuck ;-)