I'm writing a small UDP port scanner that just relys on an ICMP response to detect non-filtered/closed ports.

For some reason my code is returning an ICMP type 69 Code 1 which is not a valid type that I can see. I'd expect a type 3 ( Destination Unreachable ) not an undefined type.

Am I deciphering the ICMP packet I'm receiving wrong? Here is the code I am using: 
#!/usr/bin/perl

use IO::Socket;

#
#    Scan UDP ports
#
$|++;
my @ports = ( 53, 514, 15555 );
scan_udp_ports( 'localhost', \@ports );


sub scan_udp_ports {
    my $host = shift;
    my $ports = shift;

    my($closed, $open, $filtered);

    #    Setup ICMP listen
    my $icmp = IO::Socket::INET->new(
                        Proto        =>    'icmp',
                        Blocking    =>    0
                        ) or die("No ICMP listen");

    foreach my $port ( @$ports ) {

        print "Scanning $port\n";

        #    Setup UDP send connection
        $client = IO::Socket::INET->new(
                        PeerPort    =>    $port,
                        PeerAddr    =>    $host,
                        Proto        =>    'udp',
                        Blocking    =>    0
                        ) or die("No server $!");

        #    Send UDP packet
        $client->send( undef );
        sleep( 5 );
        my $icmpbuffer = icmp_recv( $icmp );

        #    Check for response
        my $flags;
        if( $client->recv( $dgram, 10, $flags ) ) {
            print "This udp port $port at host $host responded!\n";
        }
    }
}

sub icmp_recv {
    my $icmp = shift;

    #    Listen for ICMP response
    my $icmpbuffer;
    if( my $icmpr = $icmp->recv( $icmpbuffer, 1024, 0 ) ) {
        print "ICMP Type: " . unpack("%8C", $icmpbuffer) . "\n";
        print "ICMP Code: " . unpack("%8c", substr($icmpbuffer, 9)) . 
+"\n";
        print "ICMP Checksum: " . unpack("%8c", substr($icmpbuffer, 33
+)) . "\n";
    }
    return $icmpbuffer;
}

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In reply to Invalid ICMP type 69 by vancetech

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