We help IT Professionals succeed at work.

Invalid ICMP type 69

rivusglobal
rivusglobal asked
on
Medium Priority
1,647 Views
Last Modified: 2008-01-09
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;
}

Comment
Watch Question

Since you have already recieved the data in $icmp->recv inside icmp_recv(), why are you again doing $client_recv in scan_udp_ports.

AFAIK, you should set the listening socket ($icmp) in blocking mode; and just test the value of $icmpbuffer to see if data has  arrived....

Author

Commented:
I'm doing the $client->recv just in case any data actually gets returned over the UDP port, which would be a confirmation of the port being open.

In blocking mode, if there is no ICMP response ( ie. filtered port ) then the script would never receive a response.

Not the solution you were looking for? Getting a personalized solution is easy.

Ask the Experts

Author

Commented:
My unpacking routine wasn't working at all.  After looking at Net::Ping I understand that the actual start of the ICMP type in the returned packet starts 20 bytes into the packet.  This line of code returns the proper ICMP Type and SubCode.

my($fromtype, $fromsubcode) = unpack("C2", substr($icmpbuffer, 20, 2) );

Thanks for pointing me in the right direction manav_mathur.
Access more of Experts Exchange with a free account
Thanks for using Experts Exchange.

Create a free account to continue.

Limited access with a free account allows you to:

  • View three pieces of content (articles, solutions, posts, and videos)
  • Ask the experts questions (counted toward content limit)
  • Customize your dashboard and profile

*This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.

OR

Please enter a first name

Please enter a last name

8+ characters (letters, numbers, and a symbol)

By clicking, you agree to the Terms of Use and Privacy Policy.