#!/usr/bin/perl

use strict;
use warnings;

use Net::Pcap;

my $dev = "eth0"; # interface to listen on for CDP packets

my ($user_data, $err);

my %cdp_types = (

    '0001'        =>    'Device ID',
    '0002'        =>    'Addresses',    
    '0003'        =>    'Port ID',
    '0004'        =>     'Capabilities',
    '0005'        =>    'Software Version',
    '0006'        =>    'Platform',
    '0008'        =>    'Protocol Hello',
    '0009'        =>    'VTP Management Domain',
    '000a'        =>    'Native VLAN',
    '000b'        =>    'Duplex',
    '000e'        =>    'Voice VLAN',
    '0010'        =>    'Power Consumption',
    '0012'        =>    'Trust Bitmap',
    '0013'        =>    'Untrusted Port CoS',
    '0016'        =>    'Management Addresses',
    '001a'        =>    'Power Available',

);

my $pcap = Net::Pcap::pcap_open_live($dev, 1522, 1, 0, \$err) or die "
+Can't open device $dev: $err\n";

Net::Pcap::pcap_loop($pcap, -1, \&callback, $user_data);

sub callback {
                   
    my $packet = pop @_;
    my  $pkt = unpack "H*", $packet;

    if ((hex(substr($pkt, 24, 4)) <= 1518) && (hex(substr($pkt, 28, 2)
+) == 170) && (hex(substr($pkt, 30, 2)) == 170)) {
         
        # "SNAP detected\n";

        my (%cdp, %cdp_data, %cdp_output);

        my %ieee_snap_frame = (
                    dst_mac         =>      substr($pkt, 0, 12),
                        src_mac         =>      substr($pkt, 12, 12),
                        frame_lgt       =>      substr($pkt, 24, 4),
                        dsap            =>      substr($pkt, 28, 2), #
+ DSAP
                        ssap            =>      substr($pkt, 30, 2), #
+ SSAP
                        control         =>      substr($pkt, 32, 2), #
+ !!! 1 or 2 bytes : 1 for SNAP
                        snap            =>      substr($pkt, 34, 10),#
+ 5 bytes for SNAP - 3 vendor code - 2 ethertype 
                        data            =>      substr($pkt, 44),
               );

           if ($ieee_snap_frame{snap} eq "00000c2000") {

            # "CDP Detected\n";
                
            %cdp = (

                version        =>    substr($pkt, 44, 2),
                ttl        =>    substr($pkt, 46, 2),
                chksum        =>    substr($pkt, 48, 4),
                data        =>    substr($pkt, 52),
            );

            my @cdp_arr = split(//, $cdp{data});
    
            # Extract CDP TLV fields from the frame

            while (@cdp_arr) {

                my $type = join '', splice(@cdp_arr, 0, 4);
                my $length = join '', splice(@cdp_arr, 0,4);
                my $value = join '', splice(@cdp_arr, 0, ((hex($length
+) * 2) -8));
                $cdp_data{$type} = $value;        
            
            }

            # sort hash keys to ensure some order when printed

            foreach my $cdp_type (sort {hex($a) <=> hex($b)} keys %cdp
+_data) {
                
                if ($cdp_type =~ m/0001|0003|0005|0006|0009/) {

                   $cdp_output{$cdp_type} = join '', map(chr(hex($_)),
+ unpack "(a2)*", $cdp_data{$cdp_type});

                }

                elsif ($cdp_type =~ m/0012|0013|000a/) {

                   $cdp_output{$cdp_type} = hex($cdp_data{$cdp_type});
                }
                
                elsif ($cdp_type =~ m/0002|0016/) {
                
                   my @ip_addrs;    
                   my ($num_of_addresses, @addr) = unpack "a8 (a18)*",
+ $cdp_data{$cdp_type};
                   $num_of_addresses = hex(substr($cdp_data{$cdp_type}
+, 0, 8));
                   # Each address section consists of 9 bytes

                   foreach my $addr (@addr) {
                
                        my @addr =  map(hex($_), unpack("(a2)*", subst
+r($addr, 10, 8)));
                        push(@ip_addrs, join('.', @addr));
    
                   }

                   $cdp_output{$cdp_type} = \@ip_addrs;

                 }

                elsif ($cdp_type =~ m/0004/) {    
                   
                   my $cap = enum_capabilities(unpack "B*", pack "H*",
+ substr($cdp_data{$cdp_type}, 6, 2));
                        
                   $cdp_output{$cdp_type} = $cap;

                }
        
                elsif ($cdp_type =~ m/0007|0008/) {

                  $cdp_output{$cdp_type} = $cdp_data{$cdp_type};    

                }

                elsif ($cdp_type =~ m/000b/) {

                  $cdp_output{$cdp_type} = hex($cdp_data{$cdp_type}) ?
+ 'Full' : 'Half';
                
                }

                elsif ($cdp_type =~ m/0010|000e/) {

                   $cdp_output{$cdp_type} = hex(substr($cdp_data{$cdp_
+type}, -4));

                }

                elsif ($cdp_type =~ m/001a/) {
                    
                   my ($req_id, $man_id, $pa1, $pa2) = unpack("a4 a4 a
+8 a8", $cdp_data{$cdp_type});
                   $cdp_output{$cdp_type} = [map { $_ . " mw" } (hex($
+pa1), hex($pa2))];

                }

                else {

                  $cdp_output{$cdp_type} = $cdp_data{$cdp_type};

                }

            }

        cdp_print(\%cdp_output);

        }

    }

}

sub enum_capabilities {

    my $cap = shift;
    my (%cap, $o_key, $n_key);

    $cap =~ m/^[01]{7}[1]$/ ? ($cap{'-------1'} = "Is a Router") : ($c
+ap{'-------0'} = "Not a Router");
    $cap =~ m/^[01]{6}[1][01]$/ ? ($cap{'------1-'} = "Ia a Transparen
+t Bridge") : ($cap{'------0-'} = "Not a Transparent Bridge");
    $cap =~ m/^[01]{5}[1][01]{2}$/ ? ($cap{'-----1--'} = "Is a Source-
+Route Bridge") : ($cap{'-----0--'} = "Not a Source-Route Bridge");
    $cap =~ m/^[01]{4}[1][01]{3}$/ ? ($cap{'----1---'} = "Is a Switch"
+) : ($cap{'----0---'} = "Not a Switch");
    $cap =~ m/^[01]{3}[1][01]{4}$/ ? ($cap{'---1----'} = "Is an End De
+vice") : ($cap{'---0----'} = "Not a End Device");
    $cap =~ m/^[01]{2}[1][01]{5}$/ ? ($cap{'--1-----'} = "Is IGMP Capa
+ble") : ($cap{'--0-----'} = "Not a IGMP Capable");
    $cap =~ m/^[01]{1}[1][01]{6}$/ ? ($cap{'-1------'} = "Is a Repeate
+r") : ($cap{'-0------'} = "Not a Repeater");


    


    return \%cap;

}

sub cdp_print {

    my ($cdp_output) = @_;
    my ($cdp_type, $k, $v, $value);

format OUTPUT = 
    @<<<<    @<<<<<<<<<<<<<<<<<<<<<         @<<<<<<<<<<<<<<<<<<<<<<<<<
+<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
    $cdp_type,    $cdp_types{$cdp_type},  $cdp_output->{$cdp_type} 
.

format OUTPUT2 =
                        @<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
                        $_
.

format OUTPUT3 =
                        @<<<<<<<<<<<<    @<<<<<<<<<<<<<<<<<
                        $k, $v
.

format OUTPUT4 = 
    @<<<<    @<<<<<<<<<<<<<<<<<<<<<     
    $cdp_type,    $cdp_types{$cdp_type} 
.
    
    print "-------------------------------------------\n";

    foreach $cdp_type (sort {hex($a) <=> hex($b)} keys %$cdp_output) {

        if (ref($cdp_output->{$cdp_type}) =~ m/ARRAY/) {

            $~ = 'OUTPUT4';
            write;
             $~ = 'OUTPUT2';
                        write foreach (@{$cdp_output->{$cdp_type}});

        }

        elsif ( ref($cdp_output->{$cdp_type}) =~ m/HASH/) {

            $~ = 'OUTPUT4';
            write;
             $~ = 'OUTPUT3';

            foreach $k (sort keys %{$cdp_output->{$cdp_type}}) {
                
                $v = $cdp_output->{$cdp_type}->{$k};
                write;
            
            }

        }

        else {

             $~ = 'OUTPUT';
            write;

        }

    }

    print "-------------------------------------------\n";

}
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