use Net::Pcap;

use strict; #i am very careless

#look up a device to be used (the active NIC)

my $err="blah";

my $dev=Net::Pcap::lookup_dev(\$err) or die "error:\t$err\n";

#open the device in live mode to sniff out packets
my ($promisc,$snaplen,$to_ms);
$promisc=1; #watchout for any damn packet
$snaplen=150; #atleast 80 chars
$to_ms=100; #wait for 1 sec
$pcap=Net::Pcap::open_live($dev,$snaplen,$promisc,$to_ms);

#loop infinitely until an error occurs
#and call the packet processing subroutine
Net::Pcap::loop($pcap,-1,\&pack_pro,0);


sub pack_pro{
#this is the actual packet processor
my($user_data,$header,$packet)=@_;
# extract the source IP addr into dotted quad form
my($source) = sprintf("%d.%d.%d.%d",
        ord( substr($packet, $src_ip, 1) ),
        ord( substr($packet, $src_ip+1, 1) ),
        ord( substr($packet, $src_ip+2, 1) ),
        ord( substr($packet, $src_ip+3, 1) ));

# extract the destination IP addr into dotted quad form
my($destination) = sprintf("%d.%d.%d.%d",
        ord( substr($packet, $dst_ip, 1) ),
        ord( substr($packet, $dst_ip+1, 1) ),
        ord( substr($packet, $dst_ip+2, 1) ),
        ord( substr($packet, $dst_ip+3, 1) ));
#the above part is directly taken from "hacking linux exposed" (sorry but couldn't figure out this part)

my $data=substr($packet,$domain_start);
#change domain component seperator back into dots
$data=~s/[^-A-Za-z0-9]/./g;

#print the packet
print "$source->$destination\n$data\n";
}#sub routine ends