# 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)
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An easier way to do that is through the Socket module:

use Socket;
# extract the source IP addr into dotted quad form
my $source = inet_ntoa substr $packet, $src_ip, 4;

# extract the destination IP addr into dotted quad form
my $destination = inet_ntoa substr $packet, $dst_ip, 4;
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