The latest release of Net::Pcap (and the last GitHub activity) is about 1.5 years old and there are 13 open bugs. I have tried to interface libpcap on two occasions, and my experience has been that this is one of those cases where it seems to be easier to let the specialized tools handle the packet capturing instead of attempting to roll your own. As much as I love Perl, I have to ask: why are you trying to write this in Perl instead of using tcpdump or tshark?