FYI,
I was just going to look at the Libzero documentation on the NTOP site when I noticed the message "PF_RING ZC (Zero Copy) is the successor of Libzero and DNA. Please consider using it." It looks to be a single license now for the driver and libraries as opposed to one for each per MAC, but it also looks like there is an entirely worked API and example applications such as pfdnacluster_master get replaced with reworked and renamed versions. I hadn't seen any mention of it (or missed it) on the NTOP-misc list, so thought others may have also missed it as well.
See here: http://www.ntop.org/pf_ring/introducing-pf_ring-zc-zero-copy/
Regards,