This code aims at providing a simple example of a Netfilter hook for IPv6 packets. Refer to Figure 18-1 of "Understanding Linux Network Internals" by Christian Benvenuti for a good picture of where in the packet flow the various hooks are invoked (preview for this page is available at Google Books as of this writing). Another good books on this topic is "Designing and Implementing Linux Firewalls and QoS using netfilter, iproute2, NAT, and L7-filter" by Lucian Gheorghe.