What is it all about?
libnfnetlink is the low-level library for netfilter related kernel/userspace communication. It provides a generic messaging infrastructure for in-kernel netfilter subsystems (such as nfnetlink_log, nfnetlink_queue, nfnetlink_conntrack) and their respective users and/or management tools in userspace.
This library is not meant as a public API for application developers. It is only used by other netfilter.org projects, such as libnetfilter_log, libnetfilter_queue or libnetfilter_conntrack