Transport IPv4 packets from netfilter to user space. Used by ip_queue kernel
module. After a long period of being declared obsolete (in favor of the more advanced
nfnetlink_queue feature), it was removed in Linux 3.5.
Receives routing and link updates and may be used to modify the routing tables (both IPv4
and IPv6), IP addresses, link parameters, neighbor setups, queueing disciplines, traffic
classes and packet classifiers (see rtnetlink(7)).