This document may contained outdated information, please update!
The Haiku Network Stack is a modular and layered networking stack, very similar to what you may know as BONE.
The entry point when talking to the stack is through a dedicated device driver that publish itself in /dev/net. The userland library libnetwork.so (which combines libsocket.so, and libbind.so) directly talks to this driver, mostly via ioctl()1.
The driver either creates sockets, or passes on every command to the socket module2. Depending on the address family and type of the sockets, the lower layers will be loaded and connected.