User-land TCP/IP stack from 4.4BSD-Lite2, a companion of W. Richard Stevens's immortal work TCP/IP Illustrated, Volume 2: The Implementation, with a focus on TCP chapters. TCP/IP Illustrated vol.2 uses 4.4BSD-Lite as its example, a slightly early version. TCP/IP code of 4.4BSD-Lite2 is roughly the same as FreeBSD 2.0.

This is not a fork of https://github.com/sergev/4.4BSD-Lite2, which contains the whole 4.4BSD-Lite2.tar.gz. This repository only contains usr/src/sys of the tarball, ie. the kernel source.

$ ./build.sh

This build three executables:

• objs/test_init TCP three-way handshake, you can step through code with GDB
• objs/test_pigeon ICMP echo request/response
• objs/test_tun Connect to host with TAP/TUN device. (TODO: more instructions)

This TCP/IP stack is alive, using tap/tun device on Linux. (WIP)

Unofficial companion site of TCP/IP Illustrated vol. 2

For running recent FreeBSD TCP/IP stack in user mode, take a look at https://github.com/pkelsey/libuinet and https://github.com/cloudius-systems/osv.