netintro(4) on OpenBSD
The text 9a4fff1e6959, as OpenBSD 7.6, OpenBSD 7.5, OpenBSD 7.4, OpenBSD 7.3, OpenBSD 7.2, OpenBSD 7.1, OpenBSD 7.0, OpenBSD 6.9, OpenBSD 6.8, OpenBSD 6.7, OpenBSD 6.6, OpenBSD 6.5, OpenBSD 6.4 shipped it.
introduction to networking facilities