ipnat(5) on FreeBSD
The text bf2c3b93624f, as FreeBSD 4.5-RELEASE, FreeBSD 4.4-RELEASE, FreeBSD 4.3-RELEASE, FreeBSD 4.2-RELEASE, FreeBSD 4.1.1-RELEASE, FreeBSD 4.1-RELEASE shipped it.
IP NAT file format
The text bf2c3b93624f, as FreeBSD 4.5-RELEASE, FreeBSD 4.4-RELEASE, FreeBSD 4.3-RELEASE, FreeBSD 4.2-RELEASE, FreeBSD 4.1.1-RELEASE, FreeBSD 4.1-RELEASE shipped it.
IP NAT file format