7. IPsec: secure IP over the Internet

FIXME: editor vacancy. In the meantime, see: The FreeS/WAN project. Another IPSec implementation for Linux is Cerberus, by NIST. However, their web pages have not been updated in over a year, and their version tended to trail well behind the current Linux kernel. USAGI, an alternative IPv6 implementation for Linux, also includes an IPSec implementation, but that might only be for IPv6.