BSD Linux contains one of the most full-featured open source IPSec VPNs. It is very interoperable and has a reliable reputation in the field. The VPN's documentation, however, is weak.

The IKE module (raccoon) can be extended to accept X.509 certs, although it does not yet validate the cert to the issuing server. It also uses 3DES (triple-DES) for the encryption, which brings it up to current NIST standards. Additionally, a packet filter is built into BSD that can be configured to run as a firewall in conjunction with the VPN.

Interestingly, this VPN implementation will run on the Macintosh򳠍 OS X because OS X uses BSD networking.