The FreeBSD network stack virtualization project aims at extending the FreeBSD kernel to maintain multiple independent instances of networking state. This will allow for complete networking independence between jails on a system, including giving each jail its own firewall, virtual network interfaces, rate limiting, routing tables, and IPSEC configuration. This project is focused at virtualizing the networking stack in FreeBSD -CURRENT.
For more information and downloading, please refer to the project page
BSDTalk has a podcast with Marko Zec at EuroBSDCon 2007.