Fundament BSD 4.4 based network stack TCP/IP Illustrated, Volume 2 is still the #1 reference KAME based IPv6 stack with local modifications (e.g. IPsec) IPv6 Core Protocols Implementation good reference Stuff made by OpenBSD pf - the ultimate stateful packet filter altq - traffic shaping for QoS routing daemons - bgpd, ospfd, ripd, ospf6d