iptables-1.2.6 by Paul Russell.
Linux netfilter Hacking HOWTO by Paul Russell.
iproute2 by Alexey Kuznetsov.
Advance routing Linux HOWTO.
HTB queueing discipline implementation by Martin Devera.
Linux-Advance Networking Overview by Saravanan Radhakrishnan.
monitor.pl by Stef Coene.
netcat by Hobbit.