The kernel has lots of parameters which can be tuned for different circumstances. While, as usual, the default parameters serve 99% of installations very well, we don't call this the Advanced HOWTO for the fun of it!
The interesting bits are in /proc/sys/net, take a look there. Not everything will be documented here initially, but we're working on it.
In the meantime you may want to have a look at the Linux-Kernel sources; read the file Documentation/filesystems/proc.txt. Most of the features are explained there.