NAT configuration

[Wolfgang S. Rupprecht]

Is there some official hook in /etc one should use to setup NAT or is
it a case that one just has to slap the setting in /etc/rc.local ?  I
see tons of hits in google for how to setup NAT on linux, but can't
find anything that even looks remotely like official documentation.

What is the officially sanctioned way to set NAT up?

-wolfgang