A Handbook on how to correctly draw diagrams of complex network systems?

The main thing — a good understanding of how it works (will work) the resulting system. Next is the matter of technique and experience. Recommend doing the diagrams in Visio, as I hadn't worked for OpenSource, diagrams I draw in it. The skill of drawing beautiful and clear diagrams will come with experience.

and maybe it controlsale.ru/?p=23 you will help

Visio, of course, the flagship.
But DIA is also quite good...
And no editor-draftsman does not replace your own understanding.
For the subsequent distribution/shipment to the import picture...
And the books...
If you your network imagine clearly, and the pattern will make...
And if not, then I don't know what to suggest.
Network of several levels, which are poorly interrelated.
And at the level of TCP/IP to know the physical topology is not required, but desirable...

I've tried to use for a network diagram/configuration software is always returned to the manuscript version.
In the end over work place hung a few A3 sheets pinned to the wall of plasterboard buttons. Painted and signed — with a pencil. In this case, the diagram is always just transfer to date (eraser + pencil — to help).
How to display — it's entirely Yours.
The main thing — to make it clear to You and to your colleagues.
As an example, look at the diagram in the manual for configuring juniper devices or cisco.
And another tip: don't try to show everything on one diagram. Useless. In the best case it will become unreadable in the worst — intuitive. Better to split into separate schemes for projects/levels of abstraction.
So in my case it was two of a network diagram:
— physical links
diagram of vpn connections
Their "combination" was achieved overall for all schemes the naming of devices/hosts/physical links.
There were individual table settings of their firewalls, which has already been noted, the ports between which the host is open and why.