If you are searching for a free of use network diagramming tool you should consider the following :
Cade is a software developed for CAD purpose. As a 2D vector editor Cade runs for Windows. You can specify for each of the component in your network diagram the IP address, it’s serial number, it’s manufacturer so it can be used as a database to manage your technical components. CADE is free to use.
Diagram Designer is an oldschool freeware tool. Its main advantage, after it is free, is its ease of use. It should make it appealing for professional but also for those who start in the business. With Diagram Designer you can choose from a large selection of symbols and icons.
We experienced the GoVisual Diagram Editor software. We find it a little beat complex to use and it lacks icons and diagrams that are the essence of the tool. Even if it is free, you probably prefer a more simpler tool for appealing network diagram drawing.
In the wide range of Notepad Something, here is the Network Notepad that make network diagram in a notepad like environement. It comes with a wide range of functions and is very easy of user. Wide range of icons. Freeware.