[Click] How to draw configuration diagrams

[Alan Tang]

Dear everyone

Does anyone knows which tool do they use to draw those fancy diagrams 
e.g. the one with *fake-iprouter.click* 
<http://www.pdos.lcs.mit.edu/click/ex/fake-iprouter.html> configuration 
in The Click modular router 
<http://www.pdos.lcs.mit.edu/papers/click:tocs00> paper ?

Thanks
Greetings!
Alan