You can install dia software under Linux or windows.

Dia is a nicely presented drawing program designed to simplify the task of preparing a variety of different types of diagrams including UML, entity relationship, flowchart, electronic circuit, and network diagrams.
http://dia-installer.sourceforge.net/ : windows version
http://www.gnome.org/projects/dia/ : UNIX/Linux version

Tgif - The Tgif drawing program has some unique and interesting features that make it useful for network diagrams. http://sourceforge.net/projects/tgif

Xfig - The Xfig drawing package is a general-purpose vector drawing package. Its interface provides all the sorts of features I think are important for network diagramming packages including a "Smart Links" features which allows lines/links between symbols to be move when either symbol moves. The Xfig interface is clean and easy to learn once you become accustomed to the lack of a "select" tool; each tool has an built-in select function.
ftp://ftp.x.org/contrib/applications...ng_tools/xfig/

I recommend using xfig or dia both are quite good and can be install using apt-get or yum command.

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