Free Network Sim?
I want to start reading some stuff about networking and i need to practice what i read so, is there any tool that can simulate the design of a network?(i am using winXP)
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The best (e-learning) tool which really gives you insight into the OSI-stack in general is the one Cisco uses in it's certification course offerings. It's called ``Packet Tracer'' and AFAIK is available to the general audience. The tool is able to simulate devices, different topologies, most TCP/IP oriented protocols, high level clients - think web server and some browser,ntheir end-to-end connectivity, including the physical layers in a really simple to use GUI. I do have to admit that it's biased towards Cisco equipment, but its general enough to apply the principles.
You either want something like this to simulate network performance: http://www.nsnam.org/
Or you want something like this to simulate some hosts so you can work on configuration: http://www.virtualbox.org/
Between the two of them, you can simulate almost anything, although if you specifically want to work on configurations for Cisco or Juniper routers, you're going to need the real thing. If you just want to work with routing in general so you understand the protocols, install a linux on a virtualbox instance and install Quagga http://www.quagga.net/ on that.