Names of Softwares used for modeling
I suppose you mean simulating computer networks? because modelling is different (you can model your network as a graph for instance). If this is the case have a look at these simulators: 


NS2: built with C++, a discrete-event simulator, open source, and perhaps the most useful. You would need to use Tcl to write the script of the simulation experiments. New open source libraries are always added. I suggest it, however, i know many consider it a bet complex. Good knowledge in C++ is required if you want to maximally exploit it (at least to print your statistics and analyze them). The newer version is NS3 (i have nt used it yet), but from what I read, you can write your simulation experiments using python or c++.
Opnet: I am not a fan, and it is not open-source. I think there is a student-version. 
simjava: if you are a java person, then use this. (I haven't used it, but i saw it being cited in many research papers). 


but be careful before starting working with any "network simulator" because in many cases you don't need complex simulators. A simple C++, Java or Python code would be sufficient. (Actually, it is always a good programming exercise to create your own discrete-event simulator for a network). 

If you are interested in distributed processors simulation (from a theoretical point of view), then I would suggest erlang (a programming language). It is functional language very similar to Haskell (created by Eriksson). it is very easy to create processes with identities. But even more, you can let the processors exchange messages by sending/receiving messages in a very simple way.