I'm trying to self-learn the following topics on Linux (preferably Fedora):

1. Network programming (using sockets API), especially across proxies and firewalls

2. Proxies (of various kinds like transparent, http, socks...),

3. Firewalls (iptables) and 'basic' Linux security

4. SNAT, DNAT

5. Network admininstration power tools: nc, socat (with all its options), ssh, openssl, etc

6. etc.

Now, I know that, ideally, it would be best if I had 'enough' number of physical nodes and physical network equipment (routers, switches, etc) for this self-learning exercise. But, obviously, don't have the budget or the physical space, nor want to be wasteful -- especially, when things could perhaps be simulated/emulated in a Linux environment.

I have got one personal workstation, which is a single-homed Fedora desktop with 4GB memory, 200+ GB disk, and a 4-core CPU. I may be able to get 3 to 4 additional low-end Fedora workstations. But all of these -- including mine -- will always remain strictly behind our corporate firewall :-(

Now, I know I could use VirtualBox-based virtual nodes, but don't know if there are any better alternatives disk- and memory- footprint-wise.

Would you be able to give me some tips or suggestions on how to get started setting up this little budget- and space-constrained 'virtual lab' of mine? For example, how would I create virtual routers?

Has someone attempted this sort of thing before: namely, creating a virtual network lab behind a corporate firewall for learning/development/testing purposes?

I hope my question is not vague or too open-ended. Basically, right now, I don't know how to best leverage the Linux environment and the various 'goodies' it comes with, and buying physical devices only when it is absolutely necessary.