Setting up a virtual network using GNS3 and
By Shashank Shekhar Tewari
While I'm really interested in networking, it wasn't economically feasible for me to buy routers and
switches and multiple hosts to set up a home network. So while studying for my CCNA, I came
across GNS3 and slowly realised just how powerful it really was.
This software, along with a virtualisation software, can be used to set up very complex networks,
and can be used to simulate many common network scenarios. This tutorial aims to help a person
get an idea of how to set up such networks.
If you're studying
related to networking, you can learn with this.
Doing a Cisco cert? GNS3 has been used for everything from Cisco Voice to CCIE level labs. You
can use the virtual hosts to actually
the effect your configuration has done. Sure, you've setup
an ACL, but is it really working? Just go to your virtual host and check. If you ping from a Cisco
router just after it's setup, why is the first ping never successful? Open up Wireshark and find out.
Learning to be a sys-admin? Both GNU/Linux OSes and Microsoft OSes can be used here. You can
setup a server with multiple clients, setup a mail server, etc. and see how everything works out.
Setup a simple Apache web server, and see how it looks like from a host's point of view.
Interested in security and pen-testing? What better combination than having Backtrack on one
end, and Damn Vulnerable Linux on the other? You can play around as much as you want,
completely destroy the victim's PC, and you'll be able to go back to the original state by just
opening up a saved state in Virtual Box. You can then check the Apache web server you just setup
for open ports and vulnerabilities.
Since nearly every GNU/Linux OS comes with as a live version now, you don't even have to install
them to a virtual hard disk to use them. Just boot it in any virtual hard disk you've created, and
start using it.
Although my preferred virtualisation software is VirtualBox, you can use any you want. The
settings will obviously differ. My host and guest OSes will nearly all be GNU/Linux, but both, GNS3
and VirtualBox, are available for Windows as well, and the instructions will pretty much be the
same. So if you're a Windows user, give the tutorial a try, and just use a little geek-sense to figure
out where things might differ.
While this has many,
applications, and the idea definitely isn't new, I did not find a decent
tutorial on it, and had to figure out a lot of things myself. Hence, now that I'm free, I decided to
write a tutorial myself.