I want to install Ubuntu 11.10 on my external hardisk in order to do my assignment running NS (Network Simulator).
Can NS be running or working properly if my Ubuntu installed on an external hard disk?
Where you install Ubuntu shouldn't effect what you can run on it. As long as NS runs on it normally (no experience with this) you should be able to run it fine on your external harddrive.
NOTE: Just because it is an external harddrive, doesn't mean you will be able to move the ubuntu installation from computer to computer and it could cause issues if you have additional external devices plugged in.
Click the Try It section's
It will give you a quick idea how you can boot a USB copy of Ubuntu as "Live CD" sort of mode -- but I wouldn't count on being able to persistently store data easily with this mode. I mean, you'll be able to
Once it is up and running, you'll be able to install