Currently we have a standing instance of Cognos11 www.mysite.com/prod11 however, we would like people to use a simplified URL ie.without the alias.
Does anyone know how this is done?
You have lots of options, but the simplest might be to put a redirect in your default file (e.g. index.html).
When a user goes to www.mysite.com what actually happens is that the webserver sends back www.mysite.com/index.html. So what you do is you have index.html tell the browser to go to www.mysite.com/prod11. So now the user can go www.mysite.com whose server will send back www.mysite.com/index.html that tells the browser to automatically go to www.mysite.com/prod11. The end result is the user enters www.mysite.com and the URL will change to www.mysite.com/prod11.
One advantage of this is that it should be trivial to change the index.html to point to a different URL if you need (www.mysite.com/prod12).
Alternatively, you could look into proxy settings so that www.mysite.com loads www.mysite.com/proxy, and I expect the documentation for your webserver is detailed enough to help with that.