Mintain user login status

Question

Hi,
 
I am developing a web site for test and forum in ASP.NET. I want to maintain user login status through out whole website till user logout. User can login any time, not necessary at a time when he opens web site. I have so many pages, so is there any easy way to check weather user is logged in or not on each page and display his status accordingly on each page.
 

Please help to solve my problem.
 
Thanks.