Securing web pages

Im new to asp .net and ive been given a task to secure our current intranet site with authentication to our active directory domain.

Im using vd 2008 and have created a login page and a test page which works fine.

i now need to know how to secure the rest of the site so if some one goes to a direct page without authenticating it will redirect them to the login page like my test does.

Note the current intranet site is written in asp

Thanks for any help 
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