Most people on installing .NET 3.5 on the server "expect" an entry for  v3.5 under the ASP.NET version Tab in IIS manager. And not finding that entry start panicking. If you have been one of those read on. The more tech savvy folks try to run aspnet_regiis -i from the v3.5 framework folder... but even that is missing :)

That brings us to the question

What exactly is ASP.NET 3.5 ?

Read the answer + Full article @ Vijayshinva Karnure's Blog