Why SessionID changes in every request in asp.net?

This may happen if your application has never stored anything in the session state.  In this case, a new session state (with a new ID) is created in every request, but is never saved because it contains nothing.  

However, there are two exceptions to this same session ID behavior: 

• If the user has used the same browser instance to request another page that uses the session state, you will get the same session ID every time.  For details, see "Why does the SessionID remain the same after the Session times out?"

•  If the Session_OnStart event is used, ASP.NET will save the session state even when it is empty.