ASP.NET Web Forms extensively use postback mechanism in order to maintain the state of the server-side controls on the web page. This makes it somewhat tricky to perform URL rewriting for ASP.NET pages. When a server side form control is added to the web page, ASP.NET will render the response with HTML <form> tag that contains an action attribute pointing back to the page where the form control is. This means that if URL rewriting was used for that page, the action attribute will point back to the rewritten URL, not to the URL that was requested from the browser. This will cause the browser to show rewritten URL any time a postback occurs.
The PostBackUrl property is used to gets or sets the URL of the page to post when the Button control is clicked.
<asp:Button PostBackUrl="string" runat="server" />
Name:<asp:textbox id="TextBox1" runat=Server />
<asp:button id="Button1" Text="Submit"
PostBackUrl="demo_postbackurl.aspx" runat="Server" />