At run time, master pages are handled in the following sequence:
1.Users request a page by typing the URL of the content page.
2.When the page is fetched, the @ Page directive is read. If the directive references a master page, the master page is read as well. If this is the first time the pages have been requested, both pages are compiled.
3.The master page with the updated content is merged into the control tree of the content page.
4.The content of individual Content controls is merged into the corresponding ContentPlaceHolder control in the master page.
5.The resulting merged page is rendered to the browser.
The process is illustrated in the following diagram.
At This Image Link