Understanding Extending A Web Application in SharePoint

SharePoint allows to expose the same content to two different set of users with different URL's and with different authentication. This is called Extending a Web Application. I will try to explain this concept in this post.

Lets say a company has a Web Site on SharePoint for Internal users. The users access the site using a URL http://demo-intranet. The internal users are using Windows Authentication to access the site. Now we need to expose the same content over extranet using another URL as http://extranet-demo.com. The external users will be accessing the application using Form Based Authentication. This situation can be dealt using this concept.

As we know each Web Application has a corresponding IIS Web Site. When we extend a Web Application another Web Application gets created which in turn also creates a new IIS Web Site. This extended Web Application uses the same Content DB used by the original Web Application . This new web site has its own Web.Config file but SharePoint does not copy the content of the original Web.config into this new Web.Config. So any modification which are done in the file needs to be manually done in this new Web.Config File.

The extended Web Application uses the same authentication type of the original Web Application. So if the original Web Application is configured using Classic mode then the extended Web Application will be configured using Classic mode or if it Claims based then the extended one will also use Claims based authentication.