When we done with the migration work from one environment to another environment, obviously stake holder would ask the SharePoint administrator to provide the URL redirection mechanism as users have been accessing the old URL from the favorites, outlook, and shortcuts.
There are multiple options for SP administrator to achieve this task like creating URLMapping element in the web.config, or writing URL Rewriting using HTTP Modules, etc. But these methods are time consuming and we can not test code as we are working on the production migration. So, the only option is to change the redirection URL at the IIS level. Below is the workable and quick solution for this task.
Just set “The exact URL entered above” and “A permanent redirection for this resource” on the IIS and enter your fully qualified host name entry as follows
The $S$Q will maintain all URLs on our other host names that enter.
This would redirect all your http://contoso.external.com/* HTTP calls to http://contoso.corp.com/*.
How simple is it right? 
