How to 301 Permanent Redirect in ASP.NET
In the next release of the .NET Framework (.NET Framework 4.0) there is a new response method for permanently redirecting a request: Response.RedirectPermanent. You can see the Beta MSDN documentation for Response.RedirectPermanent here. This will automatically issue the 301 moved permanently status code and redirect to the target page. A permanent redirect status code tells a search engine to update their cache and reassign the old url to the new url.
But if you need to do this now (prior to .NET Framework 4.0) you will need to do it the manual way. To do so you will need to manually add the status and location headers to the response.
The pre .NET Framework 4.0 versions are:
Response.Status = "301 Moved Permanently";
Response.AddHeader("Location", "/");
Response.Status = "301 Moved Permanently";
Response.AddHeader("Location", "/");
Response.End();
There is also a RedirectToRoutePermanent method which will allow you to redirect to a new url using route parameters (and sends the 301 Moved Permanently status code).
UPDATE: See RichardD's comment below for a different method. I have not tried it that way but I will next time because it certainly does look much cleaner.