Should I perform a 301 redirect in Global.asax or on my 404 error page

Question

I'm about to replace a current e-commerce site with a brand new site. Before, a URL to a product was like this: www.example.com/ProductDetails.aspx?ProductID=123

Now it is like this: www.example.com/en-us/product/123/The-greatest-product-in-the-world

My question is: Should the 301 permanent redirect be done in the Application_BeginRequest event of Global.asax or in the Page_Load of my 404 error page? Isn't too late to make a 301 when the 404 loads?

Answer 1

You should put it in the Application_BeginRequest event and check the URL requested.

You could put it in the Application_Error event as well and check for a 404 but I think that uses up more resources and will be slower.

Answer 2

You'll want to do it before the browser (or bot) gets the 404 error. That way you make sure search engine bots are going to properly re-index your product pages and any page rank associated with them.

Answer 3

I have done it in the 404 page, but it's a hack -- you can change the response code. The Application_BeginRequest makes a lot more sense. You want to redirect so your old links will expire from search indexing.