I wrote very simple http module to 301 Redirect old DNN v1.1.10e site URLs to new DNN v4.6.2 site URLs.

At present I haven't setup a local DNN dev environment so I can debug the DNN code I only plugged in the http module I wrote which works in my test project as expected but does not seem to work entirely the DNN site.

From performance point of view I tought it will be better if my module handles only the 404 errors and translates the URLs from a predefined list rather then handling every request. So the http module I wrote only acts only on 404 HTTP context errors where DesktopDefault.aspx and EditModule.aspx are requested. Then I have a a list to translate old IDs to new IDs for tabs and a custom module IDs that are different on the new site.

I noticed that my http module only works for those tabids that already exist in the Tabs table in the database and 302 Redirect is issued before my HTTP module kicks in...

My question is: How DNN handles the http requests? It looks like it is checking for the existence of the tabid and is issuing a redirect to avoid 404 errors!?