How to deal with link redirects when migrating from classic ASP to ASP.NET?

Question

I have a large-ish web project which is migrating from classic ASP to ASP.NET (about time), and would like to redirect requests from the old addresses, such as:

/some/path/old-page.asp?foo=bar

to the new addresses:

/other/path/new-page.aspx?qaz=bak

For a fairly long time, there will be classic ASP pages running in parallel with ASP.NET pages, with individual pages being replaced by their ASP.NET versions over time. Where possible, I want to redirect from the old pages to the new ones to keep users from receiving 404 errors, and also to keep the accumulated PageRank on the pages.

My question is, how would you do the redirection logic from the classic ASP to the new templates? The obvious solution is to replace old-page.asp with some simple VBScript that redirects to new-page.aspx, but in the long run I want to get rid of the old .asp files, so I would like to implement the redirection in such a way that they will exist also after the site is completely running in .NET.

One option would be to map the .asp extension to ASP.NET, and implement the redirection as an HttpHandler, but I guess there is no way of making the classic ASP engine run after the request has been passed to ASP.NET.

Answer 1

A couple of years ago, I ran into the very same issue at an eCommerce company where we upgraded their website to .NET. The main issue is that we had no idea how many customers had the old asp pages in their favorites, as well as the issue of SEO. Yes you can map the asp extension to ASP.net, but you lose the ability to run the asp files at all, so that would require that you update ALL asp pages, which may not be feasible.

The best solution I found at the time was to implement an ISAPI redirection filter in IIS. This is an app that is run by IIS BEFORE, the asp or asp.net runtimes. It would make a decision based on the url or any rules you want, whether it should allow the asp files to run or whether they should be redirected, or use url-rewriting to handle the request. It is not always a clean operation, since it runs before your website's request do, and confusion can happen later if other developers don't know it is running. So make sure if you go this route, that your website has plenty of comments or documentation to let developers know there is this thing in IIS running...

There is a good explanation of how to implement this in Code Project. Go here and check it out. http://www.codeproject.com/KB/ISAPI/isapiredirector.aspx

Good Luck!

Answer 2

You should use the "HTTP 301 - Permanently Moved" response code, as this is precisely what it is designed for.

http://en.wikipedia.org/wiki/HTTP_301

An ISAPI redirection filter will work in the sense that, yes, it will redirect visitors to the new URL.

However there are three key problems with the ISAPI redirection strategy.

1. More code to write/maintain
2. Bookmarks and search engine entries will never be updated with the new and correct URLs
3. If foo.asp is transparently redirected to bar.aspx and both are indexed by Google, you'll have two duplicate URLs to the same content in Google. This clogs up search results and is actually against their TOS I believe.