For most blogs and websites, Google is one of the major sources of visitor traffic. That is why it is so important to ensure that, when any web page is moved, it retains its visibility in Google. What is involved in this is what is called a 301 Permanent Redirect. The References below give a good account of the many ways this can be done. This blog has just moved and the good news is that the move was done in such a way that the Google visibility was maintained unchanged throughout the move. The specifics involved will be discussed in a more detailed post in the near future.
The reason for this post is that by accident some interesting details have emerged about how Google currently handles these 301 Permanent Redirects. Whether this was done in previous versions of the algorithm or whether it will continue to be the way they are handled is entirely unknown.
The common wisdom is that all three major search engines handle 301 redirects the same, that is to say they ignore the original URL and instead index the destination URL. This may not be exactly the way things work.
The reason for suggesting this is that a visitor to the blog on March 2nd arrived by doing a Google search for ‘Frank and Gordon‘. Frank and Gordon are the names of the Canadian beavers used in the Bell Canada advertising. This is what that visitor would have seen as part of that Google Search Engine Report Page (SERP).
You may notice that the old address for the blog post is shown as entry #3 and the new address for the blog post is at entry #4. Clicking on either brings you to the same new blog post since the old address is redirected to the new address. However clearly both URLs are still maintained in the Google index.
The Old blog post cached version shows a cached date of February 18th. The New blog post cached version shows a cached date February 28th. The new version of the blog was put online on February 26th and the 301 Permanent Redirect from old to new was put in place at that time.
As of the time of posting on March 3, both versions are still featured in the SERP but now the New version is at #3 and the Old version at #4. Perhaps this indicates that the old version is never dropped from the index but merely gradually loses all its PageRank as this is transferred to the New Version and sinks without trace.
Useful References on 301 Permanent Redirects
Permanent Redirect with HTTP 301 – a very complete and technical account of a variety of methods for doing the redirect.
Permanent 301 Redirect, Can someone post an example or a link? – a High Ranking Forums discussion
301, Parking and Other Redirects for SEOs ( FAQ ) – Ian McAnerin
Canonicalization: The Gospel of HTTP 301 – Hamlet Batista writes on a related problem
301 Permanent Redirect to Error404.htm Page is a Problem to Google – an interesting discussion on a related problem