How does URL Rewriting affect SEO?

Question

The following paragraph is from SEO Google Guide

Google is good at crawling all types of URL structures, even if they're quite complex, but spending the time to make your URLs as simple as possible for both users and search engines can help. Some webmasters try to achieve this by rewriting their dynamic URLs to static ones; while Google is fine with this, we'd like to note that this is an advanced procedure and if done incorrectly, could cause crawling issues with your site.

What makes URL re-writing implementation incorrect for GoogleBot? I am using Asp.net 3.5 framework.

Answer 1

Since rewriting URLs happens on the server side neither users nor search engines are aware of it. Where it gets to be an issue is if it is done improperly and the same content can be accessed using more then one URL. This causes your website to have duplicate content which is is considered low quality by Google. This is where their Panda algorithm comes into play. If you Google it you can see it has disastrous effects on websites it affects.

So, make sure you implement your URL rewriting correctly so pages can only be accessed via one URL. Or, use canonical URLs to tell Google all of those pages are to be considered one and the same.

Answer 2

And to complete John Conde post, if you have the choice, prefer hard 301 redirection to canonical URL. Canonical are a hint for crawler and give more depreciation in link juice transmittion than 301.