Layered navigation, a feature available in Magento without any extensions is commonly used by many merchants around the world. It is also one of the most painful Magento features for the SEOs. It creates lots (depending on the amount of filters and products – often tens of thousands) of terrible URLs with duplicate / near duplicate content and identical page titles and descriptions.
I made this video to show you what are your options and what is in my experience the best possible solution for handling Magento layered navigation indexation issues. I hope it helps:
After you watched the video, you know what to do. How do you know if you did it correctly? Log-in to your Google Webmaster Tools, click on Health -> Fetch as Googlebot and see if layered navigation shows up.
I hope I helped. Anyone have a different experience and advice on this issue?
If you need any help, we can do a Magento Website Assessment for your site.