In the world of content management and online shopping systems, it’s common for the same content to be accessed through multiple URLs. To avoid being hit by a Google Panda algorithm update, be sure to use a rel=canonical link element to specify the preferred page to index.
Add a <link> element with the attribute rel=”canonical” to the <head> section of the pages:
<link rel=”canonical” href=”https://blog.example.com/canonical_url” />
The https://blog.example.com/canonical_url will be the preferred URL for search engines to use to access the content, so that the search results will be more likely to show users that URL structure.
Note: Use absolute paths rather than relative paths with the rel=”canonical” link element.
Specify no more than one rel=canonical link for a page. When more than one is specified, all rel=canonicals will be ignored.