Duplicate content on Google rankings
After setting up your website to work through a CDN Resource with CDN77, your content may be accessible both from your domain as well as the CDN URL / CNAME, which can result in unnecessary duplicity and damage your SEO ranking.
You can prevent Google from crawling duplicate links by setting up Canonical URLs.
The best way to configure this and to achieve the best SEO is to include the HTTP header "rel=canonical" with your CDN files.
An example of such an HTTP Header is:
Link: http://www.example.com/downloads/white-paper.pdf; rel="canonical"
For more in-depth information regarding this, have a look at the following tutorial from Google.