FB did not totally disconnect from the internet as far as what I observed. They broke their backbone (from the blog post, as well as seeing that their edge was

FB did not totally disconnect from the internet as far as what I observed. They broke their backbone (from the blog post, as well as seeing that their edge was returning 503s during the incident), and FB withdrew specific BGP announcements which covered their DNS servers are what I saw. I think this is consistent with what Cloudflare actually said, although not what has been often repeated since then.