Error - Googlebot did not crawl your URL | Couldn’t communicate with the DNS server

1] DNS warnings or errors don’t affect Googlebot's ability.

2] You can use Fetch as Google to check if Googlebot can currently crawl your site.

3] If Fetch as Google returns the content of your homepage without problems, you can assume that Googlebot is generally able to access your site properly.

4] While most DNS warnings or errors don’t affect Googlebot's ability

5] Websites can be configured to respond to all subdomain requests. For example, the website at example.com can be configured to respond to requests for foo.example.com

6] User created sub-domain E.g http://www.example.com/username this may cause content to be duplicated unnecessarily across different hostnames, and it may also affect Googlebot’s crawling.

Ref - https://support.google.com/webmasters/bin/answer.py?hl=en&answer=2409681