Using google maps api behind firewall – Stack Overflow

Why it’s important: The Maps API services use a variety of domains, some which do not belong to the *google.com domain. If you are behind a restrictive firewall, it is important you understand which Maps API services use which domains. Failure to allow access to the correct domains will cause API requests to fail, which can break your applications.

https://stackoverflow.com/questions/5800955/using-google-maps-api-behind-firewall