This document https://msdn.microsoft.com/library/dn683916(v=crm.6).aspx describes the connectivity requirements for CRM in various configurations.
Three ports which must be enabled on the CRM server are:
- 80 for incoming web access using http
- 443 for incoming web access using https
- 808 for the CRM SDK Listener
A symptom of no access on port 808 is that FetchXML based reports do not work.