Description: External (Off Net) Lync client tries to make an audio call to an internal
user (On Net) and visa versa. The call however does not connect and errors out with "the call could not be
established due to network issues".
Error Code: The specific Lync Client Log file error shows "ms-client-diagnostics: 23;
reason=”Call failed to establish due to a media connectivity failure when one
endpoint is internal and the other is remote”;CallerMediaDebug="audio:ICEWarn=0x12b
Resolution: Make sure internal (On Net) client devices are not being blocked by firewall on ports 443 and 3478. This can be verfied by telneting from a client device to Edge Server in your perimter on TCP 443. No answer means firewall blocking that port. Same applies to UDP port 3478, it needs to be opened on firewall. To test UDP port 3478you will need to run port query utility from the client to the Edge server (0x000000 means successful, 0x0000002 ect indicates failure).
