Sharing a unique problem that We are facing with our Lync solution, we are close to finding the solution but atleast we have found the root cause of it.
Issue is every 15 days we see netlogon error 5719 stating:
This computer was not able to set up a secure session with a domain controller in domain due to the following: The RPC server is unavailable.
and MSMQ error 19 stating:
A connection with Active Directory Domain Services cannot be established.
These two are the main errors apart from others. When these occurs new sessions to lync have problems, Online meeting start to have issues and various other issues till we restart the server.
Another things to note when this happens you can ping domain but cant access the domain shares.
On working with Microsoft & submitting lot of logs no conclusion was occurring until yesterday when it was found that issue is because all dynamic ports(ephemeral ports)were getting exhausted.