Hi,

We have one customer experienced calls dropped off randomly issue recently, this is one Standard Edition FE server and Mediation server is by default collocated on the FE server.

We checked Lync logs and found that when the issue happened it will generate the following error in Event logs:

Source : LS Mediation Server

Event ID: 25072

Task Category: 1030

Details:

The Front End cannot be reached by the Mediation Server service. Additional failures will not be logged.

The Front End, xxx.local, cannot be reached by the Mediation Server service
Cause: The Mediation Server service cannot connect with the Front End Service due to network connectivity issues.
Resolution:
Please ensure network connectivity and availability of the Front End for the Mediation Server service to be able to function correctly.

And after around 20-30 seconds, I can see the connection is resume by itself and generated another Event log:

Source: LS Mediation Server

Event ID: 25085

Task Category: 1030

Details:

Mediation Server is able to reach the Front End xxx.local

I tried to search online but couldn't find the similar issues, it's really randomly happened and hard for us to duplicate the same issue. Lync server has the latest patches applied.

Anyone has any ideas? Thanks

What's the resource utilisation on that server?. Do you have any firewall or anti virus applications installed in that server?. Usually an antivirus or a firewall can cause such issues. 

Hi Thamara, thank you for your reply. The CPU & RAM usage is not high, so I assume the resource should not be the problem. We have Symantec Anitivirus software installed on the FE server and I just disabled it temporarily to see if any different. I also disabled Windows Firewall for testing, will update later if I found any different. 

Don't have Windows Firewall enabled in Lync Server. And set exclusions for anti virus programme.

https://technet.microsoft.com/en-au/library/dn440138.aspx?f=255&MSPPError=-2147217396

Thank you for your advise Thamara, however, I found that the issue still pop up even after I disabled Windows Firewall and Antivirus software...

Hello Steven, 

Did you find any solution for the issue as i also face the same with my SBA Servers. 

Looks like this applied to only collocated One server Model ( Like Std FE and SBAs).

I did not find any issues in the Topology just that the Event id points that the FE connection is lost and also after few minutes  says connection restored. 

Hi Sunikumar,

No, the issue is still happening, but looks like it's the know bug for Lync server, and didn't affect the Lync calls. Because we found that the lync drops were due to the SIP provider issue and not related to this.