“No available Servers to connect to” when trying to view user PIN status

Recently, someone asked me if I could check his PIN. Usually, I instruct the user to change his PIN in the Dialin Web Page, but in this case, since Lync Control Panel was already open, I check the PIN Status:

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Request failed with error No available Servers to connect to:

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The only error was managing the user PIN, so I had to wait for a off-peak to do some troubleshooting.

The first step was to get the user PIN status in Lync PowerShell, running the debug option:

Get-CsClientPinInfo -Identity david.paulino -debug

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Basically, Lync Server is saying that no server was found in the pool to connect. This was strange since all servers in the pool are up and running. No Warnings/Errors in Event Viewer.

For those who do troubleshooting, it’s really hard to find the cause when you don’t have any explicit error.

I checked Topology, Certificates, DNS records, and everything looked OK.

Before doing some extreme measures, like rebuilding Web Components, I decided to have a look in IIS Site Bindings.

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On internal site:

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External Site with the same setting:

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Both Internal and External Site were listening in 10.0.0.67, which is the Front End IP Address. This seemed strange, so I checked in another Lync Server 2013 environment and it was listening on all interfaces. The next step was obvious: change the listening setting, so IIS would listen on all interfaces.

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After changing in all web sites, I got this result on internal site:

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And on the external:

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After applying both settings, it was possible once again to check the user PIN status in Lync Control Panel:

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I also tested in the Lync PowerShell, just so to make sure:

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In conclusion, I believe there is a connection to the loopback interface while managing user PIN. Moreover, if IIS isn’t listening on loopback interface, the error No available Servers to connect to is displayed.