I was assisting a customer with the renewal of a Consolidated Edge external SSL certificate recently and upon applying the newly issued certificate to the server, audio calls with externally situated users or federated partners via the Consolidated Edge failed. Upon answering an audio call via the Lync Client, it immediately reported “Called Ended” and third party IP handsets would become stuck in a “Connecting” state once the call was answered by the remote party. While the latter error would have suggested perhaps an audio/video port issue at a firewall level, I was on the phone to the customer via a federated call when the certificate was assigned to the Consolidated Edge services, which in turn immediately caused the call to drop and as such I knew a firewall issue was not the root cause of this problem. On inspection of the Consolidated Edge servers event log, everything appeared to fine and all Consolidated Edge specific services were started, additionally all other functionality such as remote and federated instant messages were working as expected. However, upon a restart of the Consolidated Edge services the following event was logged:
The Access Edge Server failed to import a shared session key due to invalid signature.
In the past 1 minutes, the server rejected 1 shared session keys presented from the network due to an invalid signature. This suggests an incorrect certificate configuration. A large number of failures could indicate spoofed session key data sent by an attacker.
Cause: This is most likely to be a configuration problem in a server array.
Resolution: Ensure that all servers in an Access Edge Server Array have the same certificate configured for the external IP address on the Edge Interfaces tab. Inspect the serial number of each certificate. If the problem persists, use the Administrator Log to help identify the source of these messages.
Upon reading the error this immediately prompted me to inspect the certificate via the certificates MMC snap-in and upon reviewing the new SSL certificate everything appeared to be correct, the certificate chain was reporting as valid as was the private key. In this customers case a GoDaddy SSL certificate had been procured and while the certificate chain stated the implemented certificate was trusted, it transpired an intermediate GoDaddy certificate was missing. On adding the missing intermediate certificate into the Local Computer certificate store, which was also included in the downloaded certificates .zip file, the audio calling issue was resolved. In summary, always check intermediate SSL certificates for your chosen provider, specifically if you are not utilising one of the bigger SSL vendors such as VeriSign or Digicert. Hope this helps!