Lync 2010 Web App presentations drops

Recently I’ve encounter a problem at a customer in which Lync 2010 Web App client was dropping presentations or desktop sharing sessions on sporadic times while users were connected externally.

The environment consist of the following:

  • Lync 2010 Enterprise Environment load balanced by F5 BIP IP on the internal network
  • 2 TMG Servers load balanced by F5 BIG IP on the External network
  • External Web Services VIP is configured to use Source-IP persistence
  • Internal Web Services VIP for external communication (port 4443) is configured to use Cookie-based persistence

When users were connected externally to the meeting using the Lync Web App client, they were able to see the shared content (Presentation/Desktop), but after a period of time they stopped seeing the shared content and they were getting one of the following error messages saying:

screen sharing stopped due to server connectivity issues. Please share your program again.


some presenting features are unavailable due to server connectivity issues

After running fiddler on the external client machine and enabling the SSL decrypt option, we could tell that a client is accessing the External Web Services VIP as it should and the servers are returning HTTPS 200 OK messages from one of the FE in the pool based on the type of persistence configured. When the session drops , we could see that the client is getting several 404 HTTPS error messages that are coming from a different FE server.

As default, with no HTTPS stream, the Lync Web App client has no ability to maintain the SIP channel which will result in the disconnect from the meeting.
That seems to indicates that the HLB or the TMG is sending the request to an FE which does not know about the client session and therefore returns a 404 error.


In order to solve the problem, the following changes were made to the environment:

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