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Calling issues with Skype for Desktop (Windows)

Good day,

As the subject states, I've recently begun experiencing problems with Skype for Desktop (Windows) where calls are no longer successful. The symptoms vary, but essentially calls either ring endlessly or connect with no audio (and call drops after 10 seconds). I've been testing using the latest version available at this time (Skype version 8.54.0.91).

I have a few sites with UTM 9.605-1 configured in Standard Proxy mode and AD SSO. Staff in our organisation rely heavily on Skype for calls with external parties even though we have more robust options available (SfB, Zoom, etc), and therefore I will never be free from this infernal application.

I had Skype working OK for a few months using a combination of Web Protection exceptions and firewall rules (application control is also enabled for what it's worth), and I also have QoS rules enabled to ensure adequate bandwidth is available for the Skype users.

Since about a month ago, Skype calls have ceased to function and I can't figure out why. So far my attempts at massaging the various exceptions and rules has yielded bupkis.

So far the only way to get Skype to work properly is to create a firewall rule for an affected computer (DNS host) and allow UDP (3478:3481) to Internet IPv4. Then it works perfectly. But obviously not a solution.

Has anyone managed to get Skype working reliably without compromising the UTM configuration? Any tips or advice will be hugely appreciated.

Kind regards,

Byron



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  • Hello Byron,

    do you know this document from Microsoft? https://docs.microsoft.com/en-us/office365/enterprise/urls-and-ip-address-ranges

    I manage this for SfB and/or Teams on a UTM like this:

    Then you can use these objects in a firewall rule:

    Mit freundlichem Gruß, best regards from Germany,

    Philipp Rusch

    New Vision GmbH, Germany
    Sophos Silver-Partner

    If a post solves your question please use the 'Verify Answer' button.

  • Hi Philipp,

    Thanks for your reply. Yes indeed, I have set up similar definitions and rules on our UTM's and Skype for Business (SfB) works great as a result. Initially when I created these for SfB, it seemed to improve Skype for Desktop, however this no longer seems to be the case. I suspect the two applications, although similar in name, do not use the same IP ranges or protocols. It would be really great if MS published the same kind of IP list for the consumer version of Skype.

    I'm going to review the O365 list again to see whether any changes have been made to the IP ranges since I last referenced this. Would be great if Sophos UTM could subscribe to the O365 feed for this (Ideas for Sophos).

    Will post my findings here as I progress.

    Kind regards,

    Byron