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I have temporarily moved to a new university for a research project, and I'm now using their wifi Internet connection. While everything seems to work fine with the Windows 10 laptop, the Skype app on my Android phone keeps "freezing". What I mean is that although I seem to be connected and I can see my contacts, I cannot make nor receive any calls. Even if I turn off the wifi and use the mobile connection on the phone, the situation does not change.

After many attempts, I have found out that if I logoff from the app and I login again using the mobile connection, the app starts working again. At this point I can even restore the wifi connection and everything works for a while. But eventually it freezes again...

The weird thing is that this trick doesn't always work. Sometimes after I logoff from the Skype app I cannot login back even if I'm connected with the mobile data. I keep getting the error message "unable to sign in. Please check your internet connection". Also, if I try to login to my Skype account using Chrome for Android I cannot reach the page and get the message "DNS_PROBE_FINISHED_NXDOMAIN". But everything else seems to work fine and I can browse other websites or use different apps.

I understand that this might be due to some strange settings of my host university. While this is annoying, I can live with that. But what I really would like to understand, though, is why my phone behaves so strangely even when I'm switch off from the university wifi and I'm using my private mobile data connection...

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  • Could you mention the device model and the Android version? Also, while it's probably not really related to the Skype issue, there are some troubleshooting comments for DNS_PROBE_FINISHED_NXDOMAIN on How do I solve DNS_PROBE_FINISHED_NXDOMAIN on android and to the extent of Why can't I browse to my desktop using its .local hostname?
    – Andrew T.
    Jan 25 at 9:31
  • @Andrew T. The phone is a Sony Xperia XZ2 compact with Android 10, but the same problem appears on my wife's phone, which is a Honor 9 Lite with Android 9. Regarding the DNS_PROBE_FINISHED_NXDOMAIN, I mentioned it because it seems to appear only when the Skype app is frozen. As soon as I manage to restart Skype (by logging off and in again with a different Internet connection), this problem seems to go away as well
    – iwakun
    Jan 26 at 1:22
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It sounds like the skype ports are being blocked

Ask the IT staff if these ports are being blocked.

For Skype to work correctly, the following ports need to be open in your firewall:

443/TCP

3478-3481/UDP

50000-60000/UDP

For the best possible call quality experience, these ports are needed too:

1000-10000/TCP

50000-65000/TCP

16000-26000/TCP

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  • I suspected something similar. But if this is the case, shouldn't the firewall also block my desktop Skype on Windows 10? Which on the contrary works OK...
    – iwakun
    Jan 25 at 8:37
  • @iwakun As far as I know Skype uses firewall hole punching technique to establish certain connections. May be network access on Windows does allow a deeper access that simplifies hole punching and on Android the network access is only possible on a higher level? Alternatively the Skype desktop app may use a different server/API that has been white-listed by the network admins.
    – Robert
    Jan 25 at 8:45
  • Would be interesting to see what the IP of your desktop is versus the IP of the phone. Jan 25 at 9:05
  • @MarkScheck The IP changes depending on which lab or area within the university I am. But I double checked, and the issue with Skype still appears on the Android phone and does not on the PC, even when both devices are connected on the same wifi and share the same public IP.
    – iwakun
    Jan 26 at 4:11
  • Are they on the same subnet? can you post both IP's? Jan 26 at 5:44
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I still don't fully understand how, but the issue appears to be solved now.

After I changed the DNS settings from automatic to private towards dns.quad9.net, not only the DNS_PROBE_FINISHED_NXDOMAIN error on Chrome disappeared when trying to connect to my Skype account, but also the Skype app stopped freezing.

I suspect that with the previous settings the DNS request for the Skype IP (via the NAT done by the university) was somehow unintentionally lost, and the app could not reach the server nor Chrome the account webpage.

Also the apparent random behaviour was probably due to some form of caching of the DNS, by which when I switched to the mobile data connection I had to wait for some time before the app could unfreeze, and similarly when restoring the university wifi the app didn't freeze immediately...

Anyways, the issue is solved, but if you have a more sound explanation, please consider writing a better answer. Thanks.

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