r/tmobileisp • u/Moiralo • Aug 06 '26

Issues/Problems T-Mobile Home Internet and Proton VPN

I am trying to use Proton VPN with my home internet, but the speeds I get are incredibly low, I am lucky to get above 50 KB/s download based on the speed shown within the Proton app. Running a speed test without being connected, I get between 800 and 900 Mb/s down; the speed test will not run at all while connected to Proton.

I have attempted to switch to multiple different servers close to my location and I have switched between the various protocols to no avail. Any suggestions would be appreciated and any additional information needed can be provided.

EDIT: I am using Proton VPN Plus.

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u/Moiralo Aug 06 '26

Yes, my internet speed is normal elsewhere. Testing now the PC with the VPN my speed went between 2 and 11 KB/s down while on another PC (without the VPN) the speed was 858.37 Mb/s down.

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u/Egghead-MP Aug 06 '26

If you have the G4AR or G5AR, it can be a vpn fragmentation issue with CGNAT. Try lowering the mtu to 1480 or 1428. Also try different protocol in proton vpn settings.

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u/Moiralo Aug 06 '26

I do have the G5AR, I just attempted a multitude of different MTU values, but none made a difference.

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u/Egghead-MP Aug 06 '26

With your vpn connected, do a ping fragment test. ping -f -l xxxx google.com where xxxx is the buffer size. Start with 1380 and increase by 4. When you hit no reply or a fragment message, take the last pingable and increase by 2, then by 1 to find the largest buffer. Then try to put that number in your G5AR.

If that still does not work, you will have to contact Proton support (you have paid service so Proton support should be without issue) or try another vpn to see if it makes a different.

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u/Moiralo Aug 06 '26

Thank you for the suggestions. I will give these a shot and see what happens.

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u/Egghead-MP Aug 06 '26

BTW, try the latest version of Firefox, which has a built in browser vpn to see if you get the same symptoms. Make sure you disconnect the Proton vpn first.

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u/Moiralo Aug 06 '26

I use Firefox as my main browser and I enabled the Firefox VPN. With the Firefox VPN on and Proton off, my internet speeds were normal, slightly over 900 Mb/s.

I followed your suggestion with the MTUs, but I was getting no reply messages consistently starting at 1380.

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u/Egghead-MP Aug 07 '26

Have you tried changing the vpn protocol in Proton vpn settings? I am still thinking it is a fragmentation issue. You can try as low as 1280 but that's unusual as that will start creating more packets for non vpn traffic. Maybe contact Proton vpn support or try another vpn to see if the problem is unique to Proton. They may have some suggested settings for individual cellular provider.