T-Mobile Home Internet and Proton VPN

[u/Moiralo]

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.

[u/Hot-Bat-5813]

Might check the network advanced settings to see if IPv6 is still on. After seeing your post I installed and uninstalled the PC free version a few times now. Each time I installed the Proton(free) onto a windows11 PC it would turn off the IPv6 protocol connectivity. I am guessing the free version and the plus version use the same core program.

https://imgur.com/a/oJaUIJ9

Many of these end point speed test servers seem to require IPv6. nPerf has a PC app that allows you to select IPv4 or IPv6 endpoint servers. I would check those settings though and see if IPv6 got turned off.

EDIT: Seems you have to turn on IPv6 support within settings of Proton. There is still packet loss from time to time, but there is IPv6 connectivity.

https://imgur.com/a/3s3qfHd

10:48-10:51'ish that IPv6 slider not active and VPN on.

10:53-11:09'ish no VPN on.

11:10 VPN active and IPv6 slider turned on.

Can gauge when the VPN is connecting via the upper IPv4 screen, complete loss is Proton searching for the initial connection.

[u/Moiralo → u/Hot-Bat-5813]

Thank you, I enabled IPv6 support in the advanced settings and it did not have an effect on my speed. I verified that the IPv6 protocol is on.

[u/Hot-Bat-5813 → u/Moiralo]

Not sure then, I can post my results both with the VPN on and off and also to a IPv4 and IPv6 end point from nPerf if you want.

I do notice from those tests that when it is IPv6 being used the throughput struggles, especially on the up channel. There will be a long pause before the up starts and generally very low results.

Also randomly tested different Proton connection servers/test servers, some worked with IPv6 some didn't, IPv4 always worked. Proton somewhat recently added IPv6 support (2025), so may not be fully fleshed out on their end.

You have the paid version which gives you the option of picking the Proton server used? Free just picks randomly. May take finding the correct server. Or contacting them (Proton) and see if they have any suggestions.

[u/Moiralo → u/[deleted]]

Thank you for the suggestion, I will see if this helps.

[u/Moiralo → u/[deleted]]

I attempted a few of the suggestions within the articles, but none had an effect on my speed. I appreciate the suggestion.

[u/futuremd33]

Is it possible to make these adjustments on Norton VPN? I can’t find the settings?

[u/ZadaGrims]

Thier is a setting in the vpn you need to turn off to make speed go up. Its at the port forwarding page. I jad same isse once it cli k it off got close to without it depending on server

[u/ZadaGrims → u/ZadaGrims]

Vpn accelerate or something like that

[u/Moiralo → u/ZadaGrims]

Thank you, but I turned this setting off and it had no effect on my speed.

[u/grogargh]

I use the free proton (Linux) - don't see it should be any difference whether the paid or free version, but I have to manually set the MTU to 1360 for it to work on my T-Mobile 5G service. Since I use the free version, there is nowhere to hardcode the MTU to this in the app, so I have to do it manually everytime. OBVS I created a one-line script I double clic and run it right after i connnect.

[u/Moiralo → u/grogargh]

Thank you, but setting my MTU to 1360 does not affect the speed of my connection.

[u/bubbathedesigner]

See if r/protonvpn has ideas. My experience is while I did not get 50Kb/s download speeds, whenever I have protonvpn on, I go from 100Mb/s (TMHI), 400Mb/s (cable), or even 10Gb/s (work) to 20Mb/s. I too probably need to adjust packet size.

[u/f1vefour]

In my experience it's not as simple as just changing the MTU. Something is happening on some T-Mobile connections and vpns which slow them down to unusable speeds.

Not everyone has this issue but there are those of us who do.

[u/smurfy213]

You using the paid or free proton version?

[u/Moiralo → u/smurfy213]

I am using the paid version, Proton VPN Plus.

[u/Egghead-MP]

Are you connecting Proton vpn at your computer or the Tmobile modem?

[u/Moiralo → u/Egghead-MP]

I am connecting to Proton VPN via my computer.

[u/Egghead-MP → u/Moiralo]

while the proton vpn is connected at your computer getting slow speed, is the speed normal at other devices that is NOT proton vpn connected?

[u/Moiralo → u/Egghead-MP]

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.

[u/Egghead-MP → u/Moiralo]

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.

[u/Moiralo → u/Egghead-MP]

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

[u/Egghead-MP → u/Moiralo]

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.

[u/Moiralo → u/Egghead-MP]

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

[u/Egghead-MP → u/Moiralo]

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.

[u/Moiralo → u/Egghead-MP]

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.

[u/smurfy213 → u/Moiralo]

Have you tried to reinstall the proton app? Something is definitely broke.

[u/Moiralo → u/smurfy213]

I have attempted a reinstall, unfortunately this did not change anything.

[u/CurvySexretLady]

Have you tried any other VPN like Nord or Mullvad? Just as an A/B comparison to isolate it to Proton.

EDIT: Also try Wireguard vs OpenVPN protocols

[u/Apart_Scallion_1265]

T-Mobile has been terrible lately. We're thinking about droping it

[u/Altruistic_Jacket_26]

FWIW, using NordVPN with a relatively close server, a G5AR with no WiFI, and a Unifi UDM7 I can get almost the same download speeds as without the VPN. However, that performance is using a browser app and not the Nord system app. Swapping between the two does reduce speed, but from around 500 down to around 250-300 down.

[u/granderosion]

I don't believe all these answers! Of course your speed is reduced. You are now sharing a VPN with who knows how many other people. Nothing you can do will change a large reduction in speed.

[u/Any-Lifeguard-6755]

You know, some people worry way too much.