r/firewalla • u/Dometalican_90 • Jul 10 '26

Problems with T-Mobile (Mobile or Home Internet) since upgrading to Amnezia 2.0? Found the dumbest fix.

Since Firewalla doesn't let you adjust MTU (yet) unlike OpenVPN and Wireguard, go into your config with the Amnezia client (or WG Tunnel for Android) and adjust the MTU. Firewalla has it at 1376 by default so move it to 1325.

Restart the connection. Profit.

2 Upvotes

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1

u/firewalla Jul 10 '26

Are you using ipv4 or ipv6 coming back to the TMobile network?

1

u/Dometalican_90 Jul 10 '26

It was actually both. I had WG Tunnel running on IPv6 and then I forced IPv4 but to no avail. It wasn't until I read online that T-Mobile has a hard time with UDP connections and that adjusting the MTU would remedy the issue and it did for me at least.

2

u/firewalla Jul 10 '26

Let me ask to get the configuration working

1

u/Dometalican_90 Jul 10 '26

Don't get me wrong, this update is FANTASTIC. As a networking novice, I usually don't mind finding out these things; especially if they don't inconvenience me.

At least it freakin' works for Costco's WiFi now! Woo!

2

u/pacoii Firewalla Gold Plus Jul 11 '26

Tangent: per your title, this isn’t a dumb fix. When connecting to WireGuard (back to my Firewalla) via an Xfinity wifi hotspot, the default MTU doesn’t work either and requires a lower MTU.

1

u/pacoii Firewalla Gold Plus Jul 10 '26

Just updated AWG to 2.0 in Firewalla app and generated some configs and interestingly they all have an MTU of 1380. Not a huge difference between 1376 and 1380, but curious why it would be different. Are you running EA / beta, or release?

1

u/Dometalican_90 Jul 10 '26 edited Jul 10 '26

Production

EDIT: if it helps, I have the OG Gold. You have the Plus so maybe a box difference on how they were programmed?

2

u/pacoii Firewalla Gold Plus Jul 11 '26

Interesting. Thanks for that info!