Tailscale MTU 🌐

Persistent MTU management for Tailscale across reboots and interface resets.

This project helps you save the MTU you want and keep it applied after interface changes, reconnects, and reboots.

What it does

• Keeps your Tailscale MTU persistent
• Supports IPv4 and IPv6 values separately (Windows Only)
• Works on Linux and Windows
• On Windows, runs with a simple UI after install

Why this exists

Tailscale MTU can go back to another value after reconnects or reboot. This tool saves your desired value and keeps checking in the background. If the interface changes, it applies the saved MTU again.

Install

Windows 🪟

Run this in PowerShell or in CMD / Windows Terminal:

powershell -NoProfile -ExecutionPolicy Bypass -Command "Set-ExecutionPolicy -Scope Process Bypass -Force; $ProgressPreference='SilentlyContinue'; $u='https://raw.githubusercontent.com/luizbizzio/tailscale-mtu/main/windows/windows-setup.ps1'; $c=(Invoke-WebRequest -UseBasicParsing $u).Content; & ([ScriptBlock]::Create($c)) -Install"

After install:

1. Open Tailscale MTU from the Start Menu
2. Set your values
3. Click Save and Apply

Default Windows files:

%ProgramData%\TailscaleMTU\config.json
%ProgramData%\TailscaleMTU\state.json

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Linux 🐧

curl -fsSL https://raw.githubusercontent.com/luizbizzio/tailscale-mtu/main/linux/linux-setup.sh | sudo bash

After install, set the MTU like this:

sudo tailscale-mtu --mtu 1280

Optional interface:

sudo tailscale-mtu --mtu 1280 --iface tailscale0

Check status:

tailscale-mtu --status

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How it works

Linux

The installer places the binary at:

/usr/local/bin/tailscale-mtu

When you run:

sudo tailscale-mtu --mtu 1280

It:

• Saves the MTU and interface in /etc/tailscale-mtu.conf
• Applies the MTU immediately using ip link set
• Creates a udev rule (if available) to reapply MTU when the interface returns

Linux limits

• Linux uses one MTU value per interface
• IPv4 and IPv6 are not separate
• Allowed range: 576 to 9000
• Values below 1280 trigger a warning

Why 1280 matters:

• 1280 bytes is the minimum MTU required by IPv6 (RFC 8200)
• Lower values can cause IPv6 fragmentation failures and dropped traffic

In practice:

Save MTU -> apply immediately -> udev reapplies on reconnect

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Windows

The installer places all files under:

%ProgramData%\TailscaleMTU

What happens internally:

• Uses netsh to configure IPv4 and IPv6 MTU independently
• Runs as a Windows Service via NSSM
• Periodically verifies the interface state
• Reapplies MTU automatically after reboots or reconnects
• Does not modify the registry directly

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License 📄

This project is licensed under the Mozilla Public License 2.0.