Tailscale MTU Configuration ⚙️

This repository provides step-by-step instructions and scripts to make the MTU configuration for Tailscale persistent on both Linux and Windows. Each section is tailored to its operating system and includes explanations for every step.

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Important Considerations ⚠️

• Devices with Fixed MTU:

  • If you have devices in your Tailscale network that do not allow MTU adjustments (e.g., smartphones, IoT devices), increasing the MTU on other devices may cause packet fragmentation. This can lead to performance issues, including slower speeds or connectivity problems.
  • It is not recommended to use a larger MTU unless all devices in your Tailscale network support it.

• Determine the Correct MTU:

  • The ideal MTU value varies depending on your network configuration. It is crucial to determine the correct MTU for your network through careful testing.
  • For example, in some configurations, a value of 1400 works well for direct connections between devices in the Tailscale network. However, for DERP (relayed) connections, using a higher MTU may lead to packet loss and significantly degrade network performance.

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Why Adjust the MTU? 🤔

Tailscale defaults to an MTU of 1280 for compatibility with most networks, but in some situations, increasing the MTU to 1500 can improve network performance. This is particularly useful in environments where fragmentation is not a concern.

Table of Contents 📋

• Linux Configuration 🐧
• Windows Configuration 🪟
• License 📜

Linux Configuration 🐧

Option 1: Automatic Setup (Recommended) ✅

1. Run the script directly from the URL:

   • Open a terminal and run the following command as root:

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

2. What This Does:

   • The script performs the following actions:
     • Creates a udev rule to ensure the Tailscale interface (tailscale0) always has an MTU of 1500.
     • Reloads the udev rules and applies them.
     • Verifies that the MTU is correctly set.
   • This setup ensures the configuration is persistent, even after system reboots or network resets.

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Option 2: Manual Setup

1. Create a udev rule:

   • Open a terminal and run the following command to create a new rule file:

     sudo nano /etc/udev/rules.d/99-tailscale-mtu.rules

2. Add the rule to the file:

   • Paste the following content into the file:

     ACTION=="add", SUBSYSTEM=="net", KERNEL=="tailscale0", RUN+="/sbin/ip link set dev tailscale0 mtu 1500"

3. Reload the rules and apply them:

   • Run the following commands to activate the new rule:

     sudo udevadm control --reload-rules
     sudo udevadm trigger --subsystem-match=net --action=add

4. Check the MTU size

   • Verify if the MTU for the tailscale0 interface has been set to 1500:

     ip link show tailscale0

Explanation 📝

Here’s what the bash script does step by step:

• ACTION=="add": The rule triggers when a network device is added.
• SUBSYSTEM=="net": Applies only to network devices.
• KERNEL=="tailscale0": Targets the Tailscale interface.
• RUN+="/sbin/ip link set dev tailscale0 mtu 1500": Ensures the MTU is set to 1500 whenever the Tailscale interface is initialized.

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Windows Configuration 🪟

Option 1: Automatic Setup (Recommended) ✅

1. Run the script directly from the URL:

   • Open a PowerShell terminal as Administrator.
   • Run the following command:

     Set-ExecutionPolicy -Scope Process -ExecutionPolicy Bypass -Force; Invoke-Expression ((New-Object System.Net.WebClient).DownloadString('https://raw.githubusercontent.com/luizbizzio/tailscale-mtu/refs/heads/main/windows-setup.ps1'))

2. What This Does:

   • This script ensures that the Tailscale interface will always have an MTU of 1500, even after a system reboot or network reset.
   • It achieves this by creating a scheduled task that runs in the background. The task periodically checks the Tailscale interface and adjusts the MTU to 1500 if necessary, ensuring the configuration persists.

3. Verify MTU Configuration:

   • After running the command, the MTU size of the Tailscale interface will be displayed. You can confirm that it's set to 1500.

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Option 2: Manual Setup

1. Download the PowerShell script:

   • Save the windows-setup.ps1 file to your computer.

2. Run the script as Administrator:

   • Open a PowerShell terminal as Administrator.
   • Navigate to the directory where the script is saved.
   • Execute the script:

     Set-ExecutionPolicy -Scope Process -ExecutionPolicy Bypass; ./windows-setup.ps1

3. Verify the MTU configuration:

   • The script automatically displays the current MTU value for the Tailscale interface after execution.
   • If you wish to check the MTU again later, you can run the following command:

     netsh interface ipv4 show interfaces

   • Locate the Tailscale interface in the output and confirm that the MTU column displays 1500.

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Explanation 📝

Here’s what the PowerShell script does step by step:

• The first part of the command, Set-ExecutionPolicy -Scope Process -ExecutionPolicy Bypass, temporarily allows unsigned scripts to run in the current session without changing the system's global execution policy.
• $taskName: Names the task as Tailscale-MTU.
• $scriptCommand: Continuously monitors the Tailscale interface and adjusts the MTU if needed.
• Scheduled Task Settings:
  • RunLevel Highest: Ensures administrative privileges.
  • WindowStyle Hidden: Runs the script silently in the background.

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Note 📜

You can modify the MTU value to suit your needs. Replace 1500 in the commands or scripts with the desired MTU value.

For Linux, modify the RUN+="/sbin/ip link set dev tailscale0 mtu 1500" line in the udev rule file to set your preferred MTU value.

For Windows, update the 1500 in the PowerShell script on $scriptCommand part to the MTU value you want.

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License 📄

This repository is licensed under the MIT License.