linux tailscale0 set MTU

set-mtu.sh

#!/bin/bash

set -e

# ---- Configuration / Arguments ----
DEFAULT_MTU=1420 # https://github.com/tailscale/tailscale/issues/12393#issuecomment-2893170282
MTU="${1:-$DEFAULT_MTU}"

# ---- Validation ----
if ! [[ "$MTU" =~ ^[0-9]+$ ]]; then
  echo "Invalid MTU value: '$MTU'. MTU must be a numeric value."
  exit 1
fi

if [ "$(id -u)" -ne 0 ]; then
  echo "This script must be run as root. Please use sudo."
  exit 1
fi

UDEV_RULE_PATH="/etc/udev/rules.d/99-tailscale-mtu.rules"

echo "Using MTU value: $MTU"
echo "Creating udev rule file at $UDEV_RULE_PATH..."

cat <<EOF > "$UDEV_RULE_PATH"
ACTION=="add", SUBSYSTEM=="net", KERNEL=="tailscale0", RUN+="/sbin/ip link set dev tailscale0 mtu $MTU"
EOF

echo "Reloading udev rules..."
udevadm control --reload-rules
udevadm trigger --subsystem-match=net --action=add

# Give udev a moment to apply changes
sleep 2

echo "Verifying MTU for tailscale0 interface..."
ip link show tailscale0

CURRENT_MTU=$(ip link show tailscale0 | grep -oP 'mtu \K\d+')

if [ "$CURRENT_MTU" -eq "$MTU" ]; then
  echo "MTU is correctly set to $MTU for the tailscale0 interface."
else
  echo "MTU is not set correctly."
  echo "Expected: $MTU"
  echo "Actual:   $CURRENT_MTU"
  exit 1
fi

echo "Setup complete."

Download and execute script (one-liner)

curl -fsSL https://gist.githubusercontent.com/alexbaeza/77c27772a194f52bf2421e54a1dd1fc9/raw/b97b1e136bd59ff59daddac0bcf6f24667c6c285/set-mtu.sh | sudo bash

You aren't by any chance wearing a cape...my hero either way. Thank you.