fix-mtu script

fix-mtu.sh

#!/bin/bash

# script to find and set the right mtu
# 
# Usage
# fix-mtu [INTERFACE]
#
# When not INTERFACE given, wlan0 is used as default.

# check if an interface was given
if [ -z $1 ]; then
    INTERFACE=wlan0
    echo "not interface given, using default"
else
    INTERFACE=$1
fi

set -u 

echo "checking for good mtu setting for $INTERFACE"

# Start with 1500 size
NUM=1500

# ping with non defrag packets and decrease
# until fitting size is found
while ! ping -I $INTERFACE -c 1 -s $NUM www.google.com -M do; do
    (( NUM -= 1 ))
done

let RIGHT=NUM+28

echo "setting calculated working MTU as $RIGHT"

sudo ip link set dev $INTERFACE mtu $RIGHT