#!/bin/sh

PKT_SIZE=1472
INTERFACE="$1"
HOSTNAME="$2"

count=$(ping -q -w 1 -M do -c 1 -s $PKT_SIZE -I $INTERFACE $HOSTNAME | grep -cE 'Message too long|100% packet loss')

while [ $count -eq 1 ]; do
	PKT_SIZE=$((PKT_SIZE - 1))
	if [ "$PKT_SIZE" -lt "1200" ]; then 
		exit 0
	fi
	count=$(ping -q -w 1 -M do -c 1 -s $PKT_SIZE -I $INTERFACE $HOSTNAME | grep -cE 'Message too long|100% packet loss')
done

printf "$((PKT_SIZE + 28))"