touch ping.sh
chmod +x ping.sh

#!/bin/bash

if ! ping -q -c 1 10.10.10.2 -I eth1
    then
    echo 'no ping'
    ifconfig eth0 down
    else
    echo 'ping ok'
    if ! ifconfig | grep 'eth0'
        then
        echo 'up eth0'
        ifconfig eth0 up
    fi
fi

crontab -e
5 * * * * root /path/to/file/ping.sh