Run this in a one minute cron job to check network connectivity every 20 seconds

check-and-restart-net.sh

#!/bin/bash

LOCKFILE=/tmp/check-and-restart.lock

if ! mkdir "${LOCKFILE}" 2>/dev/null; then
    echo "check-and-restart is already running." >&2
    exit 1
fi

trap "rm -rf ${LOCKFILE}; exit" INT TERM EXIT

CHECK_IP=8.8.8.8

for i in `seq 1 5`;
do
    ping -c 10 $CHECK_IP > /dev/null 2>&1
    if [ $? -ne 0 ]; then
        echo >> /root/restart.log
        echo >> /root/restart.log
        echo ------------------ >> /root/restart.log
        echo Bouncing internet at `date` >> /root/restart.log
        echo >> /root/restart.log
        /sbin/ifdown eth0 >> /root/restart.log 2>&1
        echo >> /root/restart.log
        /sbin/ifup eth0 >> /root/restart.log 2>&1
        echo >> /root/restart.log
        echo ------------------ >> /root/restart.log
        if [ $? -ne 0 ]; then
            echo ifup didnt work for some reason >> /root/restart.log
            exit 1
        fi
        exit 0
    fi
    sleep 10
done