#!/bin/bash
GW1="111.111.111.111"
GW2="222.222.222.222"
TESTIP="66.94.234.13" # yahoo.com - Any reliable Internet ip that responds to ping.
CURGW=`/sbin/route -n |awk '/^0.0.0.0/ {print $2 }'`

if ping -w2 -c3 $TESTIP >/dev/null 2>&1; then
  echo "Active ISP is Ok."
else
  if [ "$CURGW" = "$GW1" ]; then
    NEWGW="$GW2"
  else
    NEWGW="$GW1"
  fi
  /sbin/route del default
  /sbin/route add default gw $NEWGW
fi