а вот на 3 канала переделано! но теперь без ошибок ;))

#!/bin/sh
PATH="/sbin:/usr/bin"

ISP1="*.*.*.*"

ISP2="*.*.*.*"

ISP3="*.*.*.*"

OVER_ISP1="*.*.*.*"
OVER_ISP2="*.*.*.*"
OVER_ISP3="*.*.*.*"

netstat -nr | grep ${OVER_ISP1} >/dev/null 2>&1
if [ $? != 0 ]; then
        echo "Add static route to ${OVER_ISP1} via ${ISP1}"
        route add ${OVER_ISP1} ${ISP1} -static
fi
netstat -nr | grep ${OVER_ISP2} >/dev/null 2>&1
if [ $? != 0 ]; then
         echo "Add static route to ${OVER_ISP2} via  ${ISP2}"
         route add ${OVER_ISP2} ${ISP2} -static
fi

netstat -nr | grep ${OVER_ISP3} >/dev/null 2>&1
if [ $? != 0 ]; then
         echo "Add static route to ${OVER_ISP3} via  ${ISP3}"
         route add ${OVER_ISP3} ${ISP3} -static

fi

current_now=`netstat -nr | grep default | awk '{print $2}'`

echo -n "ping ISP1:"
ping -c 2 ${OVER_ISP1} >/dev/null 2>&1
if [ $? -eq 0 ]; then
                echo " [OK]"
                ISP1_stat=0
                else
                echo " [FAILED]"
                ISP1_stat=1
fi

echo -n "ISP2:"
ping -c 1 ${OVER_ISP2} >/dev/null 2>&1
if [ $? -eq 0 ]; then
                echo " [OK]"
               ISP2_stat=0
                else
                echo " [FAILED]"
                ISP2_stat=1
fi

echo -n "ping ISP3:"
ping -c 1 ${OVER_ISP3} >/dev/null 2>&1
if [ $? -eq 0 ]; then
                echo " [OK]"
                ISP3_stat=0
                else
                echo " [FAILED]"
                ISP3_stat=1
fi

if [ ${ISP1_stat} -eq 1 -a ${ISP2_stat} -eq 0 -a  ${current_now} = ${ISP1} ]; then
                echo "ISP1 suck"
                route delete default
                route add default ${ISP2}
fi

if [ ${ISP1_stat} -eq 1 -a ${ISP2_stat} -eq 1 -a ${ISP3_stat} -eq 0 -a  ${current_now} != ${ISP3} ]; then
                echo "ISP1 ISP2 suck"
                route delete default
                route add default ${ISP3}
fi

if [ ${ISP1_stat} -eq 0 -a ${current_now} != ${ISP1} ]; then
                echo "Back to ISP1"
                route delete default
                route add default ${ISP1}
fi