#!/bin/bash
# Purpose: Change Gateway Script if ISP is down
# eth0: LAN - 172.17.20.100/16
# eth1: ISP1 - 182.152.162.xx
# eth2: ISP2 - 179.158.21.xx
#


# Change Gateway According to your ISP/Need
P_Gateway=182.152.162.xx
S_Gateway=179.158.21.xx


# Change DNS According to your ISP/Need 
P_DNS1=8.8.8.8
P_DNS2=8.8.4.4
S_DNS1=8.8.8.8
S_DNS2=8.8.4.4
# Change Network According to your setup
MASQUERADE=172.17.0.0/16


Gateway=`/sbin/ip route | grep "default" | awk '{print $3}'`


/bin/ping $P_Gateway -w 30 > /dev/null
if [ $? -ne 0 ];then
        echo "Primary gateway $P_Gateway is not Reachable";
/bin/ping $S_Gateway -w 30 > /dev/null
        if [ $? -ne 1 ];then
    if [ $Gateway = $S_Gateway ];then
                    echo "Secondary Gateway $S_Gateway Already Added"
            else
                    /sbin/ip r d default ; /sbin/ip r a default via $S_Gateway dev eth2;
                    echo "Secondary Gateway $S_Gateway Successfully Added"
                    /sbin/iptables -t nat -D POSTROUTING -s $MASQUERADE -o eth1 -j MASQUERADE
                    /sbin/iptables -t nat -A POSTROUTING -s $MASQUERADE -o eth2 -j MASQUERADE
                    #echo "nameserver $S_DNS1" > /etc/resolv.conf
                    #echo "nameserver $S_DNS2" >> /etc/resolv.conf
            fi;
    else
           echo "$P_Gateway and $S_Gateway both are down, Please Contact to ISP"
    fi;
else
        if [ $Gateway = $P_Gateway ];then
                echo "Primary Gateway $P_Gateway Already Added"        
        else
                /sbin/ip r d default ; /sbin/ip r a default via $P_Gateway dev eth1;
                echo "Primary Gateway $P_Gateway  Successfully Added"
                #echo "nameserver $P_DNS1" > /etc/resolv.conf
                #echo "nameserver $P_DNS2" >> /etc/resolv.conf
                /sbin/iptables -t nat -D POSTROUTING -s $MASQUERADE -o eth2 -j MASQUERADE
                /sbin/iptables -t nat -A POSTROUTING -s $MASQUERADE -o eth1 -j MASQUERADE
        fi;
fi;
exit 0;