Bash Script to check and shift ISP if unreachable || linuxtopic

Bash Script to check and shift ISP if unreachable || linuxtopic


Bash script to check internet connection, This is a script to change ISP if it’s unreachable, i have 2 ISP and  3 interface eth0 eth1 and eth2, My eth0 is connected on Intranet and ISP connected to eth1 and eth2. This script ping my Primary ISP if its reachable exit if it’s not reachable  set secondary isp


vi  /usr/local/bin/shift_gateway

#!/bin/bash
# by lokesh carpenter #


# 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;

Explanation :
Gateway=`/sbin/ip route | grep "default" | awk '{print $3}'` : checking current system gateway,
/bin/ping $P_Gateway -w 30  : ping primary gateway for 30 seconds
if [ $? -ne 0 ]; : if  response is 0 then  
/bin/ping $S_Gateway -w 30  : ping secondary gateway
if [ $? -ne 1 ]; : set secondary gateway otherwise echo both gateway are down.
if [ $Gateway = $S_Gateway ];then :check  secondary gateway,  if already  found echo “Already Set S_Gateway, otherwise set Secondary Gateway
/sbin/iptables -t nat -D POSTROUTING -s $MASQUERADE -o eth1 -j MASQUERADE delete nat rules for eth1
/sbin/iptables -t nat -A POSTROUTING -s $MASQUERADE -o eth2 -j MASQUERADE
Set nat rules for eth2
#echo "nameserver $S_DNS1" > /etc/resolv.conf
#echo "nameserver $S_DNS2" >> /etc/resolv.conf : change dns entry as per ISP , here i comment because i used 8.8.8.8 & 8.8.4.4

else

if [ $Gateway = $P_Gateway ]  echo "Primary Gateway $P_Gateway Already Added"   
else set  $P_Gateway on dev eth1;
#echo "nameserver $P_DNS1" > /etc/resolv.conf
#echo "nameserver $P_DNS2" >> /etc/resolv.conf
change dns entry as per ISP , here i comment because i used 8.8.8.8 & 8.8.4.4
/sbin/iptables -t nat -D POSTROUTING -s $MASQUERADE -o eth2 -j MASQUERADE delete nat rules for eth2
/sbin/iptables -t nat -A POSTROUTING -s $MASQUERADE -o eth1 -j MASQUERADE Set nat rules for eth1

Set Execution Permission

chmod +x /usr/local/bin/shift_gateway

Set Cron for Checking Gateway in every minutes


vi /etc/cron.d/gateway_check

* * * * *  /bin/bash  /usr/local/bin/shift_gateway >> /var/log/shift_gateway-`date -I`.log

Previous
Next Post »

1 comments:

Write comments
Linux Topic
AUTHOR
February 20, 2018 at 11:56 AM

bash script to change internet gateway after it's unreachable

http://www.linuxtopic.com/2018/02/bash-script-of-shift-isp.html

Reply
avatar