linux failover internet with auto change default gateway

this bellow is simple auto change default gateway for internet

i have two isp internet :
server  with gateway : 192.168.1.17
server  with backup gateway : 192.168.1.59
use proxy for default internet in officce that run script auto cahange gateway

first use the default gateway is 192.168.1.17
i use the google's dns ( 8.8.8.8 ) for test internet connection  via gateway 192.168.1.17 every  3 minute with crontab  do with swroute.sh

second use route host google's dns via 192.168.1.17
#route add -host 8.8.8.8  gw 192.168.1.17

and the second isp ( 192.168.1.59 ) for backup internet do with swroute.sh

                                      

sometime we need network similar with this network

i use ping for test internet connection  for first isp ( 192.168.1.17 )
and i create swroute.sh  with  bash script  for test connection and switch default default routing

#nano  swroute.sh
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#!/bin/bash
loss="`ping 8.8.8.8 -w 20 | grep loss | awk '{print $6}' | sed '$s/.$//'`"         
route="`route -n  | head -3 | grep eth0 | awk '{print $2}'`"                           
isp1="192.168.1.17"                                                                                             isp2="192.168.1.59"                                                                                          
                                                                                                            
if [ $route == $isp1 ];
    then                                                                                  
        if [ $loss -gt 15 ]                                                                                 
           then                                                                                             
              route del default gw 192.168.1.17                                                           
              route add default gw 192.168.1.59                                                          
              echo "line via isp2---   pada: `date`" >>  /root/ping/logswitch.txt
           else            
                echo "still via isp1 "                                                                       
         fi                                                                                                  
elif  [ $loss -gt 15 ];
        then echo " still via isp2"
        else
                route add default gw 192.168.1.17
                route del default gw 192.168.1.59
                echo "> back to isp1 : `date`" >> /root/ping/logswitch.txt
fi

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#chmod +x  swroute.sh

add crontab every 3 minute
*/3 * * * * /path/path/swroute.sh


this script work for my slackware server
Happy  Slackware .....