This is a script I wrote a while back but never posted up. It allows you to switch from one gateway to another by repeatedly pinging your ISP gateway (or another external IP) and--upon detection of failure--switching to another gateway. If the primary line is up upon the next run, we switch over to it.
This isn't a very advanced script and doesn't factor in other considerations, such as the state of the physical interfaces. It simply attempts a number of pings, and considers the link dead or unreliable if they don't all come back.
If you have mutt installed, you will get an email alert when the primary link is considered 'dead.' You can easily change this behavior by modifying the script.
It will probably work on other POSIX/Unix-like OSes, but I've only tested it on Linux in a BASH environment. With all that said, here are the goods:
CODE:
#!/bin/bash
# GWMover: WAN/Gateway failover
# Pings gateway and switches to backup line when it goes down.
# Reverts to primary line when gateway becomes accessible.
# Modified version of script found at:
# http://www.howtoforge.com/forums/showthread.php?p=55402#post55402
#
# Last modified: August 2, 2007
# Ameir Abdeldayem
PRIMARYPUB="66.92.162.1"
PRIMARYGW="10.0.5.1"
SECONDARYGW="10.0.0.1"
EMAILS="email@ddress1 email@ddress2"
function is_host_alive() # Returns success or failure as boolean
{
PACKETS=3
TRIES=5
IP=$1 # saving contents in $1 before is used
echo "Pinging $IP"
i=0
while [ $i -lt $TRIES ]; do
REQUEST=$(ping -qc $PACKETS $IP |grep packets| cut -d" " -f1,4)
set -- $REQUEST
echo -e "Try $i: $1 $2 "
if [ $1 != $2 ]; then
echo "Bad news. $1 sent, $2 received."
# exit
exitcode=1
else
echo "Great! $1 sent, $2 received."
exitcode=0
fi
i=$(expr $i + 1)
done
return $exitcode
}
CURRENTGW=`route | grep "default" | awk '{print $2}'`
function changegateway()
{
if [ $1 != $CURRENTGW ]; then
echo ". We need to change the default route. After: $1 Before: $2"
route add default gw $1
route del default gw $2
echo "The routing table has been changed!"
route # view current routing table
echo -e "$4 \n\nHere is the updated routing table:\n$(route)" | mutt -s "$3 ($(hostname))" $EMAILS
else
echo ", and we are already pointing to it."
fi
}
function test()
{
echo $1 $EMAILS
}
##################
# main starts here
##################
if is_host_alive $PRIMARYPUB ; then
echo -n "The primary gateway is alive"
SUBJECT="$PRIMARYPUB IS NOW UP"; BODY="The server $PRIMARYPUB is now up and was pinged via the current gateway of $CURRENTGW."
changegateway $PRIMARYGW $SECONDARYGW "$SUBJECT" "$BODY"
# test $PRIMARYGW
else
echo -n "The primary gateway is dead <img src="/blog/templates/default/img/emoticons/sad.png" alt=":-(" style="display: inline; vertical-align: bottom;" class="emoticon" /> We should be on the backup line"
SUBJECT="$PRIMARYPUB IS DOWN"; BODY="The server $PRIMARYPUB could not be pinged via the current gateway of $CURRENTGW."
changegateway $SECONDARYGW $PRIMARYGW "$SUBJECT" "$BODY"
fi
Download it here.
