Script to watch and log dynamic IP changes

[dwasifar]

Here's a Linux shell script to scrape the current IP from a Linksys router's status page once per minute and log any changes.

#!/bin/sh
# Reads internet IP from Linksys router, reports changes
clear
b=0
message='- logging start'
if [ "$2" != '' ]; then
   router_username=$2
else
   router_username="admin"
fi
if [ "$3" != '' ]; then
   output_filename=$3
else
   output_filename="~/ip_history.txt"
fi
if [ "$1" != '' ]; then
  while [ $b = 0 ]
  do IPADR2=$IPADR;
  IPADR=$(wget -q -O - http://$router_username:$1@192.168.1.1/Status_Router.asp | sed -n '/ipaddr/ {n;p;}' | sed -e 's/.*<B>//; s/<\/B>.*//')
  if [ "$IPADR" != "$IPADR2" ]; then
      dttim=$(date)
      echo $dttim $IPADR $message
      echo $dttim $IPADR $message >> $output_filename
      message=''
  fi
  sleep 60s
  done
else
  echo "Usage: ip_history [router_password] {router_username} {output /path/filename}"
  echo "Router username defaults to admin"
  echo "Output defaults to ~/ip_history.txt"
fi

Copy this code into a text editor, save it wherever you want, name it ip_history, and set it executable.

For some Linksys routers, the status page is Status_Router.htm (or something similar) instead of .asp.

If your router doesn't offer a status page, you can modify this script to pull the IP from whatismyip.com. Substitute this line to set the IPADR variable:

IPADR=$(wget www.whatismyip.com/automation/n09230945.asp -O - -q)

...and change sleep 60s to sleep 300s (or a higher value) to avoid hitting whatismyip.com's automation page more frequently than five minutes apart.

I have this script set to run automatically when I boot, so it doesn't have its own window; but if you run it manually, it will log IP changes to the terminal window as well as the log file.

[wimiadmin]

Very nice dwasifar. Thanks for your contribution.

The user should also keep in mind that if the IP to their router is different than 192.168.1.1 they'll need to make the necessary changes in the script to reflect the correct IP.

[AboveTheLogic]

Nice work! (havent tested it myself but it looks fancy)

[dwasifar]

Originally Posted by wimiadmin

Very nice dwasifar. Thanks for your contribution.

The user should also keep in mind that if the IP to their router is different than 192.168.1.1 they'll need to make the necessary changes in the script to reflect the correct IP.

Yes, absolutely. I should have pointed that out. But I'm sure anyone who has changed their Linksys router's default IP knows they have done so.

Also, if you do the alteration to pull the IP from whatismyip.com, then it doesn't matter what parms are used for the router login; they can just be any old junk, or the script could be altered so as not to require them.

[Juggernaut]

I hope you don't mind, but I've modified your script to send an email if the IP is changed taking away the need to either check the screen of the box running the script or manually checking the log file.

My only issue now is to get it to start when the box boots up. It's a FreeBSD box and I just haven't got around to setting it up yet. My current work around is using the 'nohup' from a putty connection.

Thought I'd post it in case anyone else has a need for it. Here's what I've modified it to:

#!/bin/sh
# Connects to www.whatismyip.com every 12 hours to get IP address and checks if it has changed

clear
output_filename="/usr/home/<user>/ip_history.txt"
while [ 1 ]
  do IPADR2=$IPADR;
  IPADR=$(wget www.whatismyip.com/automation/n09230945.asp -O - -q)
  dttim=$(date -j +"%d %b %Y @ %H:%M:%S")
  if [ "$IPADR" != "$IPADR2" ]; then
    echo ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ >> $output_filename
    echo ~~~~~ IP Address has changed ... $dttim >> $output_filename
    echo ~~~~~ Our Old IP Address was -- $IPADR2 >> $output_filename
    echo ~~~~~ Our New IP Address is --- $IPADR >> $output_filename
    echo ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ >> $output_filename

    mail -s "IP Changed" user@mydomain.me << E_O_M
Good day Master,

  I Regret to Inform You That Our IP Has Changed

  Our Old IP Address was -- $IPADR2
  Our New IP Address is --- $IPADR

  This Occurred Within The Past 12 Hours From -- $dttim

  Our Records Will Need To Be Updated At
     https://my.registrar.com

  Reference: $output_filename
E_O_M

  else
    echo IP Address is the same ... as of $dttim ... $IPADR  >> $output_filename
  fi
  sleep 43200 # 12h = 43200
done

[dwasifar]

Oh, by all means, modify and use freely. I like your version. This script started life not as a logging program, but to do ftp updates to a remote web server, keeping a remote link pointed at the dynamic IP, so what you're doing is actually closer to what I originally had.

For automatic startup, I don't know how FreeBSD handles it, but in Linux you could put a symlink to it in /etc/rc3.d or one of the other run level control directories. Since I'm running it on Ubuntu, I have the luxury of just using the Startup Applications tool instead.

Just because I pigheadedly specify sleep times in seconds doesn't mean you have to. You could do sleep 12h, just as I could have done sleep 1m or sleep 5m or what have you.