This is a continue to my project Raspberry Pi VPN server. In that article I explained how to create a VPN server with your Raspberry Pi. I did that and enabled my home router port forwarding for ports 22 (SSH) and 1723 (PPTP). It works perfectly but there is one small problem! Not very small though!

Raspberry Pi

Introduction

Everything is working great when I know my home route public IP address, but this address is dynamically allocated by my ISP. What happens if IP changes? Of course I loose my access to VPN server. There are a few solutions to this:

  • Requesting ISP for fixed (static) public address
  • Setup a dynamic DNS with one of existing service providers.
  • Write a simple bash script to send IP address when it changed.

Well, among those three options that came to mind quickly, I chose the third one. Because requesting for static public IP address might not be that easy and your ISP might charge you extra for that service. And I don’t want to waste my time subscribing to one on those free dynamic DNS providers. And finally I like to try something new.

If you are interested to do the same, follow this instruction. It won’t be that difficult. I consider you’ve already installed Rasbian on your Raspberry Pi, though it works with other distros as well. If not follow my other article about Raspberry Pi VPN server.

1. Install required packages

I’m going to use one of free SMTP email provider, ie. Google Mail. You may choose any other, just need to change email server and authentication information accordingly that comes later in the configuration file. In order to use external email provider I use sendEmail command line tool, which is written in Perl and available in Rasbian repositories. Because Gmail uses TLS authentication I need to install Perl TSL support using CPan. And finally we need curl to fetch public IP address.

sudo apt-get install build-essential libssl-dev sendemail curl
sudo cpan install IO::Socket::SSL
sudo cpan install Net::SSLeay

2. Email account

Create a new Gmail (or any other provider) email for your Raspberry Pi. I’m not going to explain how to create email account :)

3. Bash script

And here is a simple bash script that find public IP address and compare that with the latest IP address, if it’s different, an email with new IP will be send out. This script uses an external web site (ifconfig.me) to find public IP address because my Raspberry Pi is behind NAT.

This is configuration file. Copy and paste this text in any editor change email and password to proper values and then paste into terminal. this will create a file in /etc/sendip.conf . You can edit this file later.

cat >>'CONFIG' | sudo tee /etc/sendip.conf
# sendip config file

# SMTP Server address with port, default port is 25
SMTP_HOST="smtp.gmail.com:587"

# new IP Email subject 
EMAIL_SUBJECT="My new IP address"

# Raspberry Pi Email address, email will be send out using
# this email address
RASPBERRY_EMAIL="[email protected]"

# Password for above email address
RASPBERRY_PASSWORD="raspberry_email_password"

EMAIL_MESSAGE='
Hello,

My new IP address is $NEWIP.

Regards,
Raspberry Pi

'
CONFIG

And here is the script. Just copy and paste the whole thing in bash. This will create /usr/bin/sendip.

cat >>'CODE' | sudo tee /usr/bin/sendip
#!/bin/bash

source /etc/sendip.conf

if [[ -z $1 ]]
then
    echo "
Usage: $0 <email address> 
"
    exit 1
fi

EMAIL_ADDRESS=$1

expand_message ()
{
    echo "$1" | while read LINE
    do
        echo "$(eval echo $LINE)"
    done
}

if [[ -f "/tmp/.ipaddress" ]]
then
    OLDIP=$(cat /tmp/.ipaddress)
fi

NEWIP=$(curl -s http://ifconfig.me/ip)

if [[ "$OLDIP" != "$NEWIP" ]]
then
    echo $NEWIP | tee /tmp/.ipaddress

    MESSAGE=$(expand_message "$EMAIL_MESSAGE")

    sendEmail -f $RASPBERRY_EMAIL -t $EMAIL_ADDRESS -s $SMTP_HOST -u $EMAIL_SUBJECT -xu $RASPBERRY_EMAIL -xp $RASPBERRY_PASSWORD -m "$MESSAGE" -o tls=yes
fi

CODE

Make script executable:

sudo chmod u+x /usr/bin/sendip

4. Running script

To run script enter sendip command followed by your email addresss. The IP address will be fetched and an email will be send out to the provided email address.

sendip [email protected]

If I run script for second time and my IP is the same as before, email won’t send again. So script does not spam you.

5. Automation

To use this script effectively we need to make the process automatic. Then whenever IP changes this script will send IP to my email. In order to do this I use a simple hourly crontab script. Copy and paste the following code into bash to create one.

cat >>CRON | sudo tee /etc/cron.hourly/sendip 
#!/bin/bash
/usr/bin/sendip [email protected] 2>&1 >> /var/log/sendip.log

CRON

And make it executable:

sudo chmod u+x /etc/cron.hourly/sendip

That’s all. Now you everything settled and should work properly. Please leave comments and share if you found this article useful.



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