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Overview

This tutorial will show you how to use your Raspberry Pi as a WiFi access point that blocks ads by default for any devices using it. This is really neat in that it would work for your Android or iOS device, your Xbox 360, TiVo, laptop, and more without needing to customize any of those devices other than to use your Raspberry Pi as the access point for WiFi. Using an ad-blocker can be useful for conserving bandwidth, helping out low-power devices, or for keeping your sanity while browsing the web!
I do suggest whitelisting your favorite ad-supported sites so that you can continue to support them (this tutorial shows how to do this as well).

It's not easy keeping up with those wily ad serving companies so we'll also setup a way to keep your ad blocking lists up to date as part of this tutorial.

I used many pages as inspiration in order to set this up, including, but not limited to:
Each of those links contain useful information, but the next few pages will walk you through in detail each step necessary to successfully block ads with your Raspberry Pi.

Preparation

This tutorial assumes you have your Pi mostly set up and ready to go.

Please follow the tutorials in order to

  1. Install the OS onto your SD card
  2. Boot the Pi and configure
    Don't forget to change the default password for the 'pi' acccount!
  3. Set up and test the Ethernet and Wifi connection
  4. Set up your Raspberry Pi as an Access Point
  5. Connect with a USB console cable (optional)
When done you should have a Pi that is booting Raspbian, you can connect to with a USB console cable and log into the Pi via the command line interface. Your Pi should also be already setup as a WiFi access point from step 4.

It is possible to do this tutorial via ssh on the Ethernet port or using a console cable.

If using a console cable, even though the diagram on the last step shows powering the Pi via the USB console cable (red wire) we suggest not connecting the red wire and instead powering from the wall adapter. Keep the black, white and green cables connected as is.

Install Software

Once you've done all the preparation, setting your Pi up as an ad blocking AP is actually rather simple. The first thing we need to do is install the necessary software, and set it all up.

To start with, uninstall isc-dhcp-server and install dnsmasq. We'll be using dnsmasq as your dhcp server instead of isc-dhcp-server. You may want to do a sudo apt-get update first, and then execute the following:
sudo apt-get autoremove isc-dhcp-server
sudo apt-get install -y dnsmasq dnsutils
You can test that it installed properly by checking the status:
sudo service dnsmasq status
Create and edit a new file for the dhcp server settings:
sudo nano /etc/dnsmasq.d/dnsmasq.custom.conf
Add the following to that file:
interface=wlan0
dhcp-range=wlan0,192.168.42.10,192.168.42.50,2h
# Gateway
dhcp-option=3,192.168.42.1
# DNS
dhcp-option=6,192.168.42.1

dhcp-authoritative
Save the file by typing in Control-X then Y then return

These are the minimum settings required to get the dhcp server setup properly. There are a lot more settings available as examples in /etc/dnsmasq.conf if you want to configure it further.

Any files added to the directory /etc/dnsmasq.d are automatically loaded by dnsmasq after a restart. This is a convenient way to override or add new configuration files in Debian.
Next, let's update the dns nameservers to route to our pixelserv IP address first. We'll also go ahead and use the google nameservers.

Open the file with sudo nano /etc/resolv.conf and replace the contents with the following:
nameserver 192.168.42.1
nameserver 8.8.8.8
nameserver 8.8.4.4
After saving the resolv.conf file, let's restart dnsmasq to have the settings take effect:
sudo service dnsmasq restart
Try testing out the dns by using the dig command.
dig adafruit.com
Your results should be similar to the following:
Ok, now that we have all of that setup, let's create a script that will redirect known ad servers to an internal IP address. This will essentially cause any requests to generate an HTTP 404.

Open nano and create a file with the following command:
sudo nano /usr/local/bin/dnsmasq_ad_list.sh
Copy and paste the following into the file, and save and exit:
#!/bin/bash

ad_list_url="http://pgl.yoyo.org/adservers/serverlist.php?hostformat=dnsmasq&showintro=0&mimetype=plaintext"
pixelserv_ip="192.168.42.49"
ad_file="/etc/dnsmasq.d/dnsmasq.adlist.conf"
temp_ad_file="/etc/dnsmasq.d/dnsmasq.adlist.conf.tmp"

curl $ad_list_url | sed "s/127\.0\.0\.1/$pixelserv_ip/" > $temp_ad_file

if [ -f "$temp_ad_file" ]
then
	#sed -i -e '/www\.favoritesite\.com/d' $temp_ad_file
	mv $temp_ad_file $ad_file
else
	echo "Error building the ad list, please try again."
	exit
fi

service dnsmasq restart
Notice, in the above script there is a line starting with "#sed ". You can uncomment that, and modify it to remove your favorite sites from the ad blocking list so you can continue to support them. You can add as many of those lines as you'd like. One example would be:

sed -i -e '/ads\.stackoverflow\.com/d' $temp_ad_file

Next allow the file to be executed:
sudo chmod +x /usr/local/bin/dnsmasq_ad_list.sh
Manually run the script to test that it works:
sudo /usr/local/bin/dnsmasq_ad_list.sh
You should see the following output:
The above script will need to be run as root in order to properly update the configuration file. Basically, what it does it grab a pre-generated list of known ad server domain names from http://pgl.yoyo.org/adservers and save them to a file in /etc/dnsmasq.d/dnsmasq.adlist.conf. It then restarts dnsmasq.

You could manually do this every once in a while, but it's easier if we setup a weekly cron job with the root user.

Open crontab with the following command:
sudo crontab -e
Add the following line to the end of the file and save it:
@weekly /usr/local/bin/dnsmasq_ad_list.sh
Congratulations, you should now be blocking ads with your Raspberry Pi. You can test that it's working by executing the following:
dig doubleclick.com
And you should see that it gets routed to the 192.168.42.49 IP address:
One drawback to just stopping here is that we're now timing out on requests that are going to return an HTTP code of 404 for any ad servers. This won't be terribly fast. Another drawback is that any areas with ads will potentially still take up space in the page. We can fix this in the next section.

Improving Performance

One way to improve the performance of the ad blocker is to serve either a 1x1 transparent image, or a blank HTML page. This can be done in a number of ways so we'll show a couple of the options available to you.

Pixelserv

The first, and maybe most common is to use pixelserv. This is a really lightweight perl web server that simply serves a 1x1 transparent GIF to any requests made to it. Thus, anytime ads get redirected by dnsmasq to pixelserv, you'll actually receive a tiny image that won't be visible on the page.

To start with, download the pixelserv file:
sudo curl -o /usr/local/bin/pixelserv http://proxytunnel.sourceforge.net/files/pixelserv.pl.txt
And also change the permissions:
sudo chmod 755 /usr/local/bin/pixelserv
Now, open the file with nano:
sudo nano /usr/local/bin/pixelserv
You can see that the pixelserv is a fairly small perl script. Let's edit it to change the IP address that we're using (192.168.42.49) to redirect the ads to. Find the line with LocalHost, and change it to the following:
$sock = new IO::Socket::INET (  LocalHost => '192.168.42.49',
Save the file by typing in Control-X then Y then return

You could try running the server now, but you'd get the following error:
[email protected] /usr/local/bin $ ./pixelserv
error : cannot bind : Cannot assign requested address exit
We can resolve this by adding this IP address to our wlan0 interface (Thanks to this site for this fix!). Open nano and the interfaces file:
sudo nano /etc/network/interfaces
Update your iface wlan0 inet static section to look like the following. We're adding the last two lines (post-up and pre-down):
iface wlan0 inet static
  address 192.168.42.1
  netmask 255.255.255.0
  post-up ip addr add dev wlan0 192.168.42.49/24
  pre-down ip addr del dev wlan0 192.168.42.49/24
Save the file by typing in Control-X then Y then return

Now reboot your Pi so the settings take effect:
sudo reboot
Once your system comes back up, try running the server. It won't output anything in the console, but you can try refreshing a page you know that has ads that get blocked:
sudo /usr/local/bin/pixelserv
It could get annoying having to always run that command. The next logical step would be to create a service that will start the server for us whenever we start our Pi. Let's do that.

First, kill the server you're running by typing "Ctrl-C".

Now, create a new file with nano:
sudo nano /etc/init.d/pixelserv
Copy and paste the following to that file:
### BEGIN INIT INFO
# Provides:          pixelserv
# Required-Start:    $network
# Required-Stop:     $network
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
# Short-Description: pixelserv server for ad blocking
# Description:       Server for serving 1x1 pixels
### END INIT INFO

case "$1" in
   start)
     echo "pixelserv: starting"
     /usr/local/bin/pixelserv &
     ;;
   stop)
     echo "pixelserv: stopping"
     killall pixelserv
     ;;
   *)
     echo "Usage: service $0 {start|stop}"
     exit 1
     ;;
esac

exit 0
Save the file by typing in Control-X then Y then return

Change the permissions on that file:
sudo chmod 744 /etc/init.d/pixelserv
Test that the script works by starting and stopping it:
sudo /etc/init.d/pixelserv start
sudo /etc/init.d/pixelserv stop
Now, enable the script on startup of your Pi:
update-rc.d pixelserv defaults
You can manually start/stop the pixelserv server by executing the following:
sudo service pixelserv start
sudo service pixelserv stop
If you decide you'd rather use the Apache solution, you can disable the pixelserv service on startup:
sudo update-rc.d -f pixelserv remove

Apache

As an alternative to pixelserv, we can use Apache to serve a blank html file with an HTTP 200 response. Apache is a bit heavier but likely much more stable than pixelserv.

Let's start by installing Apache (make sure to stop and disable pixelserv if you've already installed that):
sudo apt-get install apache2 -y
By default apache is listening to all IP addresses on port 80. You can change this if you like, but it's not necessary.

Test that apache is picking up our redirected requests:
curl doubleclick.com
You should get the following:
[email protected] ~ $ curl doubleclick.com
<html><body><h1>It works!</h1>
<p>This is the default web page for this server.</p>
<p>The web server software is running but no content has been added, yet.</p>
</body></html>
[email protected] ~ $ 
That's a bit more than what we want. Let's modify it so we basically just get an OK from apache instead of any content.

First enable the apache2 rewrite engine by executing the following:
sudo a2enmod rewrite
Next, let's update the default VirtualHost. Execute the following to open the default VirtualHost file in nano:
sudo nano /etc/apache2/sites-available/default
Edit the <Directory /var/www/> section to look like the following (we're adding the last three lines):
        <Directory /var/www/>
                Options Indexes FollowSymLinks MultiViews
                AllowOverride None
                Order allow,deny
                allow from all
                RewriteEngine on
                RedirectMatch 200 (.*)$
                ErrorDocument 200 " "
        </Directory>
Save the file by typing in Control-X then Y then return

Make the same change for the default-ssl file as well (sudo nano /etc/apache2/sites-available/default-ssl).

At this point if you restart Apache, you'll get an error about not being able to determine the server's fully qualified domain name. We can fix that by executing the following command:
echo "ServerName raspberrypi" | sudo tee -a /etc/apache2/conf.d/fqdn
Ok, now we can restart apache:
sudo service apache2 restart
And test that the response from Apache has changed:
[email protected] /etc/apache2/sites-available $ curl doubleclick.com
 [email protected] /etc/apache2/sites-available $ 
That's it, you're all setup for super-speedy ad-blocking from your Raspberry Pi!

FAQ

Does this work with SSL traffic?

Yes! This blocks adware and malware sites at the domain (DNS) level, so it will work with HTTPS as well as non-SSL pages

Will this work as a WiFi-to-WiFi bridge? (Or WiFi-to-Cellular)

In theory, if you can get the Access Point setup to work WiFi-to-WiFi then yes the adblocking part will too. However we don't have that part of the tutorial written, and most people get best performance with Ethernet-to-WiFi

My resolv.conf gets overwritten on reboot

If you'd like this to be permanent, and continue after a reboot, follow the tips suggested on the Adafruit Forums.