How To Set Up a Wireguard VPN Server with PiHole

2022-08-09

Introduction

In this guide we will see how to set up a VPN server with advertisement blocking capabilities using Debian, Wireguard and PiHole. To follow this guide, make sure to have an updated installation of Debian; at the time of writing the latest version available is Debian 11, but any newer version should also work. For the rest of the tutorial we will be using the firewalld firewall, but you can use any other netfilter frontend of your choice.

Installation

Let us start by installing wireguard-tools and firewalld packages:

                    
marco@vpnnode:~$ sudo apt install wireguard firewalld

and let us enable the firewall daemon at boot:

                    
marco@vpnnode:~$ sudo systemctl enable firewalld --now

Configure Wireguard(Server)

Let us now start configuring the wireguard server by generating the keypair and the configuration file; to do so, we will create a reserved directory:

                    
root@vpnnode:~# mkdir -p /etc/wireguard/
root@vpnnode:~# cd /etc/wireguard/

Once inside it, we can generate a new keypair with the wg(8) utility:

                    
root@vpnnode:/etc/wireguard# wg genkey | tee privkey | wg pubkey > pubkey
root@vpnnode:/etc/wireguard# ls -lh
total 8.0K
-rw-r--r-- 1 root root 45 Aug  6 08:46 privkey
-rw-r--r-- 1 root root 45 Aug  6 08:46 pubkey
root@vpnnode:/etc/wireguard# cat privkey
+LoX/Rrh2VR6nFiExOweXR37HluHdOhjBiFu7jqK7mo=

at this point, copy the content of privkey file and create a new file called wg0.conf where:

PrivateKey is equal to privkey;
Address is the CIDR mask of the VPN(i.e. from 192.168.2.1 to 192.168.2.254);
ListenPort is the UDP port where the Wireguard server will listen to.

You should have a similar structure:

                    
root@vpnnode:/etc/wireguard# cat wg0.conf
[Interface]
PrivateKey = +LoX/Rrh2VR6nFiExOweXR37HluHdOhjBiFu7jqK7mo=
Address = 192.168.2.1/24
ListenPort = 48965

Configure the firewall

The next step is to configure the firewall to listen to the selected UDP port and to create a NAT between the internal Wireguard interface(wg0) and the server external interface(in my case enp1s0). To do that, issue the following commands:

                    
root@vpnnode:/etc/wireguard# firewall-cmd --permanent --add-port=48965/udp
root@vpnnode:/etc/wireguard# firewall-cmd --permanent --add-masquerade
root@vpnnode:/etc/wireguard# firewall-cmd --reload
root@vpnnode:/etc/wireguard# firewall-cmd --list-all
public
  target: default
  icmp-block-inversion: no
  interfaces:
  sources:
  services: dhcpv6-client ssh
  ports: 48965/udp
  protocols:
  forward: no
  masquerade: yes
  forward-ports:
  source-ports:
  icmp-blocks:
  rich rules:

After reloading the firewall rules, you should have a new udp port open and the IP masquerading activated for the public firewall zone. Now let us do the same thing for the wg0 interface on the internal firewall zone:

                    
root@vpnnode:/etc/wireguard# firewall-cmd --zone=internal --add-interface=wg0
root@vpnnode:/etc/wireguard# firewall-cmd --permanent --zone=internal --add-masquerade
root@vpnnode:/etc/wireguard# firewall-cmd --zone=internal --list-all
internal
    target: default
    icmp-block-inversion: no
    interfaces:
    sources:
    services: dhcpv6-client mdns samba-client ssh
    ports:
    protocols:
    forward: no
    masquerade: yes
    forward-ports:
    source-ports:
    icmp-blocks:
    rich rules:

Routing is complete, the last thing to do is to enable ip forwarding.

Enable IP forwarding

In order to route packets between VPN's clients and a remote host, we need to enable the ip forwarding feature. To do so, type the following command:

                    
root@vpnnode:/etc/wireguard# sysctl -w net.ipv4.ip_forward=1
net.ipv4.ip_forward = 1

and to make it permanent, edit the /etc/sysctl.d/99-sysctl.conf file and uncomment the following line:

                    
# Uncomment the next line to enable packet forwarding for IPv4
net.ipv4.ip_forward=1

Configure Wireguard(Client)

Wireguard can be installed in a wide spectrum of operating system, in this guide I will not cover the installation process; in order to install the wireguard client for your computer/table/phone, please refer to this page. After that, open up the configuration file and add the following content:

                    
[Interface]
PrivateKey = ni16f/oyWn8G0rdsJ7YGyytjXvJSfaNzhzFSG5Bv4Gg= # <-- client private key
Address = 192.168.2.2/24
DNS = 192.168.2.1

[Peer]
PublicKey = 4wzgj/0u53Jiheq8DjwQ9GRnvnzv0qcsisKARdnrr1c= # <-- server public key
PresharedKey = PW21sz8kl+nY8WRNJEypkqWJGLARSX2A5KjbPfaEUp0= # <-- wg genpsk
AllowedIPs = 0.0.0.0/0, ::/0
Endpoint = <SERVER_IP_ADDRESS>:48965
PersistentKeepalive = 15

Be sure to replace the following fields according to your needs:

PrivateKey: replace it with client's private key(you can generate a new keypair using wg genkey | tee privkey | wg pubkey > pubkey command if you do not use a graphical client);
PublicKey: replace with server's public key(i.e. /etc/wireguard/pubkey file on the VPN server);
PresharedKey: you can generate a preshared key with wg genpsk(this field is optional);
Endpoint: the IP address of your server with the Wireguard UDP port.

Let us now complete the configuration by adding a new client in the server configuration file.

Back to the server

Open the /etc/wireguard/wg0.conf file and add the following entry at the end:

                    
[Interface]
PrivateKey = +LoX/Rrh2VR6nFiExOweXR37HluHdOhjBiFu7jqK7mo=
Address = 192.168.2.1/24
ListenPort = 48965

# Add this
[Peer]
PublicKey = 1+54fGF/zZlVTxDiJ3rlmrH65+5K1NMFKwxlniA/2js= # <-- Client public key
PresharedKey = PW21sz8kl+nY8WRNJEypkqWJGLARSX2A5KjbPfaEUp0=
AllowedIPs = 192.168.2.2/32

where:

PublicKey is the public key of the client;
PresharedKey is the preshared key previously generated on the client configuration;
AllowedIPs is the client's IP address.

This means that every time you want to add a new client to the network, you simply create a new keypair, add the public key to the server configuration file and restart the Wireguard network interface. Just be sure to assign a unique IP address to each client.

Finally, let us start the Wireguard server:

                    
root@vpnnode:/etc/wireguard# systemctl enable wg-quick@wg0 --now
root@vpnnode:/etc/wireguard# wg
interface: wg0
    public key: 4wzgj/0u53Jiheq8DjwQ9GRnvnzv0qcsisKARdnrr1c=
    private key: (hidden)
    listening port: 48965

peer: 1+54fGF/zZlVTxDiJ3rlmrH65+5K1NMFKwxlniA/2js=
    preshared key: (hidden)
    allowed ips: 192.168.2.2/32

You can now enable the VPN connection from your client. Right now, you will only be able to ping the VPN gateway(192.168.2.1) without being able to access the internet. This is normal because the DNS server we have specified in the client's configuration file(i.e. 192.168.2.1) is not yet active. We will fix this in a second by installing PiHole.

Configuring PiHole

PiHole is an internet tracking blocking system which acts as a DNS sinkhole. It is designed primarily for embedded devices such as the RaspberryPi, but it can be easily installed on any other Linux operating system. Since PiHole makes use of many different daemons(such as a DNS server, lighttpd and the AdminLTE dashboard), we will install it using Docker. This approach allows us to avoid manual configuration and simplify update operations.

Installing Docker on Debian is outside the scope of this guide, so please refer to the official documentation.

After that, set up a password for the PiHole dashboard(i.e. the password needed to log in to the web interface) and configure the docker container with the following docker-compose.yml file:

                    
version: "3"

# More info at https://github.com/pi-hole/docker-pi-hole/ and https://docs.pi-hole.net/
services:
  pihole:
    container_name: pihole
    image: pihole/pihole:latest
    # For DHCP it is recommended to remove these ports and instead add: network_mode: "host"
    ports:
      - "53:53/tcp"
      - "53:53/udp"
      - "8888:80/tcp"
    dns:
      - 127.0.0.1
      - 1.1.1.1
    environment:
      TZ: 'Europe/Rome'
      WEBPASSWORD: 'BADPW'
    # Volumes store your data between container upgrades
    volumes:
      - './etc-pihole:/etc/pihole'
      - './etc-dnsmasq.d:/etc/dnsmasq.d'
    restart: unless-stopped

Launch it with docker-compose up -d, you should see its status in the docker logs:

                    
marco@vpnnode:~$ docker-compose ps
docker-compose ps
 Name    Command       State                                      Ports                                
-------------------------------------------------------------------------------------------------------
pihole   /s6-init   Up (healthy)   0.0.0.0:53->53/tcp, 0.0.0.0:53->53/udp, 67/udp, 0.0.0.0:8888->80/tcp

Finally, let us configure PiHole to listen to our network interface. To do so, open up your browser and go to the admin page(be sure to be connected to the VPN, PiHole does not expose the port 8888/80 to the external interface). You should see a page like this:

Enter your password and follow these instructions:

Go to "settings" in the left pane;
Go to the "DNS" tab;
Selected the "Respond only on interface eth0" radio button in the "interface settings" section.

After that go to the bottom of the page and click the "save" button.

Conclusions

At this point you should be able to reach the internet. Let us try our new VPN on some sites(apart from whatismyipaddress.com):