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 12, but any newer version should also work. For the rest of the tutorial we will be using the IPFilter firewall, but you can use any other netfilter frontend of your choice.

Installation

Let us start by installing wireguard-tools:


marco@vpnnode:~$ sudo apt install wireguard

The version of NFTables I am currently using is:


marco@vpnnode:~$ sudo nft -v
nftables v1.0.6 (Lester Gooch #5)

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 accept incoming packets from the chosen UDP port and to create a NAT for the Wireguard interface(wg0). To keep things as simple as possible, I will be using nftables but you can accomplish the same result with pretty much any netfilter frontend.

On Debian, an empty nftables ruleset looks like this:


flush ruleset

table inet filter {
	chain input {
		type filter hook input priority filter;
	}
	chain forward {
		type filter hook forward priority filter;
	}
	chain output {
		type filter hook output priority filter;
	}
}

And, if you don't have any additional firewall rule, you will just need the following configuration:


# Wireguard NAT
add table wireguard-nat

table ip wireguard-nat {
	chain prerouting {
		type nat hook prerouting priority -100; policy accept;
	}

	chain postrouting {
		type nat hook postrouting priority 100; policy accept;
		oifname "ens3" masquerade # Be sure to replace 'ens3' with your network interface
	}
}

However, if you are planning to filter the input chain by dropping all packets and allowing only a specific set of ports, be sure to allow inbound traffic for the selected UDP port using the following rule:


chain input {
        type filter hook input priority filter; policy drop; # Drop all packets by default
        iifname "lo" accept comment "Accept loopback interface" # Accept traffic from loopback device

        # Accept established and related packets
        ct state established,related counter accept comment "Accept established and related packets"
        ct state invalid counter drop comment "Drop invalid packets"

        # Allow ICMP requests
        icmp type echo-request counter accept comment "Accept incoming ICMP"

        # Allow inbound HTTP and HTTPS traffic
        tcp dport { 80, 443 } counter accept comment "Accept incoming services"
        # Allow inbound UDP traffic for Wireguard
        udp dport { 48965 } counter accept comment "Accept Wireguard packets"
}


chain input {
        type filter hook input priority filter; policy drop; # Drop all packets by default
        iifname "lo" accept comment "Accept loopback interface" # Accept traffic from loopback device

        # Accept established and related packets
        ct state established,related counter accept comment "Accept established and related packets"
        ct state invalid counter drop comment "Drop invalid packets"

        # Allow ICMP requests
        icmp type echo-request counter accept comment "Accept incoming ICMP"

        # Allow inbound HTTP and HTTPS traffic
        tcp dport { 80, 443 } counter accept comment "Accept incoming services"
        # Allow inbound UDP traffic for Wireguard
        udp dport { 48965 } counter accept comment "Accept Wireguard packets"
}

After that, we can reload the ruleset by issuing the following command:


$> sudo systemctl restart nftables

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:
      - "192.168.2.1:53:53/tcp"
      - "192.168.2.1:53:53/udp"
      - "192.168.2.1:8888:80/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: login pihole

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.