====== Setup a VPN Server with WireGuard on Debian 9======

-- //Tested with **Debian 9** (server side) and **Ubuntu 18.04** (client side) on **September 2018**// --

===== Server Setup ======

==== Install WireGuard on the Server ====

Install WireGuard from Debian packages
  echo "deb http://deb.debian.org/debian/ unstable main" | sudo tee /etc/apt/sources.list.d/unstable.list
  echo -e "Package: *\nPin: release a=unstable\nPin-Priority: 150\n" | tee /etc/apt/preferences.d/limit-unstable
  sudo apt update
  sudo apt install wireguard
Check if wireguard kernel has been loaded correctly
  lsmod | grep wireguard
the output should not be blank. If necessary, you can try to load wireguard kernel module manually with
  sudo modprobe wireguard

==== Generate Server Keys ====

Generate server private key with
  wg genkey
Copy and note down the generated key (should be something like ''SeRvErPRIVATEkEySeRvErPRIVATEkEySeRvErPRIVA='').

Then, generate the corresponding public key with:
  echo "SeRvErPRIVATEkEySeRvErPRIVATEkEySeRvErPRIVA=" | wg pubkey
and note down the generated public key (in our example will be ''SeRvErPUBLICkEySeRvErPUBLICkEySeRvErPUBLICk='').

==== Generate User Keys ====

Generate user private key (one per user!) with
  wg genkey
Copy and note down the generated key (should be something like 
''UsEr1PRIVATEkEyUsEr1PRIVATEkEyUsEr1PRIVATE='').

Then, generate the corresponding public key with:
  echo "UsEr1PRIVATEkEyUsEr1PRIVATEkEyUsEr1PRIVATE=" | wg pubkey
and note down the generated public key (in our example will be ''UsEr1PUBLICkEyUsEr1PUBLICkEyUsEr1PUBLICkey='').

==== Configure the Server ====

Check the name of the network interface with
  ip l

  1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1
      link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
  2: ens32: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000
      link/ether 00:0c:29:5a:8c:02 brd ff:ff:ff:ff:ff:ff

In our case the public network interface is ens32. Note down the public IP address of the server associated to the interface. In our example will be 1.2.3.4 (no, I'm not from APNIC) - you can check yours with
  ip a show dev ens32

Now, create a file for the wireguard interface (''wg0s'' in our example) with
  sudo vim /etc/wireguard/wg0s.conf
and add the following content (replace the sample keys with your actually generated keys and ens32 with your server's public interface):

  [Interface]
  Address = 172.16.16.1/24
  PostUp = iptables -A FORWARD -i %i -j ACCEPT; iptables -A FORWARD -o %i -j ACCEPT; iptables -t nat -A POSTROUTING -o ens32 -j MASQUERADE
  PostDown = iptables -D FORWARD -i %i -j ACCEPT; iptables -D FORWARD -o %i -j ACCEPT; iptables -t nat -D POSTROUTING -o ens32 -j MASQUERADE
  ListenPort = 5544
  PrivateKey = SeRvErPRIVATEkEySeRvErPRIVATEkEySeRvErPRIVA=
  
  [Peer]
  PublicKey = UsEr1PUBLICkEyUsEr1PUBLICkEyUsEr1PUBLICkey=
  AllowedIPs = 172.16.16.2/32
  
You can also change the ListenPort from 5544 to a different, unused port (and open the corresponding port on the server's firewall).

==== Start the server ====

Start Wireguard on the server with
  sudo wg-quick up wg0s
and check if the VPN tunnel is up and running with
  wg show

If needed, you can kill the tunnel with
  sudo wg-quick down wg0s

===== Client Setup ======

==== Install WireGuard on the Client ====

Install wireguard on your Ubuntu client with
  sudo add-apt-repository ppa:wireguard/wireguard
  sudo apt-get update
  sudo apt-get install wireguard

==== Configure the Client ====

Now, create a file for the wireguard interface (''wg0c'' in our example) on your Ubuntu client
  sudo vim /etc/wireguard/wg0c.conf
and add the following content (remember replace the IP address of the Endpoint with server public address and the keys).

  [Interface]
  Address = 172.16.16.2/24
  SaveConfig = true
  ListenPort = 47824
  FwMark = 0x1234
  PrivateKey = UsEr1PRIVATEkEyUsEr1PRIVATEkEyUsEr1PRIVATE
  
  [Peer]
  PublicKey = SeRvErPUBLICkEySeRvErPUBLICkEySeRvErPUBLICk
  AllowedIPs = 0.0.0.0/0, ::/0
  Endpoint = 1.2.3.4:5544
  PersistentKeepalive = 10

==== Start the client ====

Start Wireguard on with
  sudo wg-quick up wg0c
and check if the VPN tunnel is up and running with
  wg show

If needed, you can kill the tunnel with
  sudo wg-quick down wg0c

===== Throubleshooting =====

  - Do not mess up the keys - it's quite easy to switch client and server, public and private (and break the tunnel)
  - If you have a firewall running on your server, open the corresponding UDP port (5544 in the example above)
  - If you are behind the Great Firewall, probably it will not work