Ubuntu22.04でOpenVPNサーバーをセットアップおよび構成する方法

これまで、サーバーにOpenVPNをインストールして構成し、クライアントがVPNにアクセスするために必要なキーと証明書を生成しました。ただし、クライアントからの着信Webトラフィックの送信先に関する指示はOpenVPNにまだ提供されていません。ファイアウォールルールとルーティング構成を確立することで、サーバーがクライアントトラフィックを処理する方法を指定できます。

このチュートリアルの開始時に前提条件に従っていると仮定すると、すでにufwが必要です。 サーバーにインストールして実行します。 OpenVPNがファイアウォールを通過できるようにするには、マスカレードを有効にする必要があります。これは、クライアント接続を正しくルーティングするためのオンザフライの動的ネットワークアドレス変換（NAT）を提供するiptablesの概念です。

ファイアウォール構成ファイルを開いてマスカレードルールを追加する前に、まずマシンのパブリックネットワークインターフェイスを見つける必要があります。これを行うには、次のように入力します：

ip route list default

パブリックインターフェイスは、このコマンドの出力内にある「dev」という単語に続く文字列です。たとえば、この結果はeth0という名前のインターフェースを示しています 、以下で強調表示されています：

Outputdefault via 159.65.160.1 dev eth0 proto static

デフォルトルートに関連付けられたインターフェースがある場合は、/etc/ufw/before.rulesを開きます。 関連する構成を追加するファイル：

sudo nano /etc/ufw/before.rules

UFWルールは通常、ufwを使用して追加されます 指図。 before.rulesにリストされているルール ただし、ファイルは、従来のUFWルールがロードされる前に読み取られ、配置されます。 Towards the top of the file, add the highlighted lines below. This will set the default policy for the POSTROUTING chain in the nat table and masquerade any traffic coming from the VPN. Remember to replace eth0 in the -A POSTROUTING line below with the interface you found in the above command:

#
# rules.before
#
# Rules that should be run before the ufw command line added rules. Custom
# rules should be added to one of these chains:
#   ufw-before-input
#   ufw-before-output
#   ufw-before-forward
#
 
# START OPENVPN RULES
# NAT table rules
*nat
:POSTROUTING ACCEPT [0:0]
# Allow traffic from OpenVPN client to eth0 (change to the interface you discovered!)
-A POSTROUTING -s 10.8.0.0/8 -o eth0 -j MASQUERADE
COMMIT
# END OPENVPN RULES
 
# Don't delete these required lines, otherwise there will be errors
*filter
. . .

終了したら、ファイルを保存して閉じます。

Next, you need to tell UFW to allow forwarded packets by default as well. To do this, open the /etc/default/ufw ファイル：

sudo nano /etc/default/ufw

Inside, find the DEFAULT_FORWARD_POLICY directive and change the value from DROP to ACCEPT ：

DEFAULT_FORWARD_POLICY="ACCEPT"

終了したら、ファイルを保存して閉じます。

Next, adjust the firewall itself to allow traffic to OpenVPN. If you did not change the port and protocol in the /etc/openvpn/server.conf file, you will need to open up UDP traffic to port 1194 。 If you modified the port and/or protocol, substitute the values you selected here.

In case you forgot to add the SSH port when following the prerequisite tutorial, add it here as well:

sudo ufw allow 1194/udp
sudo ufw allow OpenSSH

注 :If you are using a different firewall or have customized your UFW configuration, you may need to add additional firewall rules. For example, if you decide to tunnel all of your network traffic over the VPN connection, you will need to ensure that port 53 traffic is allowed for DNS requests, and ports like 80 and 443 for HTTP and HTTPS traffic respectively. If there are other protocols that you are using over the VPN then you will need to add rules for them as well.

After adding those rules, disable and re-enable UFW to restart it and load the changes from all of the files you’ve modified:

sudo ufw disable
sudo ufw enable

Your server is now configured to correctly handle OpenVPN traffic. With the firewall rules in place, you can start the OpenVPN service on the server.

Step 10 — Starting OpenVPN

OpenVPN runs as a systemd service, so you can use systemctl to manage it. You will configure OpenVPN to start up at boot so you can connect to your VPN at any time as long as your server is running. To do this, enable the OpenVPN service by adding it to systemctl ：

sudo systemctl -f enable [email protected]

Then start the OpenVPN service:

sudo systemctl start [email protected]

Double check that the OpenVPN service is active with the following command. You should see active (running) in the output:

sudo systemctl status [email protected]

Output● [email protected] - OpenVPN service for server
     Loaded: loaded (/lib/systemd/system/[email protected]; enabled; vendor preset: enabled)
     Active: active (running) since Thu 2022-04-21 17:58:24 UTC; 6s ago
       Docs: man:openvpn(8)
             https://community.openvpn.net/openvpn/wiki/Openvpn24ManPage
             https://community.openvpn.net/openvpn/wiki/HOWTO
   Main PID: 144351 (openvpn)
     Status: "Initialization Sequence Completed"
      Tasks: 1 (limit: 4665)
     Memory: 1.8M
        CPU: 27ms
     CGroup: /system.slice/system-openvpn\x2dserver.slice/[email protected]
             └─144351 /usr/sbin/openvpn --status /run/openvpn-server/status-server.log --status-version 2 --suppress-timestamps --config server.conf

. . .

You have now completed the server-side configuration for OpenVPN. Next, you will configure your client machine and connect to the OpenVPN Server.

Step 11 — Creating the Client Configuration Infrastructure

Creating configuration files for OpenVPN clients can be somewhat involved, as every client must have its own config and each must align with the settings outlined in the server’s configuration file. Rather than writing a single configuration file that can only be used on one client, this step outlines a process for building a client configuration infrastructure which you can use to generate config files on-the-fly. You will first create a “base” configuration file then build a script which will allow you to generate unique client config files, certificates, and keys as needed.

Get started by creating a new directory where you will store client configuration files within the client-configs directory you created earlier:

mkdir -p ~/client-configs/files

Next, copy an example client configuration file into the client-configs directory to use as your base configuration:

cp /usr/share/doc/openvpn/examples/sample-config-files/client.conf ~/client-configs/base.conf

Open this new file using nano or your preferred text editor:

nano ~/client-configs/base.conf

Inside, locate the remote 指令。 This points the client to your OpenVPN server address — the public IP address of your OpenVPN server. If you decided to change the port that the OpenVPN server is listening on, you will also need to change 1194 to the port you selected:

. . .
# The hostname/IP and port of the server.
# You can have multiple remote entries
# to load balance between the servers.
remote your_server_ip 1194
. . .

Be sure that the protocol matches the value you are using in the server configuration:

proto udp

Next, uncomment the user およびgroup directives by removing the ; sign at the beginning of each line:

# Downgrade privileges after initialization (non-Windows only)
user nobody
group nogroup

Find the directives that set the ca , cert , and key 。 Comment out these directives since you will add the certs and keys within the file itself shortly:

# SSL/TLS parms.
# See the server config file for more
# description. It's best to use
# a separate .crt/.key file pair
# for each client. A single ca
# file can be used for all clients.
;ca ca.crt
;cert client.crt
;key client.key

Similarly, comment out the tls-auth directive, as you will add ta.key directly into the client configuration file (and the server is set up to use tls-crypt ):

# If a tls-auth key is used on the server
# then every client must also have the key.
;tls-auth ta.key 1

Mirror the cipher and auth settings that you set in the /etc/openvpn/server/server.conf ファイル：

cipher AES-256-GCM
auth SHA256

Next, add the key-direction directive somewhere in the file. You must set this to “1” for the VPN to function correctly on the client machine:

key-direction 1

Finally, add a few commented out lines to handle various methods that Linux based VPN clients will use for DNS resolution. You’ll add two similar, but separate sets of commented out lines. The first set is for clients that do not use systemd-resolved to manage DNS. These clients rely on the resolvconf utility to update DNS information for Linux clients.

; script-security 2
; up /etc/openvpn/update-resolv-conf
; down /etc/openvpn/update-resolv-conf

Now add another set of lines for clients that use systemd-resolved for DNS resolution:

; script-security 2
; up /etc/openvpn/update-systemd-resolved
; down /etc/openvpn/update-systemd-resolved
; down-pre
; dhcp-option DOMAIN-ROUTE .

終了したら、ファイルを保存して閉じます。

Later in Step 13 - Installing the Client Configuration step of this tutorial you will learn how to determine how DNS resolution works on Linux clients and which section to uncomment.

Next, you’ll create a script that will compile your base configuration with the relevant certificate, key, and encryption files and then place the generated configuration in the ~/client-configs/files ディレクトリ。 Open a new file called make_config.sh within the ~/client-configs ディレクトリ：

nano ~/client-configs/make_config.sh

Inside, add the following content:

#!/bin/bash
 
# First argument: Client identifier
 
KEY_DIR=~/client-configs/keys
OUTPUT_DIR=~/client-configs/files
BASE_CONFIG=~/client-configs/base.conf
 
cat ${BASE_CONFIG} \
    <(echo -e '<ca>') \
    ${KEY_DIR}/ca.crt \
    <(echo -e '</ca>\n<cert>') \
    ${KEY_DIR}/${1}.crt \
    <(echo -e '</cert>\n<key>') \
    ${KEY_DIR}/${1}.key \
    <(echo -e '</key>\n<tls-crypt>') \
    ${KEY_DIR}/ta.key \
    <(echo -e '</tls-crypt>') \
    > ${OUTPUT_DIR}/${1}.ovpn

終了したら、ファイルを保存して閉じます。

Before moving on, be sure to mark this file as executable by typing:

chmod 700 ~/client-configs/make_config.sh

This script will make a copy of the base.conf file you made, collect all the certificate and key files you’ve created for your client, extract their contents, append them to the copy of the base configuration file, and export all of this content into a new client configuration file. This means that, rather than having to manage the client’s configuration, certificate, and key files separately, all the required information is stored in one place. The benefit of using this method is that if you ever need to add a client in the future, you can run this script to quickly create a new config file and ensure that all the important information is stored in a single, easy-to-access location.

Please note that any time you add a new client, you will need to generate new keys and certificates for it before you can run this script and generate its configuration file. You will get some practice using this script in the next step.

Step 12 — Generating Client Configurations

If you followed along with the guide, you created a client certificate and key named client1.crt and client1.key , respectively, in Step 6. You can generate a config file for these credentials by moving into your ~/client-configs directory and running the script you made at the end of the previous step:

cd ~/client-configs
./make_config.sh client1

This will create a file named client1.ovpn in your ~/client-configs/files ディレクトリ：

ls ~/client-configs/files

Outputclient1.ovpn

You need to transfer this file to the device you plan to use as the client. For instance, this could be your local computer or a mobile device.

While the exact applications used to accomplish this transfer will depend on your device’s operating system and your personal preferences, a dependable and secure method is to use SFTP (SSH file transfer protocol) or SCP (Secure Copy) on the backend. This will transport your client’s VPN authentication files over an encrypted connection.

Here is an example SFTP command which you can run from your local computer (macOS or Linux). This will copy the client1.ovpn file you created in the last step to your home directory:

sftp sammy@openvpn_server_ip:client-configs/files/client1.ovpn ~/

Here are several tools and tutorials for securely transferring files from the OpenVPN server to a local computer:

• WinSCP
• How To Use SFTP to Securely Transfer Files with a Remote Server
• How To Use Filezilla to Transfer and Manage Files Securely on your VPS

Step 13 — Installing the Client Configuration

This section covers how to install a client VPN profile on Windows, macOS, Linux, iOS, and Android. None of these client instructions are dependent on one another, so feel free to skip to whichever is applicable to your device.

The OpenVPN connection will have the same name as whatever you called the .ovpn ファイル。 In regards to this tutorial, this means that the connection is named client1.ovpn , aligning with the first client file you generated.

Windows

Installing

Download the OpenVPN client application for Windows from OpenVPN’s Downloads page. Choose the appropriate installer version for your version of Windows.

注 :OpenVPN needs administrative privileges to install.

After installing OpenVPN, copy the .ovpn file to:

C:\Program Files\OpenVPN\config

When you launch OpenVPN, it will automatically locate the profile and make it available.

You must run OpenVPN as an administrator each time it’s used, even by administrative accounts. To do this without having to right-click and select Run as administrator every time you use the VPN, you must preset this from an administrative account. This also means that standard users will need to enter the administrator’s password to use OpenVPN. On the other hand, standard users can’t properly connect to the server unless the OpenVPN application on the client has admin rights, so the elevated privileges are necessary.

To set the OpenVPN application to always run as an administrator, right-click on its shortcut icon and go to Properties 。 At the bottom of the Compatibility tab, click the button to Change settings for all users 。 In the new window, check Run this program as an administrator 。

Connecting

Each time you launch the OpenVPN GUI, Windows will ask if you want to allow the program to make changes to your computer. Click Yes 。 Launching the OpenVPN client application only puts the applet in the system tray so that you can connect and disconnect the VPN as needed; it does not actually make the VPN connection.

Once OpenVPN is started, initiate a connection by going into the system tray applet and right-clicking on the OpenVPN applet icon. This opens the context menu. Select client1 at the top of the menu (that’s your client1.ovpn profile) and choose Connect 。

A status window will open showing the log output while the connection is established, and a message will show once the client is connected.

Disconnect from the VPN the same way:Go into the system tray applet, right-click the OpenVPN applet icon, select the client profile and click Disconnect 。

macOS

Installing

Tunnelblick is a free, open source OpenVPN client for macOS. You can download the latest disk image from the Tunnelblick Downloads page. Double-click the downloaded .dmg file and follow the prompts to install.

Towards the end of the installation process, Tunnelblick will ask if you have any configuration files. Answer I have configuration files and let Tunnelblick finish. Open a Finder window and double-click client1.ovpn 。 Tunnelblick will install the client profile. Administrative privileges are required.

Connecting

Launch Tunnelblick by double-clicking the Tunnelblick icon in the Applications フォルダ。 Once Tunnelblick has been launched, there will be a Tunnelblick icon in the menu bar at the top right of the screen for controlling connections. Click on the icon, and then the Connect client1 menu item to initiate the VPN connection. If you are using custom DNS settings with Tunnelblick, you may need check “Allow changes to manually-set network settings” in the advanced configuration dialog.

Linux

Installing

If you are using Linux, there are a variety of tools that you can use depending on your distribution. Your desktop environment or window manager might also include connection utilities.

The most universal way of connecting, however, is to just use the OpenVPN software.

On Ubuntu or Debian, you can install it just as you did on the server by typing:

sudo apt update
sudo apt install openvpn

On CentOS you can enable the EPEL repositories and then install it by typing:

sudo dnf install epel-release
sudo dnf install openvpn

Configuring Clients that use systemd-resolved

First determine if your system is using systemd-resolved to handle DNS resolution by checking the /etc/resolv.conf ファイル：

cat /etc/resolv.conf

Output# This file is managed by man:systemd-resolved(8). Do not edit.
. . .

nameserver 127.0.0.53
options edns0

If your system is configured to use systemd-resolved for DNS resolution, the IP address after the nameserver option will be 127.0.0.53 。 There should also be comments in the file like the output that is shown that explain how systemd-resolved is managing the file. If you have a different IP address than 127.0.0.53 then chances are your system is not using systemd-resolved and you can go to the next section on configuring Linux clients that have an update-resolv-conf script instead.

To support these clients, first install the openvpn-systemd-resolved パッケージ。 It provides scripts that will force systemd-resolved to use the VPN server for DNS resolution.

sudo apt install openvpn-systemd-resolved

One that package is installed, configure the client to use it, and to send all DNS queries over the VPN interface. Open the client’s VPN file:

nano client1.ovpn

Now uncomment the following lines that you added earlier:

script-security 2
up /etc/openvpn/update-systemd-resolved
down /etc/openvpn/update-systemd-resolved
down-pre
dhcp-option DOMAIN-ROUTE .

Configuring Clients that use update-resolv-conf

If your system is not using systemd-resolved to manage DNS, check to see if your distribution includes an /etc/openvpn/update-resolv-conf script instead:

ls /etc/openvpn

Outputupdate-resolv-conf

If your client includes the update-resolv-conf file, then edit the OpenVPN client configuration file that you transferred earlier:

nano client1.ovpn

Uncomment the three lines you added to adjust the DNS settings:

script-security 2
up /etc/openvpn/update-resolv-conf
down /etc/openvpn/update-resolv-conf

If you are using CentOS, change the group directive from nogroup to nobody to match the distribution’s available groups:

group nobody

Save and close the file.

Connecting

Now, you can connect to the VPN by just pointing the openvpn command to the client configuration file:

sudo openvpn --config client1.ovpn

This should connect you to your VPN.

注： If your client uses systemd-resolved to manage DNS, check the settings are applied correctly by running the systemd-resolve --status command like this:

systemd-resolve --status tun0

You should see output like the following:

OutputLink 22 (tun0)
. . .
         DNS Servers: 208.67.222.222
                      208.67.220.220
          DNS Domain: ~.

If you see the IP addresses of the DNS servers that you configured on the OpenVPN server, along with the ~. setting for DNS Domain in the output, then you have correctly configured your client to use the VPN server’s DNS resolver. You can also check that you are sending DNS queries over the VPN by using a site like DNS leak test.com.

iOS

Installing

From the iTunes App Store, search for and install OpenVPN Connect, the official iOS OpenVPN client application. To transfer your iOS client configuration onto the device, connect it directly to a computer.

The process of completing the transfer with iTunes is outlined here. Open iTunes on the computer and click on iPhone> apps 。 Scroll down to the bottom to the File Sharing section and click the OpenVPN app. The blank window to the right, OpenVPN Documents , is for sharing files. Drag the .ovpn file to the OpenVPN Documents window.

Now launch the OpenVPN app on the iPhone. You will receive a notification that a new profile is ready to import. Tap the green plus sign to import it.

Connecting

OpenVPN is now ready to use with the new profile. Start the connection by sliding the Connect button to the On position. Disconnect by sliding the same button to Off 。

注 :The VPN switch under Settings cannot be used to connect to the VPN. If you try, you will receive a notice to only connect using the OpenVPN app.

Android

Installing

Open the Google Play Store. Search for and install Android OpenVPN Connect, the official Android OpenVPN client application.

You can transfer the .ovpn profile by connecting the Android device to your computer by USB and copying the file over. Alternatively, if you have an SD card reader, you can remove the device’s SD card, copy the profile onto it and then insert the card back into the Android device.

Start the OpenVPN app and tap the FILE menu to import the profile.

Then navigate to the location of the saved profile (the screenshot uses /storage/emulated/0/openvpn ) and select your .ovpn ファイル。 Tap the IMPORT button to finish importing this profile.

Connecting Once the profile is added, you will see a screen like this:

To connect, tap the toggle button close to the profile you want to use. You’ll see real time stats of your connection and traffic being routed through your OpenVPN server:

To disconnect, just tap the toggle button on the top left once again. You will be prompted to confirm that you want to disconnect from your VPN.

Step 14 — Testing Your VPN Connection (Optional)

注： This method for testing your VPN connection will only work if you opted to route all your traffic through the VPN in Step 7 when you edited the server.conf file for OpenVPN.

Once everything is installed, a simple check confirms everything is working properly. Without having a VPN connection enabled, open a browser and go to DNSLeakTest.

The site will return the IP address assigned by your internet service provider and as you appear to the rest of the world. To check your DNS settings through the same website, click on Extended Test and it will tell you which DNS servers you are using.

Now connect the OpenVPN client to your Droplet’s VPN and refresh the browser. A completely different IP address (that of your VPN server) should now appear, and this is how you appear to the world. Again, DNSLeakTest’s Extended Test will check your DNS settings and confirm you are now using the DNS resolvers pushed by your VPN.

Step 15 — Revoking Client Certificates

Occasionally, you may need to revoke a client certificate to prevent further access to the OpenVPN server.

To do so, follow the example in the prerequisite tutorial on How to Set Up and Configure a Certificate Authority on Ubuntu 22.04 under the Revoking a Certificate セクション。

Once you have revoked a certificate for a client using those instructions, you’ll need to copy the generated crl.pem file to your OpenVPN server in the /etc/openvpn/server ディレクトリ：

sudo cp /tmp/crl.pem /etc/openvpn/server/

Next, open the OpenVPN server configuration file:

sudo nano /etc/openvpn/server/server.conf

At the bottom of the file, add the crl-verify option, which will instruct the OpenVPN server to check the certificate revocation list that you created each time a connection attempt is made:

crl-verify crl.pem

Save and close the file.

Finally, restart OpenVPN to implement the certificate revocation:

sudo systemctl restart [email protected]

The client should no longer be able to successfully connect to the server using the old credential.

To revoke additional clients, follow this process:

1. Revoke the certificate with the ./easyrsa revoke client_name コマンド
2. Generate a new CRL
3. Transfer the new crl.pem file to your OpenVPN server and copy it to the /etc/openvpn/server/ directory to overwrite the old list.
4. Restart the OpenVPN service.

You can use this process to revoke any certificates that you’ve previously issued for your server.