Step 1: Install OpenVPN

Let’s start by updating our apt cache and installing both openvpn and easy-rsa, which we’ll use to set up certificates.

$ sudo apt-get update $ sudo apt-get install openvpn easy-rsa
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Step 2: Set up the Certificate Authority

The OpenVPN server uses certificates to encrypt traffic between the server and various clients. Thus, we need to set up a certificate authority (CA) on the VPS to create and manage these certificates.

We can utilize the easy-rsa template by copying it to a new directory, and then entering that directory to move into the configuration.

$ make-cadir ~/openvpn-ca $ cd ~/openvpn-ca

We need to edit some of the variables that help decide how to create the certificates. Use nano—or another favorite editor—to open the file. We’ll be editing some variables toward the end of the file.

$ nano vars

Look for the section below—the easy-rsa template provides some default fields for these variables, but you should change them according to your needs. Make sure you also change the KEY_NAME variable as well. It’s not so important what you change these to, rather that you don’t leave them in the default state, or blank.

# These are the default values for fields # which will be placed in the certificate. # Don't leave any of these fields blank. export KEY_COUNTRY="US" export KEY_PROVINCE="CA" export KEY_CITY="SanFrancisco" export KEY_ORG="Fort-Funston" export KEY_EMAIL= class="hljs-string">"me@myhost.mydomain" export KEY_OU="MyOrganizationalUnit" # X509 Subject Field export KEY_NAME="EasyRSA"

After some tweaks:

# These are the default values for fields # which will be placed in the certificate. # Don't leave any of these fields blank. export KEY_COUNTRY="US" export KEY_PROVINCE="CA" export KEY_CITY="Tustin" export KEY_ORG="SSD Nodes" export KEY_EMAIL= class="hljs-string">"joel@example.com" export KEY_OU="Marketing" # X509 Subject Field export KEY_NAME="vpnserver"

Now, source the vars file you just edited. If there aren’t any errors, you’ll see the following output.

$ source vars NOTE: If you run ./clean-all, I will be doing a rm -rf on /home/user/openvpn-ca/keys

Now we can clean up the environment and then build up our CA.

$ ./clean-all $ ./build-ca

A new RSA key will be created, and you’ll be asked to confirm the details you entered into the vars file earlier. Just hit Enter to confirm.

Step 3: Create the server public/private keys

Next up, you need to create the server certificate and key pair. When you run the below command you can change [server] to the name of your choice. Later, you’ll need to reference this name. For the sake of this tutorial, we’re choosing with vpnserver.

Note: When prompted, do not enter a password.

Finally, you’ll be asked two questions about signing the certificate and committing it. Hit y and then Enterfor both, and you’ll be done.

$ ./build-key-server [server]

Next, you need to build Diffie-Hellman keys.

$ ./build-dh

Finally, you need to generate an HMAC signature to strengthen the certificate.

$ openvpn --genkey --secret keys/ta.key

Step 4: Create the client public/private keys

This process will create a single client key and certificate. If you have multiple users, you’ll want to create multiple pairs.

When running the below command, hit Enter to confirm the variables we set and then leave the password field blank.

$ source vars $ ./build-key client1

If you want to create password-protected credentials, use build-key-pass instead:

$ source vars $ ./build-key-pass client1

Step 5: Configure the OpenVPN server

First, you need to copy the keyfiles we created in ~/openvpn-ca into the /etc/openvpn directory. Note: change the vpnserver.crt and vpnserver.key files according to the [server] name you chose earlier.

$ cd ~/openvpn-ca/keys $ sudo cp ca.crt ca.key vpnserver.crt vpnserver.key ta.key dh2048.pem /etc/openvpn
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Now, extract a sample OpenVPN configuration to the default location.

$ gunzip -c /usr/share/doc/openvpn/examples/sample-config-files/server.conf.gz | sudo tee /etc/openvpn/server.conf

We now need to make some edits to the configuration file.

$ sudo nano /etc/openvpn/server.conf

First, let’s ensure that OpenVPN is looking for the right .crt and .key files.

Before:

ca ca.crt cert server.crt key server.key # This file should be kept secret
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After (change according to the [server] name you chose earlier):

ca ca.crt cert vpnserver.crt key vpnserver.key # This file should be kept secret
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Next, enforce identical HMAC between clients and the server.

Before:

;tls-auth ta.key 0 # This file is secret
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After:

tls-auth ta.key 0 # This file is secret key-direction 0
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Because we are going to use this VPN to route our traffic to the internet, we need to uncomment a few lines to help us establish DNS. You should also remove bypass-dhcp from the first line in question.

If you would prefer to use a DNS other than opendns, you should change the two lines that begin with push "dhcp-option.

Before:

# If enabled, this directive will configure # all clients to redirect their default # network gateway through the VPN, causing # all IP traffic such as web browsing and # and DNS lookups to go through the VPN # (The OpenVPN server machine may need to NAT # or bridge the TUN/TAP interface to the internet # in order for this to work properly). ;push "redirect-gateway def1 bypass-dhcp" # Certain Windows-specific network settings # can be pushed to clients, such as DNS # or WINS server addresses. CAVEAT: # http://openvpn.net/faq.html#dhcpcaveats # The addresses below refer to the public # DNS servers provided by opendns.com. ;push "dhcp-option DNS 208.67.222.222" ;push "dhcp-option DNS 208.67.220.220"
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After:

# If enabled, this directive will configure # all clients to redirect their default # network gateway through the VPN, causing # all IP traffic such as web browsing and # and DNS lookups to go through the VPN # (The OpenVPN server machine may need to NAT # or bridge the TUN/TAP interface to the internet # in order for this to work properly). push "redirect-gateway def1" # Certain Windows-specific network settings # can be pushed to clients, such as DNS # or WINS server addresses. CAVEAT: # http://openvpn.net/faq.html#dhcpcaveats # The addresses below refer to the public # DNS servers provided by opendns.com. push "dhcp-option DNS 208.67.222.222" push "dhcp-option DNS 208.67.220.220"
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Then we need to select the ciphers to use. Uncomment the AES cipher and change it to 256, and then add auth SHA512 at the bottom of the block.

Before:

# Select a cryptographic cipher. # This config item must be copied to # the client config file as well. ;cipher BF-CBC # Blowfish (default) ;cipher AES-128-CBC # AES ;cipher DES-EDE3-CBC # Triple-DES
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After:

# Select a cryptographic cipher. # This config item must be copied to # the client config file as well. ;cipher BF-CBC # Blowfish (default) cipher AES-256-CBC # AES ;cipher DES-EDE3-CBC # Triple-DES auth SHA512
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Finally, let’s have OpenVPN use a non-privileged user account instead of root, which isn’t particularly secure.

user openvpn group nogroup

You can now save and close this file in order to create that user:

$ sudo adduser --system --shell /usr/sbin/nologin --no-create-home openvpn

The OpenVPN server should now be set up!

Step 6: Start up the OpenVPN server

Before we configure our clients, let’s make sure the OpenVPN server is running as we hope it will.

Make sure to turn on TUN/TAP in the SSD Nodes dashboard.

$ sudo systemctl enable openvpn@server $ sudo systemctl start openvpn@server

You can double-check that OpenVPN is running with the systemctl status command:

$ sudo systemctl status openvpn@server

If you’re having problems getting OpenVPN to start, commenting out the LimitNPROC in /lib/systemd/system/openvpn@.service, as discovered in this Ask Ubuntu thread may be useful. You’ll then need to run sudo systemctl daemon-reload and then sudo systemctl start openvpn@server.

You will also need to set up iptables to properly direct traffic. First, look for the default interface.

$ sudo ip route | grep default default dev venet0 scope link
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The venet0 field is what we’re looking for. And then we set up iptables. In order to ensure this rule is persistent between reboots, isntall the iptables-persistent package, which will prompt you to save existing rules. Choose Yes and your rules will be persisted movign forward.

$ sudo iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o venet0 -j MASQUERADE $ sudo apt-get install iptables-persistent
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Step 7: Configure clients

Lastly, you need to create client configurations. You can store these in any folder you’d like—they don’t need to be kept secret—as long as it isn’t the /etc/openvpn folder. We’ll create a directory in home for this purpose.

$ cd ~ $ mkdir openvpn-clients cd openvpn-clients

Now, copy the sample client configuration into this new directory, and then open it in nano for editing.

$ cp /usr/share/doc/openvpn/examples/sample-config-files/client.conf ~/openvpn-clients/base.conf $ nano base.conf
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Look for the following block of lines. You’ll need to change the my-server-1 to the public IP address of this VPS. You can find this information in the SSD Nodes dashboard, or by typing in the ifconfig command and looking for the inet field that does not look like 127.0.0.x.

# The hostname/IP and port of the server. # You can have multiple remote entries # to load balance between the servers. remote my-server-1 1194 ;remote my-server-2 1194
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Next, uncomment the following two lines by removing the semicolon.

Before:

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

# Downgrade privileges after initialization (non-Windows only) user nobody group nogroup
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Because we’ll be adding keys and certificates directly into the .ovpn file, let’s comment out the following lines by adding semicolons to the beginning.

Before:

# 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
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After:

# 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
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Finally, jump to the bottom of the file and add the following lines. The first two mirror the cipher/auth options we added to the server.conf file earlier, and the third establishes that this files will be used to connect to the server, not the other way around.

We’re also adding three commented-out files that should be uncommented for Linux-based systems that use update-resolv-conf.

# Added lines via SSD Nodes tutorial cipher AES-256-CBC auth SHA512 key-direction 1 # script-security 2 # up /etc/openvpn/update-resolv-conf # down /etc/openvpn/update-resolv-conf
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Finally, you need to embed the keys and certificates into an .ovpn file using base.conf as a framework. Copy this entire command and execute it to embed the keys and create a final client1.ovpn file.

$ cat base.conf <(echo -e '<ca>') ~/openvpn-ca/keys/ca.crt <(echo -e '</ca>') <(echo -e '<cert>') ~/openvpn-ca/keys/client1.crt <(echo -e '</cert>n') <(echo -e '<key>') ~/openvpn-ca/keys/client1.key <(echo -e '</key>n') <(echo -e '<tls-auth>') ~/openvpn-ca/keys/ta.key <(echo -e '</tls-auth>') >> client1.ovpn
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This tutorial won’t cover client configurations in detail, but we’ll share one easy way to transfer the .ovpn file to your Linux or OS X client. This command will ssh into your VPS, and then use cat to write a new client1.ovpn file on your local machine.

$ ssh USER@SERVER-IP "cat ~/openvpn-clients/client1.ovpn" > client1.ovpn
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Once you configure your client, you should be able to connect to the VPN and access the wider internet through it. Congratulations!

分类: Linux

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