OpenVPN (Ubuntu 18.04)

Installation

Um die Installation anzuzeigen bitte aufklappen

sudo apt-get install -y openvpn easy-rsa 

Ordner zur Schlüsselerzeugung kopieren:

sudo cp -r /usr/share/easy-rsa /etc/openvpn/easy-rsa2 

Konfiguration

Um die allgemeine Konfiguration anzuzeigen bitte aufklappen

Schlüssel und Zertifikate generieren

Variablen anpassen

In das RSA-Verzeichnis wechseln:

cd /etc/openvpn/easy-rsa2/

Die Datei /etc/openvpn/easy-rsa2/vars kopieren

sudo cp vars.example vars
sudo vi vars

und folgende Zeilen einkommenieren und anpassen (nicht leer lassen):

#set_var EASYRSA_REQ_COUNTRY    "US"
#set_var EASYRSA_REQ_PROVINCE   "California"
#set_var EASYRSA_REQ_CITY       "San Francisco"
#set_var EASYRSA_REQ_ORG        "Copyleft Certificate Co"
#set_var EASYRSA_REQ_EMAIL      "me@example.net"
#set_var EASYRSA_REQ_OU         "My Organizational Unit"

...

#set_var EASYRSA_KEY_SIZE        2048

Certificate Authority (CA) erstellen

sudo ./easyrsa init-pki
sudo cp vars.example pki/vars
sudo vi pki/vars

Die Variablen EASYRSA_CA_EXPIRE und EASYRSA_CERT_EXPIRE auf gewünschte Werte setzen:

set_var EASYRSA_CA_EXPIRE	7300
set_var EASYRSA_CERT_EXPIRE	3650

Danach kann die CA erstellt werden:

sudo ./easyrsa build-ca nopass

Bei der Frage Common Name (eg: your user, host, or server name) [Easy-RSA CA]: einfach ENTER klicken.

Server Schlüssel erstellen

Mittels folgendem Befehl wird ein Server-Schlüssel und ein Zertifikatsantrag erstellt:

sudo ./easyrsa gen-req server nopass

Bei der Frage nach dem Common Name einfach den Standardwert server übernehmen.

Danach muss der Zertifikatsantrag von der CA unterschrieben werde:

sudo ./easyrsa sign-req server server

Diffie-Hellman-Schlüssel für den Austausch

sudo ./easyrsa gen-dh

Keyed-Hash Message Authentication Code

sudo mkdir /etc/openvpn/server/keys
cd /etc/openvpn/server/keys
sudo openvpn --genkey --secret ta.key

Client-Zertifikat und Schlüssel

Schlüssel und Zertifikatsantrag erstellen:

cd /etc/openvpn/easy-rsa2/
sudo ./easyrsa gen-req client1 nopass

Bei der Frage nach dem Common Name einfach den Standardwert übernehmen.

Der Zertifikatsantrag muss, wie beim Server, wieder von der CA unterschrieben werden:

sudo ./easyrsa sign-req client client1

Danach die Dateien in ein Verzeichnis pro Client kopieren und ein TAR-Archiv daraus erstellen:

sudo su
mkdir -p /etc/openvpn/easy-rsa2/client-configs/client1/keys 
chmod -R 700 /etc/openvpn/easy-rsa2/client-configs 

cp /etc/openvpn/easy-rsa2/pki/issued/client1.crt /etc/openvpn/easy-rsa2/client-configs/client1/keys/server.crt
cp /etc/openvpn/easy-rsa2/pki/private/client1.key /etc/openvpn/easy-rsa2/client-configs/client1/keys/server.key
cp /etc/openvpn/easy-rsa2/pki/ca.crt /etc/openvpn/easy-rsa2/client-configs/client1/keys
cp /etc/openvpn/server/keys/ta.key /etc/openvpn/easy-rsa2/client-configs/client1/keys

cd client-configs/client1/
tar -czf client1.tgz keys/*
exit

Auflistung aller Serverdateien

Die für die Serverkonfiguration benötigten Dateien liegen danach unter folgenden Verzeichnissen:

../easy-rsa2/pki/ca.crt
../easy-rsa2/pki/issued/server.crt
../easy-rsa2/pki/private/server.key
../easy-rsa2/pki/dh.pem

Kopieren der Files nach /etc/openvpn/server/keys/:

sudo cp /etc/openvpn/easy-rsa2/pki/ca.crt /etc/openvpn/server/keys/ca.crt
sudo cp /etc/openvpn/easy-rsa2/pki/issued/server.crt /etc/openvpn/server/keys/server.crt
sudo cp /etc/openvpn/easy-rsa2/pki/private/server.key /etc/openvpn/server/keys/server.key
sudo cp /etc/openvpn/easy-rsa2/pki/dh.pem /etc/openvpn/server/keys/dh2048.pem

Client Konfiguration

Um die Client-Konfiguration anzuzeigen bitte aufklappen

Beispiel einer client.conf-Konfigurationsdatei

##############################################
# Sample client-side OpenVPN 2.0 config file #
# for connecting to multi-client server.     #
#                                            #
# This configuration can be used by multiple #
# clients, however each client should have   #
# its own cert and key files.                #
#                                            #
# On Windows, you might want to rename this  #
# file so it has a .ovpn extension           #
##############################################

# Specify that we are a client and that we
# will be pulling certain config file directives
# from the server.
client

# Use the same setting as you are using on
# the server.
# On most systems, the VPN will not function
# unless you partially or fully disable
# the firewall for the TUN/TAP interface.
;dev tap
dev tun

# Are we connecting to a TCP or
# UDP server?  Use the same setting as
# on the server.
;proto tcp
proto udp

# The hostname/IP and port of the server.
# You can have multiple remote entries
# to load balance between the servers.
remote <ip or dns name> 10004

# Keep trying indefinitely to resolve the
# host name of the OpenVPN server.  Very useful
# on machines which are not permanently connected
# to the internet such as laptops.
resolv-retry infinite

# Most clients don't need to bind to
# a specific local port number.
nobind

# 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 ./keys_linux_server/ca.crt
cert ./keys_linux_server/server.crt
key ./keys_linux_server/server.key

tls-auth ./keys_linux_server/ta.key 1

# Verify server certificate by checking
# that the certicate has the nsCertType
# field set to "server".  This is an
# important precaution to protect against
# a potential attack discussed here:
#  http://openvpn.net/howto.html#mitm
#
# To use this feature, you will need to generate
# your server certificates with the nsCertType
# field set to "server".  The build-key-server
# script in the easy-rsa folder will do this.
remote-cert-tls server

# Select a cryptographic cipher.
# If the cipher option is used on the server
# then you must also specify it here.
cipher AES-256-CBC

# Enable compression on the VPN link.
# Don't enable this unless it is also
# enabled in the server config file.
comp-lzo

# Set log file verbosity.
verb 3

pull

auth-user-pass

Route hinzufügen

Wenn der OpenVPN-Server so konfiguriert wurde, dass das dahinterliegende Netzwerk erreicht werden kann, dann müssen die erreichbaren Rechner, in dem dahinterliegenden Netzwerk, die Route zurück zum Server kennen. Andernfalls schlägt die Verbindung fehl, weil die Pakete den Weg zurück nicht finden.

Falls möglich, sollte man die Route beim Router hinterlegen. Falls dies jedoch nicht möglich ist, muss bei jedem Rechner direkt eine Route hinterlegt werden.

Dazu in der Datei /etc/dhcpcd.exit-hook (Datei gegebenenfalls erstellen) folgende Zeile hinzufügen:

ip route add <network> via <openvpn server ip> metric 1

Beispiel:

ip route add 10.8.4.0/24 via 10.0.0.156 metric 1

Gesetzte Routen anzeigen lassen:

netstat -r

Für Raspbian siehe auch Route hinzufügen (Raspbian)

Masquerade hinzufügen

Der Client-Internetverkehr kann mittels folgender Zeile (in der server.conf) vollständig über den VPN-Server geleitet werden:

push "redirect-gateway def1 bypass-dhcp"

Damit der externe Netzverkehr funktioniert, muss in der Datei /etc/dhcpcd.enter-hook (auf dem VPN-Server - Datei gegebenenfalls erstellen) folgende Zeile hinzufügt werden:

iptables -t nat -A POSTROUTING -s 10.8.4.0/24 -o eth0 -j MASQUERADE

Für Raspbian siehe auch dhcpcd-run-hooks.

Client GUI

OpenVPN-GUI installieren (falls nicht vorinstalliert):

sudo apt-get install network-manager-openvpn network-manager-openvpn-gnome

Danach die Datei xxxxxx.ovpn mittels Gespeicherte VPN-Konfiguration importieren... hinzufügen.

Siehe auch https://torguard.net/knowledgebase.php?action=displayarticle&id=53

Server Konfiguration

Um die Server-Konfiguration anzuzeigen bitte aufklappen

IPV4-Weiterleitung aktivieren

Siehe dazu IPV4-Weiterleitung_aktivieren

Benutzer openvpn anlegen

Zur Erhöhung der Sicherheit wird der Server mit dem Benutzer openvpn ausgeführt.

Zum Anlegen eines systemspezifischen Benutzers siehe User Administration

server.conf-Konfigurationsdatei

sudo vi /etc/openvpn/server/server.conf

Beispiel einer server.conf-Konfigurationsdatei

(Basis zu finden unter /usr/share/doc/openvpn/examples/sample-config-files/server.conf.gz)

#################################################
# Sample OpenVPN 2.0 config file for            #
# multi-client server.                          #
#                                               #
# This file is for the server side              #
# of a many-clients <-> one-server              #
# OpenVPN configuration.                        #
#                                               #
# OpenVPN also supports                         #
# single-machine <-> single-machine             #
# configurations (See the Examples page         #
# on the web site for more info).               #
#                                               #
# This config should work on Windows            #
# or Linux/BSD systems.  Remember on            #
# Windows to quote pathnames and use            #
# double backslashes, e.g.:                     #
# "C:\\Program Files\\OpenVPN\\config\\foo.key" #
#                                               #
# Comments are preceded with '#' or ';'         #
#################################################

# Which local IP address should OpenVPN
# listen on? (optional)
local 10.0.0.156

# Which TCP/UDP port should OpenVPN listen on?
# If you want to run multiple OpenVPN instances
# on the same machine, use a different port
# number for each one.  You will need to
# open up this port on your firewall.
port 1194

# TCP or UDP server?
;proto tcp
proto udp

# "dev tun" will create a routed IP tunnel,
# "dev tap" will create an ethernet tunnel.
# Use "dev tap0" if you are ethernet bridging
# and have precreated a tap0 virtual interface
# and bridged it with your ethernet interface.
# If you want to control access policies
# over the VPN, you must create firewall
# rules for the the TUN/TAP interface.
# On non-Windows systems, you can give
# an explicit unit number, such as tun0.
# On Windows, use "dev-node" for this.
# On most systems, the VPN will not function
# unless you partially or fully disable
# the firewall for the TUN/TAP interface.
;dev tap
dev tun

# Windows needs the TAP-Win32 adapter name
# from the Network Connections panel if you
# have more than one.  On XP SP2 or higher,
# you may need to selectively disable the
# Windows firewall for the TAP adapter.
# Non-Windows systems usually don't need this.
;dev-node MyTap

# SSL/TLS root certificate (ca), certificate
# (cert), and private key (key).  Each client
# and the server must have their own cert and
# key file.  The server and all clients will
# use the same ca file.
#
# See the "easy-rsa" directory for a series
# of scripts for generating RSA certificates
# and private keys.  Remember to use
# a unique Common Name for the server
# and each of the client certificates.
#
# Any X509 key management system can be used.
# OpenVPN can also use a PKCS #12 formatted key file
# (see "pkcs12" directive in man page).
ca ./keys/ca.crt
cert ./keys/server.crt
key ./keys/server.key  # This file should be kept secret

# Diffie hellman parameters.
# Generate your own with:
#   openssl dhparam -out dh2048.pem 2048
dh ./keys/dh2048.pem

# Network topology
# Should be subnet (addressing via IP)
# unless Windows clients v2.0.9 and lower have to
# be supported (then net30, i.e. a /30 per client)
# Defaults to net30 (not recommended)
topology subnet

# Configure server mode and supply a VPN subnet
# for OpenVPN to draw client addresses from.
# The server will take 10.8.0.1 for itself,
# the rest will be made available to clients.
# Each client will be able to reach the server
# on 10.8.0.1. Comment this line out if you are
# ethernet bridging. See the man page for more info.
server 10.8.4.0 255.255.255.0

# Maintain a record of client <-> virtual IP address
# associations in this file.  If OpenVPN goes down or
# is restarted, reconnecting clients can be assigned
# the same virtual IP address from the pool that was
# previously assigned.
ifconfig-pool-persist /var/log/openvpn/ipp.txt

# Configure server mode for ethernet bridging.
# You must first use your OS's bridging capability
# to bridge the TAP interface with the ethernet
# NIC interface.  Then you must manually set the
# IP/netmask on the bridge interface, here we
# assume 10.8.0.4/255.255.255.0.  Finally we
# must set aside an IP range in this subnet
# (start=10.8.0.50 end=10.8.0.100) to allocate
# to connecting clients.  Leave this line commented
# out unless you are ethernet bridging.
;server-bridge 10.8.0.4 255.255.255.0 10.8.0.50 10.8.0.100

# Configure server mode for ethernet bridging
# using a DHCP-proxy, where clients talk
# to the OpenVPN server-side DHCP server
# to receive their IP address allocation
# and DNS server addresses.  You must first use
# your OS's bridging capability to bridge the TAP
# interface with the ethernet NIC interface.
# Note: this mode only works on clients (such as
# Windows), where the client-side TAP adapter is
# bound to a DHCP client.
;server-bridge

# Push routes to the client to allow it
# to reach other private subnets behind
# the server.  Remember that these
# private subnets will also need
# to know to route the OpenVPN client
# address pool (10.8.0.0/255.255.255.0)
# back to the OpenVPN server.
;push "route 192.168.10.0 255.255.255.0"
;push "route 192.168.20.0 255.255.255.0"
push "route 10.0.0.0 255.255.255.0"

# To assign specific IP addresses to specific
# clients or if a connecting client has a private
# subnet behind it that should also have VPN access,
# use the subdirectory "ccd" for client-specific
# configuration files (see man page for more info).

# EXAMPLE: Suppose the client
# having the certificate common name "Thelonious"
# also has a small subnet behind his connecting
# machine, such as 192.168.40.128/255.255.255.248.
# First, uncomment out these lines:
;client-config-dir ccd
;route 192.168.40.128 255.255.255.248
# Then create a file ccd/Thelonious with this line:
#   iroute 192.168.40.128 255.255.255.248
# This will allow Thelonious' private subnet to
# access the VPN.  This example will only work
# if you are routing, not bridging, i.e. you are
# using "dev tun" and "server" directives.

# EXAMPLE: Suppose you want to give
# Thelonious a fixed VPN IP address of 10.9.0.1.
# First uncomment out these lines:
;client-config-dir ccd
;route 10.9.0.0 255.255.255.252
# Then add this line to ccd/Thelonious:
#   ifconfig-push 10.9.0.1 10.9.0.2

client-config-dir ccd

# Suppose that you want to enable different
# firewall access policies for different groups
# of clients.  There are two methods:
# (1) Run multiple OpenVPN daemons, one for each
#     group, and firewall the TUN/TAP interface
#     for each group/daemon appropriately.
# (2) (Advanced) Create a script to dynamically
#     modify the firewall in response to access
#     from different clients.  See man
#     page for more info on learn-address script.
;learn-address ./script

# 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"
push "dhcp-option DNS 10.0.0.100"

# Uncomment this directive to allow different
# clients to be able to "see" each other.
# By default, clients will only see the server.
# To force clients to only see the server, you
# will also need to appropriately firewall the
# server's TUN/TAP interface.
;client-to-client

# Uncomment this directive if multiple clients
# might connect with the same certificate/key
# files or common names.  This is recommended
# only for testing purposes.  For production use,
# each client should have its own certificate/key
# pair.
#
# IF YOU HAVE NOT GENERATED INDIVIDUAL
# CERTIFICATE/KEY PAIRS FOR EACH CLIENT,
# EACH HAVING ITS OWN UNIQUE "COMMON NAME",
# UNCOMMENT THIS LINE OUT.
;duplicate-cn

# The keepalive directive causes ping-like
# messages to be sent back and forth over
# the link so that each side knows when
# the other side has gone down.
# Ping every 10 seconds, assume that remote
# peer is down if no ping received during
# a 120 second time period.
keepalive 10 120

# For extra security beyond that provided
# by SSL/TLS, create an "HMAC firewall"
# to help block DoS attacks and UDP port flooding.
#
# Generate with:
#   openvpn --genkey --secret ta.key
#
# The server and each client must have
# a copy of this key.
# The second parameter should be '0'
# on the server and '1' on the clients.
tls-auth ./keys/ta.key 0 # This file is secret

# Select a cryptographic cipher.
# This config item must be copied to
# the client config file as well.
# Note that v2.4 client/server will automatically
# negotiate AES-256-GCM in TLS mode.
# See also the ncp-cipher option in the manpage
cipher AES-256-CBC

# Enable compression on the VPN link and push the
# option to the client (v2.4+ only, for earlier
# versions see below)
;compress lz4-v2
;push "compress lz4-v2"

# For compression compatible with older clients use comp-lzo
# If you enable it here, you must also
# enable it in the client config file.
comp-lzo

# The maximum number of concurrently connected
# clients we want to allow.
;max-clients 100

# It's a good idea to reduce the OpenVPN
# daemon's privileges after initialization.
#
# You can uncomment this out on
# non-Windows systems.
user openvpn
group openvpn

# The persist options will try to avoid
# accessing certain resources on restart
# that may no longer be accessible because
# of the privilege downgrade.
persist-key
persist-tun

# Output a short status file showing
# current connections, truncated
# and rewritten every minute.
status /var/log/openvpn/openvpn-status.log

# By default, log messages will go to the syslog (or
# on Windows, if running as a service, they will go to
# the "\Program Files\OpenVPN\log" directory).
# Use log or log-append to override this default.
# "log" will truncate the log file on OpenVPN startup,
# while "log-append" will append to it.  Use one
# or the other (but not both).
;log         /var/log/openvpn/openvpn.log
log-append  /var/log/openvpn/openvpn.log

# Set the appropriate level of log
# file verbosity.
#
# 0 is silent, except for fatal errors
# 4 is reasonable for general usage
# 5 and 6 can help to debug connection problems
# 9 is extremely verbose
verb 3

# Silence repeating messages.  At most 20
# sequential messages of the same message
# category will be output to the log.
;mute 20

# Notify the client that when the server restarts so it
# can automatically reconnect.
explicit-exit-notify 1

# Configure script-security
# level 3 — Allow passwords to be passed to scripts via environmental variables (potentially unsafe).
script-security 3
auth-user-pass-verify checklogin.sh via-env

Script checklogin.sh

cd /etc/openvpn/server/
sudo vi checklogin.sh

#!/bin/bash
# zur Sicherheit

if [ "$username" == "" -o "$password" == "" ] ; then
  exit 1
fi

# Username und Passwort werden zusammengesetzt
USER_PASS="$username:$password"

# der Eintrag wird in der Datei users gesucht
cat ./users | grep $USER_PASS > /dev/null

# wenn grep den Eintrag gefunden hat, ist der Exitcode 0
exit $?

Besitzer ändern und ausführbar machen:

sudo chown openvpn:openvpn checklogin.sh
sudo chmod a+x checklogin.sh

Inhalt der Datei users

sudo vi users

Benutzer:Passwort
<user name>:<password>

sudo chown openvpn:openvpn users
sudo chmod 660 users

client config dir (ccd)

Mit einer Datei im client config dir-Verzeichnis kann man einem Client eine statische IP-Adresse zuordnen

Zuerst ein Verzeichnis anlegen (muss mit der Direktive client-config-dir übereinstimmen), wo alle Dateien abgelegt werden:

cd /etc/openvpn/server/
sudo mkdir ccd

Danach eine Datei mit der Angabe Common Name beim Benutzerschlüssel anlegen:

sudo vi ccd/<common name>

Und folgenden Inhalt eintragen:

ifconfig-push <ip address> <net mask>

z.B.

ifconfig-push 10.8.4.8 255.255.255.0

Service starten

sudo systemctl start openvpn-server@server

Automatisch bei Systemstart:

sudo systemctl enable openvpn-server@server

Auf Fehler prüfen

sudo systemctl status openvpn-server@server.service

sudo tail -1000 /var/log/openvpn/openvpn.log

Zertifikate überprüfen und erneuern

Überprüfen

sudo openssl x509 -noout -text -in /etc/openvpn/server/keys/server.crt

Gültigkeitsdauer des Zertifikats in der Ausgabe:

        Validity
            Not Before: Mar 15 15:08:16 2020 GMT
            Not After : Feb 28 15:08:16 2023 GMT

Erneuern der CA-Zertifikate

cd /etc/openvpn/easy-rsa2/pki
mv ca.crt ca_old.crt
openssl x509 -in ca_old.crt -days 7300 -out ca.crt -signkey private/ca.key

Erneuern der Server-Zertifikate

cd /etc/openvpn/easy-rsa2/
sudo ./easyrsa renew server nopass
sudo cp /etc/openvpn/easy-rsa2/pki/issued/server.crt /etc/openvpn/server/keys/server.crt
sudo cp /etc/openvpn/easy-rsa2/pki/private/server.key /etc/openvpn/server/keys/server.key
sudo systemctl restart openvpn-server@server.service

Links

https://www.digitalocean.com/community/tutorials/how-to-set-up-an-openvpn-server-on-debian-10

https://www.codeflow.site/de/article/how-to-set-up-an-openvpn-server-on-ubuntu-18-04

https://wiki.ubuntuusers.de/OpenVPN/

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