VPN Sous Debian

Nous allons apprendre à mettre en place un serveur VPN en utilisant openvpn sous debian.

Pour la réalisation de notre TP, nous allons suivre les étapes suivantes.

  1. La réalisation des prérequis
  2. La génération des clés avec la PKI
  3. La configuration du Serveur
  4. La configuration du client

 

Prérequis

Pour notre TP nous aurons besoin de 2 machines une qui vont jouer le rôle de serveur et de client. Commencez par renommer la machine serveur en srv-vpn et la cliente en client. Vous pouvez suivre notre tutoriel sur comment renommer une machine Linux.

Le serveur et le client renommé, rassurez-vous que les 2 machines sont sur le même réseau et que la communication passe entre elles (faite un ping).Vous pouvez suivrez notre tuto sur la modification d’adresse IP.

Rassurez-vous que chaque machine possède 2 cartes réseau. Une connecté au NAT et l’autre a un réseau host (avec DHCP activé).

Si l’étape suivante a été effectuée correctement, en tapant la commande

  •   » hostname  » vous devez avoir le résultat suivant :

sur le serveur :

joel@srv-vpn:~$ hostname
srv-vpn
joel@srv-vpn:~$

sur le client

joel@client:~$ hostname
client
joel@client:~$
  •  » ip a » vous devez avoir un résultat similaire sur le serveur et le client :

    1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
        link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
        inet 127.0.0.1/8 scope host lo
           valid_lft forever preferred_lft forever
        inet6 ::1/128 scope host
           valid_lft forever preferred_lft forever
    2: enp0s3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
        link/ether 08:00:27:74:9d:cd brd ff:ff:ff:ff:ff:ff
        inet 10.0.2.15/24 brd 10.0.2.255 scope global enp0s3
           valid_lft forever preferred_lft forever
        inet6 fe80::a00:27ff:fe74:9dcd/64 scope link
           valid_lft forever preferred_lft forever
    3: enp0s8: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
        link/ether 08:00:27:e2:d8:41 brd ff:ff:ff:ff:ff:ff
        inet 192.168.56.101/24 brd 192.168.56.255 scope global enp0s8
           valid_lft forever preferred_lft forever
        inet6 fe80::a00:27ff:fee2:d841/64 scope link
           valid_lft forever preferred_lft forever
    joel@srv-vpn:~$

    Les ips seront bien sûr différentes. Mais nous pouvons constater que nous avons 2 cartes réseau par machine.

Installer les paquets openvpn sur les deux machines (srv-vpn et client-vpn)

sudo apt update  && sudo apt install openvpn

 

Génération des clés avec la PKI

Cette étape se déroule entièrement sur le serveur :

Connectez-vous au serveur srv-vpn et ouvrez une invite de commande.  Copier les fichiers de configuration de easy-rsa. Ils sont livrés avec open-vpn lors de son installation et ils contiennent notre PKI. Nous allons les utiliser pour générer nos certificats.

Copier le contenu du répertoire easy-rsa dans votre répertoire courant

sudo cp -r   /usr/share/easy-rsa   /home/votre_nom_utilisateur/easy-rsa

Ensuite on se donne les droits sur l’ensemble des fichiers du dossier en tapant la commande suivante :

joel@srv-vpn:~$ sudo chown -R $USER:$USER easy-rsa
joel@srv-vpn:~$

Placez-vous dans le répertoire ou vous avez copié easy-rsa

cd   /home/votre_nom_utilisateur/easy-rsa

Éditer le fichier « vars » et modifier les lignes suivantes :

sudo nano vars

Modifier les lignes suivantes :

KEY_COUNTRY="FR"
KEY_PROVINCE="ALS"
KEY_CITY="SaltLakeCity"
KEY_ORG="Atomit"
KEY_EMAIL="toto@atomit.fr"

On donne les droits d’exécution au fichier vars et on charge les variables:

chmod  +x vars
source  ./vars

vous devez avoir ceux-ci :

joel@srv-vpn:~/easy-rsa$ ls
build-ca          build-key-server  list-crl           sign-req
build-dh          build-req         openssl-0.9.6.cnf  vars
build-inter       build-req-pass    openssl-0.9.8.cnf  whichopensslcnf
build-key         clean-all         openssl-1.0.0.cnf
build-key-pass    inherit-inter     pkitool
build-key-pkcs12  keys              revoke-full
joel@srv-vpn:~/easy-rsa$ chmod +x vars
joel@srv-vpn:~/easy-rsa$ source ./vars
**************************************************************
  No /home/joel/easy-rsa/openssl.cnf file could be found
  Further invocations will fail
**************************************************************
NOTE: If you run ./clean-all, I will be doing a rm -rf on /home/joel/easy-rsa/keys
joel@srv-vpn:~/easy-rsa$

Nettoyer le dossier où seront générées les clés avec la commande clean-all

joel@srv-vpn:~/easy-rsa$ ./clean-all
joel@srv-vpn:~/easy-rsa$

Générer le certificat de l’autorité de certification avec./build-ca :

  1. Si vous avez une erreur dans mon cas l’erreur suivante :
    joel@srv-vpn:~/easy-rsa$ ./build-ca
    grep: /home/joel/easy-rsa/openssl.cnf: Aucun fichier ou dossier de ce type
    pkitool: KEY_CONFIG (set by the ./vars script) is pointing to the wrong
    version of openssl.cnf: /home/joel/easy-rsa/openssl.cnf
    The correct version should have a comment that says: easy-rsa version 2.x
    joel@srv-vpn:~/easy-rsa$

    Cela veut dire que vous n’avez pas configuré le fichier vars ou que vous n’avez pas chargé les sources en fessant « source vars » si vous l’avez fait et que le problème persiste vous pouvez le ressoudre en créant un lien symbolique vers le fichier openssl-1.0.0.cnf et le nommer openssl.cnf.

    joel@srv-vpn:~/easy-rsa$ ln -s openssl-1.0.0.cnf openssl.cnf
    joel@srv-vpn:~/easy-rsa$ ls
    build-ca          build-key-server  list-crl           revoke-full
    build-dh          build-req         openssl-0.9.6.cnf  sign-req
    build-inter       build-req-pass    openssl-0.9.8.cnf  vars
    build-key         clean-all         openssl-1.0.0.cnf  whichopensslcnf
    build-key-pass    inherit-inter     openssl.cnf
    build-key-pkcs12  keys              pkitool

    Ensuite vous pouvez continuer

  2. Si vous n’avez pas d’erreur, vous pouvez continuer

Vu que vous avez déjà édité le fichier de variable vous devez juste appuyer sur entrée pour répondre à chaque question, la valeur par défaut (les valeurs que vous avez enregistrées dans le fichier de vars seront utilisé)

joel@srv-vpn:~/easy-rsa$ ./build-ca
Generating a 2048 bit RSA private key
......................................................................................+++
.............................+++
writing new private key to 'ca.key'
-----
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [FR]:
State or Province Name (full name) [ALS]:
Locality Name (eg, city) [Strasbourg]:
Organization Name (eg, company) [ATOMIT]:
Organizational Unit Name (eg, section) [ATOMIT]:
Common Name (eg, your name or your server's hostname) [ATOMIT CA]:
Name [EasyRSA]:
Email Address [email@atomit.fr]:
joel@srv-vpn:~/easy-rsa$

Une fois les clés de votre CA générer nous allons générer le paramètre diffie-hellman qui sert à sécuriser les 1ers échange lors de la communication (./build-dh)  entre le serveur et le client

joel@srv-vpn:~/easy-rsa$ ./build-dh
Generating DH parameters, 2048 bit long safe prime, generator 2
This is going to take a long time
...........................................................+................+...................................................................................

joel@srv-vpn:~/easy-rsa$

La génération des clés peut prendre plus ou moins du temps en fonction des ressources de votre machine.  Une fois la génération terminée vous pouvez générer les clés pour votre serveur (./build-key-server).

joel@srv-vpn:~/easy-rsa$ ./build-key-server srv-vpn
Generating a 2048 bit RSA private key
....................................+++
.........................................................................+++
writing new private key to 'srv-vpn.key'
-----
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [FR]:
State or Province Name (full name) [ALS]:
Locality Name (eg, city) [Strasbourg]:
Organization Name (eg, company) [ATOMIT]:
Organizational Unit Name (eg, section) [ATOMIT]:
Common Name (eg, your name or your server's hostname) [srv-vpn]:
Name [EasyRSA]:
Email Address [email@atomit.fr]:

Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:
An optional company name []:
Using configuration from /home/joel/easy-rsa/openssl.cnf
Can't open /home/joel/easy-rsa/keys/index.txt.attr for reading, No such file or directory
140106726114560:error:02001002:system library:fopen:No such file or directory:../crypto/bio/bss_file.c:74:fopen('/home/joel/easy-rsa/keys/index.txt.attr','r')
140106726114560:error:2006D080:BIO routines:BIO_new_file:no such file:../crypto/bio/bss_file.c:81:
Check that the request matches the signature
Signature ok
The Subject's Distinguished Name is as follows
countryName           :PRINTABLE:'FR'
stateOrProvinceName   :PRINTABLE:'ALS'
localityName          :PRINTABLE:'Strasbourg'
organizationName      :PRINTABLE:'ATOMIT'
organizationalUnitName:PRINTABLE:'ATOMIT'
commonName            :PRINTABLE:'srv-vpn'
name                  :PRINTABLE:'EasyRSA'
emailAddress          :IA5STRING:'email@atomit.fr'
Certificate is to be certified until Nov 13 10:19:32 2027 GMT (3650 days)
Sign the certificate? [y/n]:Y


1 out of 1 certificate requests certified, commit? [y/n]Y
Write out database with 1 new entries
Data Base Updated
joel@srv-vpn:~/easy-rsa$

Tous comme précédemment vous devez juste appuyer sur entrée et répondre Y aux deux questions à la fin. N’indiquer pas de mot de passe lorsqu’il vous le demande le challenge password appuyé juste sur entrée.

On générer ensuite les clés du client avec la commande (./build-key)

joel@srv-vpn:~/easy-rsa$ ./build-key client
Generating a 2048 bit RSA private key
..............................................................+++
....+++
writing new private key to 'client.key'
-----
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [FR]:
State or Province Name (full name) [ALS]:
Locality Name (eg, city) [Strasbourg]:
Organization Name (eg, company) [ATOMIT]:
Organizational Unit Name (eg, section) [ATOMIT]:
Common Name (eg, your name or your server's hostname) [client]:
Name [EasyRSA]:
Email Address [email@atomit.fr]:

Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:
An optional company name []:
Using configuration from /home/joel/easy-rsa/openssl.cnf
Check that the request matches the signature
Signature ok
The Subject's Distinguished Name is as follows
countryName           :PRINTABLE:'FR'
stateOrProvinceName   :PRINTABLE:'ALS'
localityName          :PRINTABLE:'Strasbourg'
organizationName      :PRINTABLE:'ATOMIT'
organizationalUnitName:PRINTABLE:'ATOMIT'
commonName            :PRINTABLE:'client'
name                  :PRINTABLE:'EasyRSA'
emailAddress          :IA5STRING:'email@atomit.fr'
Certificate is to be certified until Nov 13 10:24:44 2027 GMT (3650 days)
Sign the certificate? [y/n]:Y


1 out of 1 certificate requests certified, commit? [y/n]Y
Write out database with 1 new entries
Data Base Updated
joel@srv-vpn:~/easy-rsa$

Tous comme précédemment vous devez juste appuyer sur entrée et répondre Y aux deux questions a la fin. N’indiquer pas de mot de passe lorsqu’il vous le demande le challenge password appuyé juste sur entrée. Pour être certain que l’étape s’est bien déroulée, vous devez lister le contenu du répertoire keys :

joel@srv-vpn:~/easy-rsa$ ls keys
01.pem  ca.key      client.key  index.txt.attr      serial       srv-vpn.csr
02.pem  client.crt  dh2048.pem  index.txt.attr.old  serial.old   srv-vpn.key
ca.crt  client.csr  index.txt   index.txt.old       srv-vpn.crt
joel@srv-vpn:~/easy-rsa$

Vous devez absolument avoir les fichiers suivant :  dh2048.pem, srv-vpn.key, srv-vpn.crt, ca.crt,  client.key, client.crt )

Copier les fichiers suivants dans le répertoire de configuration de openvpn sur le serveur :

sudo cp keys/dh2048.pem keys/srv-vpn.crt keys/srv-vpn.key keys/ca.crt /etc/openvpn/server/

 

Configuration du Serveur

Cette étape se déroule elle aussi entièrement sur le serveur.

Connecté vous sur le serveur openvpn (srv-vpn). Lors de l’installation de openvn il vient avec des fichiers de configuration par défaut pour le serveur vous devez juste copier ce fichier avec la ligne de commande suivante :

sudo sh -c "zcat /usr/share/doc/openvpn/examples/sample-config-files/server.conf.gz  > /etc/openvpn/server.conf"

Ensuite nous allons le modifier :

joel@srv-vpn:~/easy-rsa$ nano /etc/openvpn/server.conf

Vous devez juste modifier les lignes suivantes :

ca /etc/openvpn/server/ca.crt
cert /etc/openvpn/server/srv-vpn.crt
key /etc/openvpn/server/srv-vpn.key

dh /etc/openvpn/server/dh2048.pem

push "redirect-gateway def1 bypass-dhcp"

push "dhcp-option DNS 208.67.222.222"
push "dhcp-option DNS 208.67.220.220"

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

Vous pouvez remplacer la 1er ip des serveurs open-dns (208.67.222.222 , 208.67.220.220) par l’ip de votre serveur DNS (celui du serveur)  ou alors remplacer les 2.  Pour trouver l’ip de votre serveur DNS vous pouvez vérifier l’ip envoyé par DHCP dans le fichier resolv.conf

joel@srv-vpn:~/easy-rsa$ cat /etc/resolv.conf
domain esi-supinfo.com
search esi-supinfo.com
nameserver 10.0.2.3
joel@srv-vpn:~/easy-rsa$

Dans le fichier de configuration server.conf remplacer l’ip  208.67.222.222 par 10.0.2.3. Vous devez avoir ceux-ci au final :

#################################################
# 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 a.b.c.d

# 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 /etc/openvpn/server/ca.crt
cert /etc/openvpn/server/srv-vpn.crt
key /etc/openvpn/server/srv-vpn.key  # This file should be kept secret

# Diffie hellman parameters.
# Generate your own with:
#   openssl dhparam -out dh2048.pem 2048
dh /etc/openvpn/server/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 10.8.0.0 255.255.255.0

# 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 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"

# 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

# 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 10.0.2.3"
push "dhcp-option DNS 208.67.220.220"

# 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 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 2.4 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 (2.4+ 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 nobody
;group nogroup

# 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 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         openvpn.log
;log-append  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

Nous allons maintenant tester les configurations de notre fichier de conf. Nous allons commencer par stopper le service openvpn :

joel@srv-vpn:~/easy-rsa$ sudo systemctl stop openvpn

Tester avec la commande suivante :

joel@srv-vpn:~/easy-rsa$ sudo openvpn /etc/openvpn/server.conf
Wed Nov 15 12:00:36 2017 OpenVPN 2.4.0 x86_64-pc-linux-gnu [SSL (OpenSSL)] [LZO] [LZ4] [EPOLL] [PKCS11] [MH/PKTINFO] [AEAD] built on Jul 18 2017
Wed Nov 15 12:00:36 2017 library versions: OpenSSL 1.0.2l  25 May 2017, LZO 2.08
Wed Nov 15 12:00:36 2017 Diffie-Hellman initialized with 2048 bit key
Wed Nov 15 12:00:36 2017 ROUTE_GATEWAY 10.0.2.2/255.255.255.0 IFACE=enp0s3 HWADDR=08:00:27:74:9d:cd
Wed Nov 15 12:00:36 2017 TUN/TAP device tun0 opened
Wed Nov 15 12:00:36 2017 TUN/TAP TX queue length set to 100
Wed Nov 15 12:00:36 2017 do_ifconfig, tt->did_ifconfig_ipv6_setup=0
Wed Nov 15 12:00:36 2017 /sbin/ip link set dev tun0 up mtu 1500
Wed Nov 15 12:00:36 2017 /sbin/ip addr add dev tun0 local 10.8.0.1 peer 10.8.0.2
Wed Nov 15 12:00:36 2017 /sbin/ip route add 10.8.0.0/24 via 10.8.0.2
Wed Nov 15 12:00:36 2017 Could not determine IPv4/IPv6 protocol. Using AF_INET
Wed Nov 15 12:00:36 2017 Socket Buffers: R=[212992->212992] S=[212992->212992]
Wed Nov 15 12:00:36 2017 UDPv4 link local (bound): [AF_INET][undef]:1194
Wed Nov 15 12:00:36 2017 UDPv4 link remote: [AF_UNSPEC]
Wed Nov 15 12:00:36 2017 MULTI: multi_init called, r=256 v=256
Wed Nov 15 12:00:36 2017 IFCONFIG POOL: base=10.8.0.4 size=62, ipv6=0
Wed Nov 15 12:00:36 2017 IFCONFIG POOL LIST
Wed Nov 15 12:00:36 2017 Initialization Sequence Completed

Vous devez obtenir un résultat similaire au mien. Si vous ouvrez un 2ie terminal sur votre serveur en parallèle et que vous tapez   » ip a » vous verrez qu’une nouvelle carte réseau nommé tun0 à apparue.

joel@srv-vpn:~$ ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: enp0s3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 08:00:27:74:9d:cd brd ff:ff:ff:ff:ff:ff
    inet 10.0.2.15/24 brd 10.0.2.255 scope global enp0s3
       valid_lft forever preferred_lft forever
    inet6 fe80::a00:27ff:fe74:9dcd/64 scope link
       valid_lft forever preferred_lft forever
3: enp0s8: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 08:00:27:e2:d8:41 brd ff:ff:ff:ff:ff:ff
    inet 192.168.56.101/24 brd 192.168.56.255 scope global enp0s8
       valid_lft forever preferred_lft forever
    inet6 fe80::a00:27ff:fee2:d841/64 scope link
       valid_lft forever preferred_lft forever
5: tun0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN group default qlen 100
    link/none
    inet 10.8.0.1 peer 10.8.0.2/32 scope global tun0
       valid_lft forever preferred_lft forever
    inet6 fe80::c217:a6d3:1e15:8b9d/64 scope link flags 800
       valid_lft forever preferred_lft forever
joel@srv-vpn:~$

Ensuite vous pouvez lancer le service openvpn et le laisser tourner :

joel@srv-vpn:~/easy-rsa$ sudo systemctl start openvpn
joel@srv-vpn:~/easy-rsa$

Nous allons activer le routage des paquets ip. Afin que les paquets provenant des machines connectées en vpn puissent être routés.

Tester si l’IP forwarding est activé avec la commande :

joel@srv-vpn:~/easy-rsa$ sudo sysctl net.ipv4.ip_forward
[sudo] Mot de passe de joel : 
net.ipv4.ip_forward = 0
joel@srv-vpn:~/easy-rsa$

La commande retourne 0 donc il n’est pas activé nous allons donc l’activer de manier permanente en modifiant le fichier sysctl.conf:

nano /etc/sysctl.conf

Modifier juste la ligne suivante en changeant la valeur 0 à 1 et en décommettant cette ligne dans le fichier de conf. Vous devez avoir ces lignes ci :

# Uncomment the next line to enable packet forwarding for IPv4
net.ipv4.ip_forward=1

Ensuite l’on ajoute des règles Iptables pour le filtrage des paquets issue du réseau VPN.

joel@srv-vpn:~/easy-rsa$ sudo iptables -t filter -P FORWARD ACCEPT
joel@srv-vpn:~/easy-rsa$ sudo iptables -t filter -A INPUT -p udp --dport 1194 -j ACCEPT
joel@srv-vpn:~/easy-rsa$ sudo iptables -t nat -A POSTROUTING -o enp0s8 -j MASQUERADE
joel@srv-vpn:~/easy-rsa$ sudo iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o eth0 -j MASQUERADE

Dans notre cas nos clients sont connectés au serveur VPN via la carte réseau enp0s8 car et l’autre carte réseau est celle qui nous fournit internet sur le serveur VPN à internet. Si dans votre cas les 2 cartes sont identiques, mettez le nom de la carte réseau que vous avez. N’oubliez surtout pas d’enregistrer vos configurations iptables sinon elles disparaîtront après le reboot.

joel@srv-vpn:~/easy-rsa$ sudo sh -c "iptables-save > /etc/iptables.rules"
joel@srv-vpn:~/easy-rsa$

 

Configuration du client

Cette étape se déroule entièrement sur le client. Nous allons copier les clés du client que nous avons précédemment généré sur le serveur à l’étape de génération des clés ainsi que le fichier de configuration par défaut du client

sudo scp  joel@ip_du_serveur:/home/nom_utilisateur/easy-rsa/keys/client.key  /etc/openvpn/client/
sudo scp  joel@ip_du_serveur:/home/nom_utilisateur/easy-rsa/keys/client.crt  /etc/openvpn/client/
sudo scp  joel@ip_du_serveur:/home/nom_utilisateur/easy-rsa/keys/ca.crt  /etc/openvpn/client/
sudo cp /usr/share/doc/openvpn/examples/sample-config-files/client.conf   /etc/openvpn/

nous allons éditer le fichier de configuration et changer les chemins d’accès aux clés

nano /etc/openvpn/client.conf

Éditez le et modifier les lignes suivantes :

remote ip_du_serveur1194
;remote my-server-2 1194

ca /etc/openvpn/client/ca.crt
cert /etc/openvpn/client/client.crt
key /etc/openvpn/client/client.key

#tls-auth ta.key 1

redirect-gateway def1

Au final vous devez avoir ceux-ci dans le fichier client.conf

##############################################
# 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

# Windows needs the TAP-Win32 adapter name
# from the Network Connections panel
# if you have more than one.  On XP SP2,
# you may need to disable the firewall
# for the TAP adapter.
;dev-node MyTap

# 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 192.168.56.101 1194
;remote my-server-2 1194

# Choose a random host from the remote
# list for load-balancing.  Otherwise
# try hosts in the order specified.
;remote-random

# 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

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

# Try to preserve some state across restarts.
persist-key
persist-tun

# If you are connecting through an
# HTTP proxy to reach the actual OpenVPN
# server, put the proxy server/IP and
# port number here.  See the man page
# if your proxy server requires
# authentication.
;http-proxy-retry # retry on connection failures
;http-proxy [proxy server] [proxy port #]

# Wireless networks often produce a lot
# of duplicate packets.  Set this flag
# to silence duplicate packet warnings.
;mute-replay-warnings

# 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 /etc/openvpn/client/ca.crt
cert /etc/openvpn/client/client.crt
key /etc/openvpn/client/client.key

# Verify server certificate by checking that the
# certicate has the correct key usage set.
# 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 keyUsage set to
#   digitalSignature, keyEncipherment
# and the extendedKeyUsage to
#   serverAuth
# EasyRSA can do this for you.
remote-cert-tls server

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

# Select a cryptographic cipher.
# If the cipher option is used on the server
# then you must also specify it here.
# Note that 2.4 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.
# Don't enable this unless it is also
# enabled in the server config file.
#comp-lzo

# Set log file verbosity.
verb 3

# Silence repeating messages
;mute 20

redirect-gateway def1

 

pour tester si tous est OK, sur le client lancer la commande : sudo openvpn  /etc/openvpn/client.conf

vous devez obtenir un résultat similaire au mien avec à la fin Initialization Sequence Completed.

si se n’est pas le cas, aller sur le serveur et lancer la commande (sudo openvpn  /etc/openvpn/server.conf ).

revenez sur le client:  stoppez et relancez la commande précédente. Vous devez obtenir un résultat similaire :

joel@debian:~$ sudo openvpn  /etc/openvpn/client.conf
Wed Nov 15 14:18:24 2017 OpenVPN 2.4.0 x86_64-pc-linux-gnu [SSL (OpenSSL)] [LZO] [LZ4] [EPOLL] [PKCS11] [MH/PKTINFO] [AEAD] built on Jul 18 2017
Wed Nov 15 14:18:24 2017 library versions: OpenSSL 1.0.2l  25 May 2017, LZO 2.08
Wed Nov 15 14:18:24 2017 TCP/UDP: Preserving recently used remote address: [AF_INET]192.168.56.101:1194
Wed Nov 15 14:18:24 2017 Socket Buffers: R=[212992->212992] S=[212992->212992]
Wed Nov 15 14:18:24 2017 UDP link local: (not bound)
Wed Nov 15 14:18:24 2017 UDP link remote: [AF_INET]192.168.56.101:1194
Wed Nov 15 14:18:24 2017 TLS: Initial packet from [AF_INET]192.168.56.101:1194, sid=35ef46d3 186351f9
Wed Nov 15 14:18:24 2017 VERIFY OK: depth=1, C=FR, ST=ALS, L=Strasbourg, O=ATOMIT, OU=ATOMIT, CN=ATOMIT CA, name=EasyRSA, emailAddress=email@atomit.fr
Wed Nov 15 14:18:24 2017 Validating certificate key usage
Wed Nov 15 14:18:24 2017 ++ Certificate has key usage  00a0, expects 00a0
Wed Nov 15 14:18:24 2017 VERIFY KU OK
Wed Nov 15 14:18:24 2017 Validating certificate extended key usage
Wed Nov 15 14:18:24 2017 ++ Certificate has EKU (str) TLS Web Server Authentication, expects TLS Web Server Authentication
Wed Nov 15 14:18:24 2017 VERIFY EKU OK
Wed Nov 15 14:18:24 2017 VERIFY OK: depth=0, C=FR, ST=ALS, L=Strasbourg, O=ATOMIT, OU=ATOMIT, CN=srv-vpn, name=EasyRSA, emailAddress=email@atomit.fr
Wed Nov 15 14:18:24 2017 Control Channel: TLSv1.2, cipher TLSv1/SSLv3 ECDHE-RSA-AES256-GCM-SHA384, 2048 bit RSA
Wed Nov 15 14:18:24 2017 [srv-vpn] Peer Connection Initiated with [AF_INET]192.168.56.101:1194
Wed Nov 15 14:18:25 2017 SENT CONTROL [srv-vpn]: 'PUSH_REQUEST' (status=1)
Wed Nov 15 14:18:25 2017 PUSH: Received control message: 'PUSH_REPLY,redirect-gateway def1 bypass-dhcp,dhcp-option DNS 10.0.2.3,dhcp-option DNS 208.67.220.220,route 10.8.0.1,topology net30,ping 10,ping-restart 120,ifconfig 10.8.0.6 10.8.0.5,peer-id 1,cipher AES-256-GCM'
Wed Nov 15 14:18:25 2017 OPTIONS IMPORT: timers and/or timeouts modified
Wed Nov 15 14:18:25 2017 OPTIONS IMPORT: --ifconfig/up options modified
Wed Nov 15 14:18:25 2017 OPTIONS IMPORT: route options modified
Wed Nov 15 14:18:25 2017 OPTIONS IMPORT: --ip-win32 and/or --dhcp-option options modified
Wed Nov 15 14:18:25 2017 OPTIONS IMPORT: peer-id set
Wed Nov 15 14:18:25 2017 OPTIONS IMPORT: adjusting link_mtu to 1624
Wed Nov 15 14:18:25 2017 OPTIONS IMPORT: data channel crypto options modified
Wed Nov 15 14:18:25 2017 Data Channel Encrypt: Cipher 'AES-256-GCM' initialized with 256 bit key
Wed Nov 15 14:18:25 2017 Data Channel Decrypt: Cipher 'AES-256-GCM' initialized with 256 bit key
Wed Nov 15 14:18:25 2017 ROUTE_GATEWAY ON_LINK
Wed Nov 15 14:18:25 2017 TUN/TAP device tun1 opened
Wed Nov 15 14:18:25 2017 TUN/TAP TX queue length set to 100
Wed Nov 15 14:18:25 2017 do_ifconfig, tt->did_ifconfig_ipv6_setup=0
Wed Nov 15 14:18:25 2017 /sbin/ip link set dev tun1 up mtu 1500
Wed Nov 15 14:18:25 2017 /sbin/ip addr add dev tun1 local 10.8.0.6 peer 10.8.0.5
Wed Nov 15 14:18:25 2017 /sbin/ip route add 192.168.56.101/32 dev
Cannot find device ""
Wed Nov 15 14:18:25 2017 ERROR: Linux route add command failed: external program exited with error status: 1
Wed Nov 15 14:18:25 2017 /sbin/ip route add 0.0.0.0/1 via 10.8.0.5
Wed Nov 15 14:18:25 2017 /sbin/ip route add 128.0.0.0/1 via 10.8.0.5
Wed Nov 15 14:18:25 2017 /sbin/ip route add 10.8.0.1/32 via 10.8.0.5
RTNETLINK answers: File exists
Wed Nov 15 14:18:25 2017 ERROR: Linux route add command failed: external program exited with error status: 2
Wed Nov 15 14:18:25 2017 Initialization Sequence Completed

Si vous avez encore des erreurs et même si vous n’en avez pas redémarrer le serveur et le client.

sudo reboot

Le service openvpn devrait se lancer au redémarrage automatiquement.
Pour vérifier que tous fonctionne bien, taper la commande  » ip a » sur le serveur et sur le client vous devrez obtenir un résultat similaire a celui-ci :

joel@debian:~$ ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: enp0s3: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state DOWN group default qlen 1000
    link/ether 08:00:27:ca:89:43 brd ff:ff:ff:ff:ff:ff
    inet 169.254.7.32/16 brd 169.254.255.255 scope link enp0s3:avahi
       valid_lft forever preferred_lft forever
3: enp0s8: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 08:00:27:40:fb:2a brd ff:ff:ff:ff:ff:ff
    inet 192.168.56.103/24 brd 192.168.56.255 scope global enp0s8
       valid_lft forever preferred_lft forever
    inet6 fe80::a00:27ff:fe40:fb2a/64 scope link
       valid_lft forever preferred_lft forever
4: tun0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN group default qlen 100
    link/none
    inet 10.8.0.6 peer 10.8.0.5/32 scope global tun0
       valid_lft forever preferred_lft forever
    inet6 fe80::aa45:8779:2353:3f64/64 scope link flags 800
       valid_lft forever preferred_lft forever
joel@debian:~$

 

Vous pouvez constater qu’il y a une nouvelle interface tun0 qui possède l’ip du VPN.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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