path: root/docs/vpn/openvpn.rst

.. _openvpn:

#######
OpenVPN
#######

Traditionally hardware routers implement IPsec exclusively due to relative
ease of implementing it in hardware and insufficient CPU power for doing
encryption in software. Since VyOS is a software router, this is less of a
concern. OpenVPN has been widely used on UNIX platform for a long time and is
a popular option for remote access VPN, though it's also capable of
site-to-site connections.

Advantages of OpenVPN are:

* It uses a single TCP or UDP connection and does not rely on packet source
  addresses, so it will work even through a double NAT: perfect for public
  hotspots and such

* It's easy to setup and offers very flexible split tunneling

* There's a variety of client GUI frontends for any platform

Disadvantages are:

* It's slower than IPsec due to higher protocol overhead and the fact it runs
  in user mode while IPsec, on Linux, is in kernel mode

* None of the operating systems have client software installed by default

In the VyOS CLI, a key point often overlooked is that rather than being
configured using the `set vpn` stanza, OpenVPN is configured as a network
interface using `set interfaces openvpn`.

Site-To-Site
============

While many are aware of OpenVPN as a Client VPN solution, it is often
overlooked as a site-to-site VPN solution due to lack of support for this mode
in many router platforms.

Site-to-site mode supports x.509 but doesn't require it and can also work with
static keys, which is simpler in many cases. In this example, we'll configure
a simple site-to-site OpenVPN tunnel using a 2048-bit pre-shared key.

First, one of the systems generate the key using the operational command
``generate openvpn key <filename>``. This will generate a key with the name
provided in the ``/config/auth/`` directory. Once generated, you will need to
copy this key to the remote router.

In our example, we used the filename ``openvpn-1.key`` which we will reference
in our configuration.

* The public IP address of the local side of the VPN will be 198.51.100.10
* The remote will be 203.0.113.11
* The tunnel will use 10.255.1.1 for the local IP and 10.255.1.2 for the remote.
* OpenVPN allows for either TCP or UDP. UDP will provide the lowest latency,
  while TCP will work better for lossy connections; generally UDP is preferred
  when possible.
* The official port for OpenVPN is 1194, which we reserve for client VPN; we
  will use 1195 for site-to-site VPN.
* The ``persistent-tunnel`` directive will allow us to configure tunnel-related
  attributes, such as firewall policy as we would on any normal network
  interface.
* If known, the IP of the remote router can be configured using the
  ``remote-host`` directive; if unknown, it can be omitted. We will assume a
  dynamic IP for our remote router.

Local Configuration:

.. code-block:: none

  set interfaces openvpn vtun1 mode site-to-site
  set interfaces openvpn vtun1 protocol udp
  set interfaces openvpn vtun1 persistent-tunnel
  set interfaces openvpn vtun1 local-host '198.51.100.10'
  set interfaces openvpn vtun1 local-port '1195'
  set interfaces openvpn vtun1 remote-port '1195'
  set interfaces openvpn vtun1 shared-secret-key-file '/config/auth/openvpn-1.key'
  set interfaces openvpn vtun1 local-address '10.255.1.1'
  set interfaces openvpn vtun1 remote-address '10.255.1.2'

Remote Configuration:

.. code-block:: none

  set interfaces openvpn vtun1 mode site-to-site
  set interfaces openvpn vtun1 protocol udp
  set interfaces openvpn vtun1 persistent-tunnel
  set interfaces openvpn vtun1 remote-host '198.51.100.10'
  set interfaces openvpn vtun1 local-port '1195'
  set interfaces openvpn vtun1 remote-port '1195'
  set interfaces openvpn vtun1 shared-secret-key-file '/config/auth/openvpn-1.key'
  set interfaces openvpn vtun1 local-address '10.255.1.2'
  set interfaces openvpn vtun1 remote-address '10.255.1.1'

The configurations above will default to using 256-bit AES in GCM mode
for encryption (if both sides supports NCP) and SHA-1 for HMAC authentication.
SHA-1 is considered weak, but other hashing algorithms are available, as are
encryption algorithms:

For Encryption:

This sets the cipher when NCP (Negotiable Crypto Parameters) is disabled or
OpenVPN version < 2.4.0.

.. code-block:: none

  vyos@vyos# set interfaces openvpn vtun1 encryption cipher
  Possible completions:
    des          DES algorithm
    3des         DES algorithm with triple encryption
    bf128        Blowfish algorithm with 128-bit key
    bf256        Blowfish algorithm with 256-bit key
    aes128       AES algorithm with 128-bit key CBC
    aes128gcm    AES algorithm with 128-bit key GCM
    aes192       AES algorithm with 192-bit key CBC
    aes192gcm    AES algorithm with 192-bit key GCM
    aes256       AES algorithm with 256-bit key CBC
    aes256gcm    AES algorithm with 256-bit key GCM

This sets the accepted ciphers to use when version => 2.4.0 and NCP is
enabled (which is default). Default NCP cipher for versions >= 2.4.0 is
aes256gcm. The first cipher in this list is what server pushes to clients.

.. code-block:: none

  vyos@vyos# set int open vtun0 encryption ncp-ciphers
  Possible completions:
    des          DES algorithm
    3des         DES algorithm with triple encryption
    aes128       AES algorithm with 128-bit key CBC
    aes128gcm    AES algorithm with 128-bit key GCM
    aes192       AES algorithm with 192-bit key CBC
    aes192gcm    AES algorithm with 192-bit key GCM
    aes256       AES algorithm with 256-bit key CBC
    aes256gcm    AES algorithm with 256-bit key GCM

For Hashing:

.. code-block:: none

  vyos@vyos# set interfaces openvpn vtun1 hash
  Possible completions:
    md5          MD5 algorithm
    sha1         SHA-1 algorithm
    sha256       SHA-256 algorithm
    sha512       SHA-512 algorithm

If you change the default encryption and hashing algorithms, be sure that the
local and remote ends have matching configurations, otherwise the tunnel will
not come up.

Static routes can be configured referencing the tunnel interface; for example,
the local router will use a network of 10.0.0.0/16, while the remote has a
network of 10.1.0.0/16:

Local Configuration:

.. code-block:: none

  set protocols static interface-route 10.1.0.0/16 next-hop-interface vtun1

Remote Configuration:

.. code-block:: none

  set protocols static interface-route 10.0.0.0/16 next-hop-interface vtun1

Firewall policy can also be applied to the tunnel interface for `local`, `in`,
and `out` directions and function identically to ethernet interfaces.

If making use of multiple tunnels, OpenVPN must have a way to distinguish
between different tunnels aside from the pre-shared-key. This is either by
referencing IP address or port number. One option is to dedicate a public IP
to each tunnel. Another option is to dedicate a port number to each tunnel
(e.g. 1195,1196,1197...).

OpenVPN status can be verified using the `show openvpn` operational commands.
See the built-in help for a complete list of options.

Server
======

Multi-client server is the most popular OpenVPN mode on routers. It always uses
x.509 authentication and therefore requires a PKI setup. Refer this section
**Generate X.509 Certificate and Keys** to generate a CA certificate,
a server certificate and key, a certificate revocation list, a Diffie-Hellman
key exchange parameters file. You do not need client certificates and keys for the server setup.

In this example we will use the most complicated case: a setup where each
client is a router that has its own subnet (think HQ and branch offices), since
simpler setups are subsets of it.

Suppose you want to use 10.23.1.0/24 network for client tunnel endpoints and
all client subnets belong to 10.23.0.0/20. All clients need access to the
192.168.0.0/16 network.

First we need to specify the basic settings. 1194/UDP is the default. The
``persistent-tunnel`` option is recommended, it prevents the TUN/TAP device from
closing on connection resets or daemon reloads.

.. note:: Using **openvpn-option -reneg-sec** can be tricky. This option is
   used to renegotiate data channel after n seconds. When used at both server
   and client, the lower value will trigger the renegotiation. If you set it to
   0 on one side of the connection (to disable it), the chosen value on the
   other side will determine when the renegotiation will occur.

.. code-block:: none

  set interfaces openvpn vtun10 mode server
  set interfaces openvpn vtun10 local-port 1194
  set interfaces openvpn vtun10 persistent-tunnel
  set interfaces openvpn vtun10 protocol udp

Then we need to specify the location of the cryptographic materials. Suppose
you keep the files in `/config/auth/openvpn`

.. code-block:: none

  set interfaces openvpn vtun10 tls ca-cert-file /config/auth/openvpn/ca.crt
  set interfaces openvpn vtun10 tls cert-file /config/auth/openvpn/server.crt
  set interfaces openvpn vtun10 tls key-file /config/auth/openvpn/server.key
  set interfaces openvpn vtun10 tls crl-file /config/auth/openvpn/crl.pem
  set interfaces openvpn vtun10 tls dh-file /config/auth/openvpn/dh2048.pem

Now we need to specify the server network settings. In all cases we need to
specify the subnet for client tunnel endpoints. Since we want clients to access
a specific network behind out router, we will use a push-route option for
installing that route on clients.

.. code-block:: none

  set interfaces openvpn vtun10 server push-route 192.168.0.0/16
  set interfaces openvpn vtun10 server subnet 10.23.1.0/24

Since it's a HQ and branch offices setup, we will want all clients to have
fixed addresses and we will route traffic to specific subnets through them. We
need configuration for each client to achieve this.

.. note:: Clients are identified by the CN field of their x.509 certificates,
   in this example the CN is ``client0``:

.. code-block:: none

  set interfaces openvpn vtun10 server client client0 ip 10.23.1.10
  set interfaces openvpn vtun10 server client client0 subnet 10.23.2.0/25

OpenVPN **will not** automatically create routes in the kernel for client
subnets when they connect and will only use client-subnet association
internally, so we need to create a route to the 10.23.0.0/20 network ourselves:

.. code-block:: none

  set protocols static interface-route 10.23.0.0/20 next-hop-interface vtun10

Generate X.509 Certificate and Keys
***********************************

OpenVPN ships with a set of scripts called Easy-RSA that can generate the
appropriate files needed for an OpenVPN setup using X.509 certificates.
Easy-RSA comes installed by default on VyOS routers.

Copy the Easy-RSA scripts to a new directory to modify the values.

.. code-block:: none

  cp -r /usr/share/easy-rsa/ /config/my-easy-rsa-config
  cd /config/my-easy-rsa-config

To ensure the consistent use of values when generating the PKI, set default
values to be used by the PKI generating scripts. Rename the vars.example filename
to vars

.. code-block:: none

  mv vars.example vars

Following is the instance of the file after editing. You may also change other values in
the file at your discretion/need, though for most cases the defaults should be just fine.
(do not leave any of these parameters blank)

.. code-block:: none

  set_var EASYRSA_DN      "org"
  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


init-pki option will create a new pki directory or will delete any previously generated
certificates stored in that folder. The term 'central' is used to refer server and
'branch' for client

.. note:: Remember the “CA Key Passphrase” prompted in build-ca command,
   as it will be asked in signing the server/client certificate.

.. code-block:: none

  vyos@vyos:/config/my-easy-rsa-config$./easyrsa init-pki
  vyos@vyos:/config/my-easy-rsa-config$./easyrsa build-ca
  vyos@vyos:/config/my-easy-rsa-config$./easyrsa gen-req central nopass
  vyos@vyos:/config/my-easy-rsa-config$./easyrsa sign-req server central
  vyos@vyos:/config/my-easy-rsa-config$./easyrsa gen-dh
  vyos@vyos:/config/my-easy-rsa-config$./easyrsa build-client-full branch1 nopass

To generate a certificate revocation list for any client, execute these commands:

.. code-block:: none

  vyos@vyos:/config/my-easy-rsa-config$./easyrsa revoke client1
  vyos@vyos:/config/my-easy-rsa-config$ ./easyrsa gen-crl

Copy the files to /config/auth/ovpn/ to use in OpenVPN tunnel creation

.. code-block:: none

  vyos@vyos:/config/my-easy-rsa-config$ sudo mkdir /config/auth/ovpn
  vyos@vyos:/config/my-easy-rsa-config$ sudo cp pki/ca.crt /config/auth/ovpn
  vyos@vyos:/config/my-easy-rsa-config$ sudo cp pki/dh.pem  /config/auth/ovpn
  vyos@vyos:/config/my-easy-rsa-config$ sudo cp pki/private/central.key /config/auth/ovpn
  vyos@vyos:/config/my-easy-rsa-config$ sudo cp pki/issued/central.crt  /config/auth/ovpn
  vyos@vyos:/config/my-easy-rsa-config$ sudo cp pki/crl.pem /config/auth/ovpn

Additionally, each client needs a copy of ca.crt and its own client key and cert files.
The files are plaintext so they may be copied either manually,
or through a remote file transfer tool like scp. Whichever method you use,
the files need to end up in the proper location on each router.
For example, Branch 1's router might have the following files:

.. code-block:: none

  vyos@branch1-rtr:$ ls /config/auth/ovpn
  ca.crt branch1.crt branch1.key

Client Authentication
---------------------

LDAP
****

Enterprise installations usually ship a kind of directory service which is used
to have a single password store for all employees. VyOS and OpenVPN support using
LDAP/AD as single user backend.

Authentication is done by using the ``openvpn-auth-ldap.so`` plugin which is
shipped with every VyOS installation. A dedicated configuration file is required.
It is best practise to store it in ``/config`` to survive image updates

.. code-block:: none

  set interfaces openvpn vtun0 openvpn-option "--plugin /usr/lib/openvpn/openvpn-auth-ldap.so /config/auth/ldap-auth.config"

The required config file may look like:

.. code-block:: none

  <LDAP>
  # LDAP server URL
  URL             ldap://ldap.example.com
  # Bind DN (If your LDAP server doesn't support anonymous binds)
  BindDN          cn=LDAPUser,dc=example,dc=com
  # Bind Password password
  Password        S3cr3t
  # Network timeout (in seconds)
  Timeout         15
  </LDAP>

  <Authorization>
  # Base DN
  BaseDN          "ou=people,dc=example,dc=com"
  # User Search Filter
  SearchFilter    "(&(uid=%u)(objectClass=shadowAccount))"
  # Require Group Membership - allow all users
  RequireGroup    false
  </Authorization>

Active Directory
****************

Despite the fact that AD is a superset of LDAP

.. code-block:: none

  <LDAP>
    # LDAP server URL
    URL ldap://dc01.example.com
    # Bind DN (If your LDAP server doesn’t support anonymous binds)
    BindDN CN=LDAPUser,DC=example,DC=com
    # Bind Password
    Password mysecretpassword
    # Network timeout (in seconds)
    Timeout  15
    # Enable Start TLS
    TLSEnable no
    # Follow LDAP Referrals (anonymously)
    FollowReferrals no
  </LDAP>

  <Authorization>
    # Base DN
    BaseDN        "DC=example,DC=com"
    # User Search Filter, user must be a member of the VPN AD group
    SearchFilter  "(&(sAMAccountName=%u)(memberOf=CN=VPN,OU=Groups,DC=example,DC=com))"
    # Require Group Membership
    RequireGroup    false # already handled by SearchFilter
    <Group>
      BaseDN        "OU=Groups,DC=example,DC=com"
      SearchFilter  "(|(cn=VPN))"
      MemberAttribute  memberOf
    </Group>
  </Authorization>

If you only want to check if the user account is enabled and can authenticate
(against the primary group) the following snipped is sufficient:

.. code-block:: none

  <LDAP>
    URL ldap://dc01.example.com
    BindDN CN=SA_OPENVPN,OU=ServiceAccounts,DC=example,DC=com
    Password ThisIsTopSecret
    Timeout  15
    TLSEnable no
    FollowReferrals no
  </LDAP>

  <Authorization>
    BaseDN          "DC=example,DC=com"
    SearchFilter    "sAMAccountName=%u"
    RequireGroup    false
  </Authorization>

A complete LDAP auth OpenVPN configuration could look like the following example:

.. code-block:: none

  vyos@vyos# show interfaces openvpn
   openvpn vtun0 {
       mode server
       openvpn-option "--tun-mtu 1500 --fragment 1300 --mssfix"
       openvpn-option "--plugin /usr/lib/openvpn/openvpn-auth-ldap.so /config/auth/ldap-auth.config"
       openvpn-option "--push redirect-gateway"
       openvpn-option --duplicate-cn
       openvpn-option --client-cert-not-required
       openvpn-option --comp-lzo
       openvpn-option --persist-key
       openvpn-option --persist-tun
       server {
           domain-name example.com
           max-connections 5
           name-server 1.1.1.1
           name-server 9.9.9.9
           subnet 172.18.100.128/29
       }
       tls {
           ca-cert-file /config/auth/ca.crt
           cert-file /config/auth/server.crt
           dh-file /config/auth/dh1024.pem
           key-file /config/auth/server.key
       }
   }

Client
======

VyOS can not only act as an OpenVPN site-to-site or Server for multiple clients.
You can indeed also configure any VyOS OpenVPN interface as an OpenVPN client
connecting to a VyOS OpenVPN server or any other OpenVPN server.

Given the following example we have one VyOS router acting as OpenVPN server
and another VyOS router acting as OpenVPN client. The Server also pushes a
static client IP address to the OpenVPN client. Remember, clients are identified
using their CN attribute in the SSL certificate.

Server
------

.. code-block:: none

  set interfaces openvpn vtun10 encryption cipher 'aes256'
  set interfaces openvpn vtun10 hash 'sha512'
  set interfaces openvpn vtun10 local-host '172.18.201.10'
  set interfaces openvpn vtun10 local-port '1194'
  set interfaces openvpn vtun10 mode 'server'
  set interfaces openvpn vtun10 persistent-tunnel
  set interfaces openvpn vtun10 protocol 'udp'
  set interfaces openvpn vtun10 server client client1 ip '10.10.0.10'
  set interfaces openvpn vtun10 server domain-name 'vyos.net'
  set interfaces openvpn vtun10 server max-connections '250'
  set interfaces openvpn vtun10 server name-server '172.16.254.30'
  set interfaces openvpn vtun10 server subnet '10.10.0.0/24'
  set interfaces openvpn vtun10 server topology 'subnet'
  set interfaces openvpn vtun10 tls ca-cert-file '/config/auth/ca.crt'
  set interfaces openvpn vtun10 tls cert-file '/config/auth/server.crt'
  set interfaces openvpn vtun10 tls dh-file '/config/auth/dh.pem'
  set interfaces openvpn vtun10 tls key-file '/config/auth/server.key'
  set interfaces openvpn vtun10 use-lzo-compression

Client
------

.. code-block:: none

  set interfaces openvpn vtun10 encryption cipher 'aes256'
  set interfaces openvpn vtun10 hash 'sha512'
  set interfaces openvpn vtun10 mode 'client'
  set interfaces openvpn vtun10 persistent-tunnel
  set interfaces openvpn vtun10 protocol 'udp'
  set interfaces openvpn vtun10 remote-host '172.18.201.10'
  set interfaces openvpn vtun10 remote-port '1194'
  set interfaces openvpn vtun10 tls ca-cert-file '/config/auth/ca.crt'
  set interfaces openvpn vtun10 tls cert-file '/config/auth/client1.crt'
  set interfaces openvpn vtun10 tls key-file '/config/auth/client1.key'
  set interfaces openvpn vtun10 use-lzo-compression

Options
=======

We do not have CLI nodes for every single OpenVPN options. If an option is
missing, a feature request should be opened at Phabricator_ so all users can
benefit from it (see :ref:`issues_features`).

If you are a hacker or want to try on your own we support passing raw OpenVPN
options to OpenVPN.

.. cfgcmd:: set interfaces openvpn vtun10 openvpn-option 'persistent-key'

Will add ``persistent-key`` at the end of the generated OpenVPN configuration.
Please use this only as last resort - things might break and OpenVPN won't start
if you pass invalid options/syntax.

.. cfgcmd:: set interfaces openvpn vtun10 openvpn-option 'push &quot;keepalive 1 10&quot;'

Will add ``push "keepalive 1 10"`` to the generated OpenVPN config file.

.. note:: Sometimes option lines in the generated OpenVPN configurarion require
   quotes. This is done through a hack on our config generator. You can pass
   quotes using the ``&quot;`` statement.

.. include:: ../common-references.rst