.. _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`. 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 one of the systems generate the key using the operational command `generate openvpn key `. 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:: sh 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:: sh 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 128-bit Blowfish in CBC mode for encryption and SHA-1 for HMAC authentication. These are both considered weak, but a number of other encryption and hashing algorithms are available: For Encryption: .. code-block:: sh vyos@vyos# set interfaces openvpn vtun1 encryption 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 aes192 AES algorithm with 192-bit key aes256 AES algorithm with 256-bit key For Hashing: .. code-block:: sh 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:: sh set protocols static interface-route 10.1.0.0/16 next-hop-interface vtun1 Remote Configuration: .. code-block:: sh 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. OpenVPN Server ^^^^^^^^^^^^^^ Multi-client server is the most popular OpenVPN mode on routers. It always uses x.509 authentication and therefore requires a PKI setup. This guide assumes you have already setup a PKI and have a CA certificate, a server certificate and key, a certificate revokation 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. .. code-block:: sh 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:: sh 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:: sh 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:: sh 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:: sh set protocols static interface-route 10.23.0.0/20 next-hop-interface vtun10 LDAP Authentication ******************* Enterprise installations usually ship a kind of directory service which is used to have a single password store for all employes. VyOS and OpenVPN support using LDAP/AD as single user backend. Authentication is done by using the ``openvpn-auth-ldap.so`` plugin which is shiped 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:: sh 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:: sh # 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 # 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 Active Directory **************** Despite the fact that AD is a superset of LDAP .. code-block:: sh # 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 # 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 BaseDN "OU=Groups,DC=example,DC=com" SearchFilter "(|(cn=VPN))" MemberAttribute memberOf If you only wan't to check if the user account is enabled and can authenticate (against the primary group) the following snipped is sufficient: .. code-block:: sh URL ldap://ds0001.gefoekom.de BindDN CN=SA_OPENVPN,OU=ServiceAccounts,OU=GS,OU=GeFoekoM,DC=gefoekom,DC=de Password g7LjfjmlPhhHnvmal75hbfdknms-44 Timeout 15 TLSEnable no FollowReferrals no BaseDN "OU=GeFoekoM,DC=gefoekom,DC=de" SearchFilter "sAMAccountName=%u" RequireGroup false A complete LDAP auth OpenVPN configuration could look like the following example: .. code-block:: sh 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 } }