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diff --git a/docs/vpn/openvpn.rst b/docs/vpn/openvpn.rst new file mode 100644 index 00000000..2064860d --- /dev/null +++ b/docs/vpn/openvpn.rst @@ -0,0 +1,222 @@ +.. _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. + +The 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 + +The 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 <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:: 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 |