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--- wiki:openvpn_installation [2024/04/09 09:25] – created antisa
+++ wiki:openvpn_installation [2025/03/03 16:15] (current) – [See also] add Revoke openvpn certificates antisa
@@ Line 1: / Line 1: @@
-{{tag>vpn}}
+{{tag>vpn openvpn}}
 ====== Openvpn installation ======
@@ Line 54: / Line 54: @@
 To verify that the VPN is running, you should be able to ping 10.8.0.2 from the server and 10.8.0.1 from the client.
+===== Setup for multiple clients - one server =====
+This is the "proper" way to do it when there are multiple clients involved.
+==== Certificate generation ====
+Download the easy-rsa:
+  wget https://github.com/OpenVPN/easy-rsa/releases/download/v3.1.7/EasyRSA-3.1.7.tgz
+  tar xf EasyRSA-3.1.7.tgz
+  cd EasyRSA-3.1.7
+Copy vars.example to vars and change variables accordingly. vars will be automatically sourced by easy-rsa script.
+  cp vars.example vars
+Also add the ''keyEncipherment'' option in //x509-types/client// file otherwise you will get an error like
+''Client failed: unsupported certificate purpose'' eg.
+<code>
+etc/openvpn/EasyRSA-3.1.7# cat x509-types/client
+# X509 extensions for a client
+basicConstraints = CA:FALSE
+subjectKeyIdentifier = hash
+authorityKeyIdentifier = keyid,issuer:always
+extendedKeyUsage = clientAuth
+keyUsage = digitalSignature, keyEncipherment
+</code>
+. Initialize the PKI directories
+  ./easyrsa init-pki
+. Create the CA. Used in client and server configuration:
+  ./easyrsa build-ca
+. Generate Diffie-Hellman (DH) params.
+  ./easyrsa gen-dh
+. Create the vpn server's sign request and then certificate. This should be used in server.conf ''cert'' along with ''key'' which will also be generated with these commands.  Here you need to provide the password of the CA.key in step 2:
+  ./easyrsa gen-req server nopass
+  ./easyrsa sign-req server server
+. Create client signing request and certificate. Change EntityName, ''nopass'' if you don't want private key to be encrypted
+  ./easyrsa gen-req EntityName nopass
+  ./easyrsa sign-req client EntityName
+For each new client just repeat last step.
+==== Creating configuration files for server and clients ====
+=== Server ===
+You can copy the example file and adapt the fields to your config
+  cp /usr/share/doc/openvpn/examples/sample-config-files/server.conf server.conf
+Edit the ca, cert, key, and dh parameters to point to the files you generated and any other configuration you need. Also create the ta.key
+  openvpn --genkey tls-auth ta.key
+Also create the openvpn user
+  adduser --no-create-home --disabled-login openvpn
+and uncomment this in server.conf
+  ...
+  ;user openvpn
+  ;group openvpn
+  ...
+=== Client ===
+  cp /usr/share/doc/openvpn/examples/sample-config-files/client.conf client.conf.example
+  * Like the server configuration file, first edit the ca, cert, and key parameters to point to the files you generated.
+  * Edit the ''remote'' directive to point to the hostname/IP address and port number of the OpenVPN server
+  * Ensure that the client configuration file is consistent with the directives used in the server configuration. The major thing to check for is that the dev (tun or tap) and proto (udp or tcp) directives are consistent. Also make sure that comp-lzo and fragment, if used, are present in both client and server config files.
+You can now try running the openvpn on client and server like mentioned in Simple setup above.
+==== Redirecting traffic over VPN ====
+=== Redirect all traffic ===
+In server.conf add
+  push "redirect-gateway def1 bypass-dhcp"
+In client.conf add:
+  redirect-gateway def1
+=== Redirect only some IPs (aka Split tunnel) ===
+In server.conf add:
+  push "route 192.168.10.0 255.255.255.0"
+  push "route 192.168.20.0 255.255.255.0"
+  ...
+Remove the redirect-gateway lines from conf.
+<WRAP center round important 60%>
+[[https://web.archive.org/web/20240521145319/https://i.sstatic.net/KNr6M.png|Ubuntu Network Manager]] doesn't seem to need above settings, so you can just uncheck the "Use this connection only for resources on its network" to redirect all traffic over VPN.
+</WRAP>
+===== Redirect DNS through VPN =====
+First uninstall any other DNS server/resolver like ''systemd-resolved''. Now install dnsmasq
+  apt install dnsmasq
+Now make the ///etc/resolv.conf// look like this
+  nameserver ::1
+  nameserver 127.0.0.1
+  options trust-ad
+You might need to [[https://wiki.archlinux.org/title/Domain_name_resolution#Overwriting_of_/etc/resolv.conf|write protect]] this file because some other programs might overwrite this.
+In ///etc/dnsmasq.conf// add one or more upstream servers that dnsmasq will use for name resolution i.e.
+  listen-address=::1,127.0.0.1,10.8.0.1
+  interface=tun0
+  # Google's nameservers, for example
+  server=8.8.8.8
+  server=8.8.4.4
+Adapt the listen-address IP to your VPN interface IP and interface as well and uncomment ''no-resolv''.
+In ///etc/openvpn/server/server.conf// make sure you push DNS and redirect gateway:
+  ...
+  push "redirect-gateway def1 bypass-dhcp"
+  push "dhcp-option DNS 10.13.13.1"
+  ...
+<WRAP center round info 60%>
+If you run into problems with DNS not going through VPN in Windows installed as a VM in Virtualbox for example, you will need to disable automatic metric on VPN interface and set it to lower then the default Ethernet or wifi. To check open the powershell and type ''nslookup example.org'' and you should get a response from VPN IP e.g. 10.8.0.1.
+{{ :wiki:screenshots:windows:windows_metric-2024-05-22_14-17.png?400 |}}
+</WRAP>
+==== Resolve specific domains names to hard-coded IP ====
+Say you need to always resolve example.org to 1.2.3.4 address, you have two options.
+. Add the resolution to ///etc/hosts// i.e.
+  ...
+.2.3.4 www.example.org example.org
+. Remove the above from ///etc/hosts// and in ///etc/dnsmasq.conf// add following
+  address=/example.org/1.2.3.4
+Also [[https://wiki.archlinux.org/title/dnsmasq#Tips_and_tricks|there are other]] stuff you can do.
 ===== Firewall setup =====
@@ Line 65: / Line 211: @@
 #ZONE   INTERFACE       BROADCAST       OPTIONS
 net     eth0      detect          tcpflags,logmartians,nosmurfs,dhcp
-vpn     tun0
+vpn     tun0      detect
 </code>
@@ Line 111: / Line 257: @@
   iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o eth0 -j MASQUERADE
+===== Running openvpn server as a service =====
+Debian 12 ships with systemd units for this. The way to run it is to first make sure the server configuration file is located in ///etc/openvpn/server// directory. The file must end with .conf. So if you have a configuration file called ''myvpnserver.conf'' you need to run it as
+  systemctl enable --now openvpn-server@myvpnserver
+Check logs with
+  journalctl -xefu openvpn-server@server.service
 ====== Tested on ======
   * Debian 12 Bookworw
@@ Line 117: / Line 272: @@
 ====== See also ======
+  * [[wiki:ovpn_file_example]]
+  * [[wiki:vpn_troubleshooting|VPN troubleshooting]]
+  * [[wiki:revoke_openvpn_certificates|Revoke openvpn certificates]]
 ====== References ======
   * https://openvpn.net/community-resources/static-key-mini-howto/
   * https://wiki.archlinux.org/title/Shorewall#/etc/shorewall/masq
   * https://serverfault.com/questions/480069/how-to-force-all-traffic-through-vpn
+  * https://openvpn.net/community-resources/how-to/#setting-up-your-own-certificate-authority-ca-and-generating-certificates-and-keys-for-an-openvpn-server-and-multiple-clients
+  * https://www.openssl.org/docs/man1.1.1/man5/x509v3_config.html
+  * https://shorewall.org/OPENVPN.html
+  * https://openvpn.net/community-resources/reference-manual-for-openvpn-2-4/
+  * [[https://superuser.com/a/966833|windows metric issue]]