Tuesday, August 14, 2018

OpenVPN configuration for server and multiple clients

This is a simple post showing a basic configuration for setting up OpenVPN server accepting multiple clients with TLS.

First of all generate self-signed server and client private key and certificates, and dh params. Make sure to write the Common Name (CN) when asked, otherwise openvpn will fail to verify the certificates.

openssl req -newkey rsa:2048 -nodes -keyout serverkey.pem -x509 -days 365000 -out servercert.pem
openssl req -newkey rsa:2048 -nodes -keyout clientkey.pem -out client.csr
openssl x509 -req -days 365000 -in client.csr -CA servercert.pem -CAkey serverkey.pem -set_serial 01 -out clientcert.pem
openssl dhparam -outform PEM -out dh.pem 1024


Server configuration:

dev tun
mode server
tls-server
server 10.8.0.0 255.255.255.0
ca servercert.pem
cert servercert.pem
key serverkey.pem
dh dh.pem
duplicate-cn
topology subnet
keepalive 10 60
ping-timer-rem
persist-tun
persist-key

If you plan to use the server as gateway like configured below, don't forget to enable IP forwarding and masquerading:

sysctl net.ipv4.ip_forward=1
iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -j MASQUERADE

Client configuration:

client
proto tcp-client
redirect-gateway
tls-client
key clientkey.pem
cert clientcert.pem
ca servercert.pem
keepalive 10 60
dev tun


Have fun, tune as needed.

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