HOWTOs, tips and tricks

HOWTO setup traffic routing via OpenVPN server using NAT

Create file /etc/openvpn/server/<config-name>.up. Put the following script into the file:

#!/bin/bash

VPNIF=${dev}
WANIF=`ip route | grep default | egrep -o 'dev [^ ]+' | cut -f 2 -d\  `

iptables -P FORWARD DROP
iptables -A FORWARD -i ${VPNIF} -j ACCEPT
iptables -A FORWARD -o ${VPNIF} -m state --state ESTABLISHED -j ACCEPT
iptables -t nat -A POSTROUTING -o ${WANIF} -j MASQUERADE

echo 1 > /proc/sys/net/ipv4/ip_forward

Make this file executable: sudo chmod a+x /etc/openvpn/server/<config-name>.up

Add the following lines into a server OpenVPN config:

script-security 2
up /etc/openvpn/server/<config-name>.up

Restart OpenVPN server, check that:

cat /proc/sys/net/ipv4/ip_forward outputs 1.

sudo iptables-save | grep FORWARD outputs:

  :FORWARD DROP [0:0]
  -A FORWARD -i <VPNIF> -j ACCEPT
  -A FORWARD -o <VPNIF> -m state --state ESTABLISHED -j ACCEPT

sudo iptables-save | grep POSTROUTING outputs:

  :POSTROUTING ACCEPT [0:0]
  -A POSTROUTING -o <WANIF> -j MASQUERADE

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