CentOS

To have your vpn traffic be able to reach the internet you just need to add the following iptable rules:

iptables -A FORWARD -i tun0 -j ACCEPT
iptables -A FORWARD -i tun0 -o eth0 -m state –state RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -i eth0 -o tun0 -m state –state RELATED,ESTABLISHED -j ACCEPT
iptables -t nat -A POSTROUTING -s 192.168.0.0/24 -o eth0 -j MASQUERADE

This would take the tunnel adapter of tun0 and route the traffic through eth0 for the vpn subnet of 192.168.0.0.