A short howto, as I was unable to find any clear ones on the net.
I’m using Mac OS X (Leopard) as client, and a Gentoo server as server/host.
I both tried Viscosity and Tunnelblick on my Mac as OpenVPN software, and Viscosity is probably somewhat easier to configure (using the GUI), it was shareware. So I ended up using Tunnelblick and it seems to be doing its job quite well.
First of all, make sure Gentoo is set up and working as intended. I used my home router as VPN server (having both eth0 and eth1 (= ppp0).
Using this howto, you’ll be able to get the server up and running.
Besides the installation, and perhaps (config) file locations it should be pretty similar on other Linux distros.
As I have dnsmasq running on my server (taking care of DNS) I added the following to the server.conf:
push "dhcp-option DNS 10.0.0.1"
push "redirect-gateway def1"
route 10.20.30.0 255.255.255.252
Don’t forget to allow DNS requests over tun0 interface in dnsmasq.conf.
The first line tells the server to hand out 10.0.0.1 as DNS server to its connecting clients (10.0.0.1 being the internal eth0 IP of my server).
The 2nd line, tells all clients to route ALL of their traffic through the VPN. I used the VPN to access a website that allowed only Belgian IPs, and I was in The Netherlands at the time I had to access the site (Skynet’s Rock Werchter stream). So I connected through my server at home.
And the 3rd and 4th line are needed if the client access the VPN is on a private IP subnet (like being connected on a WiFi router, using IP 192.168.178.x).
You’ll have to add, in the client-config directory a file per username connecting to the VPN with something similar to this:
iroute 192.168.178.0 255.255.255.0
I’m not entirely sure if you can add multiple iroutes; something I’ll have to figure out when being on a different network.
This is what my client config looks like (vpn-server-name.conf, located in ~/Library/openvpn/):
remote home.tiete.be 9000
tls-auth "ta.key" 1
Yeri being my username. Don’t forget to download and add the ca.crt, user.crt, user.key (located in /usr/share/openvpn/easy-rsa/keys/) and ta.key (located in /etc/openvpn/) you’ve created on the server.
If your client asks for “directions”, pick 1.
Start up server and client software.
Hitting connect in Tunnelblick should connect you to the VPN server, and (in my case) giving me an IP similar to 10.20.30.6. You can check this using “ifconfig” in Terminal.
tun0: flags=8851 mtu 1500
inet 10.20.30.6 --> 10.20.30.5 netmask 0xffffffff
open (pid 20551)
tun0 Link encap:UNSPEC HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00
inet addr:10.20.30.1 P-t-P:10.20.30.2 Mask:255.255.255.255
UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1500 Metric:1
RX packets:407595 errors:0 dropped:0 overruns:0 frame:0
TX packets:574351 errors:0 dropped:0 overruns:0 carrier:0
RX bytes:27473209 (26.2 MiB) TX bytes:603524377 (575.5 MiB)
Don’t forget; when using “tun” as driver, your gateway/VPN server will always have the IP ending on .1 (e.g.: 10.20.30.1).
Now, if you want to route all traffic throug the VPN, like I did, you’ll have to change some stuff in iptables (as the server is also acting as my home router, I already did have a few rules in it).
Allow all traffic through tun0 interface:
iptables -A OUTPUT -o tun0 -j ACCEPT
iptables -A INPUT -i tun0 -j ACCEPT
Allow traffic through the external port 9000 (UDP):
iptables -A INPUT -i ppp0 -p udp -m udp --dport 9000 -j ACCEPT
Enable forwarding and NAT:
iptables -A FORWARD -s 10.20.30.0/24 -i tun0 -j ACCEPT
iptables -A FORWARD -d 10.20.30.0/24 -i ppp0 -j ACCEPT
iptables -A POSTROUTING -o ppp0 -j MASQUERADE
And lastly, as I have Squid running on my server, I want to transparently forward all port 80 requests to the Squid server running on port 8080:
iptables -t nat -A PREROUTING -i tun0 -p tcp -m tcp --dport 80 -j REDIRECT --to-ports 8080
That’s about it. You should have a running VPN from your current location to your VPN server. And you’re able to use it as a gateway.
You can always traceroute/tracepath to your VPN server (10.20.30.1). It should only find one hop.