OpenVPN Tunnels Simon Mater Tom Eastep 2005-02-08 2003 2004 2005 Simon Mater Thomas M. Eastep Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover, and with no Back-Cover Texts. A copy of the license is included in the section entitled GNU Free Documentation License. OpenVPN is a robust and highly configurable VPN (Virtual Private Network) daemon which can be used to securely link two or more private networks using an encrypted tunnel over the internet. OpenVPN is an Open Source project and is licensed under the GPL. OpenVPN can be downloaded from http://openvpn.net/. OpenVPN support was added to Shorewall in version 1.3.14. The default port number for OpenVPN changed from 5000 to 1194 in Shorewall version 2.2.0 RC2. This change follows OpenVPN 2.0 which also changed its default port to 1194. In the text that follows, where you see Port 1194 this can also refer to port 5000 depending on which version of Shorewall and OpenVPN that you are using.
Preliminary Reading I recommend reading the VPN Basics article if you plan to implement any type of VPN.
Bridging two Masqueraded Networks Suppose that we have the following situation: We want systems in the 192.168.1.0/24 subnetwork to be able to communicate with the systems in the 10.0.0.0/8 network. This is accomplished through use of the /etc/shorewall/tunnels file and the /etc/shorewall/policy file and OpenVPN. While it was possible to use the Shorewall start and stop script to start and stop OpenVPN, I decided to use the init script of OpenVPN to start and stop it. On each firewall, you will need to declare a zone to represent the remote subnet. We'll assume that this zone is called vpn and declare it in /etc/shorewall/zones on both systems as follows.
/etc/shorewall/zones — Systems A & B #ZONE DISPLAY COMMENTS vpn VPN Remote subnet
On system A, the 10.0.0.0/8 will comprise the vpn zone.
In /etc/shorewall/interfaces on system A: #ZONE INTERFACE BROADCAST OPTIONS vpn tun0
In /etc/shorewall/tunnels on system A, we need the following:
#TYPE ZONE GATEWAY GATEWAY ZONE openvpn net 134.28.54.2
Shorewall versions prior to 2.2.0 Beta 1 enforced use of the same port number for both the source and destination port. Some OpenVPN clients (notabley on Windows) do not use the same source and destination ports which can cause problems. If system B is a Windows system or if you find that Shorewall is blocking the UDP port 1194 traffic from the remote gateway and you are running a version of Shorewall prior to 2.2.0 Beta 1, then you will want the following entry in /etc/shorewall/tunnels instead of the one above: #TYPE ZONE GATEWAY GATEWAY ZONE generic:udp:1194 net 134.28.54.2 This entry in /etc/shorewall/tunnels opens the firewall so that OpenVPN traffic on the default port 1194/udp will be accepted to/from the remote gateway. If you change the port used by OpenVPN to 7777, you can define /etc/shorewall/tunnels like this:
/etc/shorewall/tunnels with port 7777: #TYPE ZONE GATEWAY GATEWAY ZONE openvpn:7777 net 134.28.54.2
This is the OpenVPN config on system A:
dev tun local 206.162.148.9 remote 134.28.54.2 ifconfig 192.168.99.1 192.168.99.2 up ./route-a.up tls-server dh dh1024.pem ca ca.crt cert my-a.crt key my-a.key comp-lzo verb 5
Similarly, On system B the 192.168.1.0/24 subnet will comprise the vpn zone
In /etc/shorewall/interfaces on system B: #ZONE INTERFACE BROADCAST OPTIONS vpn tun0 192.168.1.255
In /etc/shorewall/tunnels on system B, we have:
#TYPE ZONE GATEWAY GATEWAY ZONE openvpn net 206.191.148.9
And in the OpenVPN config on system B:
dev tun local 134.28.54.2 remote 206.162.148.9 ifconfig 192.168.99.2 192.168.99.1 up ./route-b.up tls-client ca ca.crt cert my-b.crt key my-b.key comp-lzo verb 5
You will need to allow traffic between the vpn zone and the loc zone on both systems -- if you simply want to admit all traffic in both directions, you can use the policy file:
/etc/shorewall/policy on systems A & B #SOURCE DEST POLICY LOG LEVEL loc vpn ACCEPT vpn loc ACCEPT
On both systems, restart Shorewall and start OpenVPN. The systems in the two masqueraded subnetworks can now talk to each other.
Roadwarrior OpenVPN 2.0 provides excellent support for roadwarriors. Consider the setup in the following diagram: On the gateway system (System A), we need a zone to represent the remote clients — we'll call that zone road.
/etc/shorewall/zones — System A: #ZONE DISPLAY COMMENTS road Roadwarriors Remote clients
On system A, the remote clients will comprise the road zone.
In /etc/shorewall/interfaces on system A: #ZONE INTERFACE BROADCAST OPTIONS road tun+
In /etc/shorewall/tunnels on system A, we need the following:
#TYPE ZONE GATEWAY GATEWAY ZONE openvpn:1194 net 0.0.0.0/0
We want the remote systems to have access to the local LAN — we do that with an entry in /etc/shorewall/policy (assume that the local LAN comprises the zone loc).
#SOURCE DESTINATION POLICY road loc ACCEPT
The OpenVPN configuration file on system A is something like the following:
dev tun server 192.168.2.0 255.255.255.0 dh dh1024.pem ca /etc/certs/cacert.pem crl-verify /etc/certs/crl.pem cert /etc/certs/SystemA.pem key /etc/certs/SystemA_key.pem port 1194 comp-lzo user nobody group nogroup ping 15 ping-restart 45 ping-timer-rem persist-tun persist-key verb 3
Configuration on the remote clients follows a similar line. We define a zone to represent the remote LAN:
/etc/shorewall/zones — System B: #ZONE DISPLAY COMMENTS home Home Home LAN
On system A, the hosts accessible through the tunnel will comprise the home zone.
In /etc/shorewall/interfaces on system B: #ZONE INTERFACE BROADCAST OPTIONS home tun0
In /etc/shorewall/tunnels on system B, we need the following:
#TYPE ZONE GATEWAY GATEWAY ZONE openvpn:1194 net 206.162.148.9
We want the remote clien to have access to the local LAN — we do that with an entry in /etc/shorewall/policy.
#SOURCE DESTINATION POLICY $FW home ACCEPT
The OpenVPN configuration on the remote clients is along the following line:
dev tun remote 206.162.148.9 up /etc/openvpn/home.up tls-client pull ca /etc/certs/cacert.pem cert /etc/certs/SystemB.pem key /etc/certs/SystemB_key.pem port 1194 user nobody group nogroup comp-lzo ping 15 ping-restart 45 ping-timer-rem persist-tun persist-key verb 3
If you want multiple remote clients to be able to communicate openly with each other then you must: Include the client-to-client directive in the server's OpenVPN configuration; and Specify the routeback option on the tun+ device in /etc/shorewall/interfaces. If you want to selectively allow communication between the clients, then see this article by Marc Zonzon