Copyright © 2003, 2004, 2005, 2006 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”.
2007/12/31
Table of Contents
Caution
This article applies to Shorewall 3.0 and later and to OpenVPN 2.0 and later. If you are running a version of Shorewall earlier than Shorewall 3.0.0 then please see the documentation for that release.
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/.
Unless there are interoperability issues (the remote systems do not support OpenVPN), OpenVPN is my choice any time that I need a VPN.
It is widely supported -- I run it on both Linux and Windows XP.
It requires no kernel patching.
It is very easy to configure.
It just works!
I recommend reading the VPN Basics article if you plan to implement any type of VPN.
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 TYPE OPTIONS IN OUT # OPTIONS OPTIONS vpn ipv4
On system A, the 10.0.0.0/8 will comprise the vpn zone.
In
/etc/shorewall/interfaceson 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
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
Similarly, if you want to use TCP for your tunnel rather than UDP (the default), then you can define /etc/shorewall/tunnels like this:
/etc/shorewall/tunnels using TCP:
#TYPE ZONE GATEWAY GATEWAY ZONE openvpn:tcp net 134.28.54.2
Finally, if you want to use TCP and port 7777:
/etc/shorewall/tunnels using TCP port 7777:
#TYPE ZONE GATEWAY GATEWAY ZONE openvpn:tcp: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 route 10.0.0.0 255.0.0.0 192.168.99.2 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/interfaceson system B:#ZONE INTERFACE BROADCAST OPTIONS vpn tun0
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 route 192.168.1.0 255.255.255.0 192.168.99.1 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/policyon 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.
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 TYPE OPTIONS IN OUT # OPTIONS OPTIONS road ipv4
On system A, the remote clients will comprise the road zone.
In
/etc/shorewall/interfaceson 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
If you are running Shorewall 2.4.3 or later, you might prefer the
following in /etc/shorewall/tunnels on system A.
Specifying the tunnel type as openvpnserver has the advantage that the VPN
connection will still work if the client is behind a gateway/firewall that
uses NAT.
#TYPE ZONE GATEWAY GATEWAY ZONE openvpnserver: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 TYPE OPTIONS IN OUT # OPTIONS OPTIONS home ipv4
On system A, the hosts accessible through the tunnel will comprise the home zone.
In
/etc/shorewall/interfaceson 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
Again in you are running Shorewall 2.4.3 or later, in
/etc/shorewall/tunnels on system B you might
prefer:
#TYPE ZONE GATEWAY GATEWAY ZONE openvpnclient:1194 net 206.162.148.9
We want the remote client 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
This section will describe how we once secured our home wireless network using OpenVPN. Our network as it was then[1] is as shown in the following diagram.
The Wireless network is in the lower right of the diagram and
consists of two laptops: Eastepnc6000 (Dual Boot Windows XP - SP1, SUSE
10.0) and Tipper (SUSE 10.0). We used OpenVPN to bridge those two laptops
with the local LAN shown in the lower left hand corner. The laptops were
configured with addresses in the 192.168.3.0/24 network connected to the
firewall's eth0 interface which
places them in the firewall's Wifi zone.
OpenVPN bridging allowed them to be assigned an additional IP address from
the 192.168.1.0/24 network and to be securely bridged to the LAN on the
lower left.
Note
Eastepnc6000 is shown in both the local LAN and in the Wifi zone with IP address 192.168.1.6 -- clearly, the computer could only be in one place or the other. Tipper could also be in either place and would have the IP address 192.168.1.8 regardless.
The firewall ran Debian Sarge so the bridge was defined in
/etc/network/interfaces.
# LAN interface
auto br0
iface br0 inet static
address 192.168.1.254
netmask 255.255.255.0
pre-up /usr/sbin/openvpn --mktun --dev tap0
pre-up /sbin/ip link set tap0 up
pre-up /sbin/ip link set eth3 up
pre-up /usr/sbin/brctl addbr br0
pre-up /usr/sbin/brctl addif br0 eth3
pre-up /usr/sbin/brctl addif br0 tap0
pre-down /usr/sbin/brctl delif br0 eth3
pre-down /sbin/ip link set eth3 down
pre-down /usr/sbin/brctl delif br0 tap0
pre-down /sbin/ip link set tap0 down
post-down /usr/sbin/brctl delbr br0
post-down /usr/sbin/openvpn --rmtun --dev tap0Note that the IP address assigned to the bridge is 192.168.1.254 -- that was the default gateway address for hosts in the local zone.
We used X.509 certificates for authentication.
/etc/openvpn/server-bridge.conf defined a bridge and reserved IP addresses 192.168.1.64-192.168.1.71 for VPN clients. Note that the bridge server only used local IP address 192.168.3.254. We ran two instances of OpenVPN; this one and a second tunnel-mode instance for remote access.
dev tap0 local 192.168.3.254 server-bridge 192.168.1.254 255.255.255.0 192.168.1.64 192.168.1.71 client-to-client dh dh1024.pem ca /etc/certs/cacert.pem crl-verify /etc/certs/crl.pem cert /etc/certs/gateway.pem key /etc/certs/gateway_key.pem port 1194 comp-lzo user nobody group nogroup keepalive 15 45 ping-timer-rem persist-tun persist-key client-config-dir /etc/openvpn/bridge-clients ccd-exclusive verb 3
The files in /etc/openvpn/bridge-clients
were used to assign a fixed IP address to each laptop. For example,
tipper.shorewall.net:
ifconfig-push 192.168.1.8 255.255.255.0
/etc/openvpn/wireless.conf:
dev tap remote 192.168.3.254 tls-remote gateway.shorewall.net client redirect-gateway ca /etc/certs/cacert.pem cert /etc/certs/tipper.pem key /etc/certs/tipper_key.pem port 1194 comp-lzo ping 15 ping-restart 45 ping-timer-rem persist-tun persist-key mute-replay-warnings verb 3
C:\Program Files\Openvpn\config\homewireless.ovpn:
dev tap remote 192.168.3.254 tls-remote gateway.shorewall.net tls-client pull ca "/Program Files/OpenVPN/certs/cacert.pem" cert "/Program Files/OpenVPN/certs/eastepnc6000.pem" key "/Program Files/OpenVPN/certs/eastepnc6000_key.pem" redirect-gateway port 1194 comp-lzo ping 15 ping-restart 45 ping-timer-rem persist-tun persist-key verb 3
The configuration was the same as shown above only with "/Program Files/OpenVPN" replaced with "/etc/openvpn" (I love OpenVPN).
In December 2007, I acquired a new laptop that runs Windows Vista. After a frustrating effort, I managed to get it working. The keys to getting it working were:
It is essential to run a version of OpenVPN that is "Vista Ready" -- I used Matias Sundman's combined OpenVPN 2.1_rc4/OpenVPN GUI 1.0.3 installer (see http://openvpn.se/).
OpenVPN GUI must be run as the Administrator. In the Explorer, right click on the OpenVPN GUI binary and select Properties->Compatibilty and select "Run this program as an administrator".
If you encounter problems where everything looks correct but it doesn't work, reboot and try it again. "It worked for me"™.
dev tap remote 192.168.3.254 tls-remote gateway.shorewall.net client tls-client explicit-exit-notify ca "/Program Files/OpenVPN/certs/cacert.pem" cert "/Program Files/OpenVPN/certs/vista.pem" key "/Program Files/OpenVPN/certs/vista_key.pem" route-delay redirect-gateway port 1194 comp-lzo ping 15 ping-restart 45 ping-timer-rem persist-tun persist-key mute-replay-warnings verb 3
In this configuration, we didn't need any firewalling between the laptops and the local LAN so we set BRIDGING=No in shorewall.conf. The configuration of the bridge then became as described in the Simple Bridge documentation. If you need to control the traffic allowed through the VPN bridge then you will want to configure Shorewall as shown in the Bridge/Firewall documentation.
Note that the bridge (br0) is defined as the interface to the local zone and has the routeback option.
#ZONE INTERFACE BROADCAST OPTIONS
net eth2 206.124.146.255 dhcp,norfc1918,logmartians,blacklist,tcpflags,nosmurfs
loc br0 192.168.1.255 dhcp,routeback
dmz eth1 - logmartians
Wifi eth0 192.168.3.255 dhcp,maclist
#LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVEWireless networks pose a threat to all systems that are connected to them and we therefore ran Firewalls on the two Laptops. Eastepnc6000 ran Sygate™ Security Agent and Tipper ran a Shorewall-based Netfilter firewall.
#ZONE TYPE OPTIONS IN OUT
# OPTIONS OPTIONS
lan ipv4 #Wired LAN at our home
net ipv4
#LAST LINE - ADD YOUR ENTRIES ABOVE THIS ONE - DO NOT REMOVE
#ZONE INTERFACE BROADCAST OPTIONS
#
net eth0 detect routefilter,dhcp,tcpflags
lan tap0 192.168.1.255
#LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVESince we didn't expect any traffic between the net zone and the lan zone, we used NONE policies for that traffic. If any such traffic would have occurred, it would have been handled according to the all->all policy.
#SOURCE DEST POLICY LOG LIMIT:BURST
# LEVEL
fw net ACCEPT
fw lan ACCEPT
lan fw ACCEPT
net lan NONE
lan net NONE
net all DROP info
# The FOLLOWING POLICY MUST BE LAST
all all REJECT info
#LAST LINE -- DO NOT REMOVE