Continued from Part 2…

Okay, time for the hard part… well, at least it was for me.  Please understand, the instructions at The ‘Point and Click’ Home VPN HowTo Guide, combined with the knowledge I acquired from the book OpenVPN: Building and Integrating Virtual Private Networks (Amazon affiliate link) by Markus Feilner, enabled me to get a tunnel going using a software client with no sweat. But getting it to work with the Tomato VPN client, and in particular, to get it to work the way we needed it to, was a whole other thing. It turned out, as so often happens that some simple configuration changes were all that was needed – but finding the correct configuration changes to make were pure grief.

EDIT: The above-mentioned book has been updated and expanded under a new title — see Mini-review of Beginning OpenVPN 2.0.9 by Markus Feilner and Norbert Graf (Packt Publishing)

I want to digress just a moment to speak about those elitists that seem to frequent certain forums and IRC channels, and just love to tell newbies (often in not so polite terms) that all the answers can be found by using Google. I’ve pretty much figured out that most of the time, the person saying that doesn’t know the answer either, but they are like the schoolyard bully that gets their kicks by picking on others. In this case, Google may have had the answers somewhere, but they sure weren’t showing up in the first few pages of results. Instead, what was showing up was many others who were having the same problems and asking the same questions, but not getting answers! And usually after the first four or five pages of results, the results became even less relevant, if that were possible. Finally, after taking a more or less scattershot approach to seeking help, I came up with a “recipe” that works in this situation. Of course I cannot guarantee it will work for you… heck, I can’t guarantee it will work for me next week… but at least it’s working as I write this. But the next time someone suggests that you should just Google it (or something like that), I suggest you ask them what search terms they would suggest using that will bring you the answer to your question. When whatever they suggest doesn’t work, let them know and ask for more suggestions, and just keep repeating until you find the answer or they get sick of talking to you. If we all did that, I suspect some of the online bullies would discover that maybe they should keep quiet if they don’t know the answer.

Okay, so to begin, let’s make sure we are all on the same page. I assume you’ve installed the Webmin OpenVPN + CA module (again, following the instructions at The ‘Point and Click’ Home VPN HowTo Guide) but if you had difficulty locating the module, try here — as I write this, it appears that the newest version of the module is the OpenVPNadmin WebMin pre-release 2.5 version. And when you try to download it, if you get “Unauthorized access to downloads!”, try a different browser, or make sure JavaScript and cookies are enabled.  You will probably need to download it to your computer first, then upload it to Webmin, if your experience is anything like mine was.

When you go into the module, you’ll initially see a page like this:

This is “home base” for this module, so when I say “return to the admin page”, this is the page I mean. It’s also the page you use to create a new Certification Authority (normally you only need to do that once, but if you really want to you can make more). In the upper left corner there is a link labeled “Module Config” – click on it and make sure all the paths are correct:

A couple notes on this page:  First, although it indicates that “Server Hint for Clients” is a required field, there is no indication of what actually goes there, nor any default value.  Second, the information under “If you use bridge device” is only applicable if you use TAP mode (remember, we’re using TUN), but I do know the defaults are not correct.  Just in case you ever want to try to get TAP mode working, here is what these paths should be (at least on our installation):

Command to start Bridge:
/usr/libexec/webmin/openvpn/br_scripts/bridge_start

Command to stop Bridge:
/usr/libexec/webmin/openvpn/br_scripts/bridge_end

Path to DOWN-ROOT-PLUGIN:
/usr/share/openvpn/plugin/lib/openvpn-down-root.so

Do check the paths on this page, because the defaults aren’t totally correct.  Now let’s return to the admin page.  I probably should have mentioned that you don’t really need to change any of the defaults for making a certificate for just your own use – those values are probably only important if you are creating a certificate that will be used by the public.  Once you have made a certificate, you can click on the Certification Authority List, where you’ll see this page:

I really don’t know why you can create a new Certification Authority on both this page and the main admin page, but oh well… once you have created one it will show up in the list at the top of the page.  You can click on it to view what you created, but there’s nothing you can change there. The main thing of importance is the “Keys List” link, where you can actually create new keys and view existing ones:

Okay, now here’s the important thing to remember about key creation: You need one key for your server, and one key for each client.  You will note we have a server key, and client key for the software client (used for testing) and one more for the OpenVPN client on the Asus router.

As you may have surmised, except for the key name field, you can leave everything else at the defaults. However, there is one thing on this page that will lead you astray.  It says, “Server key doesn’t need password!“, which might lead you to think that a client key does need one, but that’s not true.  And if you use a password with your Tomato-based client key, you will never make a successful connection.  The keys are far stronger protection than passwords anyway, so the only reason you might even consider using one is for a software client where you want to keep anyone other than an authorized user from connecting to the VPN tunnel.  Anyway, don’t use a password for your server key or your Tomato OpenVPN client key!!!

Okay, now it’s time to navigate back to the admin page, then click on “VPN list”. Once you have created a server key, you can create your actual server. So click on the New VPN Server button and a page will come up that permits you to create a server configuration.  This is where things get really tricky.  Here is how ours is filled out:

Now the above is actually the edit page you get once the server is created and you have returned to edit it.  Note that some values cannot be changed after the initial entry, so be sure you get them right the first time.  In particular, make sure to select tun and not tap. If you do make a mistake, you can always delete the entire server configuration and start over, but that’s a bit of a pain. There are some differences in our configuration and the one at The ‘Point and Click’ Home VPN HowTo Guide, and generally speaking there are good reasons for the differences. But that said, nobody is claiming our configuration is perfect, just that it works! If you see something here you think should be changed, feel free to leave a comment.

Note in particular the text fields at the bottom of the page. Getting those right is the key to making this thing work! So, here’s what’s in each of those:

Additional Configurations:

push “route 192.168.0.0 255.255.255.0”
push redirect-gateway
push “dhcp-option WINS 192.168.0.50”
script-security 2 system

up (script execute after VPN up):

route add -net 192.168.5.0 netmask 255.255.255.0 gw 10.8.0.2 tun0
echo 1 > /proc/sys/net/ipv4/conf/tun0/proxy_arp
echo 1 > /proc/sys/net/ipv4/conf/eth0/proxy_arp

down-pre (script execute before VPN down):

route delete -net 192.168.5.0 netmask 255.255.255.0 gw 10.8.0.2 tun0

Of course, in the Additional Configurations section you want the line push “dhcp-option WINS 192.168.0.50” to point to a WINS server on your network, if you have one (if you don’t, just leave that line out).

In the up and down-pre scripts, if you want to be able to reach the local network behind the WAN port of the router on the client side, you should add additional route add and route delete lines in a format similar to those above, but substituting that network’s address range.

Now, once again, I’m NOT saying this is a perfect configuration, just that it works for us. However, if you notice something that just doesn’t look right, feel free to leave a comment. Much of the added configuration was put in so that traffic from the primary LAN to addresses in the 192.168.5.x address space would actually go through the tunnel – that was the hardest part. It was (relatively) easy to create a tunnel in the first place, but getting packets to and from their intended destinations was another matter entirely.

When you have configured your server and clicked “Save”, it should show up in your server list:

Now click on “Clients List” – there will be a button labeled “New VPN Client” (no screenshot, it’s just a button to click at this point).  Click that button and you will be presented with a client configuration page.  Here’s the one we created for our Tomato OpenVPN client running on the Asus router (again, this is actually the edit page, since the client is already created on our system):

Most of the settings here will be the defaults but there are two things to pay particular attention to:  First, the “Remote IP” must be the external address of your server – remember that this is the configuration that goes to the client. And second, notice the ccd file content box at the bottom – it is crucial that this be filled in correctly. In our case, we used this line:

iroute 192.168.5.0 255.255.255.0

If you miss this – and I speak from experience on this one – the packets from the Internet or your local LAN just aren’t going to get back to the client end of the tunnel! And remember to add an additional, similar line if you also want to be able to reach the network connected to the WAN port at the client router, substituting the base address of that network for the 192.168.5.0.

Once you have saved this, it should appear in the VPN client list:

Once you have configured a client, the next step is to export its configuration, particularly the certificate and key files, to your computer using the “Export” link – all the necessary files will be packed up in a ZIP file.  The instructions at The ‘Point and Click’ Home VPN HowTo Guide tell you how to use this file with a software client, but with your Tomato firmware you will have to unzip the file and then open each of the three files (ca.crt, plus the client certificate and key files), in a text editor or viewer. Only those three files are used with the Tomato OpenVPN client; the others in the ZIP archive are not. Then you will need to cut and paste the contents of those files into the three fields that appear under VPN Tunneling | Client | Keys tab in the Tomato firmware (see the screenshot of that page in Part 1 if you’re not sure what file’s contents goes where). With regard to the Client Certificate, there is some extra information at the top of the file that does not need to be pasted into the text field – you only need the two lines —–BEGIN CERTIFICATE—– and —–END CERTIFICATE—– plus all the lines in between those two tags. On an Asus WL-520GU router it doesn’t matter much, but there have been cases with some other makes of router where leaving that excess information in was just enough excess data to “brick” the router! So if in doubt, leave the data above the —–BEGIN CERTIFICATE—– line out.

Once you have everything ready, you can go to the OpenVPN admin page in Webmin and start the server, then in your Tomato firmware start the client.  HOPEFULLY the client and server will connect and start communicating.  You can check from the server’s  admin page by clicking on “Active Connection” – hopefully you will see something like this:

If you do, congratulations! If not, you have some troubleshooting to do. On the server, take a look at the log file: /etc/openvpn/servers/servername/logs/openvpn.log. On the client, click on Logs (under Status in the left-hand menu) and look at the last several lines. OpenVPN usually doesn’t suffer in silence — when something isn’t working, chances are one or both logs will be filled with messages that may or may not be helpful. You can always try going to Google and using OpenVPN plus the actual error message text (enclosed in quotation marks); once in a while that will actually bring up something useful.

Still stuck? My plan is to add a Part 4 to this series, that will provide links to some of the most useful resources I’ve collected along this journey.  But you can certainly help — if I’ve made any errors in these instructions (not at all unlikely given the sleep I’ve missed during this project), and you find them and can figure out what was incorrect, PLEASE leave a comment. I will warn you that writing to me with your error message will probably get you nowhere – I can definitely play the part of the blind leading the blind, so to speak, but first I have to heal from all the bruises encountered on this journey! 🙂

I sincerely hope these posts have been useful to you! In Part 4 I’ll wrap this up with brief instructions for rotating the log file so it doesn’t grow forever, provide the aforementioned list of links, and give you a bit more insight into why I set this up using TUN mode even though I’d probably have preferred to use TAP.

EDIT (Jaunary 2011): Since I originally wrote this article in 2009, a new project has appeared called Easy OpenVPN, which is described as “a collection of bash scripts which will install and configure the Open VPN software on your PBXIAF server. Also includes scripts for creating client certificate files.”  The project’s page further notes that these scripts are compatible with the security models used in, and have been tested with PBX In A Flash and Elastix, and that they may be compatible with other PBX distributions, but have not been formally tested.  It also notes that the scripts do not interact directly with Asterisk or FreePBX.  I have NOT tested these scripts, but it sounds as if it they might work on just about any CentOS-based OS.  Certainly, if you are using one of those distributions, it’s worth looking into — it might be a faster and easier way to set up OpenVPN on your server than the procedure I outline here.  Some instructions can be found in this thread.  Even if you go that route, you might still want to read the rest of this series, since it gives some explanations and usage tips that may come in handy if the scripts don’t configure OpenVPN the way you’d like. FURTHER EDIT: If you want a dedicated OpenVPN server, check this out: Create a VPN with the Raspberry Pi (from Linux User & Developer).

Before you can begin to set up the OpenVPN server, there is some preparation work that needs to be done. But first, let’s talk about the prerequisites and assumptions we are making here. In the case of the tunnel I was helping to set up, the OpenVPN server was located on a box that runs the Elastix PBX distribution, which includes the CentOS operating system, plus FreePBX and Asterisk and a few other things. It doesn’t really matter whether the box has other servers on it (of course, if it’s a really old/slow box there may be performance issues), but for the purposes of our instructions here, the most important thing is that you have Webmin installed.  Let me repeat that loud and clear:

You MUST have Webmin installed to use these instructions!

You don’t have Webmin installed and you don’t want to install it? Fine, shoo, away with you then. There are hundreds of other installation guides on the Internet, go find one you like.  You have to keep in mind that with me, whenever there’s a choice between using the Linux command line or manually editing a configuration file, and using a nice GUI, I’ll pick the GUI every time.  Some people (usually long time Linux users) seem to have some philosophical objection to using Webmin – if that’s you then you’re obviously much too smart to need these instructions, so what are you doing here?

I’m going to assume you already have Webmin installed, but if you don’t, try doing yum install webmin — it might already be in a CentOS repository.  If that doesn’t work, you should be able to do this:

wget download.webmin.com/devel/rpm/webmin-current.rpm
rpm -ivh webmin-current.rpm

Once you get Webmin installed (or if you are using a Debian-based distribution such as Ubuntu) go to The ‘Point and Click’ Home VPN HowTo Guide — we’re going to refer to that document several times, so you may want to keep it open in another browser tab. But for now, just follow the instructions related to installing Webmin, starting (for CentOS users) with the subheading “Access Webmin”.  For now, just follow the instructions in the two paragraphs in that section.  On a Debian-based system, I’d try following the entire document, but I can tell you there are parts missing for a CentOS-based system, so stick with us for a bit.

Another assumption we are making is that your primary network (the one the server in on) has addresses in the 192.168.0.1 through 192.168.0.255 range.  It’s okay if the “0” in the third octet is some other number (hopefully it’s not 5, because that what we used at the client end) but the main point is that we’re assuming it’s a small network.  If you’re using more than 255 addresses on the primary network it’s not an insurmountable problem, as long as the client end has its own unique address space.

Open the file /etc/hosts.allow at the server – you should see something like this:

ALL : 192.168.0.0/255.255.255.0

If you do, you could change it to the following two lines (note the change in the netmask in the first line):

ALL : 192.168.0.0/255.255.0.0
ALL : 10.8.0.0/255.255.255.0

However,  if there are any addresses in the range 192.168.0.0 through 192.168.255.255 that are normally reachable but not in your LAN — a primary example is a cable modem status page on 192.168.100.1 — you may not want to extend the scope of your local network quite that much. You could use a more restrictive netmask — for example, you could use these two lines, which is what I’d recommend for this project:

ALL : 192.168.0.0/255.255.240.0
ALL : 10.8.0.0/255.255.255.0

That would specify that anything in the range 192.168.0.0 through 192.168.15.255 is on your local network (including subnets on the other side of your tunnel).  Alternately, if you wish to be a bit more precise and/or secure, you could specify the network(s) at the distant ends of the tunnel individually (using a more restrictive netmask), e.g.:

ALL : 192.168.0.0/255.255.255.0
ALL : 192.168.5.0/255.255.255.0
ALL : 10.8.0.0/255.255.255.0

(If you do the latter, you may also want to add a line for the network on the WAN side of the client router, e.g. ALL : 192.168.1.0/255.255.255.0 to be able to reach devices in that subnet from the server side of the tunnel — assuming that won’t conflict with any addresses on your own local network).

You also need to go into your router (the one between the OpenVPN server and the Internet, that controls the LAN at the server end – not the client router running the Tomato firmware) and expand the scope of your local network.  I can’t give you specific instructions for your router, but generally the principle is the same as in the hosts.allow file – in most cases you need to expand the scope of the local netmask to 255.255.something.0, where something is less restrictive than 255 and includes all local nets on both sides of the tunnel, but not your cable or DSL modem’s status page (don’t worry about the 10.8.0.x addresses, your router won’t see those).  I suggest using 255.255.240.0 and then making sure that your local networks on both ends of the tunnel fall within the range 192.168.0.x through 192.168.15.x. The reason you need to change the netmask is so that when something on your primary LAN tries to connect to an address in the 192.168.5.x range (on the other side of the tunnel), your router will send out an ARP probe to find out which device on the network has that address (getting the OpenVPN server to respond is another issue that we’ll cover later). But if you are trying to get to something on the backside of your router (the modem status page being the prime example), you don’t want your router thinking it’s on your LAN – hence the need for care when changing the netmask.

If for some reason you can’t follow my suggestions about local network range, you’ll still need to figure out an appropriate netmask, both for the etc/hosts.allow file and your server-side router configuration.  Fortunately, there are many pages on the Web that will help you – Google the phrase “netmask calculator” (include the quotes) and you’ll find several sites that will help you calculate an appropriate netmask.  Of course, there are limits on this – you’re going to have a much harder time making this all work if all the local networks on both sides of the tunnel aren’t in the 192.168.x.x range (or, more specifically, don’t have at least the first two octets of the LAN IP address in common).

While you are in the router on the server side of your connection, you need to open UDP port 1194 for incoming traffic and point it at your OpenVPN server – otherwise outside connection attempts will never be received by the server. Don’t open the corresponding TCP port – it’s really not a good idea to use TCP for OpenVPN unless you are forced to do so (by an overly restrictive ISP, for example).

You also need to open up the file /etc/sysctl.conf and make sure that the following line is NOT commented out (add it if it doesn’t already exist):

net.ipv4.ip_forward=1

Also, at a terminal prompt, execute the following:

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

While in the terminal, you SHOULD upgrade OpenVPN to the most current version (or install it if it’s not already installed).  Older versions of OpenVPN will not work with these instructions.  Just type openvpn from a command prompt and at the top of the resulting output it should show you what version you have, if it is installed.  It will look something like this:

OpenVPN 2.2.0 i686-redhat-linux-gnu [SSL] [LZO2] [EPOLL] [PKCS11] [eurephia] built on Jun  6 2011

2.2.0 is the version in this example.  But on a recent CentOS install, just doing yum install openvpn only offered to install version 2.0.9, which is too old to work with these instructions!  Here is how I installed a newer version (edited July 27, 2011 to reflect a better way):

Add the dag repository if you haven’t done so already.  In the /etc/yum.repos.d directory, create a new file called dag.repo:

touch /etc/yum.repos.d/dag.repo

Edit the file using any text editor (for example, nano /etc/yum.repos.d/dag.repo) and add the following lines exactly as shown:

[dag]
name=Dag RPM Repository for Red Hat Enterprise Linux
baseurl=http://apt.sw.be/redhat/el$releasever/en/$basearch/dag
gpgcheck=1
enabled=1

Save the edited file and then from a command prompt import the repository’s key:

rpm –import http://apt.sw.be/RPM-GPG-KEY.dag.txt

Now if you do

yum install openvpn

You should get the latest version plus any dependencies (it should offer to upgrade your current version if it is older).  Note that you must use compatible versions of OpenVPN at both the client and server ends, so once you have an OpenVPN tunnel working, it might not be a good idea to just go upgrading the software at one end or the other unless you know the newer version is still compatible with what you’re using on the other end (minor version upgrades are probably okay, but I am not guaranteeing that!).

Now return to The ‘Point and Click’ Home VPN HowTo Guide — you want to find the section headed “Setting Firewall rule(s) to allow VPN web traffic to redirect out eth0” — now I will just say that you need to follow those instructions, but when setting up the actual rules, I found that only two were really important.  So if I were rewriting their instructions, here is how I’d say it:

First we’ll assume that the firewall is not set up yet so click Reset Firewall. Now we need to add some rules. From the Showing IPTable: dropdown select Packet filtering  (filter) where we’ll create the following rule:

Forwarded Packets (FORWARD)

Then, from the Showing IPTable: dropdown select Network address translation (nat) where we’ll create the following rule — this is the rule that goes along with the VPN “push redirect-gateway”. This allows the VPN web traffic to be routed out through your connection:

Packets after routing (POSTROUTING)

Why not add the rest of the rules? Well, if you Reset Firewall as instructed, you don’t need them, because they are specifying default conditions. But if you didn’t want to reset the firewall because you already have some preexisting rules, or if you ever actually decide to go in and configure some more restrictive firewall rules, then you may need some of the other rules listed. There’s certainly no harm in adding the other rules, but I’d rather emphasize the two that are absolutely necessary to get this working, assuming you started with a clean slate.

When you are finished, the two rules pages should look like this:

(I know that at this point, some Elastix and FreePBX users may be wondering if the above would interfere with the operation of fail2ban, in the event they have installed it. As far as I can tell, the answer is no… fail2ban communicates with the firewall in a different way, and unless you add rules that explicitly contradict what fail2ban does, I don’t think there will be any issues. However, I do recommend that you temporarily disable fail2ban, possibly from Webmin’s System | Bootup and Shutdown page, prior to connecting a new VoIP adapter or similar device on the client end of a tunnel for the first time. The reason is that if the device fails to register for any reason, such as a mis-typed password, fail2ban might refuse connections even after you fix the issue, and it might even clamp down on other connections from the client end of your tunnel. So get your devices registered and working, then restart fail2ban. Alternately, if turning off fail2ban makes you nervous, you could open /etc/fail2ban/jail.conf in a text editor, then edit the ignoreip option under the [DEFAULT] section to include the IP addresses or network on the client side of your tunnel — for example, you could add 10.8.0.0/24 and 192.168.5.0/24 as address ranges you don’t ever want to ban.)

Once again, return to The ‘Point and Click’ Home VPN HowTo Guide — now you want to start at the section, “Install OpenVPN-admin module” and continue through to the part entitled “Testing the VPN Server using the OpenVPN client GUI from Windows.” If their suggested download method doesn’t work, use the download link on this page to download it to your local machine, then in Webmin install the module “From uploaded file” rather than “From ftp or http URL” as the article suggests. What I suggest you do here is setup TWO clients, one for a soft client you can use for testing purposes, and one that you will use with the OpenVPN client in the Tomato firmware. While you might be able to get a Windows-based client to work using the instructions shown, I can assure you that the Tomato client isn’t going to work until you add a few additional tweaks, which we’ll cover in Part 3. But you can certainly set up and test the Windows-based client if you like, just to assure yourself that the server is actually working.

Just so you don’t spend a couple hours beating yourself up wondering why the server won’t start, I will point out that there’s a glitch in the Webmin OpenVPN module. When you click on the VPN server list and then click on Start to start a server, the server name is supposed to turn from red to black, and the word Start is supposed to turn to Stop. For whatever reason, that doesn’t happen on our server… you can click Start until the cows come home and it still won’t turn black. It probably has something to do with the module configuration itself – for example there’s a setting for PID file path of running OpenVPN processes (*) which by default is set to /var/run, which may not be correct — however, when I changed it to /var/run/openvpn, which does seem to be correct, it made no difference. I just start and stop the server using the buttons at the bottom of the main “OpenVPN Administration” page, which seem to work fine.  EDIT:  See Leon Baker’s comment in the comments section below for a fix for this problem.  Thanks, Leon!

Next up, in Part 3: Configuring the OpenVPN server using Webmin (or more specifically, the changes and additions you need to make to actually get it working as expected). More screenshots!!!

Some readers of this blog may recall that several months ago I had wished for a Simple VPN device – back then I had written:

There is another type of software that ought to be moved into its own box, and that is Virtual Private Network (VPN) client and server software. Yes, I’m aware of OpenVPN, and I tried to find setup instructions that someone like me could understand, but to no avail – it looks like you need a degree in computer networking to understand how to set up this type of software. And yet, built into hardware devices, it could be immensely useful in certain circumstances. Let’s consider the following diagram:

In this particular case we have a SIP-based VoIP adapter at a remote location. Anyone who has worked with Asterisk behind the wrong kind of firewall knows the issues involved with using SIP and not having things set up just so (one-way audio, anyone)? But also, we may for whatever reason want that “remote” VoiP adapter to appear as if it were on the local network (maybe we have an ISP playing games with SIP packets?). So we plug the VoIP adapter into our “VPN Client-Side Device” and on the other end, we have a companion “VPN Server-Side Device” which in this case makes two connections to the router – one to receive the “tunneled” data and the second to send the unencrypted data back onto the local network. The green arrows represent the “tunnel”, the orange arrows show where the data from the VoIP adapter enters and exits the tunnel. Please note this is entirely a wired connection, we aren’t using wireless anywhere here. Also note that as far as the VoIP adapter is concerned, the only network it can “see” is the one at the other end of the tunnel – under no circumstances can it access the Internet other than by going through the tunnel.

I show this using a VoIP adapter, but I’m sure that people could think of a lot of other ways this could be used, and a lot of other devices that could be connected to the client end.

Now some will probably argue that it is inefficient to have a device that does nothing but provide the tunnel. But that’s the point – almost anyone could set this up. If you send the client-side device to your grandmother, she can set it up (well, maybe that’s pushing it a bit, but you get my point). People who would never touch a Linux box or a server could use this.

I want to tell you, when I wrote that I had no idea just how difficult it would be to actually get VPN tunneling working using OpenVPN.  The problem isn’t that it doesn’t work — actually, it works quite well — the problem is that it’s a real bear to set up, unless you have someone who knows what they are doing walk you through it.  Unfortunately, you may not haves someone who knows what they are doing to help you, so you’re stuck with me (unless you can find a better page on the subject – if such exists, please let us know in a comment).

The real issue is that you have to learn so many new things at once to make this work.  So, my attempt here is going to be to try and give you a “cookbook”, with plenty of screenshots so you can see how things actually look when everything is configured.  I’m actually also going to approach this in a slightly backward manner, showing you how to configure the client first, then the server.  My theory is that you will think that configuring the client is so simple that configuring the server can’t be much harder, and you’ll get sucked into the project before you realize what you’ve gotten yourself into! 🙂

By the way, what we are doing here doesn’t look exactly like the diagram above – instead it looks more like this (note that the “Primary Router” on the client side can be omitted if you don’t need any UN-tunneled connections, or if the DSL or Cable modem has a built-in router):

For our client, we need something that you can plug your desired device into. You may have a laptop, and you want to communicate securely with a home office. You may have a VoIP adapter, and you want to make secure calls to a remote Asterisk server.  While you can run a software client on the Laptop, when you have a hardware device like a VoIP adapter your choices become more limited.  The solution is to purchase a router that is capable of being re-flashed with custom firmware.  In this case we are going to use the Tomato firmware, and in particular, a version of the firmware designed to support OpenVPN as either a client or a server. Here we’re going to use it as a client. The idea will be that ANY device plugged into the router will automatically use the VPN tunnel, and if for some reason the tunnel isn’t available then the connected device will not be able to communicate, therefore there’s little chance that an insecure communication can take place.

Some readers will already have a router capable of running Tomato firmware, and some will not.  The main Tomato Firmware page shows which routers are supported.  If you do not already have one of these and plan to buy one, I recommend that you consider the Asus WL-520GU. I know that the main Tomato firmware page says there’s no USB support for that model, but that’s not necessary for what we’re going to do, and it’s not even true if you use the recommended firmware build. The reason I suggest using the WL-520GU is because I’m told that although it’s not totally impossible to “brick” the router by doing a bad flash, if you do make a mistake, your chances of being able to recover (so that the router isn’t consigned to being an expensive paperweight) are far better than with some other models.

I should mention here that I inherited this project from someone else who couldn’t get it to work.  I had made the mistake of casually suggesting they get the Asus router if they wanted to attempt this, only to find them on my doorstep with router in hand.  So again, I’m not saying this will be easy, and the one thing I will not tell you how to do is how to get the Tomato firmware onto your router.  The reason is that if I give you instructions and leave out a step and you brick your router, you will be mad at me.  Better you find someone else’s instructions, and if they’ve left out a step, you can be mad at them. I will mention that, at least in the case of the Asus router I had here, it was a two-step process – I used the Asus Firmware Restoration Utility to first install DD-WRT (using these instructions) and then used DD-WRT’s web interface (Administration -> Firmware Upgrade) to install Tomato (I’m skipping a whole tale of woe and grief that transpired between those two events). Basically I followed the instructions at An Easy Guide to Installing Tomato on the Asus 520gu, but I’m not telling you to do that — it’s up to you which instructions you wish to follow.

Why Tomato instead of DD-WRT?  Because Tomato works, that’s why. But if you want to try getting it working on DD-WRT, go ahead, knock yourself silly (only one tip for you, from a tweet by @pista01 on Twitter —  if you keep getting TLS errors, make sure your NTP client is set up). If you succeed, great for you. If you don’t, you’re welcome to come back here and continue on.

But don’t just grab the first build of the Tomato firmware that you see. You need one that includes VPN support.  There are two versions I would highly recommend — if you have taken my advice and acquired an Asus WL-520GU (or similar model with built-in USB port), then I recommend teddy bear’s build because it enables the “missing” USB support, and also includes the VPN support from SgtPepperKSU’s build — which is the one you should get if you DON’T have the Asus WL-520GU, but instead have some other compatible router (EDIT: Advanced users may also wish to check out thor2002ro’s build, which offers both the VPN and USB support from the aforementioned builds, plus support for SDHC, SNMP, and perhaps other additional features.  I haven’t tested that one at all, and note that recent versions probably won’t work with many router models due to memory requirements, so unless you really need one of the features in that version and know that your router supports it, I’d stick with one of the other versions). Make sure you read up on the chosen build and be sure you get the correct firmware version.  For the Asus I used the binary from inside the tomato-1.25-ND-USB-8632-vpn3.3.rar archive, but since then a newer version has been released (tomato-1.25-ND-USB-8634-vpn3.4.rar was released in August, 2009), or you may prefer a different version.

In this series you will see several screenshots.  I’m using the custom “Tomato USB” theme, so the colors and “look” may be a bit different than what you see, but other than that everything’s in the same place as with the default theme. Later (after taking the screenshots) I replaced the tomato.png file from the theme with the one you see at the right, which I happen to like a little bit better.

Two other caveats: Although this router has wireless capability, for this application we aren’t going to use it — it’s going to be used on a wired network only.  That said, once you get it set up and working, feel free to experiment with the wireless capabilities if you like — just be aware that if something on the wireless side of things doesn’t work, I really can’t assist you. And also, we’re assuming that everything plugged into this router will be using the VPN tunnel full time, which implies that this router might (perhaps in a majority of cases) be plugged into another router, so that some other devices can access the local Internet connection, while the devices plugged into this router are limited to going through the tunnel. Note that if this router is plugged into another router, it would be preferable (but not absolutely essential) if it were in that router’s DMZ, so that you don’t have double NAT (Network Address Translation) taking place.

And now, a word about OpenVPN.  OpenVPN supports two different modes of operation — TAP and TUN.  In this case, we are using TUN.  We MIGHT explore TAP at a later time, but TUN is easier to set up, and ANYTHING that can be done to simplify this process is worthwhile.  The main difference, from the users point of view, is that using TUN the two ends of the tunnel occupy two different portions of the local address range.  In this case, on our “home” LAN, the addresses are in the 192.168.0.x range and are assigned by the main router.  At the client end of the tunnel, the router running the Tomato firmware will hand out addresses in the 192.168.5.x range.  Neither router steps on the other’s toes, so to speak, when handing out addresses.  And there is one other difference — although shared directories can be accessed across the network, Windows/Samba shares cannot be “seen” on opposite ends of the tunnel. If you know they are there and know the IP address and share name of the hosting device, you can still access them, but the mechanism that advertises shares doesn’t cross the tunnel.

With TAP, on the other hand, the router at the primary location hands out IP addresses in the same local address range to devices on both sides of the tunnel, and also (in theory, anyway) shares will be “advertised” across the tunnel.  Sound like what you’d want, right?  Except that when we tried to set it up on the server side, somehow we managed to bring down the entire network – it basically acted like a denial-of-service attack on the entire LAN, and the problem stopped the moment we went back to using TUN. After you’ve messed with this stuff long enough, something like that can leave a rather bitter taste in your mouth, so we decided to stick with what worked.  In our particular application, seeing shares across the LAN would not be essential. Even if you eventually want to try using TAP, I suggest setting it up using TUN first, then when you have achieved that you can cross your fingers and try switching the mode to TUN at both ends.  I doubt it will work easily for you, but experimentation is certainly welcome.

If you want to know more about TUN/TAP and other OpenVPN options, you might want to get the book Beginning OpenVPN 2.0.9 (Amazon affiliate link) by Markus Feilner and Norbert Graf — see my recent mini-review of this book (links edited February, 2010 to reflect updated and expanded edition of the book).

So with the preliminaries out of the way, let’s get to the client screenshots…

This first shot shows the header, sidebar, and Save/Cancel buttons. Since the settings are probably a bit hard to read, we’ll zoom in on the pertinent part:

The main thing to keep in mind here is that the subnet you select must not conflict with address assignments on the primary network at the server. Next, on the Router Identification page, enter a Hostname to identify the router:

One thing I have read in several places is that it’s important for the time to be set accurately at the client.  For your choice of time servers there are several presets, but if you use Custom you can specify one or more of your own as the first choice(s), if you have a machine on your network that acts as an NTP server:

At this point you should probably go to the Administration | Admin Access page and set things up there to your liking. Remember that anything you make accessible on the router’s local LAN will also be accessible on the other side of your tunnel using the same security methods, so be careful.

Now to what we came for… setting up the VPN client. Click on VPN Tunneling and then on Client. I’ll say that one more time – you MUST click on Client. It’s far too easy to skip that step and accidentally be trying to configure a server! Then you should be at the Client 1, Basic tab:

Of course, the button at the bottom of the page will sat “Start Now” instead of “Stop Now” – I took these screenshots through the tunnel, so I couldn’t very well stop it to get that little detail right! After setting that up you want to click on the Advanced tab:

Note that the connection retry value is -1 (which means infinite retries) and there are two added lines in the custom configuration section:

keepalive 10 120
float

In case the connection to the server or the Internet goes down for a time, those settings should cause the client to keep attempting to re-establish the connection to the server. The float command is useful if your client is at a location where the ISP might change the IP address without advance notice — it is supposed to allow the VPN connection to survive an IP address change. You can omit float if your client is at a fixed IP address that is not subject to change.

And then the Keys tab – just take a look now, when we move on to the server I’ll explain how these are filled in:

There is one more thing that needs to be done (besides adding the keys) for our tunnel on the client side. Go to Administration | Scripts and click on the WAN Up tab. Enter the following two lines into the text box:

route del -net 0.0.0.0
route add -host `nvram get vpn_client1_addr` gw `nvram get wan_gateway`

The second line may wrap on your display due to length. You may want to copy and paste those lines so you get them right, but if you must type them, note that the ` characters are actually backticks – the small apostrophe-like character on the key to the left of the “1” key (the number 1) near the top left corner of most keyboards (well, in my part of the world, anyway). Then click on the Save button way down at the bottom of the page. If you fail to do this and your tunnel ever goes down (server dies or is inaccessible, etc.) there is a possibility that traffic that should go through the tunnel will use the local Internet connection instead.  These two lines will keep that from happening. When you are done it should look like this:

Just a note for future reference: You can optionally add an additional line here to allow you to get to something “upstream” of the network on the WAN side of the router. For example, let’s say you have configured the server to allow you to connect to devices on both the LAN subnet (192.168.5.x in our example here) and also devices connected to the primary router, in other words, on the WAN side of the router running the Tomato firmware (which were in the 192.168.1.x range on our example setup). But let’s suppose that upstream of that, you have a cable modem at 192.168.100.1 at the client location that you’d also like to be able to access. As long as you don’t have a conflicting address elsewhere in your network, you could add a line such as this in your WAN Up script:

route add -net 192.168.100.0 netmask 255.255.255.0 gw `nvram get wan_gateway`

… which would allow access to anything in the range of 192.168.100.0 through 192.168.100.255. If you want to be more specific, you can narrow it down to an exact address:

route add -host 192.168.100.1 gw `nvram get wan_gateway`

We’ll cover what else has to be done to enable this type of additional routing at the server end in the upcoming installments, but the above is what has to be done at the client-side router that is running the Tomato firmware. Note that you do not normally have to a a line such as this to get to devices on the same subnets as the LAN or WAN ports of the router, but just for anything upstream of the network that the WAN port of the router is connected to. If you don’t understand why you might want to add this type of additional routing now, just ignore this information for the time being, but make sure you do add the first two lines I mentioned above.

Once your tunnel is operational, you should go to the Advanced | Routing page and look at the Current Routing Table. Your addresses will differ (this was a test setup; you probably will see a wider range of addresses) but the main thing you want to make sure is that there is never an entry of default (or 0.0.0.0) in the destination column that goes to any interface other than a tunnel (tun11 in this illustration) — you should never see that whether the tunnel is enabled or disabled. If you do, then something’s likely wrong with the two lines you entered above (under the WAN Up tab):

So, that’s the basic client setup. Wasn’t too difficult, right? Ah, but just wait until we get going on the server — hopefully I can make it easy enough that you won’t have about three weeks worth of sleepless nights, when you occasionally mutter under your breath things like “Why? Why?? Why??? WHY won’t this damn thing work!”, and other things I’d rather not put on the Internet! But before I can write the next part, I REALLY need to catch some ZZZ’s, so the server will have to wait for part 2.