DIY VPN access point

I would like to use an anonymising VPN in my house. I could install separate software on each, but this is unsatisfactory. Per default, our household devices should not have to route communications between one another via Amsterdam. This is terrible for sharing files from the network files server or copying photos, or streaming from the household media server etc. Instead, our network should be a normal wifi network, but the wire that connects us to the outside world, everything that goes over that wire should be encrypted.

To do that, one sets up a VPN router/access point. If you are taking one of the VPN options, an understanding of basic firewall management is advisable.

Flash a router

Getting a non-VPN router and flashing it with VPN-friendly firmware. Tedious. You need a fancy router, and the crappy free one you got from your ISP isn’t fancy. Basic routers typically have about 64MB RAM and unbelievably feeble CPUs. They are computers that would have seemed under-powered in the year 2000 that for some reason we pay a giant premium to have wired into the broadband, and if you try to do something even mildly taxing, such as securing their communications, they fall over and die. I suppose there is a good antenna on these things, but also the debugging/upgrading experience is bad. So you need to buy a fancy router and upgrade it. This requires more time and research and money than you would ideally like.

Vyprvpn distributes custom router images on tomato by shibby for certain routers.

ExpressVPN supports a custom VPN app on certain routes.

BlackVPN has good documentation on how you would use DD-WRT firmware to enable privacy on their system.

Pre-rolled VPN router

Gradually becoming more affordable although still expensive because decent modern routers are still remarkably expensive. If you trust the vendors, this might be a viable option. Techradar reviews some options. Flashrouters reconfigures third party routers (affiliate link); Their surcharge is small; It is hard to imagine beating their total price unless you value your labour at nothing or work as a network tech and flash routers all day or something.

Make a spare laptop into a VPN access point

Any linux machine with wifi can be a wireless access point—even, or especially, a crappy old spare laptop too slow for anything else. This is typically cheaper than buying fancy router and even a crappy laptop is faster than most routers, although with worse antennae. If you want to understand what you are doing here without doing a whole IT degree, the smoothest theoretical intro I have found is Carla Schroder’s Linux Networking cookbook, (although it is no longer a practical intro because it came out more than a decade ago) and there are various explanations on the theory of netfilter. Also Jim Salter’s rant that routers are terrible computers for the price, in the form of a HOWTO, is kinda interesting. You can even do this all with a GUI on recent ubuntu. It seems that a minimally decent computer with a good antenna would be a better value proposition and also easier for idiots like me who want to plug in a keyboard or such. Nitty-gritty-I-don’t-care-why-tell-me-how intros? See this grumpy but simple and acclaimed stackoverflow answer. There are some wrinkles.

Single-board-computer VPN access points

One can do this especially economically using a single board computer such as the Raspberry Pi, which even out-of-the-box has respectable wireless performance. This seems like a good idea when you first think of it. My, you think, that will use little power and require little space and I can keep the computer stuck to the ceiling somewhere and that will be fine. In practice it has been much more difficult for me since the reason that the computer is so tiny and efficient is that it has no screen or keyboard, and inevitably something breaks down in the network stack and I need a screen and keyboard attached to diagnose it and they are both really hard to attach to a tiny computer stuck to the ceiling. Many hours have I lost in diagnosing a problem, thinking it was fixed forever and then the moment I put the raspberry pi somewhere inconvenient, everything falls apart. This is the nature of networking problems in general, of course.

Pro tip: if you are doing this is a raspberry pi 4, do not use a case unless it has a fan, or the device will overheat and crash.

Pro tip: There is a hard limit of 7 clients for a raspberry pi in access point mode.

Basic WAP (Wireless access point) setup is supported by the rasppi folks themselves. Here is their recommended setup that worked fine for me as a vanilla (non-VPN) AP. I did run into problems with the iptables-restore not running after a VPN reconnect. Mustafa Çalap’s setup is even simpler but seems to handle VPN disconnection with even less grace. The Zentralwerkstatt howto uses a slightly different software profile (adding in isc-dhcp-server and iptables-persistent) than the others, which means you can avoid some of the manual iptables configuration but I’m less familiar with what is going on. I will try this next in the hope it is more reliable. AFAICS the necessary bits of the classic dovyez universal firewall are

#hostAP stuff
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
iptables -A FORWARD -i eth0 -o wlan0 -m state \
iptables -A FORWARD -i wlan0 -o eth0 -j ACCEPT

# HostAP requires the lines below to both be ACCEPT to function
iptables -A INPUT -j ACCEPT >> /dev/null 2>&1
iptables -A OUTPUT -j ACCEPT >> /dev/null 2>&1

The ZadenRB one includes a hand-rolled web interface, which looks convenient but also flakey. 🤷‍♂ I ignored the bits about web interfaces with this howto. I had the problem that the dnsmasq configuration would never update after openvpn launched on restart, which seemed to be about setup of the /etc/dnsmasq.conf being fragile when things booted up in the wrong order. Also it made lots of rules to enable VPN access TO the pi externally, which is not an extra attack surface I need right now.

So far, even though it looks long, the two part pimylifeup write-up seems to have worked best. It’s only long because it overexplains; there are not in fact many steps and the setup seems fairly robust.

For any of these, one should also secure the pi.

Bonus tip: the wifi might crash for issues related to the brcmfmac driver. Possibly a firmware updates helps. I have experienced this bug on the Raspberry pi 3B+ but it is not clear to me how widespread it is, and I have not reproduced in on recent raspbian builds. Update: this firmware update seems better.

To make sure your intranet does not leak information during a vpn disconnect, perhaps vpnfailsafe would be a good idea.

In practice, even the simplest options are stupidly complex for something that should be a ubiquitous default. Realistically, what I do is usually: try to configure an access point, then discover that there is some weird kernel error/bug specific to the particular device I am using, which has never been seen on the internet, which requires a specialist network nerd, and which I don’t have time to fix. The latest version of the pi and its OS work fine, mind you, but this kind of challenge is much typical of trying to cobble together security for non-spooks.

I am somewhere in the topmost single-digit percentiles of the population in terms of fluency in stupid geeky shit like this and it is at best marginally feasible for me to work this stuff out and set it up. Realistically most of my friends who have a worse ROI on time spent doing this are not using VPNs and therefore too much data is being leaked to unaccountable surveillance programs. The world is awful.

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