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Configuring open emergency WiFi at home

Why?

I remember Cory Doctorow writing that, in a crisis, you are more likely to be okay if you treat your neighbours as allies rather than threats. If everything does go sideways, as things are looking like they could to a lesser or greater degree in the UK, then one of the most important things to do is to rapidly make friends with your neighbours, if you're not acquainted already - because together, you can make things better.

One of the things I started doing a few years ago — just before the COVID-19 pandemic hit, in fact — was to set up an open WiFi channel called Emergency Internet on my home router that didn't provide access to my own machines, but did provide open, unrestricted access to the public Internet. Because it would cost me nothing, and it could help out a neighbour in need.

Before you do this yourself, you should consider potential liabilities. Your ISP may have rules that don't allow this, and it's conceivable that someone could badly misuse your network connection and get you in trouble. (Though you might hope that, "I have an open network connection useable by any passer-by!" should be a plausible exculpatory explanation, it's not guaranteed and it could have to endure some significant distress for a long time before it's accepted.)

How

The specifics for how to configure this will vary from router to router. Mine makes it easier than most, and some might not make it possible at all.

The basic idea is to set up a new WiFi name — an ESSID in technical perlance — that's seperate from your normal one. I called mine Emergency Internet, but you can pick whatever you like. Once created, you'll want to put it on its own compartmentalised network, with its own IP address range, that has no access to your other domestic machines — but with permission to connect to the public Internet, probably using Network Address Translation (NAT).

Finally, having set up the new network, you want to make sure that t