<p>Both expo laptops Clowley and Aziraphale use DHCP over wifi to get an IP4 address and the identity of a DNS nameserver. Neither laptop has any other configuration.
<p>If you connect your laptop or phone to the Potato hut wifi you will connect in the same way.
<p>The Gasthof WiFi - which you can use if you are close enough - is "StaudnGast" and has no WiFi password but there is a login webpage. It allocates IP addresses in the range <samp>192.168.2.x</samp> etc. The antenna is now on the first-floor balcony within sight of the tatty hut window. You can get the password from the Gasthof front desk, or during expo it is usally written on the whiteboard in the potato hut. In the scripts published in this handbook we use the word GASTSECRET instead of the real password.
<p>If you are not actively using the internet, the Gasthof system will close the connection and you will have to re-login again, typing the password into the login page.
<h3>The Potato hut Wifi</h3>
<p>The potato hut WiFi has <ahref="https://www.howtogeek.com/334935/what-is-an-ssid-or-service-set-identifier/">SSID</a> "tattyhut" with our usual cavey:beery password. Like almost every other wifi anywhere it is running DHCP and allocating IP addresses to your device.
<p>The <ahref="https://en.wikipedia.org/wiki/Acer_Aspire_One">Acer Aspire One</a> netbook is running Debian Linux operating system with the lightweight <ahref="https://xfce.org/">[xfce]</a> window mananger. It runs a script once every 60s which checks whether it can access the internet. If it can't, it attempts a re-login to the Gasthof wifi system, which takes 5-10 seconds. If it still can't access the internet it deletes nearly all the configuration and reloads everything - which takes about 30s. The mere fact that it accesses the internet every minute is enough for the Gasthof system to keep the connection open - until it times out completely which it does after an hour or so.
<p>Because of a permissions difficulty, the scripts on the netbook live in <var>/root/fakenet</var> so that the cron job (running as root) can access them. [This is not the usual Linux place to keep such things.] The cron file lives in the usual place in <var>/etc/cron/cron.d/fakenet</var>.
<p>The Netgear ethernet/wifi hub holds the radio transceiver that provides the wifi coverage inside the potato hut.
It is configured using its web control panel. It has an <ahref="https://manualmachine.com/netgear/wndr4000/816208-user-manual/">online manual</a> but it needs no configuration at all during expo. Just turn it on at the beginning of expo and off again at the end.
<h4>IP6</h4>
<p>While you can use 5Ghz wifi and IP6 to connect within the hut, there is no IP6 connectivity to the external internet. Sorry. We are dependent on the Gasthof system for this.
<h3>4 different 'networks'</h3>
<p>To understand how the network is configured, you need to realise that we have to manage these different 'networks':
<ul>
<li><samp>192.168.2.x</samp> The Gasthof wifi network
<li><samp>192.168.1.x</samp> The potato hut wifi network
<li><samp>10.0.x.y</samp> The network on the short bit of cable connecting the netbook with the Netgear box.
<li>The network on the longer length of cable connecting the Netgear box with the <var>expo laptop</var> (and sometimes the printer).
</ul>
We bridge the hut wifi with the hut ethernet cable to the <var>expo laptop</var> so they are both <samp>192.168.1.x</samp>, but this is a matter of choice. This is configured in the netbook config files.
<h4>Where the DNS happens</h4>
<p> DNS is what connects a computer name (such as <var>expo.survex.com</var>) with an internet address (such as <samp>78.129.164.125</samp>). To make the internet work, we need to tell every laptop and phone where to find a DNS nameserver, or what machine to ask in order to get DNS queries forwarded to a DNS nameserver.
<p>The DNS configuration happens in the netbook. The Netgear box just forwards DNS queries to the netbook, and tells laptops connected to the hut wifi to use that too.
<h4>Where the DHCP happens</h4>
<p>DHCP is what decides what the <samp>x</samp> is when the wifi issues an address that a laptop must use when it connects to the wifi as <samp>192.168.1.x</samp>.
<p>We have done this in two different ways:
<ul>
<li>2017-2019 : in the netbook.
<li>2022 : in the Netgear box.
</ul>
<p>The benefit of doing it in the Netgear box is that you get to play with a graphical web interface not text files.
<p>The benefit of doing it in the netbook is that all the configuration is in the same place, and you only have to learn one way of doing things instead of having to use text files <em>and</em> a web interface. Aslo, by making the Netgear box completely dumb, it is swap-replaceable if it dies with no reconfiguration required.
<h4>Static addresses</h4>
<p>The netbook has two interfaces: the Alfa wifi antenna (which has an address issud by the Gasthof wifi system), and its ethernet cable socket which is configured to have the address <samp>10.0.1.2</samp>.
<p>The Netgear box has its yellow ethernet cable socket set to the address <samp>10.0.1.1</samp>. The four other ethernet sockets are all on the address range <samp>192.168.1.x</samp> and the wifi network interface is set to <samp>192.168.1.1</samp> on the same network range.
<p>Because the netbook is on a different network from the laptops connecting to the hut wifi, you can't directly login to the netbook using <var>ssh</var> to the IP address (ssh expo@10.0.1.2), but you can using its name, so <var> ssh expo@tclaspire3.potatohut</var> should work if everything has been configured correctly.
This used to need running once or twice a day when the internet stops working, but it was radically fettled in 2022 and so should be much more reliable.
Sometimes you may have to walk over to the blue Acer Aspire netbook and run this script directly by typing on its keyboard
as the network has collapsed so badly that <spanstyle="font-family:monospace">ssh</span> doesn't work.
<p>In 2017 we arrived on expo to discover that our hard-drive in the hut had died (taking the music collection with it) which triggered the general reconfiguration to connect the tattyhut to
the internet continuously and not to have our own local server. This coincided with a much-improved WiFi service at
the Gasthof. We continued with the wifi service in the hut but now it also connects to the external internet instead of to a 'pretend' internet (which is why the system is called 'fakenet').
<p>In 2022 Wifi reception from the Gasthof was very poor. The connection script was improved so that dropped connections were restored more quickly. However the basic bandwidth with a cheap antenna was not enough.
<p>In 2023 a new Wifi device (the Alfa) should restore decent connectivity. We hope this will improve everything to how it was in 2019. However this Alfa has proved to be a right bastard to find the right drivers for. Wookey has had to be inventive in using an Ubuntu PPA to make it work with the Acer Aspire 1.
<p>Also during winter 2023/23 Wookey upgraded the operating system on the Acer Aspire One netbook from whatever ancient Debian it had been running to a decently almost-modern Debian distribution. This required much coaxing. As of 26 March, it is still a couple of Debian versions behind where we would want it to be.
<p>The structure of the system was created by Wookey in 2013 who used the fakenet principle and the netbook to run training sessions for the Cave Survey Group in the UK. [This is why the script has an extra level of parameter setting that might seem necessary: it has 'csg' and 'expo' options, but the two configurations have diverged so much over the years that this is merely a fossil.]
<p>The part of the script that logs into the Gasthof wifi was written by Mark Shinwell in 2017 and re-edited by Sam Wenham in 2019. Wookey made it more robust on expo in 2022.
