A plain-English reference for every term mentioned in our guides. If a term sent you here, click your browser’s back button to pick up where you left off.
Language & Culture
Aerouant
The Breton word for dragon. In Breton myth, the Aerouant is a symbol of fierce protection and ancient strength. This site is named for that spirit of guardianship — becoming the protectors of our own neighbourhoods rather than waiting for someone else to act.
Breton
A Celtic language spoken in Brittany, northwestern France. It belongs to the Brythonic branch of the Celtic language family, alongside Welsh and Cornish, and traces its roots to migrations from Britain during the 5th–7th centuries. Breton is classified as endangered, with around 200,000 speakers today — a steep decline from over a million in the mid-20th century. The name Aerouant comes from this language.
Hardware
Raspberry Pi
A small, affordable computer about the size of a paperback book, built by the Raspberry Pi Foundation. It runs Linux and is popular for DIY projects, home servers, and education. The Pi 5 is the latest and most powerful model; the Pi 3 is an older, lower-power model that works well for lightweight tasks like running a coordination server.
SATA
Short for Serial Advanced Technology Attachment. A standard connector and interface for hard drives and SSDs. A 2.5-inch SATA SSD is a common, affordable solid-state drive that connects to the Pi via a USB-to-SATA enclosure.
SSD
A Solid-State Drive. Unlike traditional hard drives with spinning discs, an SSD stores data on flash memory chips — making it faster, quieter, and more shock-resistant. Ideal for a portable setup that might get bumped around.
Intel AX210
A small wireless network card that plugs into the Pi’s expansion board. It supports Wi-Fi 6E, which means faster speeds and better performance in crowded wireless environments (like hotels or conferences).
USB-C Power Delivery
A charging standard that lets USB-C cables carry more power than basic USB. The Pi 5 needs 27W (5V at 5A), so your power bank or charger must support Power Delivery at that level. A 30W PD power bank can keep the Pi running for hours without mains power.
MicroSD Card
A tiny memory card (about the size of a fingernail) commonly used in phones and cameras. In this project, it’s used temporarily to set up the Pi’s boot order, then repurposed as a local backup drive.
GPIO
General-Purpose Input/Output. A row of metal pins on the Raspberry Pi that lets you connect expansion boards (HATs), sensors, and other electronics. The ZP596 HAT connects via these pins.
HAT
Hardware Attached on Top. An expansion board that sits on top of the Raspberry Pi, connecting via the GPIO pins. The ZDE ZP596 HAT adds a second Ethernet port and an M.2 slot for the Wi-Fi card.
Networking
Tailscale
A mesh networking tool that creates encrypted connections between your devices, wherever they are. It uses WireGuard under the hood and handles all the complexity of devices moving between networks, being behind firewalls, and NAT traversal. Normally it uses Tailscale’s own cloud servers, but in our setup we replace those with Headscale.
Headscale
An open-source, self-hosted replacement for Tailscale’s cloud coordination server. It runs on your own hardware (the Pi 3 in our setup) and lets all your Tailscale-connected devices find each other without relying on any third-party service. Think of it as a private phone directory for your devices.
WireGuard
A modern, lightweight VPN protocol known for being fast, simple, and secure. Tailscale uses WireGuard to create encrypted tunnels between your devices. You don’t interact with WireGuard directly — Tailscale manages it for you.
Mesh Network
A network where devices connect directly to each other rather than all going through a single central point. In a Tailscale mesh, your phone can talk to your Pi, your laptop can talk to your phone, and they can all find each other regardless of which Wi-Fi network they happen to be on.
DHCP
Dynamic Host Configuration Protocol. When your phone connects to a Wi-Fi network, DHCP is what automatically gives it an IP address, tells it where the internet gateway is, and which DNS server to use. In our setup, Pi-hole handles DHCP for all connected devices.
DNS
Domain Name System. The internet’s phone book — it translates human-readable names like aerouant.cloud into the numeric IP addresses that computers actually use. Pi-hole acts as your local DNS server, which is how it blocks adverts: when a device asks for an ad server’s address, Pi-hole simply refuses to answer.
NAT
Network Address Translation. A technique that lets multiple devices on your local network share a single public internet address. Your ISP router does this for your home network, and the Pi 5 does it for the devices connected to its own network. It also means devices on the internet cannot directly reach your local devices — which is a good thing for security.
Ethernet
A wired network connection using a cable with a rectangular clip-on connector (RJ45). More reliable and faster than Wi-Fi, and doesn’t suffer from interference. The Pi 5 has one built-in Ethernet port, and the ZP596 HAT adds a second, faster 2.5G port.
STUN
Session Traversal Utilities for NAT. A protocol that helps devices behind firewalls and NAT routers discover their public-facing address so they can establish direct connections with each other. Tailscale uses STUN (on port 3478) as part of its NAT traversal — it’s how devices on different networks manage to talk directly rather than routing through a relay.
Dynamic DNS
Your home internet connection usually gets a different public IP address each time your router restarts. Dynamic DNS gives your home a fixed name (like myhome.duckdns.org) that automatically updates to point to your current IP. This way, the travelling Pi 5 can always find the Pi 3 at home.
Port Forwarding
A setting on your ISP router that says “when traffic arrives on this port, send it to this specific device on my network.” In our setup, we forward port 443 to the Pi 3’s Headscale server, so the Pi 5 can reach it from anywhere. Only authenticated Tailscale clients can use this connection — it’s not open to the public.
Software
Docker
A tool that lets you run applications in isolated containers — each one is like a self-contained mini-computer with everything the application needs. This means you can install Kiwix, Jellyfin, and other services without them interfering with each other or making a mess of the operating system. If something breaks, you just delete the container and start again.
Pi-hole
A network-level ad blocker that runs on your Pi. Instead of installing ad blockers on every device, Pi-hole blocks adverts and trackers at the network level — every device connected to the Pi’s network gets ad-blocking automatically. It works by acting as the DNS server and refusing to resolve known advertising and tracking domains.
RaspAP
A web-based management tool for turning a Raspberry Pi into a wireless access point. Instead of editing config files by hand, RaspAP gives you a browser interface to manage your Wi-Fi network name, password, channel, and security settings.
Kiwix
An offline content reader that serves ZIM files — compressed, self-contained packages of websites. The Kiwix library includes offline copies of Wikipedia, Stack Overflow, Project Gutenberg (70,000+ books), iFixit repair guides, and much more. Once downloaded, all this content works without any internet connection.
Jellyfin
A free, open-source media server. It organises your music, films, and TV shows and lets you stream them to any device on your network through a web browser or dedicated app. Think of it as your own private Netflix/Spotify that works offline.
nftables
The Linux firewall framework that controls which network traffic is allowed and which is blocked. In our setup, the nftables rules ensure that your devices can reach the internet, Tailscale traffic flows freely, and nothing from the upstream network (hotel, ISP) can reach your devices directly.
rsync
A file synchronisation tool that efficiently copies files between two locations. It only transfers files that have changed since the last sync, making subsequent backups much faster than the initial one. Used in our setup to mirror the Pi 5’s entire SSD to the Pi 3’s backup drive.
SSH
Secure Shell. A way to remotely control a computer over the network using a text-based terminal. You type commands on your laptop, and they run on the Pi. All communication is encrypted, so nobody can see what you’re doing even on a public network.
nginx
A lightweight web server. In our setup, it serves the travel router’s landing page — the simple menu that appears when you open http://10.0.0.1 in a browser, showing links to all the available services.
systemd
The service manager built into most modern Linux distributions. It starts, stops, and monitors background services (like the failover script and backup timers). When you “enable” a service with systemd, it means it will start automatically every time the Pi boots.
DuckDNS
A free dynamic DNS service. You create a subdomain (like myhome.duckdns.org), and a small script on the Pi 3 updates it with your current home IP address every five minutes. This way, the Pi 5 can always find its way home regardless of IP changes.
OpenStreetMap
A free, community-built map of the entire world — like Google Maps, but owned by the people who contribute to it. In our setup, OpenStreetMap data is downloaded as offline map tiles so you can browse detailed maps even without an internet connection.
Concepts
Exit Node
A Tailscale device that offers to route other devices’ internet traffic through itself. When the Pi 5 advertises itself as an exit node, your phone can send all its internet traffic through the Pi — useful for getting ad-blocking and encrypted networking even when you’re not on the Pi’s Wi-Fi.
IP Forwarding
A system setting that allows a computer to pass network traffic between different network interfaces — essentially acting as a router. Without IP forwarding enabled, the Pi would keep all traffic to itself instead of passing it between your devices and the internet.
Masquerade
A form of NAT where the Pi replaces the source address on outgoing packets with its own address, so traffic from your devices appears to come from the Pi itself. This is how the Pi shares a single internet connection with all connected devices.
ZIM File
A compressed archive format used by Kiwix to store entire websites for offline reading. A single ZIM file can contain all of Wikipedia (including pictures) in around 109 GB, or the text-only version in about 12 GB.
MBTiles
A file format for storing map tiles in a single, portable database file. Used by the tile server to serve offline maps. You download an MBTiles file covering a region (e.g., the UK, Europe) and the tile server renders it as a browsable map.
USB-to-SATA Enclosure
A small case that lets you connect a SATA drive (like a 2.5-inch SSD) to a computer via USB. The controller chip inside matters — look for ASMedia ASM1153E or Realtek RTL9210 chips, and avoid JMicron chips which have known issues with the Pi.
UAS
USB Attached SCSI. A faster protocol for communicating with USB drives, compared to the older usb-storage driver. If your USB-to-SATA enclosure supports UAS, the Pi will use it automatically for better disk performance.
