WiFi is commonly used everywhere to create wireless networks and transfer data with high speed safely in an encrypted way. When you can rely on an existing WiFi network with good coverage, it is an excellent way of transferring data from DIY devices.
Many modern microcontrollers (like the ESP8266 and the ESP32 family of microcontrollers) already come with full WiFi support.
Operating WiFi
To set up and operate a WiFi network, it is important to understand a few devices and their operating modes so you don’t run into issues when later connecting DIY devices to your WiFi network.
First off, here is a quick recap of important terms:
- LAN (local area network): private network in your home or office, can be wired or wireless.
- WAN (wide area network): public network like the Internet
- NAT (network address translation): exchanges a private IP address with a public IP address, and vice versa
- Port: each IP address can receive information on up to 65.535 ports. Some port numbers are statically assigned, i.e. a webserver always expects http requests at port 80. Most ports however are dynamically assigned during communication between two devices, i.e. when you browse to a web page, your browser addresses port 80 but provides a dynamic return port for the webserver to return the requested information to.
- Firewall: acts like a data packet filter. A firewall scans incoming data packages and then determines whether these packages can pass and connect to the private LAN. A firewall makes sure that hackers cannot probe your internal network and scan for available ports. It basically acts like a concierge that only allows invited guests to enter the party.
- DNS (Domain Name System): Service that translates human-readable domain names into IP addresses. Without DNS, you would always need to use IP addresses to contact network devices and services. Thanks to DNS, you can instead resolve a friendly name and find out its current IP address.
- DHCP (Dynamic Host Configuration Protocol): crucial functionality built into most Routers. It automatically assigns IP addresses to devices on a local network.
- Router: creates a new local area network (LAN) with its own IP range and firewall, and connects it to other networks (i.e. the Internet)
- Modem: converts the digital information from your network to some format that can be carried over the cables that connect you to the Internet. Depending on your type of Internet connection, there are DSL modems, cable modems, fiber-optics modems, and GSM/cellular modems.
- Access Point: device that can send and receive wireless information and connect it to a wired network
Setting Up WiFi Network
Devices that you use to set up a WiFi network are typically called Wireless Router or WiFi Router. This term is misleading since such devices do not necessarily act as Router and can in fact work in three completely different modes:
- Router: the device creates a completely new and isolated LAN (local area network) with its own IP addresses and firewall, shielding it from other networks such as your wired LAN and the Internet. It also acts like a wireless Access Point that wireless devices can use to connect to.
- Access Point: in this mode, the device does not act as a Router. It only serves as an access point for wireless devices to connect to. The wireless devices are directly connected to the wired ethernet network, and the Router that manages your wired network now also manages the wireless devices. Together, wired and wireless devices form one big LAN, using IP addresses from the same segment.
- Extender: This mode plays a special role as it is not used to create a new WiFi: it connects to an existing WiFi and can be used to (a) extend the WiFi coverage by amplifying and forwarding signals, and (b) connect wired devices to the WiFi (provided the device has one or more ethernet jacks).
Router
A Router is the most important device in any data package-based network: it connects two or more networks and makes sure the data packages know where to go, much like a traffic manager or a navigation system.
Even with the most simple WiFi network, you typically want to connect it to the Internet. This is possible only when you operate a Router that knows how to transfer data between these two networks.
For WiFI, you do need a Router - but you do not necessarily need a dedicated Router. You can also use the existing Router that was installed by your Internet Service Provider and that already manages your wired network. Operating your WiFi in Router Mode (with its own dedicated Router turned on) versus Access Point Mode (with its own Router turned off, sharing the existing Router of your wired network) can make substantial differences and should be an educated and carefully considered decision when setting up a new WiFi.
Routers create an entirely new LAN that uses its own IP address range and can communicate with other LANs and the WAN (Internet):
- DHCP: assigns IP addresses to all connected devices from its own IP address pool in its own IP Address Range.
- Firewall: isolates the network against other networks, and i.e. prevents broadcast and mDNS messages to be passed on to other networks
When you set up a WiFi via a dedicated Router (aka: use WiFi in Router Mode), you are shielding your WiFi and all of its devices from your wired network. If you do this, make sure all of your devices are connected to WiFi (including your stationary PC, notebooks, Raspberry Pi servers, etc.).
Traffic Manager
Routers use internal routing tables: a list of paths to various network destinations. Just like a navigation system in a car, the Router reads a data packet header to determine its intended destination, then looks up the destination in its routing table to figure out the most efficient path to this destination.
Routers also take care of network address translation (NAT): your private *Internet connection gets assigned just one public IP address. Inside your private LAN, there can be numerous devices and software (like browsers), though, that all have unique private IP addresses. When such a device sends a data packet to an Internet-based device or service (i.e. a web server), NAT replaces the private IP address with the one public IP address you have, and adds a dynamically assigned port so it can later keep track of the incoming data and assign it to the correct device, essentially providing the Internet-based service a way to return information back to exactly the one private device that initiated the communication. When this return information arrives, NAT identifies the internal device that is supposed to receive this data by looking at the port at which the information was received, and then changes the public IP address back to the internal IP address matching the device that initiated the communication.
Security
Many Routers come with additional security features such as a Firewall, shielding your private LAN from the public Internet and making sure that no unsolicited data packages can penetrate your LAN. Today, with the high number of automated attacks against random IP addresses, a firewall must always be in place when connecting any LAN to the Internet.
DNS (Domain Name System)
DNS is a public service that translates friendly names such as google.com to the current IP address of that device or service. Only when you know the IP address will you be able to connect a device.
Routers typically support DNS via DNS Forwarding: when local devices want to resolve a domain name, their request is forwarded to a public DNS service. These services can be made available by your Internet Service Provider, but also exist as free services:
| DNS Service Provider | IP Addresses |
|---|---|
8.8.8.8, 8.8.4.4 |
|
| Cloudflare | 1.1.1.1, 1.0.0.1 |
| Cisco | 208.67.222.222, 208.67.220.220 |
| QUad9 | 9.9.9.9, 149.112.112.112 |
| Comodo | 8.26.56.56, 8.20.247,20 |
| Verisign | 64.6.64.6, 64.6.65.6 |
| CenturyLink | 4.2.2.1, 4.2.2.2 |
| Yandex | 77.88.8.8, 77.88.8.1 |
Routers also often support local DNS caching, reducing the number of requests made to public DNS services. Locally cached information is much faster than requesting the information via a public service.
DHCP (Automatic IP Address Assignment)
Any device on your network needs a unique IP address so other devices can contact it. Without DHCP, you would need to manually assign a unique IP address to each and every of your devices, and keep track that no IP address is accidentally used with more than one devices. Most routers have a built-in DHCP server.
DHCP takes automatically care of IP address assignment: when a devices has no statically (manually) assigned IP address, it requests one from DHCP. DHCP then assigns a random IP address from its IP address pool that has a lease period after which the device mus request a new IP address. This way, IP addresses are always assigned only for a certain period of time and can then be recycled for other devices. Since typically in a network, not all devices are turned on and used all the time, DHCP efficiently manages a scarce resource: the number of available IP addresses is limited.
DHCP is great for consumer gear that you do not want to connect to manually. For DIY projcts, you often do want to connect directly (i.e. access a microcontroller and its web interface). So here, DHCP is not ideal because the IP address of a device may change at any time. And since you are typically not running your own DNS server, you cannot use a static friendly name for your device either. That’s why some DIY Makers manually assign static IP addresses to their devices: now the IP address won’t randomly change anymore and can be used whenever you want to contact this device. A more sophisticated and user-friendly way uses mDNS (Multicast DNS) which is a decentralized DNS without the need for a dedicated DNS server. Instead, the devices themselves listen for mDNS multicast requests and provide their current IP address when asked to. Occasionally, mDNS does not seem to work right, and some users give up in frustration and return to manually assigned static IP addresses. Which is unfortunate because typically, mDNS works well when done right: you must understand that mDNS only works within a LAN. A system in one network (i.e. a Raspberry Pi connected to a wired ethernet network) cannot resolve mDNS names for devices connected to another network (i.e. wireless devices connected to a wireless network running in WiFi Router Mode).
Access Point
When you run a WiFi in Access Point Mode, you simply provide a way for your wireless devices to connect to your wired network. Once connected, your wireless devices are handled by the same Router that is already handling all of your wired devices.
Running a WiFi network in Access Point Mode prevents the WiFi from operating its own Router. This way, you keep one network, and wired and wireless devices all receive IP addresses from the same pool, and can freely communicate with each other without blocking firewalls.
WiFi Bridge
The term WiFi bridge is often used when a wired device needs to be connected to a WiFi, or when a wireless device needs to be connected to a wired ethernet network. This functionality can typically be implemented with one of the WiFi modes discussed earlier.
Wired Device To WiFi Network
There is a quite common need to connect a wired device to a WiFi network. Here are two practical scenarios:
- Solar Inverter: you may have a solar inverter in your garage or attic that may have an ethernet port to monitor its operations and transfer data to the Internet. However, at that location you don’t happen to have a wired ethernet connection available.
- Home Assistant Server: you may have found that your Home Assistant server does not discover wireless devices, and found that the reason is that your WiFi is running in Router mode, and that your Raspberry Pi server is connected to your wired network. You don’t want to switch your WiFi to Access Point mode, and you also don’t want to fiddle with your Home Assistant installation and Raspberry Pi configuration to directly connect it to WiFi.
In both cases, you can simply plug the ethernet cable into a cheap dedicated WiFi router (available for less than €4.00), and run it in one of these modes:
- Range Extender (with one or more Ethernet ports): switch it to Extender mode, connect it to your existing WiFi, and plug in the ethernet cable to one of its ethernet ports.
- Access Point (with Client or Bridge mode): switch it to Access Point mode, then look for an option to switch it to Client or Bridge mode. When these modes are activated, you can connect the device to your existing WiFi network, and connect the ethernet cable to one of its ports. Important: a normal Access Point mode would ask you to set a new SSID and password, then create a new WiFi access point. This is not what you want for this use case. Make sure the device supports a Client or Bridge mode, and then asks you to connect to an existing WiFi.
WiFi Device to Wired Network
The opposite use case may be important as well: you want to connect a wireless device to a wired network. Here is a practical use case:
- Document Scanner: you may have purchased a great new document scanner, but unfortunately it only comes with wireless connectivity. You however would like to scan documents directly to your NAS or any other wired computer.
When you connect the device to your WiFi, this may already be all you need - provided you run your WiFi in Access Point Mode. If you run it in Router mode, the scanner can connect to your WiFi, but since the WiFi is a separate network, it cannot connect to your wired devices like your NAS.
Here are the options you have:
- Change WiFi Mode: you could simply change your existing WiFi and switch it from Router Mode to Access Point Mode. Now wired and wireless networks would be combined. However, never simply switch WiFi mode for existing WiFi networks, or very bad things may happen.
Always make sure you understand all consequences, including reassignment of completely new IP addresses from a different segment for all of your wireless devices, potentially invalidation of statically assigned ip addresses that now no longer are in the appropriate ip segment, and overload of old routers that are suddenly responsible for managing numerous additional wireless devices.
- Add dedicated Access Point: a simple WiFi Access Point device can be purchased for less than €4.00, so you may simply want to add a dedicated Access Point for this use case. Assign it a distinct SSID, then connect your document scanner to this access point.
Security Considerations
When setting up a wireless network, security considerations are especially important: wireless radio waves are not confined to your property and can be picked up by anyone. With special antennas, attackers can penetrate your WiFi from many miles away.
All security settings are done in the WiFi Router (regardless of whether it runs as a Router or as a simple Access Point). Typically, you connect to it via a browser. Check the manual of your device for specific instructions.
Encryption
Encryption is part of WiFi access control: only when a legit user gains access to the WiFi network will that user be able to encrypt and decrypt the data exchanged.
When you do not enable access control (by not setting an access password), you are essentially turning off even the most basic security features: anyone can connect, and anyone can monitor any traffic. Obviously, this is no option - even if you use it just for sensor data.
Once you add a password to your SSID, you also select the encryption mode:
| Mode | Introduced | Encryption | Remarks |
|---|---|---|---|
| WEP | 1997 | RC4 stream cipher | obsolete and insecure. Do not use. |
| WPA | 2003 | TKIP 128bit | low security but ok for use in pure low-importance sensor networks: effort to break WPA is higher than value of data. Do not use for regular WiFi networks connecting to smartphones, computers, or sensitive home automation devices |
| WPA2 | 2004 | AES 128/192/256bit | standard security protocol in most WiFi networks today. It can be hacked, however effort and procedures are impractical for typical scenarios |
| WPA3 | 2018 | AES and MFP/PMF | best security, still less available |
Deauth Attacks And Spoofing
Unfortunately, WiFi does not encrypt the entire traffic. Management Frames are partially unencrypted. This opens ways for attacker to find out sensitive network data, manipulate and spoof data, and invoke deauthentication attacks: these take advantage of the fact that even without being authenticated, anonymous parties can send unencrypted deauthentication frames to your wireless devices. This forces all wireless devices to reconnect. Deauth attacks are primarily used to (a) deny service and interrupt operations, i.e. when breaking into a house that is protected by WiFi-based cameras, and (b) intercept and manipulate forced reconnection attempts, or lure devices into reconnecting at a spoofed rogue access point instead.
MFP (Management Frame Protection) aka (PMF: Protected Management Frames) aims to close this security issue by protecting management frames from unauthorized access and manipulation. This is outlined in IEEE 802.11w-2009.
(Highly) Secure WiFi
Operating a secure WiFi requires all devices to support MFP/PMF (802.11w). Most computers and quality devices today support 802.11w. For example, Windows uses this standard since Windows 8. However, wireless devices need to support WPA3 which is not the case for the majority of consumer gear.
Access Points that support 802.11w offer three different login methods:
- No PMF: no protection for management frames
- Always PMF: management frames are always protected however now any device that does not yet support 802.11w will not be able to connect
- Client decides: that’s the compatibility mode that allows older clients to connect while enabling 802.11w for any device that supports it. Put differently, this mode reduces the attack surface but does still provide room for attackers to penetrate.
802.11w aims at professional corporate wireless networks. Private users simply don’t provide enough prey that would make attacks worthwhile, and 802.11w-compliant consumer hardware is still expensive and less available. Still, being aware of 802.11w/WPA3, and what it does, makes sense for home users as well: selecting devices that support 802.11w (when cost and availability allows) enables you to eventually become ready for stepping up your security, too.
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(content created Aug 13, 2024)