DHCP Fixed IPs and ESPHome

DHCP Fixed IPs and ESPHome

The Problem

My Home Assistant installation runs in Docker, and ESPHome runs in a separate docker container. I use a separate Wifi SSID for my random ESP devices to give them some isolation from my main network, so mDNS doesn't work.

ESPHome however, loves mDNS - to discover and install devices.

I've just bought a bunch of the Athom Smart Plugs, and want to rename some of their outputs to get sensible labels - as well as generally just manage them.

ESPHome's Config Files

ESPHome is actually very well documented but it can be hard to figure out what it's documenting sometimes, since there's a combination of device and environment information in it's YAML config files. This is fine - it's a matter of approach - ESPHome likes to think of your environment as a dynamic thing.

For our purposes the issue is we need to make sure ESPHome knows to connect to our devices at their DHCP fixed IP addresses - and to do this we need the wifi.use_address setting - documented here.

This setting is how we solve the problem: we're not going to set a static IP on the ESPHome device itself (since we're letting DHCP handle that via a static reserved - i.e. a fixed IP in Unifi where I'm actually doing this). Instead, we're just telling ESPHome how to contact this specific device at it's static IP (or DNS name, but I'm choosing not to trust those on my local networks for IOT stuff.)

Importantly: wifi.use_address isn't a setting which gets configured on the device. It's local to the ESPHome application - all it does is says "use this IP address to communicate with the device". i.e. you can have a device which currently has a totally different IP address to the one you're configuring, and as long as you set use_address to the current value it's on, ESPHome will update it. This is very useful if you're changing IP addresses around, or only have a DNS name or something.

The other important thing to note about this solution is that when you're not using mDNS, you're going to want to set the environment variable ESPHOME_DASHBOARD_USE_PING=1 on the ESPhome dashboard process. This simply tells the dash to use ICMP ping to determine device availability, rather then mDNS, to have your devices show up properly as Online (though it doesn't much affect usability if you don't).

The Solution

User Level

To implement this solution for each of my smart devices, I have a stack of YAML files which layer up to provide the necessary functionality following some conventions.

At the top-level is the "user" level - one specific device on the network. After it's booted and been initially joined to my IOT SSID, it gets a YAML file named after it that looks like this.

# sp-attic-ventilation.yaml
  athom.smart-plug-v2: !include .common.athom-smartplug-v2.yaml

  name: "sp-attic-ventilation"
  friendly_name: "Attic Ventilation"
  name_add_mac_suffix: false


There's not much here - just the IP address which I assigned, plus a name which is the same as the hostname I assigned which follows the nominal convention of <device-type-abbreviation>-<location>-<controlled device>. So smartplug - sp, located in the attic, controlling the ventilation. You don't have to do this - but it helps. Then we include the friendly name - this will appear in Home Assistant, and disable adding the MAC suffix - this is a handy default when you're installing and configuring multiple devices initially using fallback APs.

The important part here is to note the include file: ESPHome's web interface will automatically hide a file named secrets.yaml as well as any files prefixed with . which is a convenient way to manage templates and packages.

Device Common Files

The next step up in the stack is a device-common file. Athom Technology publish these on their Github account. This sort of thing is why I love Athom and ESPHome - because we can customize this to work how we want it too. The default smart plug listing is here, but we're going to customize it though not extensively - namely we're adding this line:

  home: !include .home.yaml

I've included my full listing here (note the removed "time" section).

The Home File

The Home file is the apex of my little ESPHome config stack. In short it's the definition of things which I want to be always true about ESP devices in my home. All of the settings here can be overridden in downstream files if needed, but it's how we get a very succinct config. There's not a lot here but it does capture the important stuff:

# Home-specific features
  disabled: false

  port: 80

# Common security parameters for all ESPHome devices.
  ssid: !secret wifi_ssid
  password: !secret wifi_password

  domain: !secret domain

    password: !secret fallback_wifi_password

  password: !secret ota_password

  - platform: sntp
    id: my_time
    timezone: Australia/Sydney
    - !secret ntp_server1

This file extensively references into secrets.yaml, which is templated by my Ansible deployment playbook for ESPHome (which in turn uses my Keepass database for these values). It mostly sets up the critical things I always want on my smart devices: namely, the onboard HTTP server should always be available (life-saver for debugging and a fallback for control - every ESP chip I have seems to run it fine).

One of the crucial things I do is hard code the wifi parameters: the reason I do this is because for as many devices as possible I disable persistent storage to protect the ESP write flash. It's enabled for the smart plugs because they don't change state very often, but for something like a light controller it's a waste of flash cycles. But this does mean that if the wifi settings are configured via the fallback AP mode, they'll be lost if there's a power cut - and then all my devices will turn on AP mode and need to be reconfigured.

This is also the reason you definitely want to configure wifi.ap.password: because if your devices are unable to connected to your wifi (by default for 1 minute), or don't persist settings and are down, then the first thing they'll do (and out of the box Athom devices do this becaue obviously you need to configure them yourself) is open a public wifi network to let them be configured by just any random passer-by. The consequences of this range from someone having some fun toggling a button to someone implanting an advanced persistent threat.

For much the same reason, you should also configure an over-the-air password - ota.password. There's a difference between control of a device and being able to flash firmware, so this should be enforced. This value lives in my password manager, so I'll always have it around.

Beyond that there's just convenience: i.e. I force NTP to point to the Unifi router on my network so everyone has a common agreement on the definition of time.


Static IPs

ESPHome does have full support for static IPs via the wifi.manual_ip parameter. It would be entirely valid to take our wifi section from above and change it to look like this:


This device would work just fine on a network without DHCP - it would come up, grab an IP and be happy. The reason I don't do this is convenience of management: having the devices send DHCPDISCOVER packets is a nice way to make sure they're alive, and turns control of the isolated network segment they're on more over to my Unifi Router, which is what I want. If I want to re-ip a network, then updating static address allocations centrally is more convenient (you do have to coordinate rebooting the devices, but they will "get it").

You could obviously do all sorts of fancy scripting around this, but all of that is a lot of work for a very limited gain.

Enable mDNS

ESPHome uses mDNS extensively, and even with an isolated network you can make it work: my Home Assistant and ESPHome docker containers have IP addresses on that network segment so they can talk to these devices, and as a result they can also receive mDNS from them provided I configure it to be bridged properly.

The reason not to for me is ultimately just that keeping track of a list of IPs is simple: whereas mDNS in more complicated network arrangements like mine is not, and the complexity just isn't worth it - once configured, I never have to really think about these devices. I've lost my Unifi router config and just restored it from a backup and everything was fine. My configs are tracked in Git, my passwords in Keepass - rebuilding this environment is straightforward.


If you're trying to figure out how to flash an ESPDevice, you need to set wifi.use_address to the known IP of the device.

In an environment with DHCP Fixed IP addresses, this means you'll include this value in your ESPHome YAML config files, and it should match your static reservations.

A convenient way to do this is to layer your ESPHome YAML files, with your vendor/device-type files in the middle of the "stack".