Zigbee coordinator, router & end device
Every Zigbee network has exactly one coordinator — the radio in your hub or USB dongle that forms the network and stores its keys. Mains-powered devices (plugs, bulbs) join as routers that relay traffic and extend range; battery devices join as end devices that sleep between transmissions and route nothing.
The three roles explain most Zigbee network behavior. Range problems are router problems: a lone battery sensor at the far end of the house needs a plug or bulb partway along to relay through, because end devices cannot forward traffic. A healthy mesh has routers spread through the home, and adding a smart plug is the standard fix for a flaky sensor.
Because the coordinator holds the network, it is a single point of failure and identity: replace it and, in general, you re-pair everything — though coordinator backup and restore between compatible radios is routine on Zigbee2MQTT and ZHA. Dedicated coordinator dongles such as the Sonoff ZBDongle-E or SMLIGHT SLZB-06 are how DIY platforms like Home Assistant get their Zigbee radio.
| Coordinators per network | Exactly one — it forms the PAN and holds the network key |
|---|---|
| Routers | Any mains-powered device: plugs, bulbs, in-wall switches, some sirens |
| End devices | Battery devices — they sleep, poll a parent, and relay nothing |
| Children per router | Typically 10–32 depending on firmware, which is why dense areas need more routers |
| Common DIY coordinators | SONOFF ZBDongle-P (TI CC2652), ZBDongle-E (Silicon Labs EFR32), SMLIGHT SLZB-06 over Ethernet or PoE |
| Backup | Network key, PAN ID, and channel can be exported and restored on Zigbee2MQTT and ZHA |
What each role can and cannot do
The coordinator forms the network. It picks the channel, generates the network key and the extended PAN ID, maintains the trust centre that admits new devices, and is the only node that can open the permit-join window. There is one and there can only be one — a second coordinator forms a second, separate network, not a bigger one.
Routers are ordinary mains-powered devices that agreed to do extra work: they forward frames for their neighbours and act as parents for sleeping devices. Every smart plug, bulb, and in-wall switch you add is a router, which is the pleasant property of Zigbee — the mesh gets stronger as the house fills up, without you buying anything labelled “repeater”.
End devices are the battery ones. They keep their radios off, wake on a schedule to poll their parent for queued messages, and route nothing for anybody. A contact sensor that reports once an hour may be awake for a few milliseconds in that hour, which is how a CR2032 lasts two years — and also why commands to battery devices are slow or queued.
Range problems are router problems
When a sensor at the end of the garden drops off, the instinct is to move the coordinator. The correct move is almost always to add a mains-powered device between the two. End devices cannot reach further by trying harder; they need a parent within radio range, and a smart plug halfway along the path is the standard fix.
Parent capacity is a real limit people forget. A router accepts a bounded number of children — typically somewhere between ten and thirty-two depending on the chipset and firmware — and once full it turns new ones away. In a bedroom with one plug and twelve sensors, the twelfth may simply have nowhere to attach, and the symptom looks like an intermittent pairing failure rather than a capacity error.
Not all routers are good routers. Cheap bulbs, and older Zigbee bulbs generally, have a poor reputation for buffering and forwarding: they accept children and then drop their traffic under load, which produces the maddening pattern of a network that works until it does not. If a mesh is unreliable and the routers are mostly bulbs, adding two or three decent smart plugs usually resolves it.
The coordinator is a single point of failure — plan for it
A Zigbee network is defined by three values the coordinator holds: the network key, the extended PAN ID, and the channel. Devices remember them. If you can restore those values onto a new radio, every device rejoins as if nothing happened; if you cannot, you re-pair the lot, one device at a time, physically. Zigbee2MQTT and ZHA both take and restore network backups, and restoring across different chipsets has become workable rather than exotic. Take the backup before you need it.
Placement is the other lever. A USB dongle plugged into the back of a server in a metal rack is a bad coordinator no matter how good the radio is. Use a USB extension cable to get it away from USB 3.0 ports and drive enclosures, or use an Ethernet-attached coordinator like the SMLIGHT SLZB-06, which lets you mount the radio centrally in the house and keep the server in the cupboard.
Firmware matters more on the coordinator than anywhere else, because a coordinator bug affects every device. Update deliberately, not reflexively, keep a copy of the working firmware, and never update the coordinator and reorganise the network in the same session — you want one variable at a time when something goes wrong.
Frequently asked questions
Can I run two Zigbee coordinators in one house?
You can, but they form two independent networks, not one larger one. That is a legitimate design — a Hue Bridge for lights and a separate coordinator for sensors is common — but the two networks should be on well-separated channels, and devices cannot move between them without re-pairing. What you cannot do is add a second coordinator to extend an existing network; that is what routers are for.
Which Zigbee dongle should I buy?
For Home Assistant, the SONOFF ZBDongle-P (Texas Instruments CC2652) and ZBDongle-E (Silicon Labs EFR32) are the default choices, and the SMLIGHT SLZB-06 is the pick when you want the radio on Ethernet or PoE away from the server. All are supported by both Zigbee2MQTT and ZHA. Whatever you buy, budget for a USB extension cable — it matters more than the chipset.
If my hub dies, do I have to re-pair every Zigbee device?
Only if you cannot restore the network identity. Zigbee2MQTT and ZHA can export the network key, PAN ID, and channel and restore them onto a replacement radio, after which devices rejoin on their own. Consumer hubs vary — some offer cloud backup of the Zigbee network, many do not, and for those the answer is yes, every device, by hand.
Why does my Zigbee sensor keep dropping off the network?
In order of likelihood: no router within range, so it has no reliable parent; a parent router that is full or is a cheap bulb that mishandles children; 2.4 GHz interference from Wi-Fi or a USB 3.0 port next to the coordinator; or a flat battery reporting as unresponsive rather than low. Adding a good mains-powered router near the sensor fixes most cases.
Do Zigbee bulbs act as routers?
Yes — mains-powered bulbs route by definition. The catch is that they are only routers while powered, so a bulb on a wall switch someone flips off takes a chunk of your mesh with it. That, plus the poor forwarding behaviour of many cheap bulbs, is why smart plugs and in-wall switches make better backbone devices than bulbs do.