What an extender keeps in its own memory

An extender writes the settings it is given to non-volatile memory, the same kind a phone uses to remember networks. From then on it rejoins the router on its own each time it is powered, using the stored name and key, and publishes its own network using the stored settings for that. Nothing has to be repeated after the first pairing, and nothing is forgotten when the plug comes out. That is convenient until the router’s key changes, at which point the extender is faithfully offering a key the router no longer accepts.

Everything in the table. The memory is non-volatile, so a unit unplugged for a month and plugged in again starts, reads its stored settings, looks for the router by name, offers the stored key, and resumes. The only thing lost is the log buffer and the address the router had lent it, both of which are replaced within a minute of starting.

What the unit cannot store is the router’s consent. Each time it starts, it has to be accepted again by the router, using the stored key, and the router accepts or refuses on the key as it stands today.

The extender knows the router by its network name and proves itself with the key. Anything that changes either breaks the pairing, and the extender has no way of learning the new value on its own.

• The router’s key is changed. The extender keeps offering the old one, is refused, and keeps trying. Its link light reports a lost link until it is paired again with the new key.
• The router is replaced by one with a different name. The extender looks for a name that no longer exists. It has never heard of the new router and cannot join it until paired.
• The router is replaced by one given the same name and key. The extender finds a network with the name it knows, offers the key, and is usually accepted, because it identifies the network by name and key rather than by the router’s hardware. Units that had noted the old router’s hardware address may take longer to accept the new one, but most resume.
• The household moves house. The extender arrives knowing a network that is now streets away, and behaves exactly as in the first case until it is paired with the new router.

A unit sold, lent or passed on without being returned to factory state still holds its previous owner’s network name and key in memory. Powered up within range of that network it will rejoin it; powered up elsewhere it will search for it. Its configuration page, opened by whoever now holds it, shows the stored name in plain text and may allow the key to be read.

The reverse case matters too. A unit bought second-hand arrives with someone else’s settings, someone else’s configuration password, and possibly a hand-set address that clashes with the new home’s. The return to factory state, described next, is what makes it a clean unit.

Every unit has a way of erasing everything it has been given and returning to the state it left the factory in: no router, no keys, the printed configuration password, and the temporary pairing network it first published. The maker’s leaflet describes how that is invoked on a given model. What it does is the same everywhere: the stored settings in the table above are wiped, and the firmware is left in place.

Afterwards the unit is exactly as new, which means it is again advertising a temporary network and again waiting for the pairing exchange described in how extender setup works. Nothing about the return to factory state involves a website, a telephone call or anyone outside the home; it is a physical act on the unit, and the only party able to perform it is the one holding it.