Can I use my old router as a wifi extender?

Every household has an old router in a drawer, and repurposing it is the cheapest possible network upgrade. The catch is that almost all the value comes from the cable. Wired to your main router, an old router becomes a proper second access point with full speed. Bridged wirelessly, if it even supports that, it halves throughput exactly as a cheap extender does, and it will usually be less reliable than one.

What you'll need

• an ethernet cable long enough to reach where you want the second point
• a paperclip or pin for the reset button

Step by step

1. Factory reset the old router first.You do not know what state it is in or what its admin password is. Hold the recessed reset button for the documented time — usually ten to thirty seconds — with it powered on, and let it restart. Its sticker credentials now work again.
2. Find the address range your main network uses.Log into the main router and note its own address and the range of addresses it hands out. You need an address for the old router that is in the same range but outside the pool.
3. Connect a computer directly to the old router and log in.Use a cable from the computer to one of the old router's LAN ports. It is not on your network yet, so this is the only way to reach it.
4. Set its address to the one you chose.In LAN settings, change its own address to the fixed one outside the pool, and note it down. You will need it to get back in later.
5. Turn off its DHCP server.This is the critical step. Two devices handing out addresses on one network causes intermittent, baffling failures. Only the main router should do it.
6. Set the wifi to match your main network.Same network name, same password, same security type, on both bands. This lets devices move between the two access points without noticing. Set the channel manually to a different one from the main router — on 2.4 GHz, if the main is on 1, put this on 6 or 11.
7. Run the cable, LAN port to LAN port.From any numbered LAN port on the main router to any numbered LAN port on the old router. Do not use the port marked WAN, internet or with a distinct colour on either device — that is what creates double NAT.
8. Test by walking.Walk from the main router to the second point with a phone and watch the signal. If it hands over and the internet keeps working, you are done. If you get a strong signal but no internet, DHCP is still on somewhere or the cable is in the wrong port.

Common mistakes

• Using the old router's WAN port — That makes it a second router doing its own address translation, which creates double NAT and hides everything behind it from the rest of the house.
• Leaving DHCP enabled on both — Devices then receive addresses from whichever answers first, on two different networks, and the resulting faults are intermittent and very hard to diagnose.
• Putting the second point in the weakest corner of the house — A wired access point can go anywhere, so put it where it covers the most rooms rather than where the signal is currently worst.

Alternatives

• Powerline adapters with a wifi access point built in: Where running a cable is genuinely impossible. Uses the mains wiring as the link. Works well on a single ring circuit and badly across separate circuits or through extension leads with surge protection.
• A mesh system: Simpler to set up, better handover behaviour, and a single app for everything. Worth the money if the alternative is running two old routers you have to maintain by hand.
• A dedicated access point: A small ceiling or wall unit powered over the ethernet cable itself. The neatest permanent answer, and no more expensive than a mid-range router.

Questions people ask