Yes, you can buy a basic wireless repeater for cheap, even at the Goodwill. And while I'm writing this, I'm close to doing just that. You'll soon see why.
There have been free replacements for the software on consumer-grade wireless routers for awhile, and dd-wrt is the king. I've run it for awhile at home, but it frustrates me off and on. I even had one of my oldest single-band routers working as a wireless-client bridge (you have to plug into a wired port to get online). I've since moved to semi-pro networking gear, but now I have a housing plan where running wires to add an access point isn't practical, and I have serious need of a wireless bridge and repeater in one. And I have a faster router that ought to make it shine.
The specimen
I have a Linksys EA6400, from 2016. It ran my home network for a solid 4 years (after a cheap pro router died early). All internal antennas, but it has a USB port, and a gigabit LAN switch. About a year ago, it started crashing and self-rebooting every couple of minutes, running 2024 firmware.
Unique flaws
This model is known in the dd-wrt world for both being tricky to get flashed to run dd-wrt from stock, and for overheating. I had crossed the bridge to get it running open firmware years ago, but I feared the crashing was the overheating finally taking its toll. I'm starting to wonder if the crashing might be from irreversible heat damage, or from the firmware version I'm on.
Following the guide on the dd-wrt forums, I opened it up, modded the heatsink, and got it back together. It hasn't topped 70c since, but I haven't gotten it under much load yet. Not sure yet if it will be more stable now.
So many extender configuration options
The first part of getting it to connect to an existing wireless network is deciding what mode to use, for there are many.
Station: A wireless client for the "WAN" uplink, and the thing acts as a router for the wired ports. I think you can just let it do a second NAT layer, but I'm not sure if that's necessary to reach the Internet through the primary router. For some reason this is easier to set up than bridging.
Station bridge: This is where it's a wireless uplink, but it makes wired ports act like part of the existing subnet, including getting DHCP from the upstream router. I did this one with the ancient single-band router, but I reset it to be a spare wired router.
Repeater bridge: The magical full network extension, where it both serves as an uplink for wired ports and allows wireless devices to connect to it, while the uplink is wireless to a primary router that provides DHCP and Internet. This is the desired effect.
My router is a dual-band radio, so it provides additional options, as to which frequency is used for the uplink, and whether one or both provides access to wireless devices. The plan is to use the 5GHz radio for my uplink only, and set the 2.4GHz band to accept user devices.
Too much documentation
It's a classic case of everyone having an opinion: there are a lot of cookbooks out there to do this. I thought I'd start with the authoritative guide, in the dd-wrt wiki.
[to be continued...]