I have a TL-WR703N with some version (don't recall) of DD-WRT installed on it, which has been working fine for months.
Suddenly, with no configuration changes on my end, it appears to have stopped working.
When I connect it to power, I can see its wifi network appear on nearby devices, but it sometimes disappears intermittently and I usually can't connect successfully to it. (I did manage to connect one time after all this started though.)
Running nmap from another computer on the wired LAN, it's showing as online and has all the expected ports active (http, ssh, telnet, etc; though they show as "filtered"), but I can't connect to the web interface or to ssh -- there's just no response.
Is there anything that I can do to further diagnose and/or fix this, or is it just dead hardware?
While we might be able to help you install OpenWrt in your device, there are people on the DD-WRT boards that can help you with that firmware.
It’s a pretty dated device, really too under-resourced these days for current, secure Linux. I don’t know your budget, but you might want to consider replacing it with one of the GL.iNet units. I have both the GL-AR300M and the GL-AR750S. There is a less expensive GL-MT300v2 as well.
Edit: There are many other suitable devices (16 MB or more of flash, 128 MB or more of RAM) starting at around US$20. The two that I mentioned are because I can recommend them from personal experience as having excellent design, build quality, and OpenWrt support.
It said "DD-WRT OpenWRT" on the label, so I wasn't entirely sure which it was; I thought they were the same thing? Hard to say for sure what it has on there at the moment since I couldn't connect to it.
I tried long pressing the reset button, and that reset it to factory settings, and I could connect to the admin interface again. I had to reconfigure everything (I only had an older config backup, silly me), but it appears to be working ok again now, thanks!
They’re two different, third-party firmware projects. If a TP-Link label, it’s probably that you could install those. Unless you or someone else did that, you’re running years’ outdated OEM firmware that is known insecure. At the very least you should consider that.
It had DD-WRT preinstalled, as it turns out, so I apologise for asking in the wrong place after all. And yes, it's an old build (2017ish, I think it was). I'm not too fussed about security on it, it's nested inside another router rather than being directly Internet exposed. And getting in through the wifi would need the key. (And yes, I know hacking the wifi key is possible, but I doubt anyone would bother.)