There really aren't that many modem/router combos out there you can actually flash with open source firmware.
Router? Sure, no problem.
Modem? Outside of some very niche Fritzbox devices and others listed on OpenWRT Table of Hardware
There really just aren't that many.
So, fine. I will use a proprietary modem.
I will put it into bridge mode, let it decode the DSL analog signals into ethernet and feed that into a router of my choice.
Question is: Which modem?
I don't want two devices heating up my shelf. I just want a tiny modem that converts analog to digital into an RJ45 and then let's the router do its thing.
Does such a magical device exist, because my search on this front has proved largely fruitless
Honestly, I'd just use whatever the ISP provides.
Sure, it's not open source and it kinda sucks... But I mean, if you don't trust the ISP modem, you can't trust the rest of their infrastructure either anyway, so it's kinda moot.
At least that way you have a vague chance of having a modicum of support when shit breaks.
If it can't be put into bridge mode, it probably has some sort of DMZ function where it basically does port forwarding for any/all possible ports.
Double NAT isn't as bad as it sounds these days.
Now to your question...
They exist, they're mostly targeted at ISPs though, so might be a harder find than other things.
They might also be older, as basically all customers also want their ISP to provide Wi-Fi, which a bridge modem won't.
Anyway,
You'll have to know what DSL were talking about, there's... ADSL, ADSL2+, VDSL, VDSL2, etc
One old-ass model we used to use back in the day was.. a Siemens 5200, but that's ADSL2 at best, definitely not VDSL.
That's a chunky house warmer, let alone shelf warmer!
I can understand that ISP's need to protect their security (through obscurity) so that no one's going around cloning their neighbors analog signals to score free internet... but surely the actual hardware to do the tone pairing / channel matching analog-to-digital-magic-mumbo-jumbo does not need to be the size of a brick?
In the spirit of people cutting open Nintendo Wii's shearing down the chip and making compact versions[0], has no one isolated the hardware on a modem, chucked out the routing stuff, and compacted the whole device to be no bigger than a USB stick?
0: https://www.tomshardware.com/video-games/nintendo/meet-nintendo-kawaii-the-new-smallest-wii-build-that-fits-on-your-keychain
The fibre modem my ISP uses is pretty small, about the same size as one of those small unifi switches, but it still feels like there's almost nothing in it.
I have taken apart the fibre modem of a different provider before, which was just a small PCB no larger than a raspberry pi and a fibre extension cable.
It was packed in this hunk of junk.
collapsed inline media
Hmm! Good to know there's some hope with the size of fibre modems
I'm mad you started your citation at 0.
I'm telling Chicago style!