They built a program they called (relay) that sends packets between a tun network device & a uart serial device

https://github.com/mikeakohn/small_projects/blob/main/ip_ove...

I .... wonder if they considered just using PPP/SLIP?

A while back I was doing some IP-over-UART shenanigans and it took me a surprising amount of research to discover the existence of SLIP. I think it's one of those things that at some point "everyone knew about" and ended up being poorly documented as a result.

SLIP is old and mostly forgotten for sure, but PPP was almost universal in dialup and unfortunately common in DSL. PPPoE was the bane of my existence as someone who had to support third-party routers on DSL. PPTP was also very common for small VPNs even well past when it should have been retired due to insecurity because it worked out of the box on Windows and Mac without a third party client.

Mid-90s you definitely had to know about SLIP to get your Linux or NeXT boxen to connect to your ISP.

Generational thing. Back when I was supporting banks of USR 28.8s, SLIP and especially PPP were just the job (mostly PPP by that point).

But even then I don’t think I’d have thought to drag a dial-up framing protocol into a new project. Odds are I’d just recreate SLIP from muscle memory.... maybe?

Hahah, I slipped down that rabbit hole about 2 years ago. We needed network access for testing devices on one of our production lines, but the manufacture did not allow wifi at the time. So we ended up tunneling over UART to access internal APIs on the device. It worked fairly well, and was even able to load more complex customer facing react based UIs.

CSLIP is even better.

I wouldn't be surprised if they were trying to remove them from the kernel since you can use a tun interface instead. They would be very good candidates for moving kernel functionality to userspace.