3 ms·

Lots of older or low end wireless routers have only 16 or 32mb RAM. A full linux stack fits in that. I do a full HTTPS stack on ESP32-C3 in ~500k. Lots of li

Lots of older or low end wireless routers have only 16 or 32mb RAM. A full linux stack fits in that. I do a full HTTPS stack on ESP32-C3 in ~500k. Lots of limitations, of course. Probably the biggest difficulty is that most modern systems simply refuse to boot without RAM installed, so you can't choose any platform without BIOS / EFI modifications. Definitely a worthwhile idea though.

crote 2y ago
The difference is that those low end routers offload most or even all of the packet processing to dedicated networking hardware: it never even touches the CPU. The whole Linux stack is only used to host the management interface, configure the switching hardware, and deal with high-level stuff like DNS and DHCP. That's also why VPN performance is so horribly bad: there's no hardware acceleration for encryption, so it needs to be done on the CPU, which is not sized to deal with that kinds of traffic.
- timschmidt 2y ago
  Offloading the packet processing doesn't really save any RAM at all. The limitations you're discussing are related to running on a low power ~700mhz MIPS or ARM core with very low performance. As you said, using a VPN or adding additional routing rules requires the packets to pass through the CPU, which demonstrates that all the software and buffers for doing the routing on the CPU are present within the 16 or 32Mb ram. It's just attached to a very low performance CPU core. It's perfectly possible to load the same OpenWRT release on a modern x86 and run in the same amount of ram with much higher performance. That's how I do my routing on a 1gbit/s synchronous fiber connection and I can do line-speed wireguard just fine. Distributions like OpenWRT require so little RAM because they select very conservative options when compiling everything, are very selective about what they include, build against minimal C libraries like musl libc, make use of highly integrated system utilities like busybox, and strip things like debugging symbols from the resulting binaries.

crote 2y ago

The difference is that those low end routers offload most or even all of the packet processing to dedicated networking hardware: it never even touches the CPU. The whole Linux stack is only used to host the management interface, configure the switching hardware, and deal with high-level stuff like DNS and DHCP. That's also why VPN performance is so horribly bad: there's no hardware acceleration for encryption, so it needs to be done on the CPU, which is not sized to deal with that kinds of traffic.

timschmidt 2y ago
Offloading the packet processing doesn't really save any RAM at all. The limitations you're discussing are related to running on a low power ~700mhz MIPS or ARM core with very low performance. As you said, using a VPN or adding additional routing rules requires the packets to pass through the CPU, which demonstrates that all the software and buffers for doing the routing on the CPU are present within the 16 or 32Mb ram. It's just attached to a very low performance CPU core. It's perfectly possible to load the same OpenWRT release on a modern x86 and run in the same amount of ram with much higher performance. That's how I do my routing on a 1gbit/s synchronous fiber connection and I can do line-speed wireguard just fine. Distributions like OpenWRT require so little RAM because they select very conservative options when compiling everything, are very selective about what they include, build against minimal C libraries like musl libc, make use of highly integrated system utilities like busybox, and strip things like debugging symbols from the resulting binaries.