Martijn Braam’s Uncommon Ethernet Change Has One Reversed Port — for Linux Administration Experiments

Martijn Braam has designed a {custom} gigabit Ethernet change with administration capabilities — and, for causes that may develop into obvious, one in every of its 5 ports dealing with the incorrect manner.

“Making my very own community change cannot be that onerous proper? These issues can be found for the value of a cup of espresso and are almost definitely extremely built-in to succeed in that value level,” Braam explains by the use of his background considering previous to launching the challenge. Since I do not see any selfmade switches round on the web I suppose the chips for these should be fairly exhausting to get… Nope, very simple to get. There’s even a datasheet accessible for these. So I created a brand new KiCad challenge and began creating some footprints and symbols.”

Braam’s purpose for going {custom} slightly than shopping for an off-the-shelf managed change is straightforward: a need to experiment with managing a change from inside Linux, utilizing a system usually solely discovered inside consumer-grade routers and infrequently made accessible externally. “Controlling your normal off-the-shelf change utilizing this technique merely is not potential,” Braam explains, “as a result of the required connections of the change chip aren’t uncovered for this.”

Braam’s {custom} change, against this, goals to make this type of low-level administration simple to entry, constructing across the Realtek RTL8367S five-port Ethernet chip. “It is really not a five-port chip,” the maker explains. “It is a seven port change chip the place 5 ports have an built-in PHY and two are for CPU connections. My plan is totally different although, whereas there are these CPU ports accessible there’s really nothing within the Linux switchdev subsystem that requires the CPU connection to be to these ports. As an alternative I will be connecting to port 0 on the change with a community cable and so far as the switchdev driver is aware of there is no Ethernet PHY in between.”

The ensuing system is uncommon in its structure: 4 of the 5 PHY-equipped Ethernet ports accessible on the change chip are introduced out externally, as you’d count on — however the fifth port is discovered on the opposite aspect of the board, dealing with in the wrong way. Energy is supplied over a 0.1″-spaced pin header, or via a USB Sort-C connector — not populated in Braam’s preliminary prototype.

In testing on a PINE64 single-board laptop with a custom-built kernel, Braam discovered the change fully-operational and manageable from inside Linux itself — although with caveats. “It is not likely potential to make use of this technique on common computer systems/servers because you want system bushes to configure the kernel for this,” Braam admits. “So far as I can discover there’s additionally no manner to make use of this with a community port on the pc aspect that is not mounted, USB community interfaces do not have a tool tree node deal with to check with to set the conduit port.”

Braam’s full write-up is on the market on his weblog.