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Sunday, July 7, 2024

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



Martijn Braam has designed a {custom} gigabit Ethernet change with administration capabilities — and, for causes that can grow to be obvious, one in all its 5 ports going through the mistaken manner.

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

Braam’s purpose for going {custom} somewhat than shopping for an off-the-shelf managed change is easy: a want to experiment with managing a change from inside Linux, utilizing a system usually solely discovered inside consumer-grade routers and infrequently made obtainable externally. “Controlling your commonplace off-the-shelf change utilizing this technique merely is not doable,” 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 obtainable there may be 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 gadget is uncommon in its format: 4 of the 5 PHY-equipped Ethernet ports obtainable on the change chip are introduced out externally, as you’d anticipate — however the fifth port is discovered on the opposite aspect of the board, going through in the other way. Energy is supplied over a 0.1″-spaced pin header, or by a USB Kind-C connector — not populated in Braam’s preliminary prototype.

In testing on a PINE64 single-board pc with a custom-built kernel, Braam discovered the change fully-operational and manageable from inside Linux itself — although with caveats. “It is not likely doable to make use of this technique on common computer systems/servers because you want gadget 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 fastened, USB community interfaces do not have a tool tree node deal with to confer with to set the conduit port.”

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

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