Ghost in the Ethernet Optic

> While the optical transceiver is a gigabit optic, the actual Linux system inside the SFP appears to be limited to 125 Mbits/sec. Something that is quite reasonable given the CPU power on-hand.

Is that in the hot path, or is it like a lot of Linux-powered routers where most packets just go through hardware offload?

> The kernel on my smart SFP is too old for mainline kernel wireguard (4.14.22-stcmtk-0.2.33), and the kernel does not come with headers making DKMS not possible.

> There might be a newer version of the kernel and OS distribution. Software upgrades can be done either with a special script that writes into the boot partition, and then a factory reset with the micro–DIP switches, or using a special tool that uses the extra pins on the back of the SFP:

There might be a newer version? That exact version (4.14.22) is from 2018, and the series (4.14) went EOL in January 2024; for something as security sensitive as a network interface that's kind of a deal-breaker.

This guy purchased a smart ethernet interposer with an FPGA + eMMC filled with an embedded Linux from Russia.