4

Hardware issue, common to virtually all consumer-grade SoCs.

At least from what I’ve read from the data sheets to which I have access is that the switch comes up in a pre-configured mode at power-on that is “leaky” in this way. Potentially one could write a custom U-Boot that pre-configured the switch differently, closing the window somewhat, but there would still be the problem during any subsequent reconfiguration. This class of SoC is designed for home use where DHCP leakage is generally not a problem, nor are users aware of it when it is (“Oh, you’re having problems? It’s your equipment, not ours. Please reboot your router.”). There is little incentive for the SoC manufacturers to complicate the silicon with power-controlled phys and the resulting boot code required to “carefully” bring up the switch subsystem.