Hi,
It turns out that all A64 boards have the same Ethernet MAC address (02:ba:7b:d5:c6:6f), which means that they cannot be connected to the same switch. Unfortunately, this cannot be overridden in uBoot, but overriding in /etc/network/interfaces works.
While it's clearly a hardware bug, it would be neat if it were fixed in software. Could the people responsible for the images please recompile uBoot with the right options to allow overriding the Ethernet address, and do some magic to generate distinct (but stable) MAC addresses?
I've reported this at https://github.com/OLIMEX/olimage/issues/3