I purchased the widely recommended Plugable USB Gigabit Ethernet adapter (USB2-E1000) to substitute for an increasingly flaky onboard ethernet port on an aging core2duo macbook.
Having installed the drivers, and disabled IPv6, the adapter will connect to the LAN and I can access the internet and local file servers over the interface. However, Airplay will not see any clients or stream over that interface. If I re-enable my airport/wifi connection, then Airplay comes back to life and the clients are visible in iTunes (or Airfoil).
What’s the deal? How can I fix this?