The system core is definitely the C10, in spite of Meridian's protestations. I have unchecked the system core box for the C10, and now it cannot find a core - i.e. the Ensemble is not providing it. Should it/can it be forced to?
No sign of the ID40 in the system debug screen (when the C10 was core).
I am far too familiar with the setup of my router - too many years with too many routers dealing with network configuration problems. That said, I am an amateur not a professional computer scientist.
The ID40 is definitely not identifying itself, but then nor are some other devices (e.g. this computer is not currently in the DHCP table, although it was before a recent reboot). Hence my lack of certainty.
The setup is complex, unfortunately - beyond my previous experience. A Draytek Vigor 2830 series modem, a Netgear 24 port Cat 6 switch, Cat 6 cables run between the switch and the various locations. The Meridian network locations are each taken out of the router ports directly rather than through the switch. That said, I remain convinced there is a networking problem. There is another intermittent symptom, which is that that the Ensemble albums sometimes do not appear in the system nor are it's zones visible to the C10 nor to the Control apps (requiring either a reboot or a wait).