@Panda

That was my [perfectly logical, as per every other SOHO router, ISP-supplied or not] assumption; that connected via a LAN port, with DHCP disabled (and the internal modem/broadband disabled), that it would act as a switch, 4 physical LAN ports and one internal WLAN port, and would pass DHCP packets to the PFSense box.

It doesn't. It DOES act as a switch, and passes WLAN<->LAN traffic over the ports, but not DHCP packets - or thinking about it, maybe it isn't forwarding broadcast packets, as DHCP Discover is a broadcast packet, and perhaps it 'expects' DHCP discover to be 'routed' internally to itself, or disabling DHCP disables the service but not the listening port.

I deleted the post as I noticed you had (switch port 1) afterwards, which pretty much invalidated by reply...

I clearly don't have personal experience of every CPE in existence, but I have yet to encounter one that doesn't behave as we expect when used in this way.

Is there a 'Wireless isolation' setting or somesuch that would prevent the WLAN interface communicating with the LAN ports?

I thought wireless isolation stopped wireless clients communicating with each other

Not unless it is called something other than "wireless isolation" - or anything even remotely indicating that that is what the setting does!

The router logs are not exactly helpful - well, I wouldn't expect a sufficient degree of granularity from such a box to display "dropped UDP Port 67" in the log

But it has got me thinking about another couple of tests; isolate the router (disconnect from network), enable DHCP, and ensure WLAN traffic can see, and communicate with, devices on the LAN. Then assign static devices,and disable DHCP, and repeat. Then enable the GS105 DHCP server and repeat with DHCP clients. If that works, then I'll use the GS105 as a workaround.

Completely off-topic, but the last five posts all claim to be deleted, which is a bit confusing in Threaded Mode .