Strange DHCP Behaviour....

So, as a follow on from my new VLAN config, I have set up an "IOT_TRUSTED" VLAN - VLAN 200. 

I have an older AV reciever - an ONKYO TX-NR509. In my old setup (a flat, no VLAN GS116), this worked flawlessly. 

Since switching to the new GS324T, this device does not, and will not, get a DHCP address. I thought, dodgy cable (the cable test told me there was a short), so swapped the cable.. no change.

I asked the pfense firewall (DHCP server for all VLAN scopes) to do a packet capture -

the Onkyo sends a DHCPDISCOVER.

the firewall assigns an address, and sends a DHCPOFFER..

but the Amp either doesn't see this, or never sends a DHCPACK. 

I tried a straight Default VLAN 1 port, no DHCP.

I tried a MAC Based VLAN - no DHCP

I tried a Port with PVID 200, untagged 200, and no other VLAN. 

I updated firmware - no dice. 

If I set a static IP, that doesn't work either. I can't ping. 

Now, if I plug another laptop on the end of the cable, it gets DHCP assigend IP address in the right VLAN, instantly. 

So tonight, before resigning myself to simply losing the network features of the reciever, I tried plugging a "dumb old switch" in the way - I plugged the Onkyo into an old unmanaged GS105 I had on my desk, and plugged this into the same PVID Port on VLAN 200. 

It works. perfectly, first time, every time. 

Any ideas? is there some configuration on the newer switches that old chipsets don't like for DHCP? If I *have* to keep a legacy switch plugged in for older kit to connect to, I guess that's acceptable... but I would rather not.