@jakobp I've been doing some Wireshark captures with various devices to see how they process DHCP/ARP requests. My ISP uses PPPoE so I can't test with that, but I've tested connecting devices to the...

@jakobp I'm located in Austria, it's a local fiber to the home provider. That might mean they will at least look into the problem. I was afraid that it was going to be a UK ISP using the BT/Openreach...

@jakobp Interesting! I'll have to have a good read through the RFC myself. I wonder if, in the case of the ER605, the ARP announce is sent when the ISP systems are still finalising the IP allocation,...

@jakobp Is there a chance you could get a packet capture using the router that works, so we can see any difference in the DHCP/ARP conversations

It does look like something not quite right. Strange that everything else seems to work ok apart from the ER605 ? TBH I've not much experience of ISPs using DHCP , mine uses PPPoE. I've dropped you a...

@jakobp Looks like your ISP might be insisting on the connection being from a 'fixed' MAC address. Try using the MAC address clone function on the ER605 ( manual page 33 ) to set the same MAC address...