Update. For anyone else that may get this issue.
I did an IP scan and found the two MAC addresses. They belong to the two Dell printers we have. They both have static IPv4 addresses but constantly request IPv6 addresses. Unlike the FX-c5005d printer, there is no way to turn off IPv6 on the Dell printers. Dell printers are made by Xerox, hence the Fuji MAC address range.
Since it isn't a Xerox device I really don't know, but printers have a MAC per connection, So Wired/Wireless/WiFi Direct etc all have a MAC of their own.
And Routers lie
Extenders are weird
IPv6 was disabled but I just realised the IPv6 DNS was still set to auto. The thing is, the mystery MAC address is different to the one that is used by the active connection. There is no other connection from the printer to the network.
Disable IPv6 and make sure the DNS settings are not set to DHCP (they can be even when the IP is static)
We have a Fuji Xerox c5005d Docuprint printer. It has been set up with manual IP address with IPv4 only. It has been working fine. However, our DHCP server randomly receives a series of DHCP request, all with the same MAC address (08:00:37:F4:XX:XX) which our DHCP server denies as it is not in its whitelist. Our server is isolated from the internet and there is no other Fuji Xero device on our network. There is only one network cable plugged into the printer.
Anyone else had this issue?
Solved! Go to Solution.