I have a Cisco Catalyst that has a port that is up up, and the device does not show in the ARP table. The MAC address-table shows a MAC address for the port. What can I do from that switch to find out what the device is?
ARP is a protocol to resolve a layer-3 address to a layer-2 address. If there is no layer-3 address assigned to the device, then ARP cannot help you.
Apparently, the device is sending frames because the MAC address shows in your MAC address table. You can check the OUI to see the NIC manufacturer of the device. You could also try CDP and LLDP to see if the device responds to either of those.
You mention it's a multilayer switch but don't say if the VLAN this device is in has an associated Layer 3 interface / IP on this switch. The device may be sending frames but if it doesn't have a Layer 3 interface to talk with on that VLAN, there will be no ARP entry. You could try enabling IP Device Tracking which will initiate ARP probes out the Layer 2 interface. The result is a Layer 3 address can be stored as being associated with the Layer 2 interface/ MAC, without the ARP table.
globally --> ip device tracking interface --> ip device tracking maximum 10 show ip device tracking all