I have these log entries where I am unable to decipher the client.
Feb 21 14:07:31 dnsmasq-dhcp[27767]: DHCPSOLICIT(br0) 00:04:b3:0c:0b:7e:03:bc:dd:e1:ac:06:fc:4c:0b:b0:84:d5
These are repeated over and again, while it does no harm, maybe the client is misconfigured.
It appears to be an IPv6 discovery message, probably from the client w/ MAC address 00:04:b3:0c:0b:7e. Why? Not sure, but in my own case, I've disabled IPv6 on my local clients to avoid any such messages and unnecessary traffic.
Not easy to identify if it otherwise has not been given an IPv4 IP address. If it has, you should be able to get the assigned IP, and perhaps the hostname as well w/ an arp dump (arp -a) from a shell (ssh) on the router. Only other suggestion I can make is checking its MAC address against an OUI database.
That's what I thought too. There is nothing with that MAC found on the LAN.
Looks like I'll need to get wireshark installed.
I keep IPv6 running across the network.