UPDATE 10/4 6:47 EDT
I have been going through all the comments. THANKS!!! I did not know about the techniques listed, so they are extremely helpful. Sorry for the slow update. As I mentioned below, I got behind with this yesterday so work cut into my evening.
I ran a port scan. The first syntax, -p, brought no joy. The nmap software itself suggested changing to -Pn. That brought an interesting response:
nmap -Pn 1-9999 <Local IP Addr>
Starting Nmap 7.93 ( https://nmap.org ) at 2024-10-04 11:44 BST
Failed to resolve “1-9999”. Nmap scan report for <Local IP Address> Host is up (0.070s latency). All 1000 scanned ports on 192.168.0.46 are in ignored states. Not shown: 990 filtered tcp ports (no-response), 10 filtered tcp ports (host-unreach) Nmap done: 1 IP address (1 host up) scanned in 6.03 seconds Just to be absolutely sure, I turned off my work computer (the only windows box on my network) and reran the same syntax with the same results.
As I read this, there is definitely something on my network running windows that is not showing up on the DHCP.
UPDATE 10/6
I am working through all these suggestions. I am sorry for the slow responses, but I have my hands full with family weekend. I will post more next tomorrow. But I did do one thing that has me scratching my head and wondering if this may be a wild goose chase.
I ran the nmap again per below with a completely fictional IP address within my normal range. It gave the exact same results:
nmap -A -T4 -p- -Pn <Fictional IP>
Starting Nmap 7.93 ( https://nmap.org ) at 2024-10-05 13:36 BST Nmap scan report for <Fictional IP>
Host is up (0.054s latency).
All 65535 scanned ports on <Fictional IP> are in ignored states.
Not shown: 65525 filtered tcp ports (no-response), 10 filtered tcp ports (host-unreach)
Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 182.18 seconds
If you can, power stuff off and check if that web page is still available. Start with any Windows machines. It could be a virtual machine running inside of something else though.
Edit: here’s how to disable that web server https://superuser.com/a/1377078 . I’d do that on any Windows machines as well.
The mac address can also tell you the hardware vendor.
I shut off my only windows machine and it is still there.
I’d go around unplugging anything that might be connected to the network, like game consoles, smart TV, etc. It’s unlikely, but maybe something has copied that same screen to throw you off.
It is probably going to come to this.