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
This is interesting. I had to modify it to nmap -A -T4 -p- -Pn <IP>.
It said the host is up with 0.077 seconds of latency. All 64k ports were scanned with 7 filtered tcp ports (host-unreachable) and the rest (no-response).
What’s weird about this is that it should be getting a response from IIS like you showed us in the screenshot.
77ms of latency is pretty slow. Based off that I’d assume (but not rule out) that it’s not: on the machine you used to run nmap, not on ethernet, probably wifi with a shitty connection
So, some really dumb, likely irrelevant, questions that might spark an idea:
Do you see anything weird connected in the wifi client list? (You said it wasn’t given a dhcp lease, but it would still show as a wireless client even if it were static)
Are you running a VPN server or using VPN to bridge any networks?
You said you’re running dual WAN, are those configured properly and not leaking random internet shit into your LAN?
Do you have anything that might be running some kind of out-of-band management system like DRAC on a dell server?
What’s your IoT situation?
Do you have an on-site NVR for security cams?
Did you find the mac? If so what are the first 3 octets? Even if the vendor can’t be found, there’s always the chance some crazy ubernerd is going to recognize it. (If it’s 00:d0:2c or 44:d9:e7 I got ya covered)
Again, most of those are probably irrelevant, but throwing the thoughts out there :)