No, my lan has been on 10.0.0.* for decades. It’s a valid set of private ip addresses for home, or business use. That’s not going to change, thank you very much. Changing the ip is not even optional in this discussion. The computer in question has an ip address of 10.0.0.17, and it will not change. The router knows this computers Mac address, and won’t give it a different ip address. Because that is how the router has been set up.
Anyway, thank you to everyone that was trying to help. I have to apologize - I fell asleep last night, sitting in my chair, typing this message. On a different computer.
So. Everythings working again. Automagically. When I woke up, the laptop I had been using was not working. Again, automagically, Neither was my main workstation. But I could send pings from a third computer, but the laptop nor the workstation were reachable - even though I could see the pings in wireshark. And, like I was trying to say yesterday, I was only seeing a few different protocols in wireshark, on that workstation. Even though the local network always has tons of TCP, TLS, and ICMP packets flying around, I couldn’t see them in wireshark on that workstation. Until all of a sudden, like magic, I could. And everything is working again on the workstation. And everything is working on that laptop.
Yeah…