Wow, thanks for taking the time to try all that! The motherboard I'm using right now only has one NIC, so it's definitely the right port.
I have no problem establishing a connection to my LAN, the issue is keeping it working properly. It just sort of half dies on me, no matter what. Weird thing is when it happens, I can no longer ping my router (192.168.1.1) or the WWW (google.com for example) but I can still ping other rigs on my LAN and they can also ping the troubled Ubuntu rig (192.168.1.200).
I set everything up on a VM using virtualbox, and for some reason it works flawlessly. I can't wrap my head around this.
You're welcome, I enjoyed it. It gives me a topic for learning something new.
Sounds insulting, but not intended so, try a different ethernet cable. I get this sort of issue regularly with all the cat 5 / cat 6 ethernet cables I have ... I swap out a cable and it's all better. I even have brand new, never used, cables that don't work at all or work on one computer but not another - true story. Now, I only buy high-quality cat7 cables - no more junk.
Have you made sure that both the router and your network connection are set to the same thing? ... for example, both set for dhcp or both for static ip assignment. A router set up for static IPs and a computer connection set to dhcp won't get much traffic moving.
If no change, and just for fun, you could try this:
Delete existing connection (from within the Edit Connections applet) ... DON'T create a new one,
disable networking (option from network applet at top of ubuntu desktop),
count to 10,
enable networking (option from same applet),
select autoethernet to connect to (that's the auto generated name my ubuntu comes up with),
additionally:
sudo service network-manager stop && sudo rm /var/lib/NetworkManager/NetworkManager.state && sudo service network-manager start ... then reboot
Cheers.