On both my home and work networks, if I plug in an ethernet cable into my laptop, gnome's network manager starts cycling between saying "Wired network Disconnected" and "wired network Connection Established". It does this back and forth about once every couple seconds.
The network card is Intel Corporation 82579LM Gigabit Network Connection and the laptop is a Dell Precision M6600.
Thanks in advance!
I would first start from external causes (Hardware) and work my way into internal causes (Software and internal hardware).
Make sure the cables are correctly plugged in and the cable connectors are correctly made (Should not disconnect if you for example try to slightly pull the cable).
Verify that the cable does not have a huge rotten chewing on it or some mutated monster dropping radiactive goo on the ethernet cable.
Check that the network cards are, if they are PCI, correctly connected. Over exaggerating this but it happened 3 times in my life experience.
After doing this 3 cases then read this post that it might solve the same problem: Sharing any Network Connection starts a connection/disconnection loop
The solution was to update Ubuntu packages and it was solved, not only for sharing connections wirelessly and wired but also for connecting to shared ones or directly to wired/wifi ones.
I found something similar. I don't know why, but every now and then, my wired connection falls.
I used to check phone line, connections from the phone line, connections to/from the router and try to reset the router.
That was with no result until I found that unticking "Enable connections" on the "Connections" icon on the panel and tick it again, would reset my internet and it would stay fine until the next time.
I don't bother checking hardware and phone line any more. I go straight for the icon, and so far, it has worked every time.
