I have a Lenovo G780. The ethernet NIC is an Atheros AR8162.

I had problems with the device not working at all when I first got it in 2012 (Running kernel 3.4). Solution at the time was to install alx kernel module via backports.

Now the alx driver is apparently included in the mainline. It seems to be loaded successfully out-of-the-box.

I can connect and ping normally. UNTIL I start using a browser or try speedtest-cli. The device just stops. There's no indication from NetworkManager or dmesg or journalctl that anything has gone wrong. Traffic just stops. If I detach and reattach the cable, same procedure. (With the strange side-effect of WiFi association failing immediately until reboot, but not sure if related)

So, watching ethtool -S from connect onwards shows rx_address_errors climbing consistently.
As soon as rx_1024B_to_1518B_packets occur (like a browser or speedtest-cli) netstat -ie will show all additional RX packets are counted as RX errors and RX overruns.

I am running Arch Linux kernel 4.2.1 and I have also tried installing alx through backports compat.

Any advice on getting my ethernet working?

Sounds like it could be an MTU problem if it only affects longer packets.
http://www.mseri.me/fixing-wifi-on-o...aking-the-mtu/

Thanks, smallpond. I briefly tried lower MTU values to no avail. Your link taught me something new. For Linux users, find optimal MTU by means of:
And then lowering the size by 10 until a stable ping is achieved. Then increase by 2 until it fragments again.

UNFORTUNATELY... This did not apply to my issue. There is something funny going on with the alx driver. MTU range for 100Mb/s "Fast Ethernet" devices is 1500-1998 bytes. I found that setting my NIC MTU higher and higher would delay the failure ever so slightly. Currently I'm using an MTU of 4000 and no rx_errors so far. This is definitely not the correct setting and I don't know the side-effects, but it seems to work for now.