No Ethernet on Lenovo P50, (`ifplugstatus` reports unplugged) Intel I219-LM network card

Question

Issue

On a Lenovo P50, the network card does not seem to be able to detect Ethernet cables or establish a network connection. The ethernet conection is set-up to be hot-plugged and managed by avahi. The wired connection once worked, but seems to have failed some time in the past six months or so.

Debugging so far

• Computing support confirms that network ports are working
• Other machines plugged into network ports work, indicating cables are good
• Plugging in ethernet cables to laptop does not cause port to light up (but it is not clear that this port has lights)
• Wireless connection works
• Network configuration appears ok, common pitfalls not present

System information

$ cat /etc/lsb-release 
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=16.04
DISTRIB_CODENAME=xenial
DISTRIB_DESCRIPTION="Ubuntu 16.04.3 LTS"

$ cat /proc/version
Linux version 4.4.0-112-generic (buildd@lgw01-amd64-010) (gcc version 5.4.0 20160609 (Ubuntu 5.4.0-6ubuntu1~16.04.5) ) #135-Ubuntu SMP Fri Jan 19 11:48:36 UTC 2018

$ lspci | grep Ethernet
00:1f.6 Ethernet controller: Intel Corporation Ethernet Connection (2) I219-LM (rev 31)

$ sudo lshw -C network
  *-network               
       description: Wireless interface
       product: Wireless 8260
       vendor: Intel Corporation
       physical id: 0
       bus info: pci@0000:04:00.0
       logical name: wlp4s0
       version: 3a
       serial: [MAC_ADDRESS]
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress bus_master cap_list ethernet physical wireless
       configuration: broadcast=yes driver=iwlwifi driverversion=4.4.0-112-generic firmware=16.242414.0 ip=172.20.174.88 latency=0 link=yes multicast=yes wireless=IEEE 802.11abgn
       resources: irq:133 memory:c4c00000-c4c01fff
  *-network
       description: Ethernet interface
       product: Ethernet Connection (2) I219-LM
       vendor: Intel Corporation
       physical id: 1f.6
       bus info: pci@0000:00:1f.6
       logical name: enp0s31f6
       version: 31
       serial: [MAC_ADDRESS]
       capacity: 1Gbit/s
       width: 32 bits
       clock: 33MHz
       capabilities: pm msi bus_master cap_list ethernet physical tp 10bt 10bt-fd 100bt 100bt-fd 1000bt-fd autonegotiation
       configuration: autonegotiation=on broadcast=yes driver=e1000e driverversion=3.2.6-k firmware=0.8-3 latency=0 link=no multicast=yes port=twisted pair
       resources: irq:130 memory:c5700000-c571ffff

$ ifconfig
enp0s31f6 Link encap:Ethernet  HWaddr 50:7b:9d:e4:d8:49  
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)
          Interrupt:16 Memory:c5700000-c5720000 

enp0s31f6:avahi Link encap:Ethernet  HWaddr 50:7b:9d:e4:d8:49  
          inet addr:[IP_ADDRESS]  Bcast:169.254.255.255  Mask:255.255.0.0
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          Interrupt:16 Memory:c5700000-c5720000 
...

$ ifplugstatus
lo: link beat detected
enp0s31f6: unplugged

$ cat /etc/network/interfaces
# interfaces(5) file used by ifup(8) and ifdown(8)
auto lo
iface lo inet loopback

allow-hotplug enp0s31f6
iface enp0s31f6 inet dhcp

$ sudo ifdown enp0s31f6 && sudo ifup -v enp0s31f6
Killed old client process
Internet Systems Consortium DHCP Client 4.3.3
Copyright 2004-2015 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Listening on LPF/enp0s31f6/[MAC_ADDRESS]
Sending on   LPF/enp0s31f6/[MAC_ADDRESS]
Sending on   Socket/fallback
Configuring interface enp0s31f6=enp0s31f6 (inet)
/bin/run-parts --exit-on-error --verbose /etc/network/if-pre-up.d
run-parts: executing /etc/network/if-pre-up.d/ethtool
run-parts: executing /etc/network/if-pre-up.d/wireless-tools
run-parts: executing /etc/network/if-pre-up.d/wpasupplicant

/sbin/dhclient -1 -v -pf /run/dhclient.enp0s31f6.pid -lf /var/lib/dhcp/dhclient.enp0s31f6.leases -I -df /var/lib/dhcp/dhclient6.enp0s31f6.leases enp0s31f6  
Internet Systems Consortium DHCP Client 4.3.3
Copyright 2004-2015 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Listening on LPF/enp0s31f6/[MAC_ADDRESS]
Sending on   LPF/enp0s31f6/[MAC_ADDRESS]
Sending on   Socket/fallback
DHCPDISCOVER on enp0s31f6 to 255.255.255.255 port 67 interval 3 (xid=0xf5fca319)
DHCPDISCOVER on enp0s31f6 to 255.255.255.255 port 67 interval 6 (xid=0xf5fca319)
DHCPDISCOVER on enp0s31f6 to 255.255.255.255 port 67 interval 7 (xid=0xf5fca319)
No DHCPOFFERS received.
No working leases in persistent database - sleeping.

$ sudo ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: enp0s31f6: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state DOWN group default qlen 1000
    link/ether [MAC_ADDRESS] brd ff:ff:ff:ff:ff:ff
    inet [IP_ADDRESS]/16 brd 169.254.255.255 scope link enp0s31f6:avahi
       valid_lft forever preferred_lft forever

The following questions with similar symptoms do not resolve the issue:

Suggested solutions that do not work in this case:

The suggested command ip link set enp1s0 up does not resolve it. The suggested commands ifconfig .. down ... up do not resolve it.

Similar symptoms, but probably unrelated hardware issues:

This issue is common with Realtek cards, and there are several related questions (1234), but this machine has an Intel card.

This question seems specific to a USB Ethernet device, related to hot-plug issues.

This question involves the network interface disappearing entirely, and returning on reboot.

This question is a bit vague and lacks definitive answers.

This question pertains to Ethernet, but the answer is a link to wifi troubleshooting.

This question appears to be different, as it involves the Ethernet adapter being unavailable, wheres it is available on my machine but registers as disconnected.

This question has similar symptoms, but was due to a conflicting configuration from a previous network card.

This question related to a corrupted driver (I think?).

In this case they were able to regain network access simply by deleting /etc/network/interfaces and rebooting. I have tried this and it did not work in this case.

Potentially related questions without resolution

This question may be related (unclear), but does not have an answer. Likewise for this question.

In this question it was assumed that the problem lay with the building network configuration. I have been assured by the building support staff that this is not the case here.

This question was diagnosed as a hardware fault of the network card. It is not clear that it applies in this case. This one seemed also to be a hardware failure. (I would like to rule out other explanations before presuming hardware failure).

Update and resolution

We determined that the machine could not use Ethernet when booted from a different operating system on removable media, indicating a hardware issue. Indeed, on the Lenovo P50 there are status LEDs (yellow and green) on the port, and these should respond when Ethernet is plugged in. They were dark on this machine, indicating a hardware issue.