Unable to connect to ethernet. ethtool reports unknown speed and unknown duplex

I am trying to receive an internet connection through ethernet. My desktop is running Ubuntu 16.04.

The network manager applet reports as having connected to enp0s31f6, yet my computer has not received a DHCP address.

dhclient output seems to indicate that no DHCPOFFERs are being received from the server (more DHCPDISCOVER requests are sent with no change in the output):

~$ sudo dhclient -v enp0s31f6
Internet Systems Consortium DHCP Client 4.3.3
Copyright 2004-2015 Internet Systems Consortium.
All rights reserved.
For info, please visit
Listening on LPF/enp0s31f6/0c:9d:92:bd:9b:57
Sending on LPF/enp0s31f6/0c:9d:92:bd:9b:57
Sending on Socket/fallback
DHCPDISCOVER on enp0s31f6 to 255.255.255.255 port 67 interval 3 (xid=0xfff5a066)
DHCPDISCOVER on enp0s31f6 to 255.255.255.255 port 67 interval 8 (xid=0xfff5a066)
DHCPDISCOVER on enp0s31f6 to 255.255.255.255 port 67 interval 13 (xid=0xfff5a066)
DHCPDISCOVER on enp0s31f6 to 255.255.255.255 port 67 interval 13 (xid=0xfff5a066)

ethtool reports the following information. The value of Unknown! for the Speed and Duplex attributes seems suspect. Will I ever be able to connect when these values are unknown? If not, how can I fix this unknown values problem?

~$ sudo ethtool enp0s31f6
Settings for enp0s31f6: Supported ports: [ TP ] Supported link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full 1000baseT/Full Supported pause frame use: No Supports auto-negotiation: Yes Advertised link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full 1000baseT/Full Advertised pause frame use: No Advertised auto-negotiation: Yes Speed: Unknown! Duplex: Unknown! (255) Port: Twisted Pair PHYAD: 2 Transceiver: internal Auto-negotiation: on MDI-X: Unknown (auto) Supports Wake-on: pumbg Wake-on: g Current message level: 0x00000007 (7) drv probe link Link detected: no

I've tried to set their values manually, to no avail:

~$ sudo ethtool -s enp0s31f6 speed 1000 duplex full
~$ sudo ethtool enp0s31f6
Settings for enp0s31f6: Supported ports: [ TP ] Supported link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full 1000baseT/Full Supported pause frame use: No Supports auto-negotiation: Yes Advertised link modes: 1000baseT/Full Advertised pause frame use: No Advertised auto-negotiation: Yes Speed: Unknown! Duplex: Unknown! (255) Port: Twisted Pair PHYAD: 2 Transceiver: internal Auto-negotiation: on MDI-X: Unknown (auto) Supports Wake-on: pumbg Wake-on: g Current message level: 0x00000007 (7) drv probe link Link detected: no

Here's some snippets filtered from dmesg, in case they're relevant:

~$ dmesg | grep enp
[ 1.719930] e1000e 0000:00:1f.6 enp0s31f6: renamed from eth0
[ 7.980215] IPv6: ADDRCONF(NETDEV_UP): enp0s31f6: link is not ready
[ 8.221865] IPv6: ADDRCONF(NETDEV_UP): enp0s31f6: link is not ready
[ 314.654059] IPv6: ADDRCONF(NETDEV_UP): enp0s31f6: link is not ready
~$ dmesg | grep e1000e
[ 1.339047] e1000e: Intel(R) PRO/1000 Network Driver - 3.2.6-k
[ 1.339047] e1000e: Copyright(c) 1999 - 2015 Intel Corporation.
[ 1.406037] e1000e 0000:00:1f.6: Interrupt Throttling Rate (ints/sec) set to dynamic conservative mode
[ 1.651130] e1000e 0000:00:1f.6 0000:00:1f.6 (uninitialized): registered PHC clock
[ 1.719235] e1000e 0000:00:1f.6 eth0: (PCI Express:2.5GT/s:Width x1) 0c:9d:92:bd:9b:57
[ 1.719236] e1000e 0000:00:1f.6 eth0: Intel(R) PRO/1000 Network Connection
[ 1.719304] e1000e 0000:00:1f.6 eth0: MAC: 12, PHY: 12, PBA No: FFFFFF-0FF
[ 1.719930] e1000e 0000:00:1f.6 enp0s31f6: renamed from eth0

The Ubuntu Network Manager GUI reports that the 'Wired' connection is 'Connected', but there's no assigned address.

I've rebooted the machine at various points through the debugging so far, which did not fix the problem.

Additional info:

~$ ip link show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000 link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: enp0s31f6: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state DOWN mode DEFAULT group default qlen 1000 link/ether 0c:9d:92:bd:9b:57 brd ff:ff:ff:ff:ff:ff
3: wlxe091f519b0f3: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN mode DORMANT group default qlen 1000 link/ether e0:91:f5:19:b0:f3 brd ff:ff:ff:ff:ff:ff
~$ ip route
default via ABC.DEF.176.1 dev wlxe091f519b0f3 proto static metric 600
default dev enp0s31f6 scope link metric 1002 linkdown
ABC.DEF.176.0/20 dev wlxe091f519b0f3 proto kernel scope link src ABC.DEF.188.112 metric 600
HIJ.KLM.0.0/16 dev enp0s31f6 proto kernel scope link src HIJ.KLM.9.24 linkdown

[some IP numbers masked with letters in the above]

A potentially interesting bit from:

journalctl /usr/sbin/NetworkManager:

<info> [1564430899.7494] device (enp0s31f6): state change: unmanaged -> unavailable (reason 'managed') [10 20 2]
Jul 29 16:08:19 computer NetworkManager[947]: nm_device_get_device_type: assertion 'NM_IS_DEVICE (self)' failed

1 Answer

In the output of ip link show you see

enp0s31f6: <NO-CARRIER 

and dmesg shows

enp0s31f6: link is not ready

both indicate that there exists a problem with the physical connection.

Some possible causes:

• a plug is not snapping into place properly
• a defective cable
• a switch port is deactivated or defective