Upon bootup the network connection appears to be connected, for several reboots, I was shortly able to ping 8.8.8.8. However, I'm not longer able to do this. Then after logging in (<30 seconds) the network manager says the cable is disconnected. Unplugging and re-plugging the cable does not change this status.

The wireless connection is working.

I have previously used the wired connection in older versions of ubuntu (16.10 & 16.04) on this laptop, although I haven't tested them recently.

The network cable works with other computers.

The NIC device is a BCM5762.

Here is the output of ifconfig

 enp1s0: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500 ether 40:b0:34:09:9a:c0 txqueuelen 1000 (Ethernet) RX packets 91 bytes 54152 (54.1 KB) RX errors 0 dropped 1 overruns 0 frame 0 TX packets 146 bytes 32104 (32.1 KB) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0 device interrupt 36 lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536 inet 127.0.0.1 netmask 255.0.0.0 inet6 ::1 prefixlen 128 scopeid 0x10<host> loop txqueuelen 1000 (Local Loopback) RX packets 294 bytes 23870 (23.8 KB) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 294 bytes 23870 (23.8 KB) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
wlp2s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500 inet 10.87.252.202 netmask 255.255.0.0 broadcast 10.87.255.255 inet6 fe80::3260:ab36:9b89:9e58 prefixlen 64 scopeid 0x20<link> ether 7c:b0:c2:4e:13:d0 txqueuelen 1000 (Ethernet) RX packets 1247 bytes 1208923 (1.2 MB) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 881 bytes 160559 (160.5 KB) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

Here is the output of lshw -C network

 *-network description: Ethernet interface product: NetXtreme BCM5762 Gigabit Ethernet PCIe vendor: Broadcom Limited physical id: 0 bus info: pci@0000:01:00.0 logical name: enp1s0 version: 10 serial: 40:b0:34:09:9a:c0 capacity: 1Gbit/s width: 64 bits clock: 33MHz capabilities: pm vpd msi msix pciexpress bus_master cap_list ethernet physical tp 10bt 10bt-fd 100bt 100bt-fd 1000bt 1000bt-fd autonegotiation configuration: autonegotiation=on broadcast=yes driver=tg3 driverversion=3.137 firmware=sb latency=0 link=no multicast=yes port=twisted pair resources: irq:36 memory:e0820000-e082ffff memory:e0810000-e081ffff memory:e0800000-e080ffff *-network description: Wireless interface product: Wireless 7265 vendor: Intel Corporation physical id: 0 bus info: pci@0000:02:00.0 logical name: wlp2s0 version: 59 serial: 7c:b0:c2:4e:13:d0 width: 64 bits clock: 33MHz capabilities: pm msi pciexpress bus_master cap_list ethernet physical wireless configuration: broadcast=yes driver=iwlwifi driverversion=4.15.0-23-generic firmware=29.1044073957.0 ip=10.87.252.202 latency=0 link=yes multicast=yes wireless=IEEE 802.11 resources: irq:47 memory:e0d00000-e0d01fff

7 Answers

I had my network card get disabled after this morning's Ubuntu update. Rebooting the machine in Win10 the network card still works, so it's an Ubuntu configuration.

The way I solved it was the following:

sudo lshw -C network

This listed the "logical name" values:

logical name: enp8s0
logical name: docker0
logical name: enp0s29f7u7c4i2

I have a Dell T7400, so I know the device is a Broadcom NetXtreme BCM5754. Dell support provides no Ubuntu drivers, but you don't really need one. Somehow my ethernet device name was renamed.

sudo vi /etc/network/interfaces

Add the logical name to the end of the file:

auto enp8s0
iface enp8s0 inet dhcp

Finally, turn the interface on:

sudo ifup enp8s0

I tried the solutions above and they did not work.

What worked for me was disabling wifi using the network icon on the upper right corner of Ubuntu's GUI then restarting the network manager using :

service network-manager restart

I think that having a working wired connection cable that is plugged-in and a connected wlan card to a wifi network at the same time creates a conflict.

Run old GUI

nm-applet

Then activate Enable Networking.

If it doesn't solve it, try running

nm-connection-editor

to edit any weird configuration in the connections.

You can also see what the NetworkManager is doing with these commands.

# Run one by one to see if anything is useful
nmcli device
nmcli
nmcli device show

if your network device says unmanaged, it means the NetworkManager will not try to use that device to connect.

Workaround to bypass the NetworkManager

Configure network with netplan

# Create a config file
sudo nano /etc/netplan/ethernet.yaml

and enter this

network: version: 2 renderer: networkd ethernets: eno1: dhcp4: true

replace eno1 with whatever your device is (mine was ens33). To see your list of devices, run ip addr.

Finally apply the new configurations

sudo netplan apply

Similar problems here, this could be related to this bug or this bug in NetworkManager.

I work around this problem by using ifupdown together with ifplugd for detecting properly if a connector is plugged in the nic or not (I'm working on a laptop) and I have no connectivity issues anymore.

I had the same problem - my newly-installed Ubunut 18.04 wasn't detecting my ethernet connection for a second, though the led at the port was constantly blinking as if it were normal. I typed lshw -C at the terminal and among the output displayed there was no eth0 ( it refers to ethernet connection, no eth0 means no ethernet connection). I searched online and found out that the particular ethernet driver might be absent in Ubuntu.

I downgraded my kernel and ... spent more than two days feverishly trying to solve the problem.

The solution : I reinstalled Ubuntu 18.04 and that solved my problem. I don't know what went wrong in the first installation.

I made had made some changes to /etc/network/interfaces to make networking work in KVM, like this:

auto br0
iface enp2s0 inet manual
iface br0 inet dhcp bridge_ports enp2s0

I got that out of some article. Unfortunately it made my physical networking not work. Wireless was fine. I found out when I went somewhere and needed to use a physical network.

I commented out those lines, rebooted, and the physical network worked.

It's just as well that I added comments to the file with my name on them saying what I had done.

Anyway, for anyone reading this, check your interfaces file to see if there is anything odd in it.

Had the same problem try: