Ubuntu – Ethernet not working after update 14.04 (64 bit)

14.04ethernetinternetipnetworking

After updating Ubuntu a few days back my ethernet has stopped working. The wifi works fine. I even managed to make my ethernet work once using sudo dhclient eth0 but could not replicate it after reboot. I have another laptop with Windows and the physical cable is fine.

My ethernet connection gets connected but internet doesn't work.
Also I am behind a proxy if that helps in anyway.

I have posted this after reading a lot of fixes on the internet. None of them seem to even temporarily fix my problem.

Any help would be appreciated.

Here are a few outputs :

ifconfig

eth0  Link encap:Ethernet  HWaddr 14:dd:a9:0d:88:29  
      inet addr:172.24.136.242  Bcast:172.24.143.255  Mask:255.255.248.0
      inet6 addr: fe80::16dd:a9ff:fe0d:8829/64 Scope:Link
      UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
      RX packets:0 errors:0 dropped:0 overruns:0 frame:0
      TX packets:1443 errors:0 dropped:3302 overruns:0 carrier:0
      collisions:0 txqueuelen:1000 
      RX bytes:0 (0.0 B)  TX bytes:161427 (161.4 KB)

lo    Link encap:Local Loopback  
      inet addr:127.0.0.1  Mask:255.0.0.0
      inet6 addr: ::1/128 Scope:Host
      UP LOOPBACK RUNNING  MTU:65536  Metric:1
      RX packets:28333 errors:0 dropped:0 overruns:0 frame:0
      TX packets:28333 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:0 
      RX bytes:2407338 (2.4 MB)  TX bytes:2407338 (2.4 MB)

wlan0 Link encap:Ethernet  HWaddr 34:02:86:96:f3:98  
      inet addr:192.168.63.102  Bcast:192.168.63.255  Mask:255.255.255.0
      inet6 addr: fe80::3602:86ff:fe96:f398/64 Scope:Link
      UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
      RX packets:27733 errors:0 dropped:0 overruns:0 frame:0
      TX packets:23098 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:1000 
      RX bytes:19054557 (19.0 MB)  TX bytes:4802812 (4.8 MB)

cat /etc/resolv.conf

# Dynamic resolv.conf(5) file for glibc resolver(3) generated by   resolvconf(8)
#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
nameserver 127.0.1.1
search connectify

cat /etc/network/interfaces

auto lo
iface lo inet loopback

lspci | grep Ethernet

05:00.1 Ethernet controller: Realtek Semiconductor Co., Ltd.    RTL8111/8168/8411
PCI Express Gigabit Ethernet Controller (rev 12)

Update:

The answer below used to temporarily start my internet once in a while but didn't fix it permanently. So eventually after a couple of regular minor updates from Ubuntu my ethernet started working again. So I guess if the common solutions on the internet don't work and your ethernet stopped working just after an update you should probably wait for the next update.

Best Answer

open /etc/network/interfaces using 

sudo vi  /etc/network/interfaces

add line

auto eth0 
iface eth0 inet dhcp

then do 

sudo ifdown eth0
sudo ifup eth0

you are saying sudo dhclient eth0 working so do above change it will search for DHCP when you start system also make sure you have proper proxy setting in your system .current ifconfig output shows your system getting IP from DHCP.

EDIT: For device not managed you have to open /etc/NetworkManager/NetworkManager.conf using command :

sudo vi /etc/NetworkManager/NetworkManager.conf

and change the line managed=false to managed=true and restart NetworkManager 

sudo service network-manager restart

For more info related this problem you can take help from Askubuntu another question network manager says “device not managed”

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