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I am a beginner to Linux and Ubuntu, and my laptop currently dual-boots Ubuntu 12.04 and Windows 7. Neither of my wired and wireless connections are working. My wired network was working, but when I was searching for a solution to my wireless connection problem, it also stopped working. Not only did the wired connectioin stop working for Ubuntu, it also stopped working for Windows. :( I checked my LAN connection, and it seems fine - the cable was working fine seconds ago, and lights were flashing inside the port. It's worth noting that the computer repeatedly connects to the network - only to disconnect seconds later.

Anyway, from where I looked, the following information seems to be required:

ifconfig:

eth0      Link encap:Ethernet  HWaddr f0:de:f1:65:74:d1  
          inet6 addr: fe80::f2de:f1ff:fe65:74d1/64 Scope:Link
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:448 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:0 (0.0 B)  TX bytes:98250 (98.2 KB)
          Interrupt:41 Base address:0x8000 

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:16436  Metric:1
          RX packets:631 errors:0 dropped:0 overruns:0 frame:0
          TX packets:631 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:44610 (44.6 KB)  TX bytes:44610 (44.6 KB)

wlan0     Link encap:Ethernet  HWaddr 8c:a9:82:bd:5d:ac  
          inet6 addr: fe80::8ea9:82ff:febd:5dac/64 Scope:Link
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:840 errors:0 dropped:0 overruns:0 frame:0
          TX packets:936 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:349062 (349.0 KB)  TX bytes:131132 (131.1 KB)

sudo lshw -C network:

*-network               
       description: Wireless interface
       product: Centrino Wireless-N 1000
       vendor: Intel Corporation
       physical id: 0
       bus info: pci@0000:02:00.0
       logical name: wlan0
       version: 00
       serial: 8c:a9:82:bd:5d:ac
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress bus_master cap_list ethernet physical wireless
       configuration: broadcast=yes driver=iwlwifi driverversion=3.2.0-32-generic     firmware=39.31.5.1 build 35138 latency=0 link=no multicast=yes wireless=IEEE 802.11bgn
       resources: irq:43 memory:d0500000-d0501fff
  *-network
       description: Ethernet interface
       product: RTL8101E/RTL8102E PCI Express Fast Ethernet controller
       vendor: Realtek Semiconductor Co., Ltd.
       physical id: 0
       bus info: pci@0000:03:00.0
       logical name: eth0
       version: 05
       serial: f0:de:f1:65:74:d1
       size: 10Mbit/s
       capacity: 100Mbit/s
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress msix vpd bus_master cap_list ethernet physical tp mii 10bt 10bt-fd 100bt 100bt-fd autonegotiation
       configuration: autonegotiation=on broadcast=yes driver=r8169 driverversion=2.3LK-NAPI duplex=half firmware=rtl_nic/rtl8105e-1.fw latency=0 link=no multicast=yes port=MII speed=10Mbit/s
       resources: irq:41 ioport:2000(size=256) memory:d0404000-d0404fff memory:d0400000-d0403fff

I had tried using gksu gedit /etc/network/interfaces and adding

auto eth0
iface eth0 inet dhcp

But it didn't do anything.

EDIT: It turned out that this problem was caused by the bad university LAN - after a while, it magically started working again.

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this may solve the issue askubuntu.com/q/177083/46312 –  Ringtail Jan 7 '13 at 4:53
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1 Answer 1

Press Ctrl+Alt+T and type echo on | sudo tee /sys/class/net/eth0/device/power/control

After that, logout your machine, pull out the ethernet cable and then plug it in again after logging it in

your ethernet should work afterwards

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