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I did a first time install of Ubuntu 11.10 using Wubi and the ethernet connection on my laptop. (so I know that the ethernet interface is working and connected correctly). I finished the install and booted up Ubuntu. The wireless connection works fine, but I am not able to get the wired connection to work. Here is the output of ifconfig for eth0:

eth0      Link encap:Ethernet  HWaddr 00:08:0d:0e:88:c3  
          inet6 addr: fe80::208:dff:fe0e:88c3/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:391 errors:0 dropped:0 overruns:0 frame:0
          TX packets:84 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:25591 (25.5 KB)  TX bytes:23899 (23.8 KB)

And here is the output for lshw:

user@ubuntu:~$ sudo lshw -class network
[sudo] password for user: 
  *-network:0             
       description: Wireless interface
       product: AR5212/AR5213 Multiprotocol MAC/baseband processor
       vendor: Atheros Communications Inc.
       physical id: 5
       bus info: pci@0000:01:05.0
       logical name: wlan0
       version: 01
       serial: 00:90:96:7c:9e:56
       width: 32 bits
       clock: 33MHz
       capabilities: pm bus_master cap_list ethernet physical wireless
       configuration: broadcast=yes driver=ath5k driverversion=3.0.0-12-generic firmware=N/A latency=168 link=no maxlatency=28 mingnt=10 multicast=yes wireless=IEEE 802.11bg
       resources: irq:22 memory:cfff0000-cfffffff
  *-network:1
       description: Ethernet interface
       product: 82801DB PRO/100 VE (MOB) Ethernet Controller
       vendor: Intel Corporation
       physical id: 8
       bus info: pci@0000:01:08.0
       logical name: eth0
       version: 83
       serial: 00:08:0d:0e:88:c3
       size: 100Mbit/s
       capacity: 100Mbit/s
       width: 32 bits
       clock: 33MHz
       capabilities: pm bus_master cap_list ethernet physical tp mii 10bt 10bt-fd 100bt 100bt-fd autonegotiation
       configuration: autonegotiation=on broadcast=yes driver=e100 driverversion=3.5.24-k2-NAPI duplex=full firmware=N/A latency=64 link=yes maxlatency=56 mingnt=8 multicast=yes port=MII speed=100Mbit/s
       resources: irq:20 memory:cffef000-cffeffff ioport:cf40(size=64)

It looks like the hardware is recognized and there is a driver attached to it. I only see an inet6 addr for eth0, but no inet addr. Manually configuring the ip addr is not desirable. I would like the dhcp to work correctly.

Any ideas for further debug or fixing this appreciated.

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One more data point to add: I grepped for eth0 in a system log and saw that the eth0 would not connect because there was no IPv6 router available. This is true: my older router only supports IPv4. So the key is to understand why IPv4 is not coming up with eth0. The e100 driver seems like the right choice for the enet hardware (it's what came standard with Ubuntu 11.10). –  Bob Jan 24 '12 at 18:15
    
Another data point: I booted up recovery mode (just a console, no window manager). And IPv4 for eth0 came up fine. I could successfully ping www.google.com, etc. So, the $1M question is why IPv4 does not work for eth0 when the full Ubuntu boots up, but eth0 works fine when booting recovery mode. –  Bob Jan 26 '12 at 5:16
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1 Answer

Problem solved. WRT54G router running DD-WRT needed firmware to be reloaded. Flash memory must have become corrupted over time. Before fix, Windows devices had no problem connecting with DHCP, but DHCP was failing with non-Windows devices. Made this problem hard to diagnose.

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