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Today I was in the office using the corporate ethernet there with my Raspberry Pi, and it was working very smoothly. I was even able to tinker with some SSH and VNC connections and use the browser, and ifconfig had a working IP that I was able to use.

I went home, however and plugged in another yellow ethernet cable and the link lights didn't even come on. There was no change in ifconfig output before and after the cable was plugged in.

Here's what I've tried:

  • Countless changes to the "interfaces" file
  • Rebooting the router (with 20-sec interval)
  • Removing and plugging in and removing and... with the cable
  • Rebooting the Pi 2 multiple times
  • Using sudo ifdown and sudo ifup with the argument "eth0"
  • and much more...

After spending an hour searching on forum websites, I believe the problem is the cable though I can assure that it works with laptops. The cable is a standard Ethernet cable, with one end hooked into a wall outlet and the other into the Raspberry Pi 2.

Is there anything else you can recommend to fix this?

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  • If it works good with laptop, i don't see any reason why link shouldn't be up on Rpi. Are you sure it's locked in perfectly ?
    – dhruvvyas90
    Jul 11 '15 at 4:30
  • Try ifconfig -a (the -a is significant) or ip link.
    – goldilocks ♦
    Jul 11 '15 at 11:16
  • 1. There is absolutely no difference in the output I get from ifconfig -a and just ifconfig.
    – crownusa
    Jul 11 '15 at 14:14
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    ip link just prints out some random words, with the capitalized ones being "UNKNOWN mode DEFAULT", "<NO-CARRIER,BROADCAST,MULTICAST,UP>", "LOOPBACK,UP,LOWER_UP", etc.
    – crownusa
    Jul 11 '15 at 14:17
  • And lastly: if I ping my own router's IP address I get: connect: Network is unreachable
    – crownusa
    Jul 11 '15 at 14:18
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Available network interfaces can be listed with ip link or ifconfig -a (without -a, ifconfig does not show interfaces which are in a "down" state; this state is not a problem, it just means the interface is not in use). Note that as per the man page, ifconfig is "obsolete! For replacement check ip addr and ip link...".

The output from both is a list, although the details and presentation are different. If the list only contains one entry, it is probably lo, the local loopback. This is a conceptual IP interface (not hardware) used by the system.

On Raspbian, the ethernet NIC should by default be eth0. If it is not there, it indicates one of two problems:

  • The kernel is missing the appropriate drivers. If you are using a stock pi distro kernel, this is not the problem, unless perhaps you have moved or tinkered with /lib/modules.

  • Broken hardware.

You could try grep eth0 /var/log/syslog | tail to see what the last thing said about the interface was.

Note that the presence of an available interface does not indicate it is connected to anything.

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  • I've marked this answer as correct because it's very helpful and is full of good tips
    – crownusa
    Sep 28 '15 at 0:40

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