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Raspberry Pi - IP address using a Rj45 ethernet cable

robobosan

I connected my Rasp Pi model B by LAN but seems did not work. It does not pick up a IP address using a Rj45 ethernet cable. Is there any way to solve it?

  • I have the impression that when a 'pi boots it will turn off the ethernet port if it finds it unconnected.

     

    Did you boot with the ethernet cable attached?

  • in reply to rew

    Do you mean I have to connect the ethernet cable before boot? But not after boot?

  • in reply to robobosan

    Yeah. Although the majority of Linux computers will notice the cable suddenly getting connected while they are already up-and-running, I have the impression that the 'pi does not.

    This could be a hardware issue: the ethernet chip does not signal that the cable has become connected.

    This could be a software issue: the driver does not handle the "cable connected" signal correctly

    This could be a higher level distribution issue: someone decided that if the cable is not connected at boot, to disable the whole thing.

    This could be a mis-observation on my part. Somehow I have the impression that my 'pi needs a reboot before getting ethernet connectivity again, but that might have been a coincidence. I usually do not have a screen and keyboard connected so that I can see if the 'pi still works. I powercycle it and voila it works again!

  • I just checked this on my RasPi, which is running Debian "Squeeze".

     

    On my RasPi, Ethernet does not need to be plugged in at boot time.  I plugged in the cable after booting and Debian detected the cable and configured fine.   Use the GNU "ifconfig" command to see what your Ethernet configuration is.

     

    When debugging network problems, start at layer 1 and work your way up.

     

    1.  Plug in the cable.  RasPi's network LEDs should come up.  In my case I get FDX (full duplex), LNK (blinks when there's activity), and 100 Mb/s.  If you don't get LNK, there's something wrong with your cable or the router or other device at the other end.

     

    2.  The default configuration is for RasPi to get an IP address automatically using DHCP (Dynamic Host Control Protocol).  Your network needs to have a DHCP server somewhere.  I use a router to connect all my Ethernet devices and it's the DHCP server.  If you're connecting using an Ethernet switch or just a cable to a PC, then a PC or a router elsewhere on the network needs to be the DHCP server.

     

    Hope this helps!

  • in reply to rew

    I just tried this on mine, and it recognized the pi and I was able to log in via the network. I powered it on, waited about 30 secs. Plugged in the rj45 and it popped up on my router's list of devices.

     

    I'm running an old version of rasbian with kernel 3.6.11

     

    cat /etc/issue says Debian GNU/Linux 7.0

     

    Mike

  • Loads of good advise so far...

     

    I will put on the DUMB support specialist hat for a moment and ask this... Do you have DHCP on your network. Does the cable your plugging into work ok with another computer, do any lights come on on the PI when you connect the network cable ?

     

    this will help in the investigation ?