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Thread: DHCP dosen't work after install.

  1. #1
    Join Date
    Dec 2009
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    6

    DHCP dosen't work after install.

    Hi!

    My problem is the following. During installation everything is fine. There is network and installer downloads the latest packages from the internet. But after install there is no network.
    I checked "ifconfig" and /etc/network/interfaces. There definitely is "eth0" among devices. "ifconfig eth0 up" does nothing. "dhclient eth0" hangs up for relatively long time with no result.

    /etc/network/interfaces contains
    auto eth0
    iface eth0 inet dhcp

    I tried commenting these two lines out and using "ifconfig eth0 up", "dhclient eth0" to run DHCP manually with no result.

    I tried "Ubuntu server 12.04", "Ubuntu server 12.10" and even current version of "Debian" with same results. I.e. during installation there is internet connection. But no connection afterwards. There is one difference: in Debian attempts to get IP address are expressed with several lines "DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval XX" but in Ubuntu with no output.

    Could one, please, explain me what I should do?
    Last edited by dr_livsey; March 29th, 2013 at 09:32 AM.

  2. #2
    Join Date
    Aug 2005
    Location
    South Carolina, USA
    Beans
    20,580
    Distro
    Ubuntu 14.10 Utopic Unicorn

    Re: DHCP dosen't work after install.

    We wonder if there is a proper driver associated with the hardware. Please run:
    Code:
    ifconfig
    Is there an eth0? If not, the driver and hardware aren't associated. Let's find out what driver you need and try to figure out why it isn't loading correctly post-install:
    Code:
    lspci -nn | grep 0280
    I doubt you want a potentially changing dynamic address on a server, so I'd suggest, once we get the driver working, that we set up a static IP address.
    "Oh, Ubuntu, you are my favorite Linux-based operating system" --Dr. Sheldon Cooper, Ph.D.

  3. #3
    Join Date
    Dec 2009
    Beans
    6

    Re: DHCP dosen't work after install.

    Quote Originally Posted by chili555 View Post
    We wonder if there is a proper driver associated with the hardware. Please run:
    Code:
    ifconfig
    Is there an eth0? If not, the driver and hardware aren't associated. Let's find out what driver you need and try to figure out why it isn't loading correctly post-install:
    Code:
    lspci -nn | grep 0280
    I doubt you want a potentially changing dynamic address on a server, so I'd suggest, once we get the driver working, that we set up a static IP address.
    First of all, thank you for your assistance! I've done what you asked me about and a few more things. Results are the following.

    1) "ifconfig" gives exactly two interfaces: "lo" and "eth0". And it's output matches with what is written in /etc/network/interfaces. Yes, "eth0" presents there.

    2) "lspci -nn | grep 0280" gives nothing as network adapter is 8139. When I invoke "lspci -nn | grep 8139" it shows me that adapter.

    3) I took different router, replugged ethernet cable there and run "/etc/init.d/networking restart" - everything is perfect. DHCP works.

    4) I checked original cable/network with different computer with WindowsXP OS - DHCP also works there.

    5) I tried changing MAC address with "ifconfig eth0 hw ether xx.xx.xx.xx" when "bad" cable/network is attached. Checked if it is really changed with "ifconfig". Run "dhclient eth0" Result is the same - it thinks for about a minute and fails.

    6) With original cable DHCP (and internet as a result) works only during install time.

    7) I can't change DHCP to static addressing as a network where it works so strange is office network with many computers. And this computer was a file storage, it hosted several servers and VPN tunneling until HDD failure. And now I try to resurrect it with so unexpectable trouble at the very beginning.

    8) It worked perfectly before HDD failure with exactly the same cable and in the same network running Ubuntu server for very long time so Ubuntu version changed from 9.04 to 12.04 during it's nonstop work if I'm not mistaken.

    9) I compared "good" and "bad" ethernet cable pinouts. They perfectly match also.

    10) I tried different cable from those "bad" network - the same no connection after install and normal during install.
    Last edited by dr_livsey; March 26th, 2013 at 01:50 PM.

  4. #4
    Join Date
    Mar 2013
    Beans
    11

    Re: DHCP dosen't work after install.

    Can you get an output of "ps -ef | grep dhcp"?

  5. #5
    Join Date
    Aug 2005
    Location
    South Carolina, USA
    Beans
    20,580
    Distro
    Ubuntu 14.10 Utopic Unicorn

    Re: DHCP dosen't work after install.

    I took different router, replugged ethernet cable there and run "/etc/init.d/networking restart" - everything is perfect. DHCP works.
    I'm confused, I guess. Doesn't this suggest it's the router and not the NIC?
    "Oh, Ubuntu, you are my favorite Linux-based operating system" --Dr. Sheldon Cooper, Ph.D.

  6. #6
    Join Date
    Jan 2006
    Location
    Not heaven... Iowa
    Beans
    Hidden!
    Distro
    Ubuntu

    Re: DHCP dosen't work after install.

    It's a bit far-fetched, but check route -n and firewall settings. I'm wondering if box is "too secure".
    Linux User #415691 Ubuntu User #8629
    Iowa Team (LoCo): [Wiki] [Launchpad]
    IRC channel: #ubuntu-us-ia on irc.freenode.net

  7. #7
    Join Date
    Dec 2009
    Beans
    6

    Re: DHCP dosen't work after install.

    Dear All,

    I'm very sorry for misinforming you. It must be it really was a problem of netowrk but not a computer. At the moment we experience the same or very similar problem with a few more computers in the network. So I do believe I'll have to replace the main router.

    But it really was very strange that computer had internet during install but didn't have afterwards.

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