DHCP setup problems

[ward at pong.be (Ward Vandewege)]

On Mon, May 01, 2006 at 09:32:11PM -0400, Doug wrote:
> I made sure that line was "live" by switching the cable between my big
> box and the laptop.  If I do sudo ifdown eth0; sudo ifup eth0, the
> computer tries 6 times, but fails. 

Is Comcast one of those fascist ISP's that limits the (number of) devices
that can connect to the cablemodem to a whilelist of mac addresses?

If so, could your main linux box be on that list (i.e. you gave them the mac
address/the modem autodetected it)? And your other machines are not?

Next step is definitely doing a tcpdump on your eth0. If you see the DHCP
replies there, it means that firewalling on your 'small' machines is most
likely the culprit. If not, try switching off the cable modem, wait for 10
minutes, switch it back on, *don't connect your big linux box first*, and
hook up one of the machines that is not working - see if it works then.

> There are two clues in the output.
> First it complains that there is alread a pid file
> /var/run/dhclient.eth0.pid with pid 1.  Second, the failed lines look

Do this:

1. kill all dhclient sessions (sudo killall -9 dhclient)
2. delete all dhclient pid files (sudo rm -rf /var/run/dhclient.eth0*)
3. sudo ifup eth0

That way you'll be sure that you don't have 2 or more copies of dhclient
fighting for the interface.

Ward.

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