I am trying to set up a firewall on a Dell Dimension 3000 with server 12.04. I have a DCP3010 cable modem from Charter, when I plug my Win7 laptop directly into the modem I get an IP address through DHCP. I also get that when I boot into Ubuntu 12.04 desktop from the same laptop.
On the Dell, when I do "ifconfig eth0 up" the interface comes up with IPv6 address, but no IPv4. I tried using "dhclient -v eth0" and the DHCPDISCOVER requests go out, but nothing comes back. Tried changing the MTU on eth0 down to 750 but no change.
To eliminate a crossover cable requirement, I threw a Netgear switch in the middle. Again, the laptop got IP in both Win7 and 12.04 desktop modes, but the Dell still kept sending out requests with no response.
I brought the server to a corporate network and fired it up. Tada, "dhclient -v eth0" grabbed an address immediately, and I can then ping and browse, so I know the onboard NIC is working and my general configuration is good.
I'm running out of troubleshooting ideas. Any suggestions are appreciated,