DHCP not working on new install

A new Kubuntu 12.04 install is not getting IP addresses from either the wired connection nor from any wireless connection. The cables / router ports / wifi adapter / access point are all known good and work with other equipment. I suspected a failed NIC but seeing how the wireless connections also aren't working via USB wifi adapter, that eliminates the NIC as a possible source of the issue. What other hardware might be shared between the wired (onboard NIC) and wireless (USB wifi adapter)? I stress that with the wifi adapter I see other networks, but cannot get an IP address from them either. Testing with a Kubuntu 11.10 LiveCD has the same results.

I notice that there is no /etc/dhcp/dhclient.conf file.

Try sudo apt-get install isc-dhcp-client, which will install the dhcp client, though it won't explain why it wasn't installed to begin with. This also presumes that your problem is a lack of said client.

If that doesn't work, you should look into using the tcpdump command on one of the interfaces and post back here with the results. For example, sudo tcpdump -i eth0 -n should show you if there is any traffic passing over the eth0 interface, though you may need to correct for the right interface.

Since tcpdump didn't see any traffic, start the tcpcommand again, unplug your LAN connection, wait a couple seconds for the computer to realize you've unplugged it, then plug it back in and look at the tcpdump output. There should be several DHCP request sent out by you're computer, and under ideal circumstances, responses to those queries as well. If you don't see anything at all, then perhaps DHCP is request an address on the wrong port, maybe check DHCP configuration. If after checking your DHCP configuration you're sure that DHCP is requesting an address on the correct port but that you're not seeing any traffic with tcpdump, check the logs for any errors related to DHCP or errors transmitting network traffic. If nothing is obvious, post the logs here.

Beyond that, I don't know what else to do to diagnose this, perhaps your suspicions of faulty hardware were correct, or more unlikely, driver trouble.

The problem was in fact syndrome of issues:

1) No kernel support for this NIC in the -23 kernel. Downloading and installing the -26 kernel helped.

2) DHCP problems even with the NIC recognised. I had issues with DHCP on this hardware in openSuse 12.1 as well. Settings a static IP address got the machine online but no DNS.

3) To get DNS working, I renewed the DHCP lease even though I have a static IP address. This sounds stupid but it works. Simply configuring Google's public DNS servers did not resolve the issue.

To add insults to injury, this motherboard (ASUS P8H61-M LX) does not have PCI port to plug a NIC card into. ASUS support took two days to answer my letter of Linux support with "we don't support Linux" and the Realtek site's Linux NIC drivers wouldn't download from any of the six mirrors. They use JavaScript and HTTP access controls to prevent one from downloading the tarball over wget on a real server that I maintain, so I had a colleague download from the US and email the drivers to me. Then I couldn't build them as I could not install gcc from the Kubuntu DVD.

TL;DR: Don't buy an ASUS motherboard, they officially don't support Linux. And in any case, don't buy a motherboard without a PCI slot!