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Remember to check the MAC address

Today I encountered a weird issue with a new machine I was setting up. The NIC on the machine worked to PXE boot and install Windows XP off the WDS server at work, however once I installed the drivers for the NIC on Windows XP and obtained an IP address from DHCP I couldn’t reach anything.

I couldn’t ping my default gateway, any DNS servers, couldn’t ARP an IP address, nothing. I tried to release and renew the IP address, ran diagnostics (which all passed except the connection diagnostic) and I was getting an IP address on the correct subnet and with correct values for the gateway and DNS servers. I was stumped!

I knew the NIC was working because I’d installed the OS through the network, but even though the NIC was sending packets out, none were being received (as reported by the OS). I called my boss and started throwing ideas back and forth, I’d already done most of what he was mentioning except one thing: Look at the MAC address that the NIC is reporting. It was 00-00-00-00-00-00.

I completely skipped over that the first time I ran an ipconfig /all on the machine, but as soon as I saw the MAC address contained all zeroes I quickly went to the properties page that installed with the NIC driver, went to the MAC masquerading tab and clicked on “Use default” – nothing changed. The MAC address field was empty and while I could have maybe retrieved the MAC address off the NIC itself or motherboard, in the interest of time my boss found the vendor ID for a company I’d never heard of (maybe he’d used them before, who knows, but we didn’t have any of those adapters in the office) and gave me the first 3 pairs belonging to that vendor for the MAC address. I set the last three pairs to random numbers and seconds later after an ipconfig/release && ipconfig/renew I was finally able to send and receive traffic on the network. Ideally you’d try to retrieve the MAC address that belongs to the NIC, however, we manage the environment and know what devices come into the network so it is very unlikely that we will encounter any conflicts. No excuse, I know, but that’s just the way things are right now.

Neither of us had seen something like this before, but the advice to take with you from this post is: remember to check the MAC address if you ever encounter a similar issue.

Remember to check the physical wireless switch

On a related note, this brought back memories of a colleague of mine who while working on one of my old employer’s help desks took a  call once, minutes before the end of his shift. The user was reporting that his wireless connection was not working and my colleague spent the next 45 minutes troubleshooting with the user only to find that the problem was resolved by toggling the physical wireless switch on the laptop to the On position. Yes, that simple.

Details matter, remember this.

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