a windows pc is having trouble talking on the network - not talking at all to the network. determine one wall jack is bad. ok, switch to the other one. It does pull an IP address from the DHCP server, but it is in the wrong range, so something is wrong. [we have a bunch of machines setup to reserve an address from the DHCP server so they always get the same address.] Call the network admin, get confirmation that the DHCP server is ok. Then he asks for the MAC address - now that's odd - the MAC address is D3-59-D3-59-D3-59. definately NOT the MAC address this PC had yesterday. Reboot - now it has a different MAC address, and again the first pair of number is repeated!! this is getting stranger and stranger. I'm thinking - maybe bad chip for the NIC (it is on the motherboard)? is windows infected with something to randomize the MAC address (auto-spoofing)?
boot a couple linux distros (live CD) and can't get the network to work, at all. Then one live CD doesn't shut down correctly and I have to power off the case (I had not done that yet, just warm boots). next live CD - network works and it pulls the correct IP address and had the correct MAC address. boot windows, and it has the correct MAC and IP addresses.
So maybe there was some extra electrons on the chip controlling the network that made it work strange. Remove the power, and it is back to normal.
sometimes you see the strangest things ...