One of our Windows 2003 R2 ISA firewall servers recently had a 1-hour spell of intermittent connectivity to our Internet WAN connection, which was fixed after disabling then re-enabling the network adapter. The error log showed multiple instances of the following error:
Event 4199: The system detected an address conflict for IP address 192.0.2.123 with the system having network hardware address 00:00:00:00:00:00. Network operations on this system may be disrupted as a result
As far as I know, a null MAC address is impossible. I only found one Google result for the same error with the same strangely empty MAC address, an experts-exchange question with no answer.
The problem has not recurred, but I'm nervous having a server with unexplained issues still running as part of our live network. Without knowing the cause, I have no way of knowing that it might not happen again.
Is this a driver failure? Hardware failure? Network stack issue? Could there have been some strange conflict where something somehow tried to take over our WAN address?