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?
Best Answer
It's not "impossible" - clearly it happened (for some values of "happen"). If you were able to fix it via disabling and re-enabling the network adapter in software, then my guess is that there was a low level driver software fault. It would be probably really really hard to recreate this and take it to the vendor and say 'fix this' so unfortunately you are probably going to have to chalk it up to the gremlins.