Workshop

OUI ou Non?
Knowing the OUI came in handy for me once when I was experiencing intermittent problems with a
new application. The application vendor pointed the finger at one of my network card vendors, who, in
turn, told me to get the “latest and greatest” drivers for its network cards to eliminate the problems I
was experiencing with the application. Fortunately, I rolled out only a small set of those drivers, which
turned out not to be the “greatest.” I started to have major network problems and noticed (from the
OUIs listed by the network analyzer) that I was only experiencing problems with the cards I had just
updated. I undid the update, the network problems went away, and I leaned on the application vendor
to solve the original problem. The OUI can really be a useful concept to know.
The OUI only tells you who made the chip, not the manufacturer who put the board together. Creating a
microchip is expensive, but putting these chips together on a circuit board that becomes a NIC is less
expensive. Because of this cost differential, many vendors purchase other vendors’ chips to use on their
brand of network cards. For example, although Emulex is on the OUI list as using 00-00-c9, Proteon, Inc.
has released network boards with this OUI.
If a network configuration option ever asks you whether you want to override the MAC address of a NIC,
say no! This option is intended only for experienced network administrators and can wreak havoc if not
used correctly.
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