Answer1

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	WHAT'S YOUR ENGINEERING QUOTIENT?
Problem 3—Suppose a small manufacturer, who needs to make about 100 Ethernet devices, decides to generate random MACs instead of going to the expense and trouble of getting an OUI (organizationally unique identifier) from the IEEE. Assuming that there are 100,000,000 devices out there that are known to have unique MACs, what are the chances that they'll duplicate an existing MAC? What if 100 manufacturers do this (10,000 devices)? Answer 3 Again, it's easier to find the probability that all of the randomly-chosen MACs won't collide with existing ones and then take one minus that value. This can be expressed as: N = number of addresses = 2⁴⁸ M = number of existing devices = 10⁸ K = number of new devices = 100 or 10,000 probability of collision = 1 � ((N � M)/N)^K This works out to 0.0000355 (36 chances in a million) for 100 devices and 0.00355 (0.35%) for 10,000 devices. Contributor: Dave Tweed 03-02 — NEXT Q&A For questions or comments about Test Your EQ, e-mail eq@circuitcellar.com.