Randomized MAC Address Conflict Analysis and Implications

By: Baw Chng
Initially authored on 2021‑05‑23, revised 2021‑10‑18
Find this article online: https://bawman.com/BAWMAN/articles/RandomMAC/

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Introduction for the Casual Reader

Executive Summary

• Popular local area network (LAN) and personal area network (PAN) technologies (e.g., Wi-Fi, Ethernet, Bluetooth) rely on devices using unique MAC addresses to function correctly.
• As more device platforms introduce changes that make more frequent use of randomized MAC addresses, the probability of identical MAC addresses conflicting or colliding in systems also increases.
• With reasonable assumptions, we estimate the probability of MAC address conflict as a function of the number of randomly generated locally administered MAC addresses as follows:
  

  # of randomly generated locally administered MAC addresses in a system	Probability of MAC address conflict in the system
  Roughly 38 thousand	0.001%
  Roughly 120 thousand	0.01%
  Roughly 380 thousand	0.1%
  Roughly 1.2 million	1%
  Roughly 4 million	10%
  Roughly 10 million	50%
  (Beyond ~30 million, MAC address conflict becomes a statistical certainty)	Estimated # of non-unique MAC addresses in the system
  50 million	36
  100 million	142
  250 million	888
  1 billion	14211

• Conflict probability increases significantly if devices use per-OUI randomization. When limited to a single OUI, 5000 randomized MAC addresses are sufficient to yield a 50% conflict probability, 15000 randomized MAC addresses are sufficiently to statistically guarantee a conflict.
• This paper also discusses the potential impacts of randomized MAC address conflicts, some potential mitigation measures, and the attendant issues with these mitigation measures.
• Smaller, simpler systems are unlikely to be materially affected by MAC address randomization.
• Larger systems are more likely to be materially affected, though opportunities exist to mitigate the effects of randomized MAC addresses conflicts, at least for the data forwarding aspects of the systems.
• Outside of the data forwarding aspects of systems, there are few technical standards governing the use of MAC addresses, thus the impact of MAC address conflict on the non-data forwarding aspects of larger systems needs to be examined on a case-by-case basis.

Methodology, System Impact, Mitigation

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Select Charts and Graphs

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