I'm trying to understand if there is a certain protocol that a Wi-Fi transmitter must follow when creating a BSSID for virtual access points.

In my university building, there are a bunch of CISCO routers and each provide 2 virtual access points: "eduroam" and "wifi guest". The BSSIDs for one Wi-Fi transmitter are 58:97:bd:4a:d6:70 and 58:97:bd:4a:d6:76. Based on this example, it looks like only the last 2 characters of the BSSID are unique, and I presume that the first 10 are part of the original MAC address of the Wi-Fi transmitter.

Does anyone know if there is a certain protocol which must be followed when creating a virtual access point? Or does the CISCO Wi-Fi transmitter have it's own unique methodology of creating these? Specifically, I'm looking for a citable source for this.

  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer. – Ron Maupin Apr 1 '18 at 20:19

The OUI (Organizationally Unique Identifier) for a MAC address is assigned by the IEEE. The rest of the MAC address is assigned by the company to which the OUI is assigned, and it is completely up to the OUI owner for how to assign them.

In your example, the OUI is 58:97:bd, assigned to Cisco Systems. The rest of the MAC addresses are assigned by Cisco in whatever fashion Cisco wants to assign them.

  • So the transmitter is assigned a MAC address by CISCO, and then this is used as a base to construct several BSSIDs for Virtual Access Points. But how does the transmitter assign the BSSIDs for these? Are there any rules, or totally up to the companies? Would different companies assign BSSIDs in different ways? – Jonty800 Jan 29 '18 at 19:53
  • The BSSIDs are configured by the network administrator. The WAP will assign a MAC address per configured BSSID. – Ron Maupin Jan 29 '18 at 19:54
  • It's common for Cisco to allocate a range of MACs for a device (router, switch, etc.) so it can pick one without hassle. – Ricky Jan 29 '18 at 20:19

I’ve read that some Cisco APs have reused MACs on same AP for separate SSIDs though I have never seen it in the field. I usually see them increment by one for each SSID with Radio 0 and Radio 1 having radically different starting MAC addresses.

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