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Thread: Understanding Cisco multi BSSID

  1. #1
    Join Date
    Oct 2009
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    Bonney Lake, WA
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    Default Understanding Cisco multi BSSID

    According to
    Cisco Wireless LAN Controller Configuration Guide, Release 5.2
    Chapter 7 - Controlling Lightweight Access Points
    http://www.cisco.com/en/US/docs/wire...html#wp1104685
    In controller software release 4.2 or later, all Cisco lightweight access points support 16 BSSIDs per radio and a total of 16 wireless LANs per access point. In previous releases, they supported only 8 BSSIDs per radio and a total of 8 wireless LANs per access point. When a converted access point associates to a controller, only wireless LANs with IDs 1 through 16 are pushed to the access point.
    So my guess is that inSSIDer and any other sniffer like it would see each BSSID as a different MAC (AP) even though they are coming from the same physical AP.

    Could someone confirm this please.
    Thanks
    Dave
    Last edited by cdnbrit; 10-21-2009 at 06:35 PM.

  2. #2

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    Quote Originally Posted by cdnbrit View Post
    So my guess is that inSSIDer and any other sniffer like it would see each BSSID as a different MAC (AP) even though they are coming from the same physical AP.
    Dave,

    you are correct, they must be different so that the clients can identify them - often they are referred to as virtual APs. Usually (as in 99% of the time) they simply increment by 1 _within the same frequency band_ (2.4G or 5G), i.e. first virtual-ap will be 00:11:22:00:00:01 and the second will be 00:11:22:00:00:02.

    The manufacturer will be determined by the first three bytes known as the OUI (in my fake example, 00:11:22) and this is how inSSIDer and most other products are able to tell you that the AP is from "abc Corp". The remaining 3 bytes will be spread amongst the vendors products.

    In the case of a dual-band enterprise grade wifi (such as the one you pointed out) generally you would find that the MAC address range for VAPs would be something like the following fictitious example:

    5G 00:aa:1e:94:eb:a0 -> 00:aa:1e:94:eb:af
    2.4G 00:aa:1e:94:eb:b0 -> 00:aa:1e:94:eb:bf

    i.e. the 5G and 2.4G ranges will be contiguous and separated by the exact number of addresses that the device supports for virtual APs, in the case above 16 as well. Note that the actual ESSIDs being broadcast into the air may not show contiguous addresses since some VAPs may be defined but administratively disabled for whatever reason.

    hope that helps
    -jeff

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