What will happen if two APs are in the same area with the same MAC and SSID

networkingwireless-access-pointwireless-networking

If we were able to clone the MAC address on an access point, what would clients do when faced with two APs with the same MAC and SSID? Will this AP appear as a single device? Will the clients just randomly send information to one AP or the other, or will they flip flop between the two?

Best Answer

  • If you set up two devices to act as APs with the same wireless MAC address (BSSID) and same network name ([E]SSID), assuming you don't also load special software on them to allow them to truly work as a single AP as per the IEEE 802.11 specification for what an AP is required to do, then clients that are within radio range of both devices will effectively see a single AP behaving in ways that break the 802.11 standard, and will probably be unable to use join "the AP it sees" (i.e. unable to join either AP), and will be unable to use the network reliably.

    If the two APs are on separate, non-overlapping channels, there's a chance it might partially work, because the client might not notice the conflicting channel information in the beacons and probe responses it receives from that BSSID when scanning, so it might arbitrarily use one of the channels. Once it tunes to that one channel and stays on it, it will only be communicating with one of the APs, so things might work okay until it has some reason to go scan, at which point it may get confused by seeing its AP report a different channel than it expected.

    If the two APs are on the same channel, the client might be unable to join the network at all, because the authentication and association exchanges won't go well with two different AP devices responding from the same BSSID. If you're using WPA2-PSK security, you won't get past the key handshake because of this. Even if the client did get associated, the competing beacons, with their competing TSF timestamp values, will screw up the timer synchronization functionality of the client's 802.11 chipset, so it seems like things will be unstable at best.

    Please note that it IS possible to have multiple APs use the same BSSID and have it work, but it requires special software on the APs to coordinate their actions with each other so they (as a group) never behave in a way that violates the IEEE 802.11 spec for how an AP must behave. At least one vendor of enterprise-class 802.11 APs has done this in the past (I think it was either Meru or Meraki).

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