Managing multiple SSID’s on a single access point

The presence of several access points should enable coverage to overlap, resulting in the possibility of service being maintained, albeit at a lower level, even if one access point fails. In response to a query, I was able to set up my raspberry pi as an access point and WiFi repeater, using the instructions provided in the guide titled “Access point as WiFi router/repeater, optional with a bridge.


Question:

How is information transmitted if there are several SSIDs on a single AP?

The most basic APs come with a single wireless interface, meaning they receive and send data through the same antenna. This doesn’t seem logical to me because they end up being in the same
collision domain
.


Solution 1:

The SSID is just a component of the data exchanged between an AP and a station. In some cases, software clients merge or streamline the networks they detect, resulting in a single entry in the wireless networks. Nevertheless, in most enterprise wireless solutions, each AP has a distinct BSSID (in the form of
MAC address
) linked to a logical interface on the physical interface.

Certain software clients (previously utilized by Intel, though I’m uncertain of their current usage) display distinct AP/BSSID entries within the wireless network list. Consequently, multiple entries with identical SSIDs appear. For viewing the individual devices transmitting a shared SSID, one may employ a software tool such as InSSIDer.

While it is true that both networks share the same resources and “collision domain,” there are numerous justifiable reasons for doing so. One example is to offer distinct security measures, such as WPA2-Enterprise for your staff and an “Open” network with a captive portal for visitors.

Instead of using two sets of APs, each handling a different task, it is recommended to use a single device with multiple logical interfaces. This approach is more cost-effective and simpler to manage, compared to using multiple devices. When working in the 2.4GHz space, the channel plan is limited to three channels, which may lead to channel overlap and sharing the “collision domain” if multiple APs are used. This also adds complexity to channel planning.

It should be noted that adding more BSSID/SSID to a physical device can reduce the efficiency of RF use due to increased management traffic in the air. If you are interested, you can refer to this document for a detailed explanation of this effect, although it may be outdated.


Solution 2:


An AP with multiple SSIDs will have a shared collision domain. The SSIDs function similarly to VLANs, where the client associates with a specific SSID to identify their network and enable the AP to implement different security policies.

When it comes to broadcast collisions and throughput, having 20 devices on a single SSID is equivalent to having the same number of devices spread across 5 different SSIDs on the same AP. The use of multiple SSIDs enables the segregation of clients and allows for different treatment of each group.

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