The access points of a WiFi network are usually connected to the WiFi controller through Ethernet wiring. A wireless mesh eliminates the need for Ethernet wiring by connecting WiFi access points to the controller by radio. This is useful where installation of Ethernet wiring is impractical.
Wireless mesh topology
A wireless mesh is a multiple access point (AP) network in which only one FortiAP unit is connected to the wired network. The other FortiAPs communicate with the controller over a separate backhaul SSID that isn't available to regular WiFi clients. The AP connected to the network by Ethernet is called the mesh root node. The backhaul SSID carries CAPWAP discovery, configuration, and other communications that would usually be carried on an Ethernet connection.
The root node can be a FortiAP unit or the built-in AP of a FortiWiFi unit. APs that serve regular WiFi clients are called leaf nodes. Leaf APs also carry the mesh SSID for more distant leaf nodes. A leaf node can connect to the mesh SSID directly from the root node or from any of the other leaf nodes. This provides redundancy in case of an AP failure.
All access points in a wireless mesh configuration must have at least one of their radios configured to provide mesh backhaul communication. As with wired APs, when mesh APs start up, they can be discovered by a FortiGate or FortiWiFi unit WiFi controller and authorized to join the network.
The backhaul SSID delivers the best performance when it is carried on a dedicated radio. On a two-radio FortiAP unit, for example, the 5 GHz radio could carry only the backhaul SSID while the 2.4 GHz radio carries one or more SSIDs that serve users. You can configure background WiFi scanning in this mode.
The backhaul SSID can also share the same radio with SSIDs that serve users. Performance is reduced because the backhaul and user traffic compete for the available bandwidth. Background WiFi scanning isn't available in this mode. One advantage of this mode is that a two-radio AP can offer WiFi coverage on both bands.
There are two common wireless mesh deployment modes:
Access points are connected to a FortiGate or FortiWiFi unit WiFi controller. WiFi users connect to wireless SSIDs in the same way as on non-mesh WiFi networks.
Two LAN segments are connected together over a wireless link (the backhaul SSID). On the leaf AP, the Ethernet connection can be used to provide a wired network. Both WiFi and wired users on the leaf AP are connected to the LAN segment to which the root AP is connected.
All FortiAP units that are part of the wireless mesh network must be upgraded to FortiAP firmware version 5.0, build 003, or higher. FortiAP-222B units must have their BIOS upgraded to version 400012. The FortiWiFi or FortiGate unit used as the WiFi controller must be running FortiOS firmware version 5.0 or higher.
A WiFi mesh can provide access to widely-distributed clients. The mesh root AP which is directly connected to the WiFi controller can be either a FortiAP unit or the built-in AP of a FortiWiFi unit that is also the WiFi controller.
FortiAP units used as both mesh root AP and leaf AP
FortiWiFi unit as mesh root AP with FortiAP units as leaf APs
An alternate use of the wireless mesh is as a point-to-point relay. Both wired and WiFi users on the leaf AP side are connected to the LAN segment on the mesh root side.
Point-to-point wireless mesh
Mesh implementations for leaf FortiAP can perform background scanning when the leaf AP is associated with the root. Various options for background scanning can be configured with the CLI. For more details about the mesh variables available in the FortiAP CLI, see Mesh variables