Technical Tip: How Mesh leaf FortiAP calculates the best Mesh root FortiAP

This article describes how the Mesh leaf FortiAP calculates the best Mesh root FortiAP.

FortiAP-S and FortiAP-W2.

Related Software Versions – FortiAP version 6.4 and later.

In a scenario where there are multiple Mesh root and a Mesh leaf FortiAP configured.

The Mesh Leaf FortiAP calculates the best Mesh root FortiAP as below.

Leaf AP will always choose the lowest s_tot’s bssid as the associate target:

s_tot = s_hop + s_chan + s_rate + s_rssi +s_band

            s_hop    = value_a X MESH_SCORE_HOP_WEIGHT

            s_chan   = value_b X MESH_SCORE_CHAN_WEIGHT

            s_rate   = value_c X MESH_SCORE_RATE_WEIGHT

            s_rssi   = value_d X MESH_SCORE_RSSI_WEIGHT

            s_band   = value_e X MESH_SCORE_BAND_WEIGHT

The explanation for the above parameters is given below.

Default Mesh SCORE _ Weight config:

MESH_MAX_HOPS:          =4

MESH_SCORE_HOP_WEIGHT:  =50

MESH_SCORE_CHAN_WEIGHT: =1

MESH_SCORE_RATE_WEIGHT: =1

MESH_SCORE_BAND_WEIGHT: =100

MESH_SCORE_RSSI_WEIGHT: =100

s_hop calculation:

s_hop   = value_a X MESH_SCORE_HOP_WEIGHT   

              value_a = This bssid broadcast ap’s mesh hop count, if the parent ap direct connect to FGT value_a should be equal to zero

s_chan calculation:

s_chan  = value_b X MESH_SCORE_CHAN_WEIGHT

              value_b = Command 'cw_diag –c mesh-ap' will print out a channel status table which will calculate and show each channel’s rssi_total.  value_b equal to the bssid’s channel rssi_total.

s_rate calculation:

s_rate = value_c X MESH_SCORE_RATE_WEIGHT

              value_c = this bssid beacon frame’s data rate, after test following number show,

                                           802.11n = -28

                                           802.11bg = -10

                                           802.11b = -2

                                           802.11a = -10

s_rssi calculation:

                s_rssi = value_d X MESH_SCORE_RSSI_WEIGHT

               value_d = this bssid’s rssi print out from command 'cw_diag –c mesh-ap'.

                                           if rssi > 25, value_d = -1

                                           if rssi <=25, value_d = 0

s_band calculation:

              s_band = value_e X MESH_SCORE_BAND_WEIGHT

              value_e = this bssid broadcast at 2.4 GHz or 5 GHz band

                                           2.4GHz = 0

                                           5   GHz = 1

This information can be found in the below output from the FortiAP CLI.

Links:

FortiAP CLI config and commands: 

http://docs.fortinet.com/document/fortiap/6.2.0/fortiwifi-and-fortiap-configuration-guide/65088/fortiap-cli-configuration-and-diagnostics-commands

FortiAP mesh config:

https://docs.fortinet.com/document/fortiap/7.2.0/fortiwifi-and-fortiap-configuration-guide/196651/wireless-mesh-configuration