Improve CAPWAP stability over NAT

To minimize downtime caused by unstable Network Address Translation (NAT) device networks, you can customize an interval at which keep-alive messages are sent from FortiAPs to their managing FortiGate. Once the keep-alive message is sent, FortiAPs will not disconnect from the FortiGate even if there is a session timeout configured on the NAT device. This improves CAPWAP stability for FortiAPs that are managed by a FortiGate behind a NAT device.

CLI syntax

config wireless-controller timers
  set nat-session-keep-alive <integer>
end

set nat-session-keep-alive

Maximal time in seconds between control requests sent by the managed WTP, AP, or FortiAP (0 - 255 seconds, default = 0).

To configure NAT session keep-alive message - CLI

1. Configure the interval at which NAT session keep-alive messages are sent in seconds.

   config wireless-controller timers
     set nat-session-keep-alive 10
   end

2. Verify the configurations on the FortiAP.

   FortiAP-231F # cw_diag -c acs
   WTP Configuration
       name                 : FortiAP-231F
       loc                  : N/A
       ap mode              : thin AP
       led state            : enable
       PWR LED state        : GREEN     REASON: ACS 0 changed in DATA_CHECK state.
       poe mode cal         : full
       poe mode oper        : full
       allowaccess          : 
       lldp enable          : enable
       extension info enable: enable
       radio cnt            : 3
       sta info             : 0/0
       echo-interval        : 30
       nat-sess-keep-alive  : 10
       keep-alive-interval  : 30
   ...

   From the cwWtpd deamon output, you can see that a FTNT_WTP_NOTIF message is sent every 10 seconds to keep the connection alive if there is no ECHO_REQ sent. The timer of FTNT_WTP_NOTIF is 10 seconds while the timer of ECHO_REQ is 30 seconds.

   [12/5/2023 7:17:46 PM] 15290.608 AC0     msgType       : 3163149 FTNT_WTP_NOTIF      0       10.40.29.57:5246
   [12/5/2023 7:17:56 PM] 15300.609 AC0     msgType       : 3163149 FTNT_WTP_NOTIF      0       10.40.29.57:5246
   [12/5/2023 7:18:02 PM] 15306.680 AC0     msgType       : 13 ECHO_REQ                 163     10.40.29.57:5246
   [12/5/2023 7:18:12 PM] 15316.608 AC0     msgType       : 3163149 FTNT_WTP_NOTIF      0       10.40.29.57:5246
   [12/5/2023 7:18:22 PM] 15326.609 AC0     msgType       : 3163149 FTNT_WTP_NOTIF      0       10.40.29.57:5246
   [12/5/2023 7:18:32 PM] 15336.608 AC0     msgType       : 3163149 FTNT_WTP_NOTIF      0       10.40.29.57:5246
   [12/5/2023 7:18:32 PM] 15336.677 AC0     msgType       : 13 ECHO_REQ                 164     10.40.29.57:5246
   [12/5/2023 7:18:46 PM] 15350.609 AC0     msgType       : 3163149 FTNT_WTP_NOTIF      0       10.40.29.57:5246