FortiGate Next Generation Firewall utilizes purpose-built security processors and threat intelligence security services from FortiGuard labs to deliver top-rated protection and high performance, including encrypted traffic.
This article describes how to identify the hbdev(heartbeat port) that is used for session sync and config sync in 6/7K Chassis.

Both 6K and 7K Chassis have multiple hbdev(heartbeat port) which are fixed and built-in.
Below is an example of hbdev in 7K chassis:
# show sys ha
# config system ha
    set group-id 19
    set group-name "7K"
    set mode a-p
    set hbdev "1-M1" 100 "1-M2" 100 "2-M1" 100 "2-M2" 100  < -----------
    set session-pickup enable
    set override enable
    set priority 200
Heartbeat packets will be send out on both M1 and M2 hbdev (heartbeat port);
Session-sync only utilized the (active/highest priority) hbdev and will fall back to 2nd highest priority hbdev, if the previous hbdev failed.

To identify which heartbeat port was use for the session-sync, kindly run the following command:
# diag sys ha dump-by group

[FIM01] (global) # diag sys ha dump-by group
<hatalk>             HA information.
group-id=19, group-name='7K'


board-failover-tolerance=0, best_hbdev=1-M1, dp_rsync_hbdev=1-M1, slave_fim_dp_rsync_hbdev=2-M1
'FG76Exxxxxxxxxx': ha_ip_idx=1, hb_packet_version=14, last_hb_jiffies=66823254, last_hb_jiffies_xfim=66823254, linkfails=0, weight/o=0/0
                1-M1(mac=704c..eb, last_hb_jiffies=66823254, last_hb_jiffies_xfim=66823254, hb_lost=0, good_hb_rcvd=1, xfim_hb_rcvd=1)
                2-M1(mac=224c..e0, last_hb_jiffies=66823254, last_hb_jiffies_xfim=66823254, hb_lost=0, good_hb_rcvd=1, xfim_hb_rcvd=1)
'FG76Exxxxxxxxxx': ha_ip_idx=0, hb_packet_version=15, last_hb_jiffies=0, last_hb_jiffies_xfim=0, linkfails=0, weight/o=0/0

vcluster_0: start_time=1592213243(2020-06-15 02:27:23), state/o/chg_time=2(work)/1(helo)/1592213245(2020-06-15 02:27:25)
        'FG76Exxxxxxxxxx': ha_prio/o=1/1, link_failure=0, pingsvr_failure=0, flag=0x00000000, uptime/reset_cnt=177/0, active_worker=0/4, chassis_id=2
        'FG76Exxxxxxxxxx': ha_prio/o=0/0, link_failure=0, pingsvr_failure=0, flag=0x00000001, uptime/reset_cnt=0/0, active_worker=4/4, chassis_id=1
'Best_hbdev': show the hbdev that is use for both session sync and config sync.
'Dp_rsync_hbdev': between FIM in cross chassis.
'slave_fim_dp_rsync_hbdev': between FIM in intra chassis.