GTP load balancing and fabric channel usage
On a FortiGate-7000E, when GTP load balancing is enabled, GTP tunnels are synchronized over the fabric channel backplane (also called the data channel). The fabric channel is also used for SLBC session synchronization. On a busy FortiGate-7000E that is also load balancing GTP tunnels, the system may experience more lost SLBC heartbeats than normal.
To avoid missed heartbeats, you should increase the max-miss-heartbeats load balancing setting.
For example, when GTP load balancing is enabled, Fortinet recommends setting the max-miss-heartbeats to 40.
config load-balance setting
set max-miss-heartbeats 40
set gtp-load-balance enable
end