Traffic going through fortigate unstable often timeout, but not when bypassed from fortigate

Hi Mohit,

Thank you for your reply.

Currently I don't have complete topology for this issue but it should be like this:
User (172.17.33.14) <-> FortiGate <-> Core <-> Server (172.28.201.80).
When bypass from FortiGate the issue is solved, but when going through FortiGate issue is persist.

There are no SDWAN configuration.

I'll try disable the offloading, thanks for suggestion.

Regards.

FW.

Hi, the root cause is the switch core not adding the same VLAN between their cluster, no idea what's this cluster about, but apparently when Fortigate Master restart some of the VLAN traffic still not failover to Slave, then client add the VLAN they forgot to add, and then the traffic normal again, weird but that's how it is.

Iperf result 

# diagnose traffictest run -c 10.0.1.27 (server)
Connecting to host 10.0.1.27, port 5201
[ 12] local 10.10.61.37 port 18982 connected to 10.0.1.27 port 5201
[ ID] Interval Transfer Bandwidth Retr Cwnd
[ 12] 0.00-1.01 sec 392 KBytes 3.16 Mbits/sec 14 33.9 KBytes
[ 12] 1.01-2.01 sec 168 KBytes 1.39 Mbits/sec 9 18.4 KBytes
[ 12] 2.01-3.03 sec 119 KBytes 955 Kbits/sec 7 12.7 KBytes
[ 12] 3.03-4.02 sec 147 KBytes 1.21 Mbits/sec 10 11.3 KBytes
[ 12] 4.02-5.02 sec 212 KBytes 1.75 Mbits/sec 1 14.1 KBytes
[ 12] 5.02-6.03 sec 76.4 KBytes 619 Kbits/sec 1 14.1 KBytes
[ 12] 6.03-7.02 sec 160 KBytes 1.32 Mbits/sec 8 12.7 KBytes
[ 12] 7.02-8.02 sec 180 KBytes 1.47 Mbits/sec 1 15.6 KBytes
[ 12] 8.02-9.03 sec 366 KBytes 2.97 Mbits/sec 9 31.1 KBytes
[ 12] 9.03-10.02 sec 349 KBytes 2.89 Mbits/sec 20 33.9 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bandwidth Retr
[ 12] 0.00-10.02 sec 2.12 MBytes 1.77 Mbits/sec 80 sender
[ 12] 0.00-10.02 sec 2.09 MBytes 1.75 Mbits/sec receiver

iagnose traffictest run -R -c 10.0.1.27
Connecting to host 10.0.1.27, port 5201
Reverse mode, remote host 10.0.1.27 is sending
[ 12] local 10.10.61.37 port 21815 connected to 10.0.1.27 port 5201
[ ID] Interval Transfer Bandwidth
[ 12] 0.00-1.01 sec 512 KBytes 4.15 Mbits/sec
[ 12] 1.01-2.01 sec 512 KBytes 4.19 Mbits/sec
[ 12] 2.01-3.00 sec 2.81 MBytes 23.8 Mbits/sec
[ 12] 3.00-4.02 sec 839 KBytes 6.74 Mbits/sec
[ 12] 4.02-5.02 sec 210 KBytes 1.72 Mbits/sec
[ 12] 5.02-6.00 sec 2.05 MBytes 17.5 Mbits/sec
[ 12] 6.00-7.00 sec 3.29 MBytes 27.6 Mbits/sec
[ 12] 7.00-8.00 sec 4.19 MBytes 35.0 Mbits/sec
[ 12] 8.00-9.01 sec 789 KBytes 6.41 Mbits/sec
[ 12] 9.01-10.00 sec 2.24 MBytes 19.0 Mbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bandwidth
[ 12] 0.00-10.00 sec 17.6 MBytes 14.8 Mbits/sec sender
[ 12] 0.00-10.00 sec 17.6 MBytes 14.8 Mbits/sec receiver

The connection between server to fortigate OSPF