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The probe timeout option allows the user to set a timeout for probe packets for virtual-wan-link health-check and system link.
The probe packets are considered to be lost if the RTT of the probe packet is more than the configured value.

This article describes how to configure this option.


From CLI.

FortiOS 6.2.

# config system virtual-wan-link
# config health-check

    edit <name>
        set probe-timeout

FortiOS 6.4, 7.0 and 7.2.

# conf system sdwan
# config health-check
    edit <name>
        set probe-timeout <----- Time to wait before a probe packet is considered lost (500 - 3600000 msec, default = 500).

If the latency to the health-check server is more than 500ms then the health-check shows the dead status. Mostly this can be seen in Satelite (VSAT) links. For example, the normal latency for a health-check server over the VSAT link is 550ms then set probe-timeout more than 550ms to keep the health-check alive.



There are 2 members in the SDWAN setup and one of the interface never comes up. Link2 always show 100% packet loss and perceived as dead.


# diag sys sdwan health-check
Health Check(google_DNS):
Seq(1 Link1): state(alive), packet-loss(0.000%) latency(95.469), jitter(4.942) sla_map=0x0
Health Check(Test):
Seq(1 Link1): state(alive), packet-loss(1.000%) latency(105.085), jitter(6.899) sla_map=0x0
Seq(2 Link2): state(dead), packet-loss(100.000%) sla_map=0x0

However the Ping Server is pingable and Sniffer shows replies as follows:

# diag sniffer packet Link2 " host and icmp" 4 0 l
filters=[ host and icmp]
2021-02-04 19:08:08.761765 Link2 -- -> icmp: echo request
2021-02-04 19:08:09.368816 Link2 -- -> icmp: echo reply
2021-02-04 19:08:10.764591 Link2 -- -> icmp: echo request
2021-02-04 19:08:11.373735 Link2 -- -> icmp: echo reply


The issue is happening because of the link latency period. 


Increase the probe-timeout from default value of 500 to 1000.  Increase the probe-timeout by using these commands:


# config system sdwan

# config health-check

    edit "health_check_name"

      set probe-timeout 1000





# diagnose sys sdwan health-check

Health Check(google2):

Seq(1 Link1): state(alive), packet-loss(0.000%) latency(91.629), jitter(4.065) sla_map=0x0

Seq(2 Link2): state(alive), packet-loss(1.000%) latency(609.786), jitter(2.783) sla_map=0x0

Both health check members show healthy now.