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serverstudy514 avatar image
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serverstudy514 asked

What is the difference between interval and probe-timeout?

Hello.

I am not familiar with English and I know some of the sentences may be strange, but thank you for your help!


device:

Fortigate fortios7.0.8


I have 3 icmp failures at 5 second intervals and I am configuring static routing for the vlan to be deleted.

Here are the parameters


  config system link-monitor
      edit 1
          set addr-mode ipv4
          set srcintf vlan100
          set server 8.8.8.8
          set protocol ping
          set interval 5000
          set probe-timeout 500 <-default 
          set failtime 3
          set recoverytime 3
          set probe-count 30 <-default 


So I would like to know how probe-timeout and probe-count are different from interval and failtime.


Is there a basic problem with the default values, or is there something I should consider to determine the values?

FortiOSFortiGatelink-monitor
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Elmer avatar image
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Elmer answered

Hi serverstudy514,

probe-timeout affects how long FGT will wait for a response from the server. After 3 failures (failtime), it will consider the server dead. You may add a second server for the FGT to use to verify the link status. This allows the FGT to switch over link monitoring in the event the server is down but the link is active.

probe-count is how many probes are used to calculate latency and jitter. 30 is a good value when the interval is 500 (as this is a 15s window), but when you increase the interval as you have, the window grows to 2.5 minutes which may be too large for brief changes to latency/jitter to affect the status of the link.

Additionally, with an interval of 5000, any brief changes to latency that happens between the probes (5 second window) will be completely undetected.

The correct values are dependent on your business needs. Perhaps you aren't affected very much by brief changes and therefore you only want to take action when there is longer periods of increased latency/jitter.

Here are some further articles:

https://docs.fortinet.com/document/fortigate/7.0.9/administration-guide/580649/link-health-monitor

https://docs.fortinet.com/document/fortigate/7.0.9/cli-reference/120620/config-system-link-monitor


Hope this helps!

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