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GTM - Why is the monitor marked down after a single failure ?

Issue

You may observe the GTM marking the monitor as down even though only a single probe failure has occurred and the timeout not been reached.

Reason

When configuring a monitor there are various conditions that are considered by the GTM as a down response. This means that the GTM will mark the monitor as down rather then wait for the monitor timeout to exceed.

These conditions are :

  • All Monitors - if a RST is received or if there is no response after the 3WHS.
  • HTTP Monitors (without receive string) - If a response is not received within the probe timeout period. Note that 4xx and 5xx responses are considered valid.
  • HTTP Monitors (with receive string) - If the response does not contain the receive string. Or if the receive string is not received within the probe timeout period.

To instruct the GTM to ignore these down responses, and wait until the monitor timeout is reached before marking the monitor as down the option 'Ignore-down-response' is enabled.

Further Information : http://support.f5.com/kb/en-us/solutions/public/8000/100/sol8170.html

Tags: BIG-IP F5, Healthchecks, GTM

About the Author

RDonato

R Donato

Rick Donato is the Founder and Chief Editor of Fir3net.com. He currently works as a Principal Network Security Engineer and has a keen interest in automation and the cloud.

You can find Rick on Twitter @f3lix001