Customer received information from Zabbix Support that they need to update to the new c-ares version, as the DNS caching function is only available from version 1.31.0 onwards.

Also Customer share comment with us which they recevied from Zabbix-Support:

"Additional note I have to stress here - as of c-ares DNS caching is enabled by default starting form version 1.31.0 

https://github.com/c-ares/c-ares/releases/tag/v1.31.0

So make sure your installed lib is up to date, to expect an effect during testing."

Coustmer requirement is that Red Hat provide a new version of the c-ares package greater than 1.31.0 via the official repositories which is supported and so that they can distribute it to their systems.