https://www.zabbix.com/documentation/current/en/manual/introduction/whatsnew725

The agent poller and SNMP poller can now be configured to use the c-ares library (version 1.16.0 or newer) instead of the libevent DNS resolver. This allows for potentially faster and more flexible DNS resolution.

To enable c-ares, Zabbix must be configured with the --with-ares option.

Note that starting from c-ares 1.31.0, DNS caching is enabled by default.

There are a few problems with this

• documentations explains how to compile zabbix with support for c-ares but doesnt mention if packages are build with this support yes or no
• documentation states that since 1.31.0 dns caching is enabled by default this is basicly true but it implies that before it was not enabled by default but this is not the case before 1.31.0 there was no dns caching at all in c-ares.
• The dns caching feature with c-ares 1.31.0 is nice but the documentation is a bit showing off since this library is soo bleeding edge that its not available in the latest ubuntu LTS 22.04 or even RHEL 10 so in the end DNS caching is not available in zabbix with 7.2.5 and this should be well documented that you need to upgrade your supported library with a compiled version or a version from a 3rd party repo or the experimental ubuntu repo to work for now.