The way we configured ServerActive in the agent daemon configuration file, it connects to a single Zabbix server and sends data on items to the server. An agent can also work with multiple servers at the same time; we only have to specify additional addresses here as a comma-separated list. In that case, the agent will internally spawn individual processes to work with each server individually. This means that one server won't know what the other server is monitoring—values will be sent to each of them independently. On the other hand, even if several servers request data on individual items, this data will be collected several times, once for each server.

Working with multiple servers in active mode can be useful when migrating from one Zabbix instance to another. For a while, an agent could report to both the old and new servers. Yet another case where this is useful is a customer environment where the customer might have a local Zabbix server performing full-fledged monitoring, while an external company might want to monitor some aspects related to an application they are delivering.

For passive items, allowing incoming connections from multiple Zabbix servers is done the same way—by adding multiple IP addresses to the Server parameter.