Hi,
There is a device with 2 interfaces and I want to monitor it as 1 host. This device has 2 IP addresses on different subnets
Documentation says:

if uniqueness criteria are Zabbix agent or SNMP-returned data, the first interface found for a host will be created as the default one. Other IP addresses will be added as additional interfaces.

But that only happens if all IPs belonging to the host are discovered by the same discovery rule.
Zabbix essentially forces multiple discovery rules because it only allows one discovery process per discovery rule. So having too large an IP range within one rule really extends time needed to complete discovery