When creating a host using passive checks only (like "External Check" or "Simple Check") the interface requires to enter at least one interface (Agent, SNMP.. interface). Later the server will complain that there is no agent (/snmp) interface reachable. Its also somewhat confusing to find out which macro (host.host, .ip, .name, .conn, .dns) to use under which circumstances.

Possible solution: the current "Host name" is a descriptive key only, two new fields IP/Host + IP/Host Switch which can be used as presets for the interfaces.