zabbix zabbixtroubleshooting active check configuration update from cannot connect to started to fail first network error wait for 15 seconds assuming that agent dropped connection because of access permissions received empty response from zabbix agent at allowed hosts logrt 10051]: (null) connection from failed to accept an incoming connection no route to host dropped connection because of access permissions interrupted system call zbx_tcp_read() timed out rejected permission denied connection refused ITEM log trigger