Mozamme Hosen Faraizi

i have used this command for learn ideal scan nmap -sI 192.168.1.1 -T4 -v -Pn 172.16.1.2 192.168.1.1 = zombie IP ---------- right? 172.16.1.2 = destination IP ------------ right ? why this message " Idle scan zombie 192.168.1.1 (192.168.1.1) port 80 cannot be used because it has not returned any of our probes -- perhaps it is down or firewalled. QUITTING!" ? why this message "Host discovery disabled (-Pn)." ? please help me