How to unfilter the open ports

Question

It may sound weird but, I tried to open ports in windows firewall. However, they are set to Open|Filtered.

How do I set them to only Open and Unfiltered?

Answer 1

Hello,

A port is considered "opened" when a service is listening on it.
If no service is listening on it, nmap will see the port either closed or filtered. The standard scan (TCP Scan if unprivileged user, or Half-Open scan -sS if superuser) relies on TCP protocol . (named 3-way hanshake)

A client (you) issues a SYN, if the server replies SYN/ACK : it means that the port is open.

You issue a SYN, if the server replies RST : it means that the port is close .

You issue a SYN, if the server does not reply, or replies with ICMP error : it means that the port is filtered. Likely an IDS / statefull firewall block your request)
To figure what is the real status of the port, you can :

use the -sV, or -A option (version detection, it will help you to determine what is the status of this port.
use --tcp-flags SYN,FIN to try bypassing the fw.

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