If an application is actively accepting TCP connections on a port, what is the likely port state?

If an application is actively accepting TCP connections on a port, what is the likely port state?

• A. Open
• B. Closed
• C. Filtered
• D. Unknown

Answer: (A)

Open is the state you see when a TCP service is actively listening on a port and ready to accept connections. That means the application is bound to the port, in a listening state, and a client can complete the TCP handshake to establish a connection. If no service is listening, the port is closed and probes are typically rejected or reset. If a firewall or filter blocks the probes, the port appears as filtered because there’s no reliable response. If the scanner can’t determine the state from the responses, it shows unknown.

Open is the state you see when a TCP service is actively listening on a port and ready to accept connections. That means the application is bound to the port, in a listening state, and a client can complete the TCP handshake to establish a connection. If no service is listening, the port is closed and probes are typically rejected or reset. If a firewall or filter blocks the probes, the port appears as filtered because there’s no reliable response. If the scanner can’t determine the state from the responses, it shows unknown.