Which of the following responses from a firewall indicates that a port is open and actively listening for connections?Select one:a.RSTb.FINc.SYN-ACKd.ACK

The response from a firewall that indicates that a port is open and actively listening for connections is c. SYN-ACK.

Here's why:

a. RST (Reset) - This is sent by the host to reject a connection. It is not an indication of an open port.

b. FIN (Finish) - This is used to close a connection. It is not an indication of an open port.

c. SYN-ACK (Synchronize-Acknowledgement) - This is sent by the host in response to a SYN request (a request to open a connection) from the client. This indicates that the host is open and ready to establish a connection, hence an open port.

d. ACK (Acknowledgement) - This is sent by the client after receiving a SYN-ACK from the host, to acknowledge the response of the host. It is not an indication of an open port.