How does UDP scanning determine whether a port is closed?

How does UDP scanning determine whether a port is closed?

• A. If an ICMP port unreachable packet is returned
• B. If no response is received from the port
• C. If a TCP session hijack occurs
• D. If data manipulation is detected

Answer: (A)

UDP scanning determines whether a port is closed primarily by the receipt of an ICMP (Internet Control Message Protocol) port unreachable packet. When a scanner sends a UDP packet to a closed port, the target system, recognizing that there are no active services listening on that port, will respond with an ICMP packet specifically indicating that the port is unreachable. This is a standard behavior defined in the IP protocol, allowing the scanning tool to infer that the port is indeed closed based on this feedback. In contrast, if no response is received from the port, it could potentially indicate that the port is either open or closed, so it does not provide definitive evidence regarding the port's status. Other options involve scenarios that do not apply directly to determining the status of a UDP port. For instance, TCP session hijacking and data manipulation are techniques that do not relate to UDP scanning's operation or its method of identifying the open or closed status of ports.

UDP scanning determines whether a port is closed primarily by the receipt of an ICMP (Internet Control Message Protocol) port unreachable packet. When a scanner sends a UDP packet to a closed port, the target system, recognizing that there are no active services listening on that port, will respond with an ICMP packet specifically indicating that the port is unreachable. This is a standard behavior defined in the IP protocol, allowing the scanning tool to infer that the port is indeed closed based on this feedback.

In contrast, if no response is received from the port, it could potentially indicate that the port is either open or closed, so it does not provide definitive evidence regarding the port's status. Other options involve scenarios that do not apply directly to determining the status of a UDP port. For instance, TCP session hijacking and data manipulation are techniques that do not relate to UDP scanning's operation or its method of identifying the open or closed status of ports.