Cisco Certified Network Associate (CCNA) Practice Exam

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For matching NTP traffic in an ACL, which transport layer protocol is correct?

TCP
UDP
ICMP
IP

The correct answer is: UDP

The correct answer is UDP because Network Time Protocol (NTP) uses User Datagram Protocol (UDP) as its transport layer protocol. In NTP, communication typically takes place over port 123, which is allocated for NTP over UDP. This is significant as UDP is a connectionless protocol, allowing for quicker transmission of data without the overhead of establishing a connection, which is essential for the time-sensitive nature of NTP. The other transport layer protocols do not apply in this context. TCP, which is connection-oriented and reliable, is not utilized by NTP, making it unsuitable for matching NTP traffic in an Access Control List (ACL). ICMP, primarily used for error messages and operational queries, also does not serve in the context of time synchronization. Lastly, IP is not a transport layer protocol but rather a network layer protocol, so it is not correct for categorizing NTP traffic matching in an ACL.