Cisco Certified Network Associate (CCNA) Practice Exam

Which transport layer protocol is used to match ping (echo) traffic in an ACL?

1. UDP

2. TCP

3. ICMP

4. SCTP

The correct answer is: ICMP

The correct choice is ICMP because it stands for Internet Control Message Protocol, which is specifically designed for network diagnostics and management. The most well-known application of ICMP is the ping utility, which sends echo request messages to a target host and listens for echo replies. This interaction is essential for determining the reachability of a network device and measuring round-trip time. When configuring Access Control Lists (ACLs), it is common to specify ICMP to allow or deny ping traffic. ICMP messages, including echo requests and replies, are captured by ACLs that filter traffic based on the protocol type. Thus, to match ping traffic, you configure the ACL for ICMP. Other transport layer protocols mentioned, such as TCP and UDP, are not applicable to this context because they operate at a different layer in the OSI model and are primarily used for different types of communication. SCTP (Stream Control Transmission Protocol) is also not involved in ping requests, as it is a relatively newer transport layer protocol used for telecommunication purposes. Therefore, ICMP is the appropriate choice for handling ping traffic in ACL configurations.