Cisco Certified Network Associate (CCNA) Practice Exam

Which transport layer protocol would match all traffic in an ACL?

1. TCP

2. UDP

3. IP

4. ICMP

The correct answer is: IP

The correct answer is IP. At the transport layer, the Internet Protocol (IP) is responsible for addressing and routing packets across networks. It is the protocol that encapsulates data from the upper layers and directs it to the appropriate destination. In the context of Access Control Lists (ACLs), IP is the most appropriate choice because ACLs can be designed to match all types of traffic based on IP addresses and protocols. When using ACLs, matching traffic at the IP level affects not just transport layer protocols, but all packets traveling across the network. The other transport layer protocols—TCP, UDP, and ICMP—while they operate above IP, do not represent all traffic universally. TCP and UDP are specific transport protocols that handle different types of communication services (connection-oriented and connectionless, respectively). ICMP, on the other hand, is primarily used for network diagnostics and control messages, not for regular data transport. Therefore, the ability of IP to encompass all traffic types, regardless of the protocols used, makes it the most fitting choice for an ACL that aims to match all traffic.