Cisco Certified Network Associate (CCNA) Practice Exam

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Which protocol would you use for matching Telnet traffic in an ACL?

TCP
UDP
ICMP
IGMP

The correct answer is: TCP

The correct choice for matching Telnet traffic in an Access Control List (ACL) is TCP. Telnet operates over the Transmission Control Protocol, which is a connection-oriented protocol that ensures reliable communication between the client and server. When configuring ACLs, you need to match the transport layer protocol used by the application you are controlling—in this case, Telnet—which specifically uses TCP on port 23. By allowing or denying TCP traffic in your ACL configuration, you can effectively control access to Telnet services on your network. Other protocols listed, such as UDP, ICMP, and IGMP, serve different purposes. UDP is used for applications that require less overhead and can tolerate some data loss, such as video streaming or online gaming. ICMP is primarily used for network diagnostics and error reporting (e.g., pinging). IGMP, on the other hand, is used for managing multicast group memberships. Since they do not apply to Telnet traffic, they would not be relevant when matching it in an ACL.