Cisco Certified Network Associate (CCNA) Practice Exam

What is the correct transport layer protocol for matching DHCP traffic in an ACL?

1. UDP

2. TCP

3. SPX

4. ICMP

The correct answer is: UDP

The correct transport layer protocol for matching DHCP (Dynamic Host Configuration Protocol) traffic in an Access Control List (ACL) is UDP (User Datagram Protocol). DHCP operates primarily over UDP because it is designed for simple request-response communication where a client needs to obtain configuration information from a server, typically for IP address assignment. In the DHCP protocol, specific ports are used: the client sends requests to port 67 (the server port) and expects responses from port 68 (the client port). Since UDP is a connectionless protocol, it is suited for the nature of DHCP's operation, where speed is prioritized, and establishing a connection prior to communication isn't necessary. Using TCP (Transmission Control Protocol) would not be appropriate for DHCP since TCP is connection-oriented and includes features for reliable delivery, which are unnecessary for the simple inquiry and response model of DHCP. SPX (Sequenced Packet Exchange) is a protocol used primarily in Novell networks and is not relevant in the context of DHCP. ICMP (Internet Control Message Protocol) is used for sending control messages and error reporting, but it does not play a role in DHCP traffic either. Hence, in the context of matching DHCP traffic in an ACL, UDP is the protocol to be used.