Cisco Certified Network Associate (CCNA) Practice Exam

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Prepare for the CCNA Exam with detailed questions and thorough study materials. Each question is accompanied by hints and explanations to facilitate your learning process. Get ready to ace the CCNA Exam!

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Which WAN protocol is the default on Cisco router serial interfaces?

PPP
Frame Relay
HDLC
Ethernet

The correct answer is: HDLC

The default WAN protocol on Cisco router serial interfaces is High-Level Data Link Control (HDLC). HDLC is a bit-oriented synchronous data link layer protocol that is used for transmitting data over point-to-point links. It is designed to provide a reliable link for transporting packets and frames between nodes, making it well-suited for WAN communications. HDLC is proprietary to Cisco when used on Cisco routers, which means that it can only be utilized on Cisco equipment without needing additional configuration for encapsulation purposes. This default setting makes setup easier for users deploying Cisco routers, as they can start communicating over serial interfaces without having to specify a different WAN encapsulation protocol. Other protocols such as PPP (Point-to-Point Protocol) and Frame Relay can be used on Cisco routers and may be popular choices depending on the network requirements, but they do not serve as the default. Ethernet is also a networking standard but is not typically utilized in WAN contexts over serial interfaces in the same manner as HDLC.