Cisco Certified Network Associate (CCNA) Practice Exam

The default keepalive message interval for PPP (Point-to-Point Protocol) and HDLC (High-Level Data Link Control) links is indeed 10 seconds, and the router waits for 5 intervals before shutting down the interface if it does not receive a keepalive message. Keepalive messages are crucial for ensuring that both ends of a link are operational and can communicate effectively. If no keepalive message is received for a duration of 50 seconds (which is the result of multiplying the 10 seconds interval by the 5 intervals), the router assumes that the link is down and may take action, such as shutting down the interface or generating some form of alarm. This mechanism helps maintain network stability and prompt failure detection, allowing for quicker recovery in the case of a connectivity issue.