Cisco Certified Network Associate (CCNA) Practice Exam

What communication method does HSRP use to keep alive its router group?

1. UDP datagrams to a reserved port number

2. ICMP echo requests every second

3. Hello messages to multicast address 224.0.0.102

4. Internal routing protocol updates

The correct answer is: Hello messages to multicast address 224.0.0.102

The correct answer is indeed that HSRP (Hot Standby Router Protocol) uses hello messages to a multicast address of 224.0.0.102. HSRP is a Cisco proprietary protocol that enhances network reliability by allowing multiple routers to work together to present a single virtual gateway IP address to the hosts on a local subnet. It achieves this by designating one router as the active router and another as the standby router, with additional routers in a listening state. The hello messages sent to the multicast address help the routers determine which is the active and which is the standby. These messages are sent at regular intervals, and if the active router fails to send hello messages, the standby router can take over the role as the active router, thereby ensuring uninterrupted network service. In contrast, the use of UDP datagrams to a reserved port number does not apply here, as HSRP relies on multicast for its communication. Similarly, ICMP echo requests are generally used for network diagnostics and not for maintaining the state of router groups in HSRP. Internal routing protocol updates pertain to protocols such as OSPF or EIGRP, which serve different purposes in the network layer. Therefore, hello messages sent to the specified multicast address are essential