Cisco Certified Network Associate (CCNA) Practice Exam

How many unicast hello messages does an EIGRP router send to its neighbor before declaring that neighbor dead?

1. 4

2. 8

3. 16

4. 32

The correct answer is: 16

In EIGRP (Enhanced Interior Gateway Routing Protocol), a router uses hello messages to establish and maintain neighbor relationships. By default, EIGRP routers send hello messages every five seconds on LAN interfaces and every 60 seconds on WAN interfaces. The neighbor relationship is critical for EIGRP to function effectively, as it allows routers to share information about the network topology. When an EIGRP router does not receive any hello messages from a neighbor within a specified time, it considers that neighbor down. The process involves waiting for a predetermined number of missed hello packets before declaring the neighbor as "down." This specific number is known as the "dead interval," which defaults to the value established by the multiplier of the hello interval. In EIGRP, this dead interval is typically four times the hello interval. Since EIGRP sends hello messages every five seconds by default, this means a router will send out four hello messages in that time frame. If the router fails to receive any hello messages from a neighbor during this period, it will consider that neighbor to be down. Thus, the correct answer, indicating that EIGRP routers will send four hello messages before declaring a neighbor as dead, aligns with EIGRP's operational mechanics regarding neighbor relationships and the