How are EIGRP neighbors discovered?

EIGRP (Enhanced Interior Gateway Routing Protocol) discovers its neighbors primarily by sending multicast Hello messages to the address 224.0.0.10. This method allows EIGRP to identify and establish a neighbor relationship with other EIGRP routers on the same network or link. When these Hello packets are sent, the routers that receive them respond with their own Hello messages, confirming the neighbor relationship.

The use of multicast allows EIGRP to efficiently reach multiple routers at once, maintaining a level of network performance and minimizing overhead. These Hello messages carry important information, including hold timers and K values, which help in establishing and maintaining the neighbor relationships.

Other options do not describe the method used by EIGRP for neighbor discovery effectively. For instance, while periodic update messages can be part of EIGRP's routing process, they are not used for the discovery phase. Broadcasting routing updates doesn't align with the multicast approach of EIGRP, as broadcasting could lead to unnecessary network congestion. Finally, link-state advertisements are used in link-state routing protocols like OSPF, not in EIGRP, which is a distance-vector routing protocol. Thus, the correct method for discovering EIGRP neighbors is indeed through the use of multicast Hello messages.