When an EIGRP network configuration subcommand matches an interface, EIGRP on that router does two things:
Step 1. Attempts to find potential EIGRP neighbors by sending Hellos to the 220.127.116.11 multicast address
Step 2. Advertises the subnet connected to that interface
In some cases, however, no legitimate EIGRP neighbors might exist off an interface. For example, consider the small internetwork shown in Figure 4-5, with three routers, and with only one router connected to each LAN interface. Each router needs to advertise the subnets connected to their various FastEthernet interfaces, but at the same time, there is no benefit to multicast EIGRP Hellos on those interfaces, because only one ...