EIGRP begins sending Hello packets once it has been enabled on a router interface. These messages are used to identify neighbors, verify if these neighbors are compatible, and serve as a keepalive mechanism between neighbors.
Hello Packets are sent to multicast address 18.104.22.168 in IPv4 and FF02::A in IPv6.
If static neighbors are configured, messages are sent unicast and not multicast.
the default hello interval is 5 seconds on broadcast interfaces and 60 seconds on NBMA interfaces with bandwidth less than 1544kbps.
Hello packets have an Opcode of 5 and are not acknowledged.