EIGRP uses packet types:
Hello: Neighbor discovery and keepalive. Sent periodically.
Update: Contains routing information. Sent when topology changes or when a new neighbor appears.
Query: Asks neighbors about a route. Sent when a successor is lost and no feasible successor exists.
Reply: Response to a Query. Contains the neighbor's metric to the queried destination.
ACK: Acknowledges Updates, Queries, and Replies. EIGRP uses reliable transport for these packet types.
Hellos don't require acknowledgment. Updates, Queries, and Replies use RTP (Reliable Transport Protocol) built into EIGRP.