EIGRP uses a Reliable Transport Protocol (RTP) for the delivery and reception of EIGRP packets instead of TCP and UDP. Reliability is a key feature of the EIGRP, and it is designed to enable fast delivery of updates and tracking of data reception.
EIGRP was designed as a network layer independent routing protocol. This allows EIGRP to be used for protocols other than those from the TCP/IP protocol suite, such as IPX and AppleTalk. Figure conceptually shows how RTP operates.
Although RTP was developed for reliability it includes both reliable delivery and unreliable delivery of EIGRP packets, similar to TCP and UDP. Reliable RTP requires an acknowledgement to be returned by the receiver to the sender just like TCP. An unreliable RTP packet does not require an acknowledgement just like UDP. The example is an EIGRP update packet which required an acknowledgement but Hello packet is sent over RTP without acknowledgement. RTP can send EIGRP packets as unicast or multicast. The Multicast EIGRP packets for IPv4 use the reserved IPv4 multicast address 18.104.22.168 and the Multicast EIGRP packets for IPv6 are sent to the reserved IPv6 multicast address FF02::A.