The Reliable Transport Protocol (RTP) manages the delivery and reception of EIGRP packets. Reliable delivery means that delivery is guaranteed and that packets will be delivered in order.
Guaranteed delivery is accomplished by means of a Cisco-proprietary algorithm known as reliable multicast, using the reserved class D address 224.0.0.10. Each neighbor receiving a reliably multicast packet will unicast an acknowledgment.
In some cases, RTP may use unreliable delivery. No acknowledgment is required, and no sequence number will be included for unreliably delivered EIGRP packets.
EIGRP uses reliable for route updates
Unreliable for Hellos
With RTP, EIGRP can multicast and unicast to different peers simultaneously.
