Enhanced IGRP (EIGRP) is a Cisco-proprietary routing protocol. EIGRP is a classless routing protocol, meaning that it sends the subnet mask of its interfaces in routing updates, which use a complex metric based on bandwidth and delay.
EIRGP is an advanced distance vector protocol with some link-state features. As such, EIGRP is classified as a balanced hybrid protocol.
Protocol-independent modules: EIGRP supports IP, IPv6, Internetwork Packet Exchange (IPX), and AppleTalk.
Reliable Transport Protocol: RTP controls sending, tracking, and acknowledging updates and EIGRP messages.
Neighbor discovery/recovery: EIGRP discovers neighboring devices using periodic Hello messages.
Diffusing Update Algorithm (DUAL): ...