Balanced Hybrid Routing Protocol and EIGRP
Cisco supports two distance vector IP routing protocols, namely RIP and IGRP; two link-state IP routing protocols, namely OSPF and Intermediate System-to-Intermediate System (IS-IS); and a single balanced hybrid IP routing protocol, namely Enhance IGRP (EIGRP).
EIGRP is called a balanced hybrid protocol because it has some features that act like distance vector protocols and some features that act like link-state protocols. EIGRP uses neighbor discover and exchange full routing information. Like OSPF, EIGRP sends and receives hello packets to ensure that the neighbor is still available but uses a different Hello packet than OSPF. When link status changes or new subnets are discovered, reliable routing updates are sent, but only with the new information.
EIGRP uses a formula based on bandwidth and delay to calculate the metric associated with a route. It uses the same formula used by IGRP, but the number is multiplied by 256 to accommodate calculations when very high bandwidth values are used.