IGRP packets to all neighbors. It supports intermixed transmission of multicast and unicast
packets. Some Enhanced IGRP packets must be transmitted reliably, and others need not be.
For efficiency, reliability is provided only when necessary. For example, on a multiaccess
network that has multicast capabilities, such as Ethernet, it is not necessary to send hellos
reliably to all neighbors individually. Therefore, Enhanced IGRP sends a single multicast hello
with an indication in the packet informing the receivers that the packet need not be
acknowledged. Other types of packets, such as updates, require acknowledgment, and this is
indicated in the packet. The reliable transport has a provision to send multicast packets quickly
when unacknowledged packets are pending. Doing so helps ensure that convergence time
remains low in the presence of varying speed links.
routes advertised by all neighbors. DUAL uses the distance information to select efficient, loop-
free paths. DUAL selects routes to be inserted into a routing table based on feasible successors.
A successor is a neighboring router used for packet forwarding that has a least-cost path to a
destination that is guaranteed not to be part of a routing loop. When there are no feasible
successors, but there are neighbors advertising the destination, a recomputation must occur. The
amount of time it takes to recompute the route affects the convergence time. Even though the
recomputation is not processor-intensive, it is best to avoid recomputation when it's
unnecessary. When a topology change occurs, DUAL tests for feasible successors. If there are
feasible successors, it uses any it finds to avoid unnecessary recomputation.
example is the IP EIGRP module, which is responsible for sending and receiving EIGRP
packets that are encapsulated in IP. It is also responsible for parsing Enhanced IGRP packets
and informing DUAL of the new information received. IP EIGRP asks DUAL to make routing
decisions, but the results are stored in the IP routing table. Also, IP EIGRP is responsible for
redistributing routes learned by other IP routing protocols.
EIGRP recounts the cost.