Information Technology Reference
In-Depth Information
EIGRP is a distance-vector protocol with link-state characteristics (hybrid) that give it high
scalability, fast convergence, less routing overhead, and relatively easy configuration. If
“distance-vector” is not an answer to a question, then “hybrid” would be a valid option.
Hierarchical Versus Flat Routing Protocols
Some routing protocols require a network topology that must have a backbone network
defined. This network contains some, or all, of the routers in the internetwork. When the
internetwork is defined hierarchically, the backbone consists of only some devices. Back-
bone routers service and coordinate the routes and traffic to or from routers not in the lo-
cal internetwork. The supported hierarchy is relatively shallow. Two levels of hierarchy are
generally sufficient to provide scalability. Selected routers for ward routes into the back-
bone. OSPF and IS-IS are hierarchical routing protocols. By default, EIGRP is a flat rout-
ing protocol, but it can be configured with manual summarization to support hierarchical
designs.
Flat routing protocols do not allow a hierarchical network organization. They propagate
all routing information throughout the network without dividing or summarizing large
networks into smaller areas. Carefully designing network addressing to naturally support
aggregation within routing-protocol advertisements can provide many of the benefits of-
fered by hierarchic al rout ing protocols. Ever y router is a peer of ever y other router in flat
routing protocols; no router has a special role in the internetwork. EIGRP, RIPv1, and
RIPv2 are flat routing protocols.
Classless Versus Classful Routing Protocols
Routing protocols can be classified based on their support of VLSM and CIDR. Classful
routing protocols do not advertise subnet masks in their routing updates; therefore, the
configured subnet mask for the IP network must be the same throughout the entire inter-
network. Furthermore, the subnets must, for all practical purposes, be contiguous within
the larger internetwork. For example, if you use a classful routing protocol for network
130.170.0.0, you must use the chosen mask (such as 255.255.255.0) on all router interfaces
using the 130.170.0.0 network. You must configure serial links with only two hosts and
LANs with tens or hundreds of devices with the same mask of 255.255.255.0. The big dis-
advantage of classful routing protocols is that the network designer cannot take advantage
of address summarization across networks (CIDR) or allocation of smaller or larger sub-
nets within an IP network (VLSM). For example, with a classful routing protocol that uses
a default mask of /25 for the entire network, you cannot assign a /30 subnet to a serial
point-to-point circuit. Classful routing protocols are
RIPv1
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IGRP (this protocol not a test topic)
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