Distance Vector Routing Protocol


Dynamic routing protocols help the network administrator overcome the time-consuming and exacting process of configuring and maintaining static routes. For example, can you imagine maintaining the static routing configurations of the 28 routers shown in the figure? What happens when a link goes down? How do you ensure that redundant paths are available? Dynamic routing is the most common choice for large networks like the one shown.
Distance vector routing protocols include RIP, IGRP, and EIGRP.
RIP
Routing Information Protocol (RIP) was originally specified in RFC 1058. It has the following key characteristics:
Hop count is used as the metric for path selection.
If the hop count for a network is greater than 15, RIP cannot supply a route to that network.
Routing updates are broadcast or multicast every 30 seconds, by default.
IGRP
Interior Gateway Routing Protocol (IGRP) is a proprietary protocol developed by Cisco. IGRP has the following key design characteristics:
Bandwidth, delay, load and reliability are used to create a composite metric.
Routing updates are broadcast every 90 seconds, by default.
IGRP is the predecessor of EIGRP and is now obsolete.
EIGRP
Enhanced IGRP (EIGRP) is a Cisco proprietary distance vector routing protocol. EIGRP has these key characteristics:
It can perform unequal cost load balancing.
It uses Diffusing Update Algorithm (DUAL) to calculate the shortest path.
There are no periodic updates as with RIP and IGRP. Routing updates are sent only when there is a change in the topology.

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