So that the routers around the district can exchange routing information,
IGRP is to be implemented on the routers. The entire Washington School
District is
one autonomous system, so a routing protocol is needed that is designed for autonomous systems. IGRP is one such protocol. IGRP takes bandwidth, load, delay,
and reliability into account when making decisions on which path to route packets. Bandwidth is usually the most important, but we could tell the router to view
load, delay, or reliability as more important. Because IGRP takes all these factors into account when making routing decisions, it can make better decisions, and
thus move data faster, than other routing protocols such as RIP.
Routers running IGRP send out routing updates every 90 seconds, although a network administrator can make the updates more or less frequent. These
updates contain copies of the sending router’s routing table. This way, each router learns about the paths all routers know every 90 seconds. So if Router A has
knows of a path to network 1.0.0.0, it will broadcast this information with every IGRP update, so that all routers receiving this broadcast learns about this path.
Since these updates are sent out in data packets that are broadcast across the network, they use up bandwidth on the line. Several routers broadcasting updates at
the same time can start to add up and strain the medium.
Implementation of IGRP on the district WAN is really rather simple. Since the commands to enable IGRP cannot contain any subnet information, almost
every router on the WAN will use the same command to enable IGRP.
First, enter global configuration mode. From there enter router
igrp 32.
The router will now be in into router configuration mode, ready to configure a routing protocol. To enable IGRP, the router must be informed about the
attached network. To do so, issue the network 150.72.0.0 command.
Basically, this is a list of all the networks to which each router is attached, without subnet information. Since the entire district is running on one Class B
address, every router is attached to the one same network. The sole exception is the router at the District Office Data Center. This connects out to the global
Internet as well. IGRP, however, is an interior routing protocol. It is made to route within an autonomous system, such as the Washington School District. The
Internet is outside the scope of the District’s autonomous system, so the next hop routers on the Internet that the District Office Data Center connect to are not
covered by IGRP.