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Enhanced Interior Gateway Routing Protocol
A lower metric signifies a better route.
Redistribution Limitations
As an enterprise network grows, there is a possibility that more than one
protocol will run on the router. An example is when a company acquires
another company and needs to merge the two existing networks. The prob-
lem surfaces when the routes of the purchasing company need to be adver-
tised to the newly acquired company. IGRP solves the problem with route
When multiple protocols run on a router, you can configure IGRP to
redistribute routes from specified protocols. Since different protocols calcu-
late metrics distinctly, adjustments must be made when redistributing pro-
tocols. These adjustments cause some limitations in how the redistribution
works. The adjustments are made by using the default-metric command,
as shown previously.
IGRP may also be redistributed to other routing protocols such as RIP,
other IGRP sessions, EIGRP, and OSPF. Metrics are also configured using
the default-metric command.
Enhanced Interior Gateway Routing Protocol
nhanced Interior Gateway Routing Protocol (EIGRP) is better than
its little brother, IGRP. EIGRP allows for equal-cost load balancing, incre-
mental routing updates, and formal neighbor relationships, which overcome
the limitations of IGRP. The enhanced version uses the same distance-vector
information as IGRP, yet with a different algorithm. EIGRP uses DUAL
(Diffusing Update Algorithm) for metric calculation, which permits rapid
convergence. This algorithm allows for the following:
Backup route determination if one is available
Support of Variable-Length Subnet Masks (VLSM)
Dynamic route recoveries
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