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Lab
Activity |
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In this lab,
you will learn how to enable EIGRP routing protocol. |
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Although EIGRP was
developed as a more up-to-date and efficient alternative to IGRP, it was
also explicitly an extension of IGRP. Consequently, the two are designed
to be completely compatible. These two routing protocols share the same
distance-vector routing technology. EIGRP uses the same composite routing
metric as IGRP. EIGRP also supports all the same distance vectors, and
their mathematical weights, as IGRP. EIGRP also uses the IGRP variance
feature to provide unequal-cost load balancing.
Note: There are strong
similarities between many of the basic components of IGRP and EIGRP,
including the formula for calculating their respective composite metrics,
as well as equal or unequal-cost load balancing using the variance
mechanism.
There is only one minor difference in the
algorithm that calculates the composite metric: The IGRP metric is 20 bits
long, whereas the EIGRP metric is 32 bits long. This difference results in
the EIGRP metric being larger by a factor of 256 than a comparable IGRP
metric for any given route. The larger metric allows a better and finer
mathematical comparison of potential routes.
This minor difference is easily and
automatically compensated for by EIGRP. EIGRP automatically adjusts the
composite metric of IGRP routes and adjusts its own metric on routes being
redistributed to IGRP routers. IGRP and EIGRP metrics are directly
comparable; therefore, they can be used interchangeably after translation.
EIGRP does, however, track the translated IGRP routes as external routes.
Note: IGRP doesn't have
any concept of internal and external routes. Consequently, EIGRP routes
that are translated and redistributed into an IGRP network are treated as
native IGRP routes.
Automatic redistribution between IGRP and
EIGRP will occur only if the two protocols are configured with the same
autonomous system (AS) number. If they have different AS numbers, they
will assume that they are part of different networks (that is, ASs).
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Lab
Activity |
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In this lab,
you will learn how to configure EIGRP and IGRP routing
protocols. IGRP will automatically redistribute into EIGRP if given
the same AS#. |
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Migration from IGRP to EIGRP can be done
gradually without incurring network downtime. EIGRP can be introduced into
strategic areas of the network such as the backbone. Its automatic metric
translation mechanism would enable the network administrator to replace
IGRP with EIGRP in those strategic areas. Support for IGRP is integral to
EIGRP, so network functionality isn't compromised. The network
administrator can then selectively extend its use in the network, until
the migration to EIGRP is complete. At this point, some of the more
advanced IP architectures, such as VLSM and classless addressing, can be
implemented.
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