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Chapter 6
Troubleshooting TCP/IP Connectivity
Redistribution of Routing Protocols
W
hen multiple routing protocols are used within a network and they
need to be redistributed into one another, it is important that it be done cor-
rectly by assigning the proper metrics through the redistribution. If protocols
are redistributed without metric adjustment, many networking problems can
occur.
Although redistribution allows multiple protocols to share routing infor-
mation, it can result in routing loops, slow convergence, and inconsistent
route information. This is caused by the different algorithms and methods
used by each protocol. It is not a good practice to redistribute bidirectionally
(if, for example, you have both IGRP 100 and EIGRP 200 routing sessions
running on your router). Bidirectional redistribution occurs if you enter
redistribution commands under each protocol session. Here is an example:
Router_A#config t
Enter configuration commands, one per line. End with
CNTL/Z.
Router_A(config)#router igrp 100
Router_A(config-router)#redistribute eigrp 200
Router_A(config-router)#router eigrp 200
Router_A(config-router)#redistribute igrp 100
Router_A(config-router)#^Z
Router_A#
When a route from RIP, IGRP, or OSPF is injected into another routing
protocol, the route loses its identity and its metrics are converted from the
original format to the other protocol's format. This can cause confusion
within the router. The method of ensuring that the metric is converted prop-
erly is done through metric commands.
Dealing with Routing Metrics
The router in which multiple protocols or sessions meet is called the auton-
omous system boundary router (ASBR). When routes from one protocol or
session are injected or redistributed into another protocol or session, the
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