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Chapter 6
Troubleshooting TCP/IP Connectivity
IGRP is a classfull protocol, which means that it doesn't include any sub-
net information about the network with route information. Three types of
routes are recognized by IGRP:
Interior Networks that are directly connected to a router interface.
System Routes are advertised by other IGRP neighbors within the same
AS (autonomous system). The AS number identifies the IGRP session
because it's possible for a router to have multiple IGRP sessions.
Exterior Routes are learned via IGRP from a different AS number,
which provides information used by the router to set the gateway of last
resort. (The gateway of last resort is the path a packet takes if a specific
route isn't found on the router.)
show Commands
The show commands that are useful for troubleshooting IGRP are listed in
Table 6.6.
debug Commands
IGRP events--as well as the protocol itself--can be analyzed by the debug
tool. To watch IGRP events and protocol communications, you can enter the
following debug commands:
debug ip igrp events
debug ip igrp transactions
Depending on the problem or the activity within IP, these commands can
produce a great number of messages being logged to the console and the
router's logging buffer.
T A B L E 6 . 6
IGRP show Commands
Command
Description
show running-config
Displays the current configuration
show ip route igrp
Displays IGRP routes only
show ip route
Displays the entire route table
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