374 Chapter 6: Routing
Distance Vector Routing Protocol Summary
Distance vector routing protocols learn and advertise routes. The routes placed in the routing
table should be loop-free and should be the best known working route. Metrics are used to
choose the best route. Mechanisms such as split horizon and holddown timers are used to
prevent routing loops.
Configuration of RIP and IGRP
The CCNA exam requires you to understand RIP and IGRP configuration details. RIP and
IGRP configuration requires an understanding of two subtle nuances--namely, what the
network command really implies and how the router interprets the network command. Other
than these two details, configuration is relatively easy.
Hands-on experience is the best way to fully learn the details of configuration. In lieu of that,
this section lists commands, provides examples, and points out any tricky features. Table 6-12
and Table 6-13 summarize the more popular commands used for RIP and IGRP configuration
and verification. Two configuration samples follow. The Cisco IOS documentation is an
excellent reference for additional IP commands, and the Cisco Press book Interconnecting
Cisco Network Devices is an excellent reference, particularly if you are not able to attend the
instructor-led version of the class.
Table 6-12
IP RIP and IGRP Configuration Commands
Command
Configuration Mode
router rip
Global
router igrp process-id
Global
network net-number
Router subcommand
passive-interface type number
Router subcommand
maximum-paths x
Router subcommand
variance multiplier
Router subcommand
traffic-share {balanced | min}
Router subcommand
Table 6-13
IP RIP and IGRP EXEC
Command
Function
show ip route [subnet]
Shows entire routing table, or one entry if subnet is entered
show ip protocol
Shows routing protocol parameters and current timer values
debug ip rip
Issues log messages for each RIP update
debug ip igrp transactions
Issues log messages with details of the IGRP updates
debug ip igrp events
Issues log messages for each IGRP packet
ch06.fm Page 374 Monday, March 20, 2000 5:11 PM