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746 Appendix A: Answers to the "Do I Know This Already?" Quizzes and Q&A Sections
3
Describe the purpose and meaning of route poisoning.
Route poisoning is the distance vector routing protocol feature in which a newly bad route
is advertised with an infinite metric. Routers receiving this routing information then can
mark the route as a bad route immediately. The purpose is to prevent routing loops.
4
Describe the meaning and purpose of triggered updates.
A triggered update is the routing protocol feature in which an update is sent immediately
when new routing information is learned rather than waiting on a timer to complete before
sending another routing update.
5
Write down the steps you would take to migrate from RIP to IGRP in a router whose
current RIP configuration includes only router rip, followed by a network 10.0.0.0
command.
Issue the following commands in configuration mode:
router igrp 5
network 10.0.0.0
no router rip
If RIP still was configured, IGRP's routes would be chosen over RIP. The IOS considers
IGRP to be a better source of routing information, by default, as defined in the
administrative distance setting (default 120 for RIP, 100 for IGRP).
6
How does the IOS designate a subnet in the routing table as a directly connected network?
What about a route learned with IGRP or a route learned with RIP?
The show ip route command lists routes with a designator in the left side of the command
output. C represents connected routes, I is used for IGRP, and R represents routes derived
from RIP.
7
From a router's user mode, without using debugs or privileged mode, how can you
determine what routers are sending you routing updates?
The show ip protocol command output lists the routing sources--the IP addresses of
routers sending updates to this router. Knowing how to determine a fact without looking
at the configuration will better prepare you for the exam. Also, the show ip route
command lists next-hop router IP addresses. The next-hop routers listed identify the
routers that are sending routing updates.
8
If the command router rip followed by network 10.0.0.0, with no other network
commands, was configured in a router that has an Ethernet0 interface with IP address
168.10.1.1, would RIP send updates out Ethernet0?
No. There must be a network statement for network 168.10.0.0 before RIP will advertise
out that interface.
apA.fm Page 746 Monday, March 20, 2000 5:24 PM