What are the characteristic of link state routing protocols? (Choose all that apply.)
A. The exchange of advertisement is triggered by a change in the network.
B. All routers exchange routing tables with each other in a multipoint network.
C. Packets are routed based upon the shortest path to the destination.
D. Paths are chosen depending on the cost efficiency factor.
E. Every router in an OSPF area is capable of representing the entire network topology.
F. Only the designated router in an OSPF area can represent the entire network topology.
Answer: A C E
Explanation:
Open Shortest Path First
? Each router discovers its neighbors on each interface. The list of neighbors is kept in a neighbor table.
? Each router uses a reliable protocol to exchange topology information with its neighbors.
? Each router places the learned topology information into its topology database.
? Each router runs the SPF algorithm against its own topology database.
? Each router runs the SPF algorithm against its own topology database to calculate the best routes to each
subnet in the database.
? Each router places the best roué to each subnet into the IP routing table.
The following list points out some of the key features of OSPF:
? Converges very quickly - from the point of recognizing a failure, it often can converge in less than 10 seconds.
? Supports VLSM.
? Uses short Hello messages on a short regular interval, with the absence of hello messages indicating that a
neighbor is no longer reachable.
? Sends partial updates when link status changes, and floods full updates every 30 minutes. The flooding,
however, does not happened all at once, so the overhead s minimal.
? Uses cost for the metric.
Reference:
CCNA Self-Study CCNA INTRO exam certification Guide (Cisco press, ISBN 1-58720-094-5) Page 417
这题为什么不选d呢？
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