Chapter Glossary

This glossary provides an official Cisco definition for key words and terms introduced in this chapter. I have supplied my own definition for terms that the Cisco glossary does not contain. The words listed here are identified in the text by italics. A complete glossary, including all the chapter terms and additional terms, can be found in Appendix C, "Glossary."

Dijkstra algorithm—A complex algorithm used by routers running link-state routing protocols to find the shortest path to the destination.

flood—A term that refers to network information. When it is flooded, it is sent to every network device in the domain.

fully adjacent—When the routing tables of the two neighbors are fully synchronized, with exactly the same view of the network.

loading state—State in which, if the receiving router requires more information during the process in which two routers are creating an adjacency, it will request that particular link in more detail using the link-state request packet (LSR). The LSR will prompt the master router to send the link-state update packet (LSU). This is the same as a link-state advertisement (LSA) used to flood the network with routing information. While the receiving router is awaiting the LSUs from its neighbor, it is in the loading state.

loopback interface—A virtual interface that does not exist physically. This characteristic makes it very powerful: If it does not exist, it can never go down.

setup script—A question-and-answer dialogue that is offered by the Cisco router. If the router is booted without an existing configuration, it will ask you if you want to enter the setup script to create a basic configuration.

shortest path first (SPF)—The same as the Dijkstra algorithm, which is the algorithm used to find the shortest path.

two-way state—State during the process in which two routers are creating an adjacency. The new router sees its own router ID in the list of neighbors, and a neighbor relationship is established. This is the stage before routing information is exchanged.

Q&A

The following questions test your understanding of the topics covered in this chapter. The final questions in this section repeat of the opening "Do I Know This Already?" questions. These are repeated to enable you to test your progress. After you have answered the questions, find the answers in Appendix A. If you get an answer wrong, review the answer and ensure that you understand the reason for your mistake. If you are confused by the answer, refer to the appropriate text in the chapter to review the concepts.

1 What information is held in the topology table?

2 What command is used to manually determine which router on a LAN will become the DR?

3 What details are used to determine the metric of a route in OSPF by default on a Cisco router?

4 It is possible to have more than one OSPF process on a router—how would this be achieved?

5 Which RFC identifies the use of OSPF over an NBMA cloud?

6 State the different types of packets used to build a routing table for the first time.

7 In creating an adjacency, what is the exstart state?

8 Explain the command ip ospf network non-broadcast.

9 In which of the NBMA configuration choices is it necessary to manually state the neighbors? Why is this necessary?

10 In a Frame Relay environment, which is fully meshed, which OSPF configurations might be chosen? Give reasons for your choice.

11 How often by default does OSPF send out hello packets on a broadcast multiaccess link?

12 What is a neighbor in OSPF?

13 What is an adjacency in OSPF?

14 If the network is stable and sees no changes, how often will it send LSAs? Why are these updates sent out periodically?

15 If a router has an OSPF priority set to 0, what does this indicate?

16 What does NBMA stand for?

17 RFC 2328 describes the operation of OSPF in two modes across an NBMA cloud. What are they?

18 The Cisco solution point-to-point mode does not require the configuration of DR and BDR. Explain briefly why.

19 The address 192.100.56.10 has been allocated to an interface on the router. This interface alone is to be included in the OSPF process. State the command that would start the process on this interface.

20 What command would identify the designated router for your LAN?

21 The metric used by OSPF is cost. How would you change the default setting on an interface?

22 If the command ip ospf network non-broadcast is used, what additional statement is necessary?

23 What command shows which router on a LAN is the BDR?

24 Explain briefly what show ip ospf database will reveal.

25 What command is used to show the state of adjacencies?

It is possible to have more than one OSPF process on a router. Which command would achieve this?

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