The answers provided in this section are not necessarily the only possible answers to the questions. The questions are designed to test your knowledge and to give practical exercise in certain key areas. This section is intended to test and exercise skills and concepts detailed in the body of this chapter.
If your answer is different, ask yourself whether it follows the tenets explained in the answers provided. Your answer is correct not if it matches the solution provided in the book, but rather if it has included the principles of design laid out in the chapter.
In this way, the testing provided in these scenarios is deeper: It examines not only your knowledge, but also your understanding and ability to apply that knowledge to problems.
If you do not get the correct answer, refer back to the text and review the subject tested . Be certain to also review your notes on the question to ensure that you understand the principles of the subject.
Scenario 6-1 Answers
Which parameter determines the router that will be selected as the DR in an OSPF network?
The router with the highest OSPF priority on a segment will become the DR for that segment. The default for the interface OSPF priority is 1. If multiple routers have the same priority, the router with the highest RID will be selected as the DR.
Could a router with a priority value of zero assume the role of a DR or a BDR in the OSPF network shown in Figure 6-10?
No. A priority value of zero indicates an interface is not to be elected as a DR or BDR. The state of the interface with priority zero will be DROTHER.
How is the OSPF router ID determined on a Cisco router?
The OSPF router ID is the highest IP address on the box, or the highest loopback address, if one exists.
What is the role of the DR and BDR in the OSPF network shown in Figure 6-10?
Instead of each router exchanging updates with every other router on the segment, every router will exchange the information with the DR and the BDR. The DR and the BDR will relay the information to everybody else. In mathematical terms, the adjacencies required for a full mesh is n ( n -1)/2 and for a DR/BDR situation is 2 n -2.