# CCENT Exam Cram: Concepts in IP Addressing

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This chapter is from the book

## Answers to Exam Prep Questions

1. Answers B and D are correct. Answer A in decimal would be 551. Answer C in decimal would be 323. Answer E in decimal is 230.

2. Answers C and D are correct. Answer A in hex is 0xB4. Answer B in hex is 0xBF. Answer E is simply an attempt to trick you—the correct decimal answer is incorrectly expressed as a hex value.

3. Answer D is correct. A will only support 2 hosts; B only 6, and C only 14. Watch out for the minus 2 in the host calculation! Answer C creates 16 hosts on the subnet, but we lose 2—one for the Net ID and one for the Broadcast ID.

4. Answer D is correct. The mask 255.255.254.0 gives us nine 0s at the end of the mask; 29-2 = 510. Answer A is checking to see if you missed the 254 in the third octet because you are used to seeing 255. Answer B does the same thing plus tries to catch you on not subtracting 2 from the host calculation. Answer C tries to catch you on not subtracting 2, and Answer E is the Increment of the given mask that you might pick if you were really off track.

6. The correct answer is C. The default mask for a Class B is 255.255.0.0. Answer C extends that mask by three bits, creating eight subnets (23=8). The Zero Subnets are lost because the routers cannot use them, so we are left with six subnets. Answer A is incorrect because it is the default mask for a Class B and not subnetted at all. Answers B and D are incorrect because although they create sufficient subnets, they do not maximize the number of hosts per subnet and so are not the best answer. Answer E uses the correct mask in the wrong octet.

7. Answer E is correct. With "ip subnet zero" enabled, all 64 subnets created by the mask in use become available. Answers A, B, and C are not even close and are simply distracters. Answer D wants to catch you by subtracting the zero subnets.

8. The correct answers are B, D, F, G, H, and J. Answers A and C are incorrect because this is a Class A address. Answer E is incorrect because only 16 bits were stolen. Answer I is incorrect because it does not subtract the two IPs for the NetID and Broadcast ID.

9. Answer D is correct. With that mask, the Increment is 64. Greg is in the first subnet, and Indy is in the second. Without a router between them, their PCs will not be able to communicate above layer 2. Answer A is incorrect; the Broadcast ID for Indy would be .63. Answer B is incorrect; nothing is wrong with the mask. Answer C is incorrect; the Zero Subnets are the first and last created, and Indy is in the second subnet. The question does not mention the Zero Subnets, and in any case Windows XP fully supports them.

10. The correct answers are C and F. This is an Increment question. The Increment here is 8, so you should start by jotting down the multiples of 8 (those are all the NetIDs), and then noting what 1 less than each of the NetIDs is (those are the Broadcast IDs). From there, it is easy to find what the first and last IPs in each subnet are. (Remember that Dave says we can use the Zero Subnets.) Answers A and D are incorrect because they do not use the subnetted address space Dave requested. Answer B is incorrect because it is a NetID. Answer E is incorrect because it is a Broadcast ID.

1. Incorrect (same subnet as Fa1/0)
2. Incorrect (Network ID)
3. Incorrect (Not enough Hosts)
4. Incorrect (Fa1/0 IP already assigned)
5. Correct
6. Incorrect (Wrong subnet—not on the same network as the connected interface on Main)
7. Correct
8. Incorrect (Not enough hosts)
9. Correct
10. Incorrect (Overlaps with Fa1/1)
11. Correct
12. Incorrect (Overlaps with Fa2/0)
13. Incorrect (Not enough hosts)
14. Incorrect (There is no Fa0/2 interface on Genoa)
15. Correct
16. Incorrect (Network ID)
17. Incorrect (Overlaps with Genoa)
18. Incorrect (Network ID)
19. Correct