CCNA Routing and Switching
This chapter is from the book
Answers to Exam Prep Questions
- 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.
- 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.
- 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
- 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
- The correct answer is D. Disregarding for the moment the possibility that
Mr. Martin might be wrong, let’s look at the requirements. He says make
room for 12 managers, and make the subnets as small as possible while doing so.
You need to find the mask that has sufficient host IP space without making it
bigger than necessary. Answer A is invalid; 12 is not a valid mask value.
Remember, a mask is a continuous string of 1s followed by a continuous string of
0s. In answer B, the mask is valid, but it is not correct. This mask has eight
0s at the end, which, when we apply the formula 28 -2 gives us 254 hosts. That
makes more than enough room for the 12 managers, but does not meet the "as
small as possible" requirement. Answer C has the correct mask value in the
wrong octet. That mask gives us eight 0s in the fourth octet, plus another four
in the third octet; that would give us 4094 hosts on the subnet. Answer E gives
us 30 hosts per subnet, but that only meets half the requirement. This mask does
not provide the minimum number of hosts.
- 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 8 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. Answer 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
- Answer E is correct. With "ip subnet zero" enabled, all 64
subnets created by the mask in use become available. Answer A, B, and C are not
even close and are simply distracters. Answer D wants to catch you by
subtracting the zero subnets.
- The correct answers are B, D, F, G, H, and J. Answer 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.
- 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.
- 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.