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Exam SSCP topic 6 question 16 discussion

Actual exam question from ISC's SSCP
Question #: 16
Topic #: 6
[All SSCP Questions]

In the days before CIDR (Classless Internet Domain Routing), networks were commonly organized by classes. Which of the following would have been true of a
Class B network?

  • A. The first bit of the IP address would be set to zero.
  • B. The first bit of the IP address would be set to one and the second bit set to zero.
  • C. The first two bits of the IP address would be set to one, and the third bit set to zero.
  • D. The first three bits of the IP address would be set to one.
Show Suggested Answer Hide Answer
Suggested Answer: C 🗳️
Each Class B network address has a 16-bit network prefix, with the two highest order bits set to 1-0.
The following answers are incorrect:
The first bit of the IP address would be set to zero. Is incorrect because, this would be a Class A network address.
The first two bits of the IP address would be set to one, and the third bit set to zero. Is incorrect because, this would be a Class C network address.
The first three bits of the IP address would be set to one. Is incorrect because, this is a distractor. Class D & E have the first three bits set to 1. Class D the 4th bit is 0 and for Class E the 4th bit to 1.
Classless Internet Domain Routing (CIDR)
High Order bits are shown in bold below.
For Class A, the addresses are 0.0.0.0 - 127.255.255.255
The lowest Class A address is represented in binary as 00000000.00000000.0000000.00000000
For Class B networks, the addresses are 128.0.0.0 - 191.255.255.255.
The lowest Class B address is represented in binary as 10000000.00000000.00000000.00000000
For Class C, the addresses are 192.0.0.0 - 223.255.255.255
The lowest Class C address is represented in binary as 11000000.00000000.00000000.00000000
For Class D, the addresses are 224.0.0.0 - 239.255.255.255 (Multicast)
The lowest Class D address is represented in binary as 11100000.00000000.00000000.00000000
For Class E, the addresses are 240.0.0.0 - 255.255.255.255 (Reserved for future usage)
The lowest Class E address is represented in binary as 11110000.00000000.00000000.00000000

Classful IP Address Format -


References:
3Com http://www.3com.com/other/pdfs/infra/corpinfo/en_US/501302.pdf
AIOv3 Telecommunications and Networking Security (page 438)

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Yupata
5 months, 3 weeks ago
B is correct
upvoted 1 times
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steumi12
7 months, 2 weeks ago
Yep. It should be B
upvoted 1 times
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gurbmeister
1 year, 4 months ago
according to the explanation: Answer should be B
upvoted 3 times
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