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.
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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