# Computer Networks Questions & Answers – CIDR

This set of Computer Networks Multiple Choice Questions & Answers (MCQs) focuses on “CIDR”.

1. The CIDR value represents ____________
a) Number of bits in the network
b) Number of total bits in the IP address
c) Number of bits in the host
d) Number of hosts remaining

Explanation: The CIDR value represents the number of bits in the network. These CIDR values are represented by ‘/’ at the end of the network Id.

2. Which class does the IP address 192.168.10.5/24 represent?
a) Class A
b) Class C
c) Class B
d) Class D

Explanation: The IP address 192.168.10.5/24 represents Class C because the CIDR value of Class C is 24; i.e. Class C has 24 bits in the network portion.

3. The CIDR value affects the subnet mask of an IP address.
a) True
b) False

Explanation: Yes, as CIDR value represents the number of bits in the network, hence it can also be used to calculate the number of bits in the host portion doing so will also determine the subnet mask of the IP address. Hence CIDR value affects the subnet mask of an IP address.

4. When was the CIDR system created?
a) 2006
b) 1993
c) 1988
d) 1998

Explanation: The CIDR system was introduced in 1993 along with the IPv4 standard. During 1988, 1998 and 2006 IANA, APIPA and new IPv4 standards were introduced respectively.

5. Private IPs are calculated using CIDR values.
a) True
b) False

Explanation: Private IPs are assigned by IANA. CIDR values are used to calculate the subnet mask and range of a given IP address. CIDR values are used by network administrators to create and manage different subnets. Private IPs, on the other hand, are used by companies to create their network.

6. Determine the number of subnets for the given IP 192.13.67.0/28 using the CIDR value.
a) 16
b) 14
c) 4
d) 8

Explanation: Given,
CIDR value = 28
IP address = 192.13.67.0 (Class C)
The default number of bits in the network portion = 24
Let n be the number of bits added to the network portion of the given IP address
n = CIDR value – Default number of bits in the network portion
n = 28 – 24
n = 4
Number of Subnets = 2n
= 24
Number of Subnets = 16

7. Determine the number of valid host IPs in each subnet for the given IP 172.16.0.0/25 using the CIDR value.
a) 7
b) 128
c) 126
d) 16

Explanation: Given,
CIDR value = 25
IP address = 172.16.0.0 (Class B)
Total number of bits in an IP address = 32
Let n be the number of bits in the host portion of the given IP address
n = Total number of bits in an IP address – CIDR value
n = 32 – 25
n = 7
Number of Hosts = 2n – 2
= 27 – 2
Number of Hosts = 128 -2
Number of Hosts = 126
Since Network IP and Broadcast IP cannot be assigned to any host we remove those 2 IPs.

8. Determine the total number of valid IPs in each subnet for the given IP 192.168.10.0/26 using the CIDR value.
a) 26
b) 128
c) 6
d) 64

Explanation: Given,
CIDR value = 26
IP address = 192.168.10.0 (Class C)
Total number of bits in an IP address = 32
Let n be the number of bits in the host portion of the given IP address
n = Total number of bits in an IP address – CIDR value
n = 32 – 26
n = 6
Total number of valid IPs in a subnet = 2n
= 26
Total number of valid IPs in a subnet = 64.

Sanfoundry Global Education & Learning Series – Computer Networks.