IP Addresses in CIDR Block - Exam 200-125: Cisco Certified Network Associate Exam (Provider: Cisco)

# Which IP Addresses Fall into the CIDR Block of 115.64.4.0/22? (Choose Three)

### Question

Which of the following IP addresses fall into the CIDR block of 115.64.4.0/22? (Choose three.)

### Explanations

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A. B. C. D. E. F.

BCE

The CIDR block of 115.64.4.0/22 represents an IP address range that includes 1024 IP addresses, starting from 115.64.4.0 and ending at 115.64.7.255. The /22 notation means that the first 22 bits of the IP address are used to identify the network portion of the address, while the remaining 10 bits can be used to identify individual hosts within the network.

To determine which of the given IP addresses fall into the CIDR block of 115.64.4.0/22, we need to compare the network portion of each address to the network portion of the CIDR block.

To calculate the network portion of the CIDR block, we need to convert the subnet mask from dotted decimal notation to binary. The subnet mask for a /22 network is 255.255.252.0, which in binary is:

11111111.11111111.11111100.00000000

This means that the first 22 bits are set to 1, while the last 10 bits are set to 0.

Next, we can apply the binary AND operation between each IP address and the subnet mask to determine the network portion of the address. Any IP address that has the same network portion as the CIDR block falls into the range.

Let's check each IP address in turn:

A. 115.64.8.32: 01110011.01000000.00001000.00100000 Subnet mask: 11111111.11111111.11111100.00000000 Network portion: 01110011.01000000.00001000.00000000 (115.64.8.0) Result: outside range

B. 115.64.7.64: 01110011.01000000.00000111.01000000 Subnet mask: 11111111.11111111.11111100.00000000 Network portion: 01110011.01000000.00000100.00000000 (115.64.4.0) Result: inside range

C. 115.64.6.255: 01110011.01000000.00000110.11111111 Subnet mask: 11111111.11111111.11111100.00000000 Network portion: 01110011.01000000.00000100.00000000 (115.64.4.0) Result: inside range

D. 115.64.3.255: 01110011.01000000.00000011.11111111 Subnet mask: 11111111.11111111.11111100.00000000 Network portion: 01110011.01000000.00000000.00000000 (115.64.0.0) Result: outside range

E. 115.64.5.128: 01110011.01000000.00000101.10000000 Subnet mask: 11111111.11111111.11111100.00000000 Network portion: 01110011.01000000.00000100.00000000 (115.64.4.0) Result: inside range

F. 115.64.12.128: 01110011.01000000.00001100.10000000 Subnet mask: 11111111.11111111.11111100.00000000 Network portion: 01110011.