GATE CS 2024 Set 2 — Question 38

The range of IP addresses is from 10.12.2.0 to 10.12.3.255.Let's look at the binary representation of the third octet, as the first two octets (10.12) are constant.

• 2 in binary: 00000010
• 3 in binary: 00000011

The range covers exactly these two values in the third octet, and for each value, the fourth octet ranges from 0 to 255. This corresponds to combining two consecutive /24 blocks: 10.12.2.0/24 and 10.12.3.0/24.Comparing the binary of the third octet:
00000010
00000011The first 7 bits are identical (0000001).Total prefix length = 8 (1st octet) + 8 (2nd octet) + 7 (3rd octet) = 23 bits.The network address is the lowest address in the block: 10.12.2.0.Thus, the CIDR prefix is 10.12.2.0/23.