GATE Technical: Computer Science and Information Technology (CS) questions with solutions

Q1. Consider routing table of an organization’s router shown below: Subnet Number | Subnet Mask | Next Hop 12.20.164.0 | 255.255.252.0 | R1 12.20.170.0 | 255.255.254.0 | R2 12.20.168.0 | 255.255.254.0 | Interface 0 12.20.166.0 | 255.255.254.0 | Interface 1 default | | R3 Which of the following prefixes in CIDR notation can be collectively used to correctly aggregate all of the subnets in the routing table?

1. 12.20.164.0/20
2. 12.20.164.0/22
3. 12.20.164.0/21
4. 12.20.168.0/22

Answer: 12.20.164.0/21

The prefix 12.20.164.0/21 encompasses all the specified subnets by covering the address range from 12.20.160.0 to 12.20.167.255, which includes 12.20.164.0/22, 12.20.170.0/23, 12.20.168.0/23, and 12.20.166.0/23, thus allowing for efficient aggregation.