Which of the following subnet masks matched to the CIDR notation is correct? (A) 255.255.255.224 = /27 (B) 255.255.192.0 = /19 (C) 255.255.240.0 = /27 (D) 255.255.255.192 = /28
2. You are designing a network with subnets of variable sizes. In the figure below, identify two problems with the design. (A) Subnet A does not have enough addresses. (B) Subnet B does not have enough addresses. (C) Subnet C does not have enough addresses. (D) Computer A is assigned an incorrect address. (E) Computer B is assigned an incorrect address. (F) Computer C is assigned an incorrect address.
The Correct Answer and Explanation is:
Question 1: Matching Subnet Masks with CIDR Notation
Correct Answer: (A) 255.255.255.224 = /27
Explanation:
CIDR (Classless Inter-Domain Routing) notation represents the number of bits in the subnet mask.
- /27 means the first 27 bits are set to 1 in the subnet mask.
- In decimal, that is:
11111111.11111111.11111111.11100000
Which equals: 255.255.255.224
Let’s review the others:
- (B) 255.255.192.0 = /18, not /19
- (C) 255.255.240.0 = /20, not /27
- (D) 255.255.255.192 = /26, not /28
So only Option A is correct.
Question 2: Identify Problems with the Network Design
Correct Answers: (A) Subnet A does not have enough addresses.
(F) Computer C is assigned an incorrect address.
Explanation
When designing a network with subnets of variable sizes, it’s important to allocate a sufficient number of IP addresses for the devices in each subnet and ensure that assigned IP addresses fall within the correct range.
(A) Subnet A does not have enough addresses:
This is a common issue when subnetting without careful planning. For example, if Subnet A is meant to support 30 devices but is assigned a /27 subnet (which only supports 32 IPs, including 2 reserved addresses), only 30 devices can be supported at most. If you need more than 30, a larger subnet like /26 or /25 should be used.
(F) Computer C is assigned an incorrect address:
Each subnet has a defined IP range based on its subnet mask. If Computer C has an IP address that falls outside the defined range for its subnet, communication within the subnet or with the gateway will fail. This misconfiguration can cause connectivity issues or conflict with other devices.
Incorrect address assignments can occur if the IP assigned to a device falls outside the start and end IP range of the subnet (excluding network and broadcast addresses). This often happens due to human error or poor documentation.
To avoid such problems:
- Determine how many IPs are needed before assigning subnet sizes.
- Use tools or subnet calculators to find the valid range of IPs in each subnet.
- Double-check device IP assignments against the subnet configuration.
Proper planning and verification are critical for ensuring a scalable and error-free network infrastructure.
