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Subnetting

5 minutes 5 Questions

Subnetting is the process of dividing a larger IP address space into smaller, more manageable segments. This provides better network organization, improves performance by reducing unnecessary traffic, and enhances security by isolating different parts of the network. Subnetting is accomplished by modifying the subnet mask, which determines how many bits are assigned to the network portion and the host portion of an IP address. The subnet mask acts as a separator between the network and host portions to help route traffic to the correct destination. Using subnetting, network administrators can create a hierarchical organization of IP address spaces, which reduces the broadcast domain and conserves IP addresses. Subnetting is essential to ensure efficient use of IP address space and to facilitate better network design for organizations of various sizes.

Guide to Subnetting for CompTIA A+ Exam

Introduction:
Subnetting is a technique in network management used to partition an IP network into smaller networks. It plays an integral role in efficient network design. It's important to master subnetting for the CompTIA A+ exam as questions on this topic routinely show up.

What is Subnetting?
Subnetting is the practice of dividing a network into two or more networks to maximize efficiency, improve security and performance. In essence, it's the process of 'dividing' the available IP addresses under a network.

How does subnetting work?
Subnetting works by taking the bits from the host portion of an IP address to use them for designating the subnet address. This creates additional networking capacity with the same set of IP addresses. The mechanism is based on binary calculations.

Answering Exam Questions:
Subnetting questions on the CompTIA A+ exam often involve scenarios where you need to determine how to subnet a network based on specific requirements. Begin by identifying the subnet mask, then calculate how many hosts and subnets you can create using that mask. Familiarize yourself with CIDR and the use of subnet masks in both binary and decimal format.

Exam Tips for Answering Questions on Subnetting:
1. Practice through subnetting exercises regularly.
2. Memorize key aspects of the subnetting chart tables to quickly calculate subnets and hosts.
3. Be comfortable with binary to decimal conversion and vice versa as they form the basis of subnetting questions.
4. Check and re-check your answers. Simple calculation mistakes can lead to the wrong response in subnetting questions.

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CompTIA A+ - Networking Example Questions

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Question 1

A network segment is using the address 192.168.1.0/24 and needs to be split into two subnets with a minimum of 100 hosts in each subnet. Which subnet mask should be used to accommodate the required number of hosts while creating the fewest subnets?

Correct Answer: /25

To find the subnet mask that supports at least 100 hosts per subnet, we need to determine the number of bits required for the host portion of the IP address. Since each subnet will require a minimum of 100 hosts, we need to calculate the subnet mask that will allow for at least 100 host addresses. Each octet in an IP address represents 8 bits, so a /24 network has 256 possible addresses (2^8). However, two of these addresses are reserved: one for the network address and one for the broadcast address, leaving 254 usable IP addresses. Splitting this network into two subnets needs to still support a minimum of 100 hosts per subnet. If we use a /25 subnet mask, the network is divided into two subnets of 128 addresses each (2^7), which would leave 126 usable addresses per subnet after accounting for the network and broadcast addresses in each subnet. This satisfies the requirement. The other options do not provide the necessary number of usable host addresses. A /26 provides 64 addresses, /27 provides 32 addresses, and /28 provides 16 addresses, all of which are too small to support the minimum of 100 hosts required per subnet.

Question 2

A network administrator is configuring a subnet for a critical department that requires 22 IP addresses for devices. The department is assigned the IP block 10.10.21.0/28. To ensure there are enough usable IP addresses for the department's devices, which of the following subnet masks should the network administrator implement?

Correct Answer: 255.255.255.240

Question 3

A network administrator needs to create 16 subnets from the IP address range 192.168.0.0/24. What should be the new subnet mask?

Correct Answer: 255.255.255.240

The correct answer is 255.255.255.240. To create 16 subnets from a /24 network, we need to borrow 4 bits from the host portion of the IP address. This is because 2^4 = 16, which gives us the required number of subnets. Starting with the original subnet mask of 255.255.255.0 (/24), we add 4 bits to the network portion: 11111111.11111111.11111111.11110000 This binary representation translates to 255.255.255.240 in decimal notation. The other options are incorrect: 255.255.255.224 would create 8 subnets (3 borrowed bits) 255.255.255.248 would create 32 subnets (5 borrowed bits) 255.255.255.192 would create 4 subnets (2 borrowed bits) None of these options meet the requirement of creating exactly 16 subnets.

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