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Subnetting and IP Addressing

5 minutes 5 Questions

Subnetting is the process of dividing an IP network into smaller, more manageable subnetworks called subnets. This helps reduce network congestion, improve routing efficiency, and simplify network management. IP addressing refers to the assignment of unique IP addresses to devices within a network to ensure their proper identification and communication. In an IP network, each device needs a unique IP address to send and receive data. Subnetting and IP addressing are fundamental concepts in networking, as they provide a foundation for effective network design and traffic segmentation. They help to prevent IP address conflicts, optimize resource utilization, and enhance network performance and security. Subnetting includes the use of IP address classes, subnet masks, and the calculation of network addresses, broadcast addresses, and host ranges for different subnets.

Guide to Subnetting and IP Addressing

Subnetting and IP Addressing consist of partitioning an IP network into smaller segments. Why is it important?
Subnetting can improve network security and performance. It's crucial in separating departments tactically, and for security, speed, and workgroup segmentation.

What is Subnetting and IP Addressing?
Subnetting is the process of dividing an IP network into multiple subnets, each being a smaller network. IP address is a unique string of numbers and/or letters that identifies a device on a network.

How does it work?
In subnetting, the IP address consists of the network prefix and the host identifier. The number of bits in the network prefix determines the total number of possible subnetworks. The remaining bits determine the number of hosts you can have within each subnet.

How to answer questions regarding Subnetting and IP Addressing?
1. Understand the question: Is it asking about subnetting or IP addressing? 2. Identify the network and host portions of the IP address. 3. If it is about subnetting, think in terms of 'how much to divide'.

Exam Tips: Answering Questions on Subnetting and IP Addressing
Understand your CIDR notation, the binary and decimal systems, as well as the effects of subnetting. Practice converting between binary and decimal. Create a subnetting cheat sheet for reference. Familiarize yourself with IPv4 and IPv6 addressing. In the exam, draw out your subnetting cheat sheet on scrap paper provided. Don't rush; take your time to answer subnetting questions correctly.

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CompTIA Network+ - Infrastructure Example Questions

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Question 1

An IT administrator wants to subnet a network of 10.0.0.0/8 into 200 subnets without wasting any addresses. What should be the new subnet mask?

Correct Answer: /16

The 10.0.0.0/8 network has a default mask of 8 bits which gives you one network with 16777214 usable hosts. The administrator wants to divide it into 200 subnets. Each subnet, therefore, would have a maximum of approximately 83886 hosts (16777214/200). To provide for this number of hosts, you would need a subnet mask of /16. Each /16 subnet provides 65534 usable host addresses (2^16 - 2), which is more than enough for our requirement. On contrary, a /17 subnet would provide only 32766 usable addresses which is not sufficient, while a /15 or a /14 subnet would provide more addresses per subnet than required leading to wastage of addresses. Therefore, the new subnet mask should be /16.

Question 2

A network administrator needs to configure a new building with 5 departments, each requiring at least 62 hosts. What is the minimum subnet mask that can be used?

Correct Answer: /26

The subnet mask /26, or 255.255.255.192, is the minimum size that can support at least 62 hosts. This is because a /26 subnet mask provides up to 64 addresses, but 2 of these are reserved, the network address and the broadcast address, leaving 62 usable addresses. The other options are incorrect because /27 and /28 provide fewer addresses than required (30 and 14 usable addresses respectively), while /25 provides more addresses (126 usable) than needed, which can be inefficient.

Question 3

An administrator needs to create 5 VLANs within a single subnet of 192.168.10.0/24. Each VLAN needs to support at least 14 hosts. What is the smallest possible subnet mask for each VLAN?

Correct Answer: /28

The size of the subnet mask determines how many hosts can be supported on each network. The smallest subnet mask that can support at least 14 hosts is /28, which provides 16 IP addresses. However, 2 of these IP addresses are used for the network address and the broadcast address, which leaves 14 available for hosts. The choice of /27, /26, and /25 would provide more than 14 hosts which isn't necessary and it would be a waste of IP address space. Therefore, the smallest possible subnet mask that can support at least 14 hosts for each VLAN is /28.

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