The subnet mask of an IP address determines which part of the IP is used for the network and which part is used for hosts. It’s usually represented as four numbers, like 255.255.255.0. To find the subnet mask:

– Look at the first few numbers of the IP address.
– If it’s 255, then that portion is part of the network. If it’s less than 255, that portion is for hosts.

Example
Suppose you have an IP address 192.168.1.100 and a subnet mask of 255.255.255.0. In this case, the first three numbers (192.168.1) represent the network, and the last number (100) is for hosts.

2. What is the subnet mask of 255.255.255.0 IP address

A subnet mask of 255.255.255.0 means that the first three parts of the IP address are used for the network, and the last part is used for hosts. This is often used in small home or office networks.

3. What is the formula for finding a subnet

The formula for finding a subnet involves bitwise operations. You can calculate it using binary arithmetic, but it’s usually done with subnet calculators or tools. One common formula is:

Number of subnets = 2^(number of bits borrowed for subnetting)

4. How do I create a subnet from an IP address

To create a subnet from an IP address, you need to determine how many bits you want to allocate for the subnet and how many for hosts. Then, you adjust the subnet mask accordingly. For example, if you have IP address 192.168.1.0 and want to create subnets with 16 hosts each, you’d use a subnet mask of 255.255.255.240, creating 16 subnets.

5. Why is subnet mask always 255

Subnet masks are not always 255; they vary depending on the network’s needs. However, in common subnet masks, 255 is used to indicate that a portion of the IP is reserved for the network.

6. How do I change my IP address to a subnet mask

You don’t change your IP address to a subnet mask; they serve different purposes. Your IP address identifies your device on a network, while a subnet mask helps route traffic within that network.

7. How do I manually set a subnet mask

You can manually set a subnet mask in your device’s network settings. For example, in Windows, you can go to Control Panel > Network and Sharing Center > Change adapter settings, then right-click on your network adapter, select Properties, and manually configure the subnet mask in the IPv4 properties.

8. Should the subnet mask be the same as the IP address

No, the subnet mask and IP address should not be the same. The subnet mask defines which part of the IP address belongs to the network and which part belongs to hosts. They have different values and purposes.

9. What subnet mask is needed if an IPv4

IPv4 addresses can have various subnet masks depending on the network’s requirements. There is no specific subnet mask for all IPv4 addresses; it depends on the subnetting scheme used in the network.

10. What does the subnet mask 255.255.255.0 tell a router

Yes, a subnet mask of 255.255.255.0 indicates to a router that the first three parts of the IP address are the network portion, and the last part is for host devices within that network.

11. How do I configure IPv4 and subnet mask

To configure IPv4 and subnet mask on your device, you can go to the network settings and enter the desired values. For example, in Windows, it’s done in the IPv4 properties of your network adapter.

12. What is the default subnet mask for an IP address of

The default subnet mask for an IP address depends on the IP address class. For example, for a Class C IP address (e.g., 192.168.1.1), the default subnet mask is usually 255.255.255.0.

13. Why is 192.168 always used

The 192.168 IP range is reserved for private networks, and it’s commonly used because it provides a large number of available IP addresses while not conflicting with public internet IP addresses.

14. What is the IP address 127.0.0.1 used for

The IP address 127.0.0.1 is the loopback address, and it always refers to the local device. It’s used for testing network functionality on your own device without involving an external network.

15. Is 192.168.0.0 allowed on the Internet

No, the 192.168.0.0 IP range is reserved for private networks and is not routable on the public internet. It’s used for internal networks within homes and organizations.

16. Why do some IP addresses start with 10

IP addresses that start with 10 (e.g., 10.0.0.0) are also reserved for private networks. They are often used in larger networks where more IP addresses are needed.

17. Which IP address should you not use

You should not use IP addresses that are reserved for special purposes, such as loopback addresses (127.0.0.0/8) or addresses designated for private networks (e.g., 10.0.0.0/8, 192.168.0.0/16).

18. What is the best subnet mask

The best subnet mask depends on your network’s requirements. There is no one-size-fits-all answer. The subnet mask should be chosen based on the number of hosts and subnets needed in your network.

19. How many subnets can a router have

A router can have as many subnets as it has available interfaces. Each interface can be associated with a different subnet.

20. Can two subnets have the same IP address

No, two subnets on the same network should not have the same IP address. Each IP address should be unique within a subnet to avoid conflicts.

21. Can two routers share the same subnet

Yes, two routers can share the same subnet, but they should be properly configured to avoid routing conflicts. This scenario is common in complex network setups.

22. What IP addresses can talk to each other

IP addresses within the same subnet can easily communicate with each other. Routers are used to enable communication between different subnets or networks.

23. Can someone have the same IP as you

Yes, multiple devices can have the same private IP address within different networks, but they cannot have the same public IP address on the internet.

24. How can I tell if two computers are on the same subnet

You can determine if two computers are on the same subnet by comparing their IP addresses and subnet masks. If they have the same network portion as defined by the subnet mask, they are on the same subnet.

25. What happens if 2 IP addresses are the same

If two devices on the same network have the same IP address, it can lead to network conflicts and communication

issues. Each device on a network should have a unique IP address.

26. Can someone with my IP address see my history

No, having the same IP address as you doesn’t give someone access to your browsing history. Your browsing history is stored on your device, not on the network.

27. Does everyone in my house have the same IP address

No, each device in your house typically has its own unique private IP address on your home network.

28. Does everyone on the same WiFi have the same IP

Devices connected to the same WiFi network may have similar IP addresses (i.e., they share the same network portion), but they have different host portions, making them unique on the network.

29. Do you always have the same IP address when you connect to the internet

No, your public IP address assigned by your Internet Service Provider (ISP) can change periodically. This is known as a dynamic IP address. However, some ISPs offer static IP addresses that do not change.

30. Does an IP address change with location

Yes, your public IP address can change based on your physical location and the network you’re connected to. Different networks and locations may assign different IP addresses.

31. Is an IP address tied to a computer or router

An IP address can be tied to either a specific computer or a router, depending on the network configuration. In a home network, the router typically assigns unique IP addresses to each device connected to it.

32. What do the four numbers in an IP address mean

The four numbers in an IP address represent different levels of hierarchy. For example, in the IP address 192.168.1.1, the first number (192) represents the network, the second (168) represents a subnet within that network, and the last two (1.1) represent individual devices within that subnet.

33. What is an IP address for dummies

An IP address is like a digital address for devices on a network. It helps them find and communicate with each other on the internet or within a local network.

34. How do I find the exact location of an IP address

Finding the exact physical location of an IP address is challenging and often requires specialized tools and cooperation from Internet Service Providers. It’s not something a regular user can easily do.

35. Is it illegal to track an IP address

Tracking an IP address for legitimate network management purposes is generally not illegal. However, using IP address tracking for malicious purposes, such as stalking or hacking, is illegal and unethical.

36. Can an IP be traced to an exact location

IP addresses can be traced to a general geographic location, such as a city or region, but pinpointing an exact physical address is usually not possible without cooperation from the ISP.

37. How do I find the location of a device using an IP address

To find the approximate location of a device using an IP address, you can use online IP geolocation services or tools. These services provide general geographic information based on the IP address’s registered location.

Learn more on Subnetting; How to Calculate a Subnet Mask from IP Address

Understand Host and Subnet Quantities

For a broader understanding of subnetting, you can dive into Cisco’s extensive resources on the subject.
You can read more on the subject broadly from Cisco’s website here.

Step by step guide to IP Subnetting Video

Below is a simple 6 step by step method I use to perform subnetting calculations.

Let us look at this question below;

1: You have been given an IP Address 10.20.4.13/29 and been asked to find out the following pieces;

1. Subnet Address
2. First Valid Host Address
3. Last Valid Host Address
4. Broadcast Address
5. Subnet Mask

How to Calculate Subnet Mask from IP Address Step by Step

Before we attempt this question, let us understand that each bit in an IPv4 subnet mask corresponds to a specific value based on powers of 2. These values are represented by the following sequence:

– 128
– 64
– 32
– 16
– 8
– 4
– 2
– 1

Each bit’s position in the subnet mask corresponds to one of these values, with the leftmost bit being the highest value (128) and the rightmost bit being the lowest value (1).

Here’s how it works:

– The leftmost bit in an 8-bit subnet mask, when turned on (set to 1), represents a value of 128.
– The second leftmost bit, when turned on, represents a value of 64.
– The third leftmost bit represents 32.
– The fourth leftmost bit represents 16.
– The fifth leftmost bit represents 8.
– The sixth leftmost bit represents 4.
– The seventh leftmost bit represents 2.
– The rightmost bit, when turned on, represents a value of 1.

By combining these bits in various combinations (turning them on or off), you can create different subnet mask values that allow you to define the network and host portions of an IP address. For example, a subnet mask of 255.255.255.0 (or /24 in CIDR notation) means that the leftmost 24 bits are used for the network, and the rightmost 8 bits are used for hosts within that network. This allows for up to 256 host addresses (2^8) within that subnet.

Let us do it the hard way;

The given IP Address is 10.20.4.13/29. In IPv4, the subnet mask is represented as four 8-bit octets, so the subnet mask 255.255.255.255 is represented in binary as:

11111111.11111111.11111111.11111000

In CIDR notation, “/29” means that the leftmost 29 bits are used for the network portion of the address, leaving 3 bits for host addresses within the subnet.

To calculate the subnet mask:

Start with the binary representation of the subnet mask: 11111111.11111111.11111111.11111000.

Convert each octet to decimal: 11111111 = 255, 11111111 = 255, 11111111 = 255, 11111000 = 248.

The correct subnet mask is 255.255.255.248

With the above step, we now have a real understanding of how to calculate the Subnet Mask from a Network Prefix.

Now let us use a simpler or perhaps call it the easier way to calculate the same below;

Step 1: Find Subnet Number
Subtract the prefix number from /32: 32-29 = 3.
Calculate the subnet mask: 8 Bits – 3 Bits = 5 Bits (Network Bits Turned On).
You might wonder why 8 bits? Well, each octet requires 8 bits for a subnet mask.

To visualize this:

128 64 32 16 8 4 2 1
1 1 1 1 1 0 0 0
128 + 64 + 32 + 16 + 8 = 248
Subnet Mask = 255.255.255.248
Subnet Mask = 255.255.255.248

Step 2: Find Subnet Size
Raise 2 to the power of deduction (8-3 = 5 bits). Let’s denote these bits as ‘n’:
2^n = Subnet Size
2^5 = Subnet Sizes for each subnet.
2 * 2 * 2 = 8

Note: 8 represents the block size for the subnet. For instance, the increments will be 0, 8, 16, 32, 40, and so forth

Step 3: Find Broadcast Address
Subnet Size – 1
(2^n) – 1 = Broadcast Address
(2^3) – 1 = (8-1) = 7

Step 4: Locate IP Address Subnet
Identify the subnet block for the IP Address:
Where does the address 10.20.4.13/29 fall within the increments 0, 8, 16, 32, 40?
13 falls between 8 and 16, placing it within the valid host range of the subnet 10.20.4.8/29.

Step 5: Calculate Valid Hosts | How to calculate number of hosts in the subnet
2**n – 2 = Valid Host Range
2**3 – 2 = (8-2) = 6

Answer for question now is as follows;

Subnet Address: 10.20.4.8/29
Min Host Address: 10.20.4.9/29
Max Host Address: 10.20.4.14/29
Broadcast Address: 10.20.4.15/29

There you have it. A simple 6 step by step guide to subnetting effectively.

Related Posts:

How to connect GNS3 to a Physical Network Step by Step

What is Subnetting?

Subnetting is the process of dividing a larger network into smaller networks or subnets. It is accomplished by borrowing bits from the host portion of an IP address and using them to create subnets. The subnet mask is used to determine the network and host portions of an IP address. The subnet mask is a 32-bit number that consists of a series of ones followed by a series of zeros. The ones represent the network portion of the address, and the zeros represent the host portion of the address.

Why Subnetting is Important?

Subnetting is essential for the following reasons:

Efficient use of IP addresses: Subnetting allows you to use IP addresses more efficiently by dividing a larger network into smaller networks. This way, you can allocate IP addresses only to devices that need them, and avoid wasting IP addresses.

Better network performance: Subnetting can improve network performance by reducing network congestion and improving network efficiency.

Improved security: Subnetting can enhance network security by isolating different segments of a network and restricting access to specific devices.

Subnetting Cheat Sheet

The following subnetting cheat sheet will help you understand the basics of subnetting:

Subnet Mask: A subnet mask is a 32-bit number that determines the network and host portions of an IP address.

Network Address: The network address is the first address in a subnet and is used to identify the network.

Broadcast Address: The broadcast address is the last address in a subnet and is used to send a message to all devices on the network.

IP Address Range: The IP address range is the set of IP addresses available for use in a subnet.

CIDR Notation: CIDR notation is a shorthand notation for representing subnet masks. It is written as a slash (/) followed by the number of bits in the subnet mask.

Subnetting Formula: The subnetting formula is used to calculate the number of subnets and hosts per subnet. The formula is 2^n, where n is the number of bits borrowed for the subnet.

Subnetting Example: To subnet a network, follow these steps:

a. Choose the number of subnets required.
b. Choose the number of host bits required per subnet.
c. Calculate the subnet mask.
d. Calculate the network address and broadcast address.
e. Determine the IP address range.

Subnet Mask	CIDR Notation	Binary Value	Decimal Value
255.255.255.0	/24	11111111.11111111.11111111.00000000	255.255.255.0
255.255.255.128	/25	11111111.11111111.11111111.10000000	255.255.255.128
255.255.255.192	/26	11111111.11111111.11111111.11000000	255.255.255.192
255.255.255.224	/27	11111111.11111111.11111111.11100000	255.255.255.224
255.255.255.240	/28	11111111.11111111.11111111.11110000	255.255.255.240
255.255.255.248	/29	11111111.11111111.11111111.11111000	255.255.255.248
255.255.255.252	/30	11111111.11111111.11111111.11111100	255.255.255.252

Conclusion:

Subnetting is an essential concept in computer networking. It allows you to divide a larger network into smaller networks, use IP addresses more efficiently, improve network performance, and enhance network security. The subnetting cheat sheet provided in this article will help you understand the basics of subnetting and become a subnetting pro. Remember to use the subnetting formula and follow the subnetting example to subnet a network successfully.

Classless Inter-Domain Routing (CIDR) is a methodology for allocating IP addresses more efficiently. Prior to CIDR, IP addresses were assigned based on their class (Class A, B, or C) which could lead to inefficient use of IP addresses. CIDR was introduced to provide more flexibility and granularity in IP address allocation, allowing for better utilization of IP address space.

What is CIDR?

CIDR is a method of assigning IP addresses that allows for more efficient use of address space. It uses a prefix length to determine the number of bits in the IP address that identify the network and the host. For example, in the IP address 192.168.1.1/24, the prefix length is 24, indicating that the first 24 bits of the IP address are used to identify the network, and the remaining 8 bits are used to identify the host.

CIDR allows for more precise allocation of IP addresses, as it allows for subnets to be divided into smaller blocks, each with its own prefix length. This means that instead of allocating entire classful networks, smaller blocks can be assigned to networks, allowing for more efficient use of address space.

Advantages of CIDR

CIDR has several advantages over the older classful addressing system:

Efficient use of address space: CIDR allows for more precise allocation of IP addresses, which means that address space can be used more efficiently. This is particularly important in today’s world, where IP addresses are becoming increasingly scarce.

Simplified routing: CIDR makes routing more efficient by reducing the size of routing tables. With CIDR, routes can be aggregated, reducing the number of entries in routing tables.

Flexibility: CIDR allows for more flexibility in network design. Networks can be divided into smaller blocks, allowing for more precise allocation of resources.

CIDR Notation

CIDR notation is used to represent IP addresses and prefix lengths. It consists of the IP address followed by a slash (/) and the prefix length. For example, the IP address 192.168.1.1 with a prefix length of 24 would be represented as 192.168.1.1/24.

CIDR notation can also be used to represent a range of IP addresses. For example, the range of IP addresses from 192.168.1.1 to 192.168.1.255 with a prefix length of 24 would be represented as 192.168.1.0/24.

CIDR and Subnetting

CIDR and subnetting are closely related. Subnetting is the process of dividing a network into smaller subnetworks. CIDR allows for more precise allocation of IP addresses, which makes subnetting more efficient.

CIDR makes subnetting more efficient by allowing for subnets to be divided into smaller blocks. This means that instead of allocating entire classful networks, smaller blocks can be assigned to networks, allowing for more efficient use of address space.

CIDR and IPv6

CIDR is used with both IPv4 and IPv6. IPv6 uses a 128-bit address space, which is much larger than the 32-bit address space used by IPv4. This means that CIDR is even more important for IPv6, as it allows for more precise allocation of addresses in a much larger address space.

Conclusion

CIDR is a method of assigning IP addresses that allows for more efficient use of address space. It allows for more precise allocation of IP addresses, which means that address space can be used more efficiently. CIDR also simplifies routing and provides more flexibility in network design.

If you’re looking to optimize your network’s IP address allocation and improve its efficiency, CIDR is a great methodology to consider. By allowing for more granular control over address allocation, CIDR can help reduce wasted IP space and simplify routing, making it easier to manage your network. So if you’re looking to streamline your network and get the most out of your IP space, consider implementing CIDR today.

Example 1: Subnetting a Class A Network

Let’s say we want to subnet the Class A network 10.0.0.0/8 to create smaller subnets for different departments in our organization. We want to create 4 subnets with a maximum of 2,000 hosts per subnet.

To create 4 subnets, we need to borrow 2 bits from the host portion of the IP address. This leaves us with 14 bits for the host portion of the IP address, which gives us 16,384 IP addresses (2^14) per subnet.

To determine the subnet mask for each subnet, we need to determine the value of the bits we borrowed. In this case, we borrowed the first 2 bits, which gives us a value of 192 (11000000) in binary. Therefore, the subnet mask for each subnet will be 255.255.192.0.

The table below shows the network address, subnet mask, and valid host range for each subnet:

In this example, we created 4 subnets, each with a subnet mask of 255.255.192.0. This means that each subnet has 16,384 IP addresses available for hosts.

Example 2: Subnetting a Class B Network

As previously mentioned, we have been assigned the IP address 172.16.0.0/16, which means we have 65,536 IP addresses (2^16) available for our network. However, we want to divide this network into smaller subnets.

To subnet this network, we need to borrow bits from the host portion of the IP address. Let’s say we decide to borrow 4 bits to create 16 subnets (2^4). This leaves us with 12 bits for the host portion of the IP address, which gives us 4,096 IP addresses (2^12) per subnet.

To determine the subnet mask for each subnet, we need to determine the value of the bits we borrowed. In this case, we borrowed the first 4 bits, which gives us a value of 240 (11110000) in binary. Therefore, the subnet mask for each subnet will be 255.255.240.0.

The table below shows the network address, subnet mask, and valid host range for each subnet:

In this example, we created 8 subnets, each with a subnet mask of 255.255.248.0. This means that each subnet has 8,192 IP addresses available for hosts.

Example 3: Subnetting a Class C Network

A Class C network has an IP address range of 192.0.0.0 to 223.255.255.0. Let’s say we have been assigned the IP address 192.168.0.0/24 and we want to subnet it. This means we have 256 IP addresses (2^8) available for our network. However, we want to divide this network into smaller subnets.

To subnet this network, we need to borrow bits from the host portion of the IP address. In this case, we will borrow 3 bits to create 8 subnets (2^3). This leaves us with 5 bits for the host portion of the IP address, which gives us 32 IP addresses (2^5) per subnet.

To determine the subnet mask for each subnet, we need to determine the value of the bits we borrowed. In this case, we borrowed the first 3 bits, which gives us a value of 224 (11100000) in binary. Therefore, the subnet mask for each subnet will be 255.255.255.224.

The table below shows the network address, subnet mask, and valid host range for each subnet:

Conclusion

Subnetting can seem daunting at first, but it is an important tool for managing IP addresses and optimizing network performance. By dividing a larger network into smaller subnets, we can reduce broadcast traffic and improve network security. The examples above demonstrate how subnetting works and how to determine the subnet mask and valid host range for each subnet.

If you’re new to subnetting, it’s important to take the time to understand the basics before diving into more complex examples.

For additional resources and information on subnetting;

Subnetting Practice: https://www.subnettingpractice.com/
IP Subnet Calculator: https://www.calculator.net/ip-subnet-calculator.html

Exercise 1: Calculate Subnets

To calculate subnets, you need to understand IP addresses, subnet masks, and CIDR notation. Start by writing down the IP address and subnet mask. Then convert the subnet mask to binary, and perform an AND operation on the IP address and subnet mask. The result is the network address. Repeat this process for each subnet to get the network address and broadcast address.

Exercise 2: Determine Network and Broadcast Addresses

To determine the network and broadcast addresses, you need to know the subnet mask and the IP address. The network address is the result of performing an AND operation on the IP address and subnet mask. The broadcast address is the last address in the subnet. To calculate it, flip all the bits in the subnet mask and perform an OR operation on the network address and the inverted subnet mask.

Exercise 3: Identify Valid Host Ranges

To identify valid host ranges, you need to know the network address, broadcast address, and subnet mask. Subtract the network address from the broadcast address to get the total number of addresses in the subnet. Then subtract 2 from the total to get the number of valid host addresses. The first valid host address is the network address plus 1, and the last valid host address is the broadcast address minus 1.

Exercise 4: VLSM

Variable Length Subnet Masking (VLSM) is a technique used to allocate IP addresses to subnets of different sizes. To practice VLSM, you need to know how to divide an IP address range into smaller subnets of varying sizes. Start by identifying the largest subnet, and divide it into smaller subnets. Then repeat the process for the next largest subnet until all subnets have been allocated.

Exercise 5: CIDR

Classless Inter-Domain Routing (CIDR) is a method used to allocate IP addresses and IP routing in a more flexible and scalable way than traditional classful addressing. To practice CIDR, you need to understand how to convert an IP address into CIDR notation. The CIDR notation consists of the IP address followed by a slash (/) and the number of bits in the subnet mask.

Conclusion:

Subnetting is an important skill for network engineers and IT professionals. To master this skill, you need to practice subnetting exercises that cover the basics of IP addresses, subnet masks, network and broadcast addresses, valid host ranges, VLSM, and CIDR. With these exercises, you can improve your networking skills and become a more effective IT professional.

Remember to use subnetting formulas, subnetting charts, and other helpful tips and tricks to make subnetting easier. Happy subnetting!

Summary:
This article on subnetting exercises will help network engineers and IT professionals improve their subnetting skills. Learn how to calculate subnets, determine network and broadcast addresses, identify valid host ranges, practice VLSM, and understand CIDR notation. Use subnetting formulas and charts to make subnetting easier. Practice subnetting exercises to become a more effective IT professional.

What is an IP Address?

An IP address is a unique identifier assigned to every device on a network. It is used to identify and communicate with other devices on the network. An IP address consists of four numbers separated by periods, for example, 192.168.1.1. Each number can range from 0 to 255, giving a total of 4.3 billion possible IP addresses.

What is a Subnet Mask?

A subnet mask is a 32-bit number that is used to divide an IP address into two parts: the network ID and the host ID. The network ID identifies the network to which the device belongs, while the host ID identifies the specific device on the network.

A subnet mask consists of a series of 1’s followed by a series of 0’s. The 1’s represent the network ID, while the 0’s represent the host ID. For example, a subnet mask of 255.255.255.0 means that the first three numbers of the IP address represent the network ID, while the last number represents the host ID.

How to Subnet a Network

Subnetting a network involves dividing a larger network into smaller subnetworks, each with its own unique network ID and range of IP addresses. This allows for more efficient use of IP addresses and better management of network traffic.

To subnet a network, you first need to determine how many subnets you need and how many hosts each subnet will have. This will help you determine the appropriate subnet mask for your network.

For example, if you need to create four subnets with up to 30 hosts each, you can use a subnet mask of 255.255.255.224. This subnet mask provides for 5 bits of network ID and 3 bits of host ID, allowing for 8 subnets (2^3) and 30 hosts per subnet (2^5-2).

To calculate the network ID and host ID for a given IP address and subnet mask, you perform a bitwise AND operation between the IP address and the subnet mask. The result is the network ID. For example, if you have an IP address of 192.168.1.25 and a subnet mask of 255.255.255.0, the network ID would be 192.168.1.0.

Conclusion

Subnetting is an important networking concept that allows for more efficient use of IP addresses and better management of network traffic. Understanding the basics of subnetting, including IP addresses and subnet masks, is essential for network engineers, system administrators, and IT professionals. By following the steps outlined in this article, you can subnet a network and allocate IP addresses in a more efficient and effective manner.

Have you considered the operational view versus design view of subnetting yet?

Imagine you’ve gone to the beach with a team of friends and each person has been charged with building a sand castle or an object from sand, perhaps you may say, what has this got to do with Introduction to Subnetting from the Perspective of Design and Operation, well it does indeed have everything to do with it. The beach has an endless heap of sand readily available to your use and the weather is fantastic. You go on a nice trip to work on sand projects with the aim to create a competition amongst some friends.

Now each member of the team has been given a container to fill up with sand for their object but you have been delegated as the person responsible for giving the right amount to each individual for their selected objects based on the sizes chosen.

John has chosen to create a full size motorcycle, Jenny has chosen to create a mouse, Rebecca has chosen to create her pet dog, Kwabena has chosen to create a joystick and then the twins have decided to become the Wright brothers, you guessed it, they are creating an aircraft. Knowing the estimated sizes of their objects, you have provided each one a container to work within and have started to heap the sand for each of them.

Before undertaking a task as per the above scenario, what do you personally think should be his approach so no one is deficient of sand enough to cater for their sand objects?

Let us consider the following key points;

• Analyse Needs
• Choose Size Requirements (Sand)
• Plan how to apportion the Sand.

A big question to ask is this, will you give Jenny the same amount of sand as the Twins who wants to create a full sized aircraft? The answer is obvious, No! Someone may argue that this is a competition and so it does not matter, give them all the same portion and let them get on with it. This is not the best mindset as this will only incur waste.

So the best thing to do is measure a quantity equivalent or just slightly over the size of the object they are about to create so there is enough room for the creation of the object and any unforseeable adjustments they might need.

Translate our beach creation to the world of subnetting from the perspective of design and operation.

Consider the following diagram – Figure 1.0

Subnet Design: Class B 172.16.0.0 | First 3 Octets are Equal. | Figure 1.0 is our Sample Subnet Plan Document

In the design above, the entire network design depicts 5 separate networks broken down into three LANs and one each for the WAN links. Each subnet has the same value in the first 3 octets. For example, for the LAN on the left, the number shows 172.16.1._ meaning all addresses that begin with 172.16.1. Since this is a class B network and not all the subnets have been used, there is a great deal of room for improvement.

The skill of subnetting in designing is crucial for the network engineer. Do note that most times the role you take would have had some engineers beforehand who would have designed the network and planned the subnets before you arrived there. The concept is still very essential for you as will need to interpret what someone before you has already chosen. To completely grasp IP addressing and subnetting, you need to have a mindset from the perspective of design and operation. In our earlier example of Figure 1.0, I mentioned that the Subnet Design states that the first three octets of all the subnets were equal. A question you may ask is why was this convention chosen? Could there not have been any alternatives? Would the alternatives be better for the network today. As you can see, subnetting require a great deal of planned design rather than to operation. Let’s consider the following flow;

Figure 1.1

Analyse Needs

• Number of Subnets
• Number of Hosts per Subnet
• Size of Subnet

Design Subnets

• Choose Network
• Choose 1 Mask
• List all Subnets

Plan Implementation

• Subnets and their Locations
• Static IP
• DHCP Ranges

Let us break these down so we can have a deeper understanding of what needs doing.

Analyse Subnetting and Addressing Needs

• Which hosts should be grouped together into a subnet?
• How many sunbets does this network require?
• How many host IP addresses does each subnet require?
• Will we use a single subnet size for simplicity, or not?

Figure 1.2

Rules to consider for devices in each subnet

Every device that connects to an IP internetwork needs to have an IP address in order to do so. These devices include printers,IP phones, servers, mobile phones, tablets and end devices used by users. Major network devices like routers, switches, and firewalls must also have IP’s in order to internetwork.

Figure 1.3 – Identifying the Subnets

IP addresses must be assigned according to some fundamental rules and for for good reasons. To make routing work efficiently, IP addressing rules group addresses into groups called subnets. The rules are as follows:

Addresses in the same subnet are not separated by a router – look at figure 2.1
Addresses in different subnets are separated by at least one router – look at figure 2.2

Notice that PC A and B are in one subnet and PC C is in another subnet. For PC A to speak with PC C, at least one router (R1) would be required.

Determine the Number of Subnets

You would be given a document detailing the entire detail of your organisation’s internetwork. Once you have been given this document start applying the rules.

Consider the following:
Network Diagrams
VLAN configuration details
WAN technology used( MPLS, Frame-Relay, VPLS, Metronet, etc) Based on this information, use the above rules and plan one subnet for every;

1. VLAN
2. Point-to-point Serial link
3. Ethernet emulation WAN link (EoMPLS)
4. Frame Relay PVC.

In the above diagram, there is a clear indication of expected hosts per subnet and so it makes out design and implemention of a subnet scheme a little less daunting. I will be going through a simple method in performing subnetting in another article. Look out for more and You might also enjoy reading my article on Inter-VLAN Routing.

Good Resource for Further Study:
Get more advanced in-depth knowledge in Routing and Switching from the world’s most renown author in Networking.