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What is Subnetting?

As computer networks have grown significantly since the early '90s, network management has become increasingly essential. Sub-networks are a crucial competence for any network administrator or security administrator who supports a network environment (simply, subnet). A subnet can be a point-to-point link and a local area network (LAN) isolated in the network topology on the Internet. Subnetting is a technique for dividing a large network into several smaller networks. A subnet is a group of devices, each of which has its IP address and is connected to the others via the same connecting channel.

It is fairly simple to build subnets using IP addresses so that a single network address can be used for multiple networks. It makes sense to divide networks into smaller ones connected by routers if an organization is large or the computers are distributed.

Subnetting

Figure 1. Subnetting

What is IP Address?

An IP address is a 32-bit identification assigned to each device on a network (as defined by RFC 761). It identifies a device's precise location on the network. When we think of a network, we normally think of a group of workstations connected to a local area network via one or more servers. To differentiate itself from other computers, each server and workstation would be assigned a unique address. Servers and workstations are all referred to as hosts in IP addressing; however, each address not only identifies a host but also the network address on which the host is located. This is because IP is a protocol that permits connection not only between hosts on separate networks but also between hosts on the same network.

The 32-bit IP address is formatted as <net id, host id> and is normally shown as four bytes of data. Although each byte can be expressed as a binary, decimal, or hexadecimal value, the decimal-dot-decimal format is the most widely used. IPv4 is the widely used IP addressing standard, requiring 32-bit addresses. Although IPv6 was established in response to the rapid growth of the Internet, it appeared to supply more than enough addresses at first, but there was an initial assignment and the IP address class structure was inefficient. The notion of subnetting was developed with RFC 950 to make efficient use of IP addresses.

IP addresses can vary from 0.0.0.0 to 255.255.25.255. For example, while 104.21.8.248 is a valid IP address, determining which part of the address is the network ID and which portion is the host ID might be challenging. To comprehend the two, you must be familiar with class addressing.

What is IP Class?

For the tiny number of networks with a big number of nodes, the Internet's designer chose to define types of networks based on network size. The class designation of one's network determines how an IP address is subdivided into a network and node address. IP addresses are classified into one of five classes (as defined by RFC 761): A, B, C, D, or E. Different possible combinations of networks and host addresses are defined by classes A, B, and C. Class D is reserved for multicasting (the capacity of one host to communicate with many other hosts with a single broadcast, which is outside the scope of this article). Class E will be used in the future. A, B, and C are the subnetting classes of interest.

The first byte of a class A address is used to identify the network address, while the subsequent three bytes are used to identify the hosts. The first two bytes of a class B address are used to identify the network address, while the subsequent two bytes are used to identify the hosts. The first three bytes of a class C address are used to identify the network address, while the last byte is used to identify the hosts.

The following table summarizes the three classes of networks.

IP Class1. Octet2. Octet3. Octet4. Octet
Class ANetwork_id (8-bit) 0 - - - - - - -Host_id (8-bit) - - - - - - - -Host_id (8-bit) - - - - - - - -Host_id (8-bit) - - - - - - - -
Class BNetwork_id (8-bit) 1 0 - - - - - -Network_id (8-bit) - - - - - - - -Host_id (8-bit) - - - - - - - -Host_id (8-bit) - - - - - - - -
Class CNetwork_id (8-bit) 1 1 0 - - - - -Network_id (8-bit) - - - - - - - -Network_id (8-bit) - - - - - - - -Host_id (8-bit) - - - - - - - -

The first octet of the IP address, particularly the first few bits of the first octet, was used to determine which class a particular network belonged to. A default subnet mask and a private address range are assigned to each of these classes. The first bit in a class A address must be zero. The first two bits of a class B address must be '10'. The first three bits of the class C address must be a '110'.

What are the Subnetting Types?

There are two types of subnetting: static and variable length.

1. Variable Length Subnetting

The subnets that build the network can employ different subnet masks when variable-length subnetting is implemented. A subnet mask that allows only this few hosts is required for a tiny subnet with only a few hosts. To support a high number of hosts, a subnet with many hosts may require a distinct subnet mask. The ability to assign subnet masks based on the needs of individual subnets will aid in network address preservation. In addition, by adding another bit to the subnet mask, a subnet can be split into two pieces. The update has no effect on other subnets in the network. By altering the subnet mask for each network, variable-length subnetting allows you to partition the network and specify suitable hosts for each subnet. This can be accomplished by properly setting the routers. Please keep in mind that variable-length subnetting is not supported by all hosts and routers. Variable-length subnetting should be utilized if various numbers of hosts are required for each network. Only the necessary networks will be assigned, and routing issues will be resolved by isolating networks using routers that enable variable subnetting. A host that does not allow variable subnetting would have to link to a router that does.

2. Static Subnetting

All subnets in a subnetted network have the same subnet mask, which is known as static subnetting. This is straightforward to set up and maintain, but it wastes address space in small networks. A network of four hosts with a subnet mask of 255.255.255.0, for example, wastes 250 IP addresses. It also makes reorganizing the network with a new subnet mask more complex. Static subnetting must be supported by all hosts and routers.

3. Mixing Static and Variable Length Subnetting

At first glance, the existence of a server that only supports static subnetting appears to preclude the usage of variable-length subnetting anyplace in the network. Thankfully, this isn't the case. The routing protocols used can hide the difference between subnet masks from the hosts in a subnet if the routers linking subnets with different subnet masks use variable-length subnetting. Hosts can continue to use basic IP routing while delegating all subnetting complications to dedicated routers.

How Does Subnetting Work?

Partition your network into subnets instead of requesting extra address blocks for each network, allowing you to use one block of addresses on several physical networks. Extended network addresses are used to subnet individual computer (and another network device) addresses. A network address with additional bits that specify the subnet number is known as an extended network address.

How does Subnetting work?

Figure 2. How does Subnetting work?

Subnet devices will appear as a series of IP-scoped interfaces that are accessed by the same route in the network topology, i.e., the final interface occurring in the route towards each subnet interface is the same for each route. A subnet should contain at least one interface that relates to the last router that crossed it before linking it, and so looks one hop closer to the measurement vantage point than other subnets.

How Subnetting is Done?

The Internet cosmos was originally viewed as a two-level hierarchy, with the Internet as a whole at the top and individual networks at the bottom, each with its network number. The Internet does not have a hierarchical structure, but it does have a hierarchical interpretation of addresses. Each host perceives its network as a single entity in this two-level concept; the network can be thought of as a "black box" to which a group of hosts is attached. While this perspective has proven to be straightforward and effective, several businesses have found it to be insufficient, and have added a third approach to the explanation of Internet addresses. A given Internet network is separated into a group of subnets in this approach.

To establish subnetworks, reserve bits (x bits) from the IP address's host component to specify the subnet address. This means that there are fewer bits available for designating hosts as the number of subnets increases.

Simple steps in subnetting:

  • Identify the class of network
  • Default netmask
  • Number of networks = 2^x
  • Number of hosts per network = 2^(available bits - x) - 2

Example: Subnetting Example

Figure 3. Subnetting Example

In this scenario, you use a subnet mask to divide your network into four subnets, making the network address larger and the available range of host addresses fewer. In other words, you're 'borrowing' some of the bits that would normally be used for the host address and utilizing them for the network component. The subnet mask 255.255.255.192 is divided into four networks, each with 62 hosts.

Why is Subnetting Used?

Routers connect subnets and improve network performance by decreasing traffic and limiting disturbance caused by broadcast messages. When subnets are used, large networks become more manageable.

Subnetting is critical for a number of reasons:

  • Reduced Network Traffic: We can partition the network into as many smaller networks as we need by subnetting it, which also lessens traffic and hides the network's complexity.
  • Optimized network performance: Network performance is improved when network traffic is reduced.
  • Simplified management: Identify and address network problems more quickly in a group of smaller networks than in a single large network.
  • Security: Subnetting improves network security by allowing communication between computers on the same subnet while blocking access from systems on other subnets.
  • Facilitates spanning of large Geographical distance: A single huge network that spans extensive distances might cause problems in every location because WAN connectivity is slower and more expensive than LAN links. The system is more efficient when numerous smaller networks are connected.

What Sort of Networks Would be Best for Subnetting?

Subnets aren't necessary for small networks. Large LANs, on the other hand, are ideal candidates since IP address allocation will have a significant impact while grouping devices to maximize organization.

How Many Hosts Can You Have in Your Subnet?

It's critical to figure out how many hosts you can have in your subnet since you don't want to end up with a subnet that's either too tiny to accommodate all of the IP addresses you require or one that's too huge and wasteful. The total number of hosts a subnet can have; is calculated by subtracting the number of network bits from the total number of bits: 32 total bits minus the number of network bits. Let's use the number 28 as an example.

Six bits are provided for host IP addresses in a subnet with 28 network bits. The network IP address and the broadcast address must then be subtracted from the total.

So, the calculation is as follows:

2^(32-28) - 2 = 2^4 - 2 = 14

You can use this to calculate how many network bits you have available to build hosts for your subnet with any number of network bits.

What is Public Subnet?

A routing table with a route to an internet gateway is connected with a public subnet.

The public subnet instances can send outbound traffic straight to the internet, whereas the private subnet instances cannot. Instead, instances in the private subnet can connect to the internet using a public subnet-based network address translation (NAT) gateway. The database servers can use the NAT gateway to connect to the internet for software updates, but the internet cannot connect to the database servers.

What is the Purpose of a Subnet Mask?

To generate subnets, you'll need a subnet mask, which specifies which bits from the 32-bit IP addresses will be utilized to form the new network address. We construct a 32-bit IP address that reflects <net id, subnet id> as our new network address by 'ANDing' the 32-bit IP address with a 32-bit mask.

To transform host bits into network bits, we need to move the mask bits to the right (changing 0 bits into 1s) to establish more network addresses (subnets). This method generates a large number of subnets.

What is a Subnet Mask Address?

The TCP/IP protocol uses the subnet mask to detect whether a host is on a local subnet or a faraway network. The components of the IP address used as network and host addresses are not defined in TCP/IP. This information is provided in the form of a subnet mask, which is a 32-bit value.

When you apply a subnet mask to an IP address, you can tell which parts of the address are network and which are nodes.

When you view an IP address, you'll notice that it's always accompanied by a number that looks like one of the following:

  • 255.0.0.0 (Class A)
  • 255.255.0.0 (Class B)
  • 255.255.255.0 (Class C)

What is a Subnet Mask for XBOX One?

The most frequent Subnet masks are 255.255.255.0 (in Europe and North America) and 255.0.0.0 (in the rest of the world) depending on network size and user location. Because there is no actual value in changing subnet masks, it is recommended to keep them as default or automatic. Furthermore, Subnet Masks and IP addresses are linked, with the IP address relying on the Subnet Mask to function effectively and connect devices to the internet.

Note down the Subnet Mask/Default Gateway/DNS currently in use for your games console, and then re-enter these numbers when configuring your internet connection manually to ensure that you utilize the right Subnet Mask along with any custom IP. In other words, only the IP value changes when you configure a static/custom IP; the Subnet Mask and Default Gateway are already defined by your ISP or network administrator and should not be changed.

What is a Subnet Mask for Android?

You'll want to go to the Play Store and download a network information app. Another option is to download a terminal emulator app and run the command ifconfig to examine the network interfaces, their IP addresses, and netmasks, as Android is based on a modified version of Linux.

What is a Subnet in AWS?

To understand how AWS subnets function with VPC or Amazon VPC (virtual private cloud), consider the following example.

A VPC in AWS is like an apartment that separates your facilities from those of other customers on the Amazon Cloud. It's up to you to create your own Amazon network. A VPC can be compared to an apartment, with databases serving as the furnishing and goods. The walls of your apartment segregate and safeguard your belongings from the colony's other residents.

Subnets are individual rooms in your residence that correspond to a slice of the CIDR block defined in your VPC. Subnets allow you to assign multiple access rules to resources and arrange them in distinct containers based on those restrictions. You wouldn't install a database with sensitive information in a public subnet that allows any network traffic, just like you wouldn't put a wide-open window in your bathroom on the shower wall so others can see you nude. You could place the database on a separate network (i.e. a locked closet).

What is a Subnet Range?

When designing a network, we must always consider how many addresses the network will require. In addition, we'd like to know the IP address range in our network so that we may allocate an address to each device. A subnet mask is an integer that specifies the possible IP address range on a network. A single subnet mask limits the number of valid IP addresses for a network. Several subnet masks can be used to partition a single network into smaller networks (called subnetworks or subnets).

We treat IP addresses as 32-bit numbers with a subnet mask of and a subnet mask of 'x'. The number of possible addresses can be simply calculated using the formula 2^(32-x).

What is a Subnet Zero?

Because all of the bits in the subnet field of the IP address are set to '0,' the initial subnet we acquire from the subnetting procedure, 96.0.0.0, is known as All-Zeros-Subnet or Subnet-Zero. The following is the result of converting decimal to binary:

96.0.0.0 = 01100000. 00011000. 00011000. 00011000

The three red bits were "taken" from the host field and utilized to generate the subnet field. As can be seen, they are all set to zero in the Subnet-Zero. Because of the confusion caused by having a network and a subnet with indistinguishable addresses, the usage of subnet-zero for addressing was discouraged.

What is a Subnet of my IP Address?

Check your route table if you're on a host. A network route will appear. Your mask is /16 if your network address is 192.168. If your network address is 192.168.100, your mask is /24. /N indicates that the majority of the bills in your mask are ones. /16 refers to the IP address 255.255.0.0. To view your route table, use the netstat or route commands.