Introduction
Networking is a necessary aspect of modern technology, and understanding subnet masks is essential for anyone involved in network design or administration. Smarthost is pleased to provide this Subnet Mask Cheat Sheet which provides a clear and concise reference for subnetting.
This cheat sheet is particularly valuable for network admins, aiding them in effectively managing and distributing IP addresses within networks.
Whether you’re a seasoned professional or just starting, this cheat sheet will enhance your networking toolkit.
Further details on Subnetting can be found here: RFC 1878.
What is a Subnet Mask?
Understanding the Basics A subnet mask is a 32-bit number that divides the IP address into network and host parts. It’s used in IP networking to create subnetworks, allowing for efficient use of IP addresses and improved network security and performance.
Practical Use of Subnet Masks
Subnet masks enable the division of an IP address space into multiple network segments, managing and optimising network traffic. Each class of IP address (Class A, Class B, and Class C) has a distinct default subnet mask that determines how the IP address is split between the network ID and host ID, impacting the number of usable addresses in that network. This is important in large networks where managing traffic and resources efficiently is key.
How to Utilise the Cheat Sheet
The subnet mask cheat sheet is a valuable resource for network administrators and IT professionals. To utilise the cheat sheet effectively, follow these steps:
- Identify the IP Address Range: Determine the IP address range you want to work with. This is the starting point for your subnetting process.
- Determine the Subnet Mask: Decide on the subnet mask you want to use based on your network requirements.
- Look Up the Subnet Mask: Refer to the cheat sheet to find the corresponding number of subnets, hosts, and subnet size for the chosen subnet mask.
- Plan and Configure: Use the information from the cheat sheet to plan and configure your network. This includes setting up the network ID, broadcast address, and usable IP addresses.
- Refer as Needed: Keep the cheat sheet handy for quick reference to subnet mask values and their corresponding details.
By following these steps, you can efficiently manage your IP address space and ensure optimal network performance.
Understanding Subnetting
Subnetting is the process of dividing a large IP address space into smaller, more manageable sub-networks. This is achieved by using a subnet mask to distinguish between the network ID and the host ID within an IP address. Subnetting allows for better organisation and utilisation of IP addresses, enhancing network security and performance. By breaking down a large network into smaller subnets, network administrators can reduce network congestion and improve overall efficiency.
IP Address Blocks
IP address blocks are groups of IP addresses allocated to a specific network or organisation. These blocks can be divided into smaller sub-networks through the process of subnetting. By doing so, network administrators can create more manageable and secure networks. Subnetting within IP address blocks allows for efficient use of IP addresses, ensuring that each device on the network has a unique IP address while optimising network traffic and performance.
IP Address Blocks and Subnetting
IP address blocks can be divided into smaller sub-networks using subnetting. This technique allows for more efficient use of IP addresses and enhances network security and performance. By creating smaller sub-networks within a larger IP address block, network administrators can better manage and secure the network. Subnetting helps in allocating IP addresses more effectively, reducing the risk of IP address conflicts, and improving overall network traffic management.
How to Utilise the Cheat Sheet
This Subnet Mask Cheat Sheet lists various subnet masks along with the corresponding number of addresses, hosts, and the size of each subnet. It’s an easy-to-reference guide for quickly determining the subnetting information you need.
Before putting subnets into production, it is essential to test the IP range to ensure correct communication within the subnet. You can use a laptop to acquire IP space or statically assign addresses to confirm the accuracy of Node/Network IDs.
| Addresses | Hosts | Netmask | Amount of a Class C | |
|---|---|---|---|---|
| /30 | 4 | 2 | 255.255.255.252 | 1/64 |
| /29 | 8 | 6 | 255.255.255.248 | 1/32 |
| /28 | 16 | 14 | 255.255.255.240 | 1/16 |
| /27 | 32 | 30 | 255.255.255.224 | 1/8 |
| /26 | 64 | 62 | 255.255.255.192 | 1/4 |
| /25 | 128 | 126 | 255.255.255.128 | 1/2 |
| /24 | 256 | 254 | 255.255.255.0 | 1 |
| /23 | 512 | 510 | 255.255.254.0 | 2 |
| /22 | 1024 | 1022 | 255.255.252.0 | 4 |
| /21 | 2048 | 2046 | 255.255.248.0 | 8 |
| /20 | 4096 | 4094 | 255.255.240.0 | 16 |
| /19 | 8192 | 8190 | 255.255.224.0 | 32 |
| /18 | 16384 | 16382 | 255.255.192.0 | 64 |
| /17 | 32768 | 32766 | 255.255.128.0 | 128 |
| /16 | 65536 | 65534 | 255.255.0.0 | 256 |
Sub Class C Blocks
This section of the subnet mask cheat sheet provides information on sub-class C blocks. Sub-class C blocks are used to divide a Class C IP address into smaller subnets. In Class B IP addresses, network addresses are defined by the first two octets for the network ID and the subsequent two octets for the host ID, which has significant implications for subnetting within organisational network architecture.
/25 — 2 Subnets — 126 Hosts / Subnet
This indicates a Class C IP address with a 25-bit subnet mask, allowing for 2 subnets with 126 hosts per subnet. The remaining 7 bits represent the host ID, with 126 available addresses due to the removal of the network address and broadcast address.
| Network # | IP Range | Broadcast |
|---|---|---|
| .0 | .1 – .126 | .127 |
| .128 | .129 – .254 | .255 |
/26 — 4 Subnets — 62 Hosts / Subnet
The /26 notation indicates a Class C IP address with a 26-bit subnet mask, allowing for 4 subnets with 62 hosts per subnet. The remaining 6 bits represent the host ID, with 62 available addresses due to the removal of the network address, broadcast address, and 2 reserved IP addresses (.0 and .255) in each subnet.
| Network # | IP Range | Broadcast |
|---|---|---|
| .0 | .1 – .62 | .63 |
| .64 | .65 – .126 | .127 |
| .128 | .129 – .190 | .191 |
| .192 | .193 – .254 | .255 |
/27 — 8 Subnets — 30 Hosts / Subnet
The /27 notation indicates a Class C IP address with a 27-bit subnet mask, allowing for 8 subnets with 30 hosts per subnet.
| Network # | IP Range | Broadcast |
|---|---|---|
| .0 | .1 – .30 | .31 |
| .32 | .33 – .62 | .63 |
| .64 | .65 – .94 | .95 |
| .96 | .97 – .126 | .127 |
| .128 | .129 – .158 | .159 |
| .160 | .161 – .190 | .191 |
| .192 | .193 – .222 | .223 |
| .224 | .225 – .254 | .255 |
/28 — 16 Subnets — 14 Hosts/Subnet
The /28 notation indicates a Class C IP address with a 28-bit subnet mask, allowing for 16 subnets with 14 hosts per subnet.
| Network # | IP Range | Broadcast |
|---|---|---|
| .0 | .1-.14 | .15 |
| .16 | .17-.30 | .31 |
| .32 | .33-.46 | .47 |
| .48 | .49-.62 | .63 |
| .64 | .65-.78 | .79 |
| .80 | .81-.94 | .95 |
| .96 | .97-.110 | .111 |
| .112 | .113-.126 | .127 |
| .128 | .129-.142 | .143 |
| .144 | .145-.158 | .159 |
| .160 | .161-.174 | .175 |
| .176 | .177-.190 | .191 |
| .192 | .193-.206 | .207 |
| .208 | .209-.222 | .223 |
| .224 | .225-.238 | .239 |
| .240 | .241-.254 | .255 |
/29 — 32 Subnets — 6 Hosts/Subnet
| Network # | IP Range | Broadcast |
|---|---|---|
| .0 | .1-.6 | .7 |
| .8 | .9-.14 | .15 |
| .16 | .17-.22 | .23 |
| .24 | .25-.30 | .31 |
| .32 | .33-.38 | .39 |
| .40 | .41-.46 | .47 |
| .48 | .49-.54 | .55 |
| .56 | .57-.62 | .63 |
| .64 | .65-.70 | .71 |
| .72 | .73-.78 | .79 |
| .80 | .81-.86 | .87 |
| .88 | .89-.94 | .95 |
| .96 | .97-.102 | .103 |
| .104 | .105-.110 | .111 |
| .112 | .113-.118 | .119 |
| .120 | .121-.126 | .127 |
| .128 | .129-.134 | .135 |
| .136 | .137-.142 | .143 |
| .144 | .145-.150 | .151 |
| .152 | .153-.158 | .159 |
| .160 | .161-.166 | .167 |
| .168 | .169-.174 | .175 |
| .176 | .177-.182 | .183 |
| .184 | .185-.190 | .191 |
| .192 | .193-.198 | .199 |
| .200 | .201-.206 | .207 |
| .208 | .209-.214 | .215 |
| .216 | .217-.222 | .223 |
| .224 | .225-.230 | .231 |
| .232 | .233-.238 | .239 |
| .240 | .241-.246 | .247 |
| .248 | .249-.254 | .255 |
/30 — 64 Subnets — 2 Hosts/Subnet
| Network # | IP Range | Broadcast |
|---|---|---|
| .0 | .1-.2 | .3 |
| .4 | .5-.6 | .7 |
| .8 | .9-.10 | .11 |
| .12 | .13-.14 | .15 |
| .16 | .17-.18 | .19 |
| .20 | .21-.22 | .23 |
| .24 | .25-.26 | .27 |
| .28 | .29-.30 | .31 |
| .32 | .33-.34 | .35 |
| .36 | .37-.38 | .39 |
| .40 | .41-.42 | .43 |
| .44 | .45-.46 | .47 |
| .48 | .49-.50 | .51 |
| .52 | .53-.54 | .55 |
| .56 | .57-.58 | .59 |
| .60 | .61-.62 | .63 |
| .64 | .65-.66 | .67 |
| .68 | .69-.70 | .71 |
| .72 | .73-.74 | .75 |
| .76 | .77-.78 | .79 |
| .80 | .81-.82 | .83 |
| .84 | .85-.86 | .87 |
| .88 | .89-.90 | .91 |
| .92 | .93-.94 | .95 |
| .96 | .97-.98 | .99 |
| .100 | .101-.102 | .103 |
| .104 | .105-.106 | .107 |
| .108 | .109-.110 | .111 |
| .112 | .113-.114 | .115 |
| .116 | .117-.118 | .119 |
| .120 | .121-.122 | .123 |
| .124 | .125-.126 | .127 |
| .128 | .129-.130 | .131 |
| .132 | .133-.134 | .135 |
| .136 | .137-.138 | .139 |
| .140 | .141-.142 | .143 |
| .144 | .145-.146 | .147 |
| .148 | .149-.150 | .151 |
| .152 | .153-.154 | .155 |
| .156 | .157-.158 | .159 |
| .160 | .161-.162 | .163 |
| .164 | .165-.166 | .167 |
| .168 | .169-.170 | .171 |
| .172 | .173-.174 | .175 |
| .176 | .177-.178 | .179 |
| .180 | .181-.182 | .183 |
| .184 | .185-.186 | .187 |
| .188 | .189-.190 | .191 |
| .192 | .193-.194 | .195 |
| .196 | .197-.198 | .199 |
| .200 | .201-.202 | .203 |
| .204 | .205-.206 | .207 |
| .208 | .209-.210 | .211 |
| .212 | .213-.214 | .215 |
| .216 | .217-.218 | .219 |
| .220 | .221-.222 | .223 |
| .224 | .225-.226 | .227 |
| .228 | .229-.230 | .231 |
| .232 | .233-.234 | .235 |
| .236 | .237-.238 | .239 |
| .240 | .241-.242 | .243 |
| .244 | .245-.246 | .247 |
| .248 | .249-.250 | .251 |
| .252 | .253-.254 | .255 |
In-depth Guide
Detailed Explanations of Subnetting Options
Dive into Subnetting
Subnetting involves dividing a network into smaller parts, called subnets. Each subnet is represented by a subnet mask. Subnetting is an essential skill for network admins, as it helps in effectively managing and distributing IP addresses within networks. The cheat sheet provides a range of subnet masks from /30 to /16, detailing the number of possible addresses, the number of usable hosts, and how much of a Class C network each represents.
Example of a Subnet Mask
Consider a /24 subnet mask, which is represented as 255.255.255.0. This allows for 256 addresses with 254 usable hosts. It’s equivalent to one Class C network. This is commonly used in small to medium-sized networks.
Each class of IP address has a distinct default subnet mask that determines how the IP address is split between the network ID and host ID. For example, Class A has a default subnet mask of 255.0.0.0, Class B has 255.255.0.0, and Class C has 255.255.255.0. These default subnet masks impact the number of usable addresses in each network.
Understanding Larger Subnets
Larger subnets like /16 (255.255.0.0) allow for more hosts, suitable for larger networks. This subnet mask provides 65,536 addresses, with 65,534 hosts usable, representing 256 Class C networks.
Smaller Subnets for Efficiency
Conversely, a smaller subnet like /30 (255.255.255.252) allows for 4 addresses with 2 usable hosts, ideal for small networks or point-to-point links.
Understanding subnet masks and their application is key to efficient network management. It is important to test the newly configured subnets to ensure correct communication within the allowed IP range. We encourage you to use the Subnet Mask Cheat Sheet as a reference in your networking tasks. For further assistance or information, our support team is always ready to help.
Frequently Asked Questions about Subnet Masks
A subnet mask is a 32-bit number that divides 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 within the network.
Subnet masks are used to divide a large IP address space into smaller, more manageable networks. This is important because it allows us to improve network security, performance, and efficiency.
Each class of IP address (A, B, C) has a distinct default subnet mask that determines how the IP address is split between the network ID and host ID, impacting the number of usable addresses in that network.
There are two main types of subnet masks: classful subnet masks and classless subnet masks. Classful subnet masks are based on the class of the IP address, while classless subnet masks are more flexible and can be used to create a wider variety of subnetting schemes.
An IPv4 subnet cheat sheet is a practical tool for network administrators. It helps understand relationships between subnets, utilise binary to decimal conversions, determine broadcast addresses, and support subnet management, thus optimising performance and ensuring efficient IP address allocation.
There are many benefits to subnetting, including:
Improved network security: By dividing a large network into smaller subnets, we can make it more difficult for unauthorised users to access the network.
Enhanced network performance: Subnetting can help to reduce network congestion and improve overall performance.
Improved network efficiency: By using subnets, we can allocate IP addresses more efficiently and avoid wasting IP addresses.
Subnetting is an essential skill for network admins, as it plays an essential role in effectively managing and distributing IP addresses within networks.
There are several challenges associated with subnetting, including:
– Complexity: Subnetting can be a complex topic to understand and implement.
– Configuration: Configuring routers and other network devices to support subnetting can be time-consuming and error-prone.
– Management: Managing a large number of subnets can be challenging.
It is important to test the newly configured subnets to ensure correct communication within the allowed IP range. This can be done by using a laptop to acquire IP space or by statically assigning addresses to confirm the accuracy of Node/Network IDs before the subnets are put into production.
Subnetting is typically done by network administrators who are responsible for designing, implementing, and managing large networks.
Subnetting is an essential skill for network admins and IT professionals, as it plays an essential role in effectively managing and distributing IP addresses within networks.
