Introduction
Networking is a crucial 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
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. This is crucial in large networks where managing traffic and resources efficiently is key.
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.
| 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.
/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. 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.
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.
Summary
Understanding subnet masks and their application is key to efficient network management. 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
What is a subnet mask?
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.
Why do we use subnet masks?
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.
What are the different types of subnet masks?
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.
How do I calculate the number of subnets and hosts in a subnet?
There are some methods for calculating the number of subnets and hosts in a subnet, but the most common is to use the binary representation of the subnet mask.
What are the benefits of subnetting?
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.
What are some of the challenges of subnetting?
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.
Who should subnet?
Subnetting is typically done by network administrators who are responsible for designing, implementing, and managing large networks
