Calculate subnet masks, network ranges, and CIDR details online.
TempGBox
Subnet Calculator
Calculate subnet information from IP address and CIDR notation. Get network address, broadcast address, subnet mask, and more.
💡 CIDR Notation:
What is Subnet Calculator?
Subnet Calculator helps with Subnet Calculator Online. Calculate subnet information from IP address and CIDR notation. Get network address, broadcast address, subnet mask, and more.
TempGBox keeps the workflow simple in your browser, so you can move from input to result quickly without extra software.
How to use Subnet Calculator
- Open Subnet Calculator and enter the text, value, file, or settings you want to work with.
- Review the output and adjust the available options until the result matches your use case.
- Copy, download, or reuse the final result in your workflow, content, app, or support task.
Why use TempGBox Subnet Calculator?
- Calculate subnet information from IP address and CIDR notation. Get network address, broadcast address, subnet mask, and more
- Useful for Subnet Calculator Online
- Fast browser-based workflow with no signup required
Common uses for Subnet Calculator
Subnet Calculator is useful for Subnet Calculator Online. It fits well into quick checks, repeated office work, development flows, content updates, and everyday browser-based problem solving.
Because the tool is available instantly on TempGBox, you can handle one-off tasks and repeated workflows without installing extra software.
FAQ
Is Subnet Calculator free to use?
Yes. Subnet Calculator on TempGBox is free to use and does not require signup before you start.
What is Subnet Calculator useful for?
Subnet Calculator is especially useful for Subnet Calculator Online.
Understanding Subnet Calculator
CIDR (Classless Inter-Domain Routing) notation replaced the rigid Class A/B/C system in 1993. A CIDR prefix like /24 specifies how many of the 32 bits in an IPv4 address identify the network, with the remaining bits identifying hosts. The subnet mask is the binary representation of this division: a /24 prefix produces the mask 11111111.11111111.11111111.00000000, or 255.255.255.0 in dotted decimal. The network address is obtained by ANDing the IP with the mask; the broadcast address by ORing the IP with the inverted mask.
Every subnet has two reserved addresses: the network address (all host bits set to 0) and the broadcast address (all host bits set to 1). A /24 subnet has 256 total addresses (2^8), but only 254 are usable for hosts. A /30 subnet has 4 addresses, with only 2 usable — making it the standard choice for point-to-point links between routers. A /31 was historically unusable (0 host addresses), but RFC 3021 permits /31 for point-to-point links by eliminating the broadcast address requirement.
Variable Length Subnet Masking (VLSM) is the practice of using different prefix lengths within the same address block to allocate subnets of varying sizes. An organization with a /16 block (65,534 hosts) can carve it into a /24 for a 200-person office (254 hosts), a /28 for a 10-device server VLAN (14 hosts), and multiple /30 subnets for router links (2 hosts each). VLSM eliminates the waste inherent in fixed-size subnetting, where a /24 would be allocated to a 5-device network, leaving 249 addresses unused.
IPv4 address exhaustion has made efficient subnetting critical. The total IPv4 address space is approximately 4.3 billion addresses, and IANA allocated the last /8 blocks in 2011. Organizations must justify their allocations to regional registries, and wasteful subnetting (using /24 blocks for 5-host networks) is a disqualifying factor. Proper VLSM ensures every allocated address serves a purpose, which is also a security best practice — smaller subnets reduce the broadcast domain and limit the blast radius of network attacks.
Step-by-Step Guide
- Enter an IPv4 address and CIDR prefix length (e.g., 192.168.1.0/24) or an IPv4 address with a subnet mask in dotted-decimal format (e.g., 192.168.1.0 with mask 255.255.255.0).
- View the calculated network address, broadcast address, usable host range (first usable to last usable), and total number of usable host addresses.
- Examine the binary representation of the subnet mask to visualize the network/host bit boundary. The contiguous 1-bits represent the network portion; the 0-bits represent the host portion.
- Check the wildcard mask (inverse of the subnet mask), used in access control lists (ACLs) on Cisco routers and in OSPF area configurations.
- For VLSM planning, calculate multiple subnets by adjusting the prefix length. Increasing the prefix by 1 (e.g., /24 to /25) halves the subnet size, doubling the number of subnets.
- Verify whether a given IP address falls within a specific subnet by comparing the network addresses. Two addresses are in the same subnet if ANDing each with the subnet mask produces the same network address.
- Review the subnet class (legacy classful designation) and whether the address falls within a private range (RFC 1918: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16).
Real-World Use Cases
A network engineer designing a corporate LAN allocates a /24 for the main office (200 employees), a /27 for the server VLAN (20 servers), a /28 for the management VLAN (10 network devices), and /30 subnets for each router-to-router link, all carved from a /21 supernet.
A cloud architect configuring a VPC in AWS uses the calculator to divide a 10.0.0.0/16 VPC into public subnets (/24 in each availability zone), private subnets (/22 for application servers), and database subnets (/26 for RDS instances).
A student studying for the CCNA exam practices subnetting by entering various addresses and prefix lengths, verifying their manual calculations against the calculator and building intuition for which prefix length fits a given host count requirement.
A security analyst investigates an incident by checking whether a suspicious IP address (10.42.17.200) falls within the allowed subnet for a particular VLAN (10.42.16.0/22). The calculator confirms 10.42.17.200 is within 10.42.16.0 - 10.42.19.255.
A system administrator configuring a Docker bridge network needs a /28 subnet that does not overlap with the corporate 10.0.0.0/8 range. The calculator helps identify a suitable 172.18.0.0/28 allocation within the RFC 1918 private space.
Expert Tips
Memorize the key prefix-to-hosts mapping: /24=254, /25=126, /26=62, /27=30, /28=14, /29=6, /30=2. The pattern is 2^(32-prefix) - 2. This mental shortcut eliminates calculator dependence for common subnetting questions.
When designing a network, allocate subnets from largest to smallest within the address block. Start with the biggest subnet first, then fill remaining space with progressively smaller subnets. This prevents fragmentation that could block future expansion.
Always leave room for growth. If a VLAN currently has 50 devices, a /26 (62 hosts) leaves almost no room for expansion. A /25 (126 hosts) provides 150% headroom, which is a reasonable planning margin for a 3-5 year horizon.
Frequently Asked Questions
What does /24 mean in CIDR notation?
The /24 indicates that the first 24 of the 32 bits in the IPv4 address identify the network, leaving 8 bits for host addresses. This produces a subnet mask of 255.255.255.0 and allows 254 usable host addresses (2^8 - 2, subtracting network and broadcast addresses).
Why are two addresses reserved in every subnet?
The network address (all host bits 0) identifies the subnet itself and cannot be assigned to a device. The broadcast address (all host bits 1) sends packets to all hosts in the subnet. A /24 has 256 addresses but only 254 are assignable to hosts.
What is a wildcard mask?
A wildcard mask is the bitwise inverse of the subnet mask. For a /24 (mask 255.255.255.0), the wildcard is 0.0.0.255. It is used in Cisco ACLs and OSPF to indicate which bits of an address to match (0 = must match) and which to ignore (1 = don't care).
What is the smallest usable subnet?
A /30 provides 4 addresses with 2 usable hosts, making it the standard for point-to-point router links. RFC 3021 also allows /31 for point-to-point links (2 addresses, no broadcast), and /32 identifies a single host address, used in routing table entries and loopback interfaces.
What is VLSM and why does it matter?
Variable Length Subnet Masking allows using different prefix lengths within the same address block. Without VLSM, a network with segments of 200, 10, and 2 hosts would need three /24 subnets (762 addresses, 550 wasted). With VLSM, you use a /24, a /28, and a /30 (270 addresses, 58 wasted).
How do I check if two subnets overlap?
Two subnets overlap if any address belongs to both. The simplest check is to verify that neither subnet's range (network address to broadcast address) contains addresses from the other. If one subnet's network address falls within the other's range, they overlap.
Privacy: All subnet calculations are performed locally in your browser using standard arithmetic. No IP addresses, network configurations, or usage data are transmitted to any server.