IPFYI

Subnet Calculator

Calculate subnet details from CIDR notation or subnet mask. Find network address, broadcast, host range, and wildcard mask.

Calculator

Presets:
Ağ Adresi
Yayın Adresi
First Usable Host
Last Usable Host
Alt Ağ Maskesi
Joker Maske
Toplam Adres
Kullanılabilir Ana Makineler
CIDR Gösterimi
IP Sınıfı
İkili Alt Ağ Maskesi

Yaygın Alt Ağ Maskeleri

CIDR Alt Ağ Maskesi Kullanılabilir Ana Makineler Typical Use
/32255.255.255.2551Host route, loopback
/31255.255.255.2542Point-to-point link
/30255.255.255.2522WAN link (legacy)
/28255.255.255.24014Small office
/24255.255.255.0254Standard LAN
/16255.255.0.065,534Campus network
/8255.0.0.016,777,214Large enterprise

How to Use

  1. 1
    Enter the IP address and CIDR prefix

    Type an IPv4 address (e.g., 192.168.1.0) and select a CIDR prefix length (0-32), or enter the full CIDR notation like 192.168.1.0/24.

  2. 2
    Click Calculate or pick a preset

    Press Calculate or choose a common preset to instantly compute the results. The calculator runs entirely in your browser.

  3. 3
    Read the subnet details

    Review the network address, broadcast address, first and last usable host, total usable hosts, subnet mask, wildcard mask, and the binary mask representation.

About

Before 1993, IPv4 addresses were allocated using a classful system defined by the first few bits of each address. Class A networks (/8) contained over 16 million addresses, Class B networks (/16) held about 65,000, and Class C networks (/24) provided just 254 usable hosts. Organizations had to choose one of these fixed sizes, even when their actual needs fell between classes.

In September 1993, RFC 1519 introduced Classless Inter-Domain Routing (CIDR), which removed the class boundaries and allowed network prefixes of any length from /0 to /32. CIDR made it possible to allocate address blocks that closely matched actual requirements. CIDR also introduced Variable-Length Subnet Masking (VLSM), which lets network administrators divide a single allocation into subnets of different sizes within the same organization.

Beyond conservation, CIDR dramatically improved internet routing efficiency. Before CIDR, routers had to maintain separate entries for every classful network. With CIDR, adjacent network blocks can be aggregated into a single routing table entry, a technique called supernetting or route summarization.

Today, CIDR notation is the universal standard for describing IP network boundaries. Every subnet calculator, firewall rule, cloud VPC configuration, and access control list uses CIDR prefixes. Understanding how to calculate network addresses, broadcast addresses, and usable host ranges from a CIDR prefix is a fundamental skill for network engineers, system administrators, and cloud architects.

FAQ

What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation combines an IP address with a prefix length separated by a slash, such as 192.168.1.0/24. The prefix length indicates how many leading bits of the address identify the network portion. CIDR replaced the old classful addressing system in 1993 (RFC 1519) to allow more flexible allocation of IP address space and slow the exhaustion of IPv4 addresses.
What is the difference between a subnet and a supernet?
A subnet divides a larger network into smaller segments. For example, splitting 10.0.0.0/8 into multiple /24 networks. A supernet (or supernetting) aggregates multiple smaller networks into a single larger block, such as combining four /24 networks into one /22. Supernetting is used in route aggregation to reduce the size of routing tables and improve routing efficiency across the internet.
Why does the calculator subtract 2 from the total host count?
In any standard IPv4 subnet, two addresses are reserved. The network address (all host bits set to 0) identifies the subnet itself and cannot be assigned to a device. The broadcast address (all host bits set to 1) is used to send packets to every host on the subnet simultaneously. Because these two addresses serve special roles, the number of usable host addresses is 2^(32 - prefix) minus 2.
What about /31 and /32 subnets?
A /31 subnet has exactly two addresses and is defined by RFC 3021 for point-to-point links between two routers, where neither a network nor a broadcast address is needed. Both addresses in a /31 can be assigned to interfaces. A /32 identifies a single host address and is commonly used in loopback interfaces, host routes in routing tables, and firewall rules that target one specific IP. This calculator reports the correct host count for both special cases.
Does this calculator support IPv6?
This calculator currently supports IPv4 subnetting only. IPv6 uses a 128-bit address space with prefix lengths up to /128, and its subnetting conventions differ significantly from IPv4. A /64 is the standard subnet size for most IPv6 networks, providing 2^64 (about 18.4 quintillion) addresses per subnet. IPv6 subnet calculation is planned for a future update to IPFYI.