What does the slash number (/24) in CIDR notation mean?

The prefix number indicates how many leading bits of the 32-bit IPv4 address are reserved for the network ID, leaving the remaining bits for host devices.

Why are 2 addresses subtracted from total subnet capacity?

The lowest address in any subnet represents the network identifier, and the highest address is reserved for subnet-wide broadcast transmissions.

Are my internal network IP configurations saved on your servers?

No. All bitwise calculations run locally in your browser memory; zero network architecture data is transmitted.

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CIDR Subnet Calculator: Network & Broadcast

Calculate IPv4 Classless Inter-Domain Routing (CIDR) subnet masks, network addresses, broadcast addresses, usable host IP ranges, and wildcard masks directly in your browser. Enter any IP with CIDR slash notation (e.g., 10.0.0.0/24) to inspect full subnet details. All bitwise masking and IP range calculations execute in local browser memory without network queries.

How to use

Step 1: Input IP and CIDR Prefix

Enter an IPv4 address and select a prefix length from /0 to /32 (e.g., 192.168.1.0/24).
Step 2: Review Network Boundaries

Inspect network ID, broadcast address, subnet mask, and usable host count in real time.
Step 3: Copy Subnet Configuration

Copy the first usable IP, last usable IP, or dotted-decimal netmask for router setup.

Options explained

CIDR Prefix Selector (/0 to /32)

Configures subnet bit length and updates host capacity from 1 to over 4 billion addresses.

When to use: Use when planning VPC topologies in AWS, Azure, or corporate networks.

Usable Host Range

Identifies the assignable IP boundaries by reserving the network address (.0) and broadcast address (.255).

When to use: Use when provisioning DHCP pools and static server allocations.

Wildcard Mask (Cisco Style)

Calculates the bitwise inverse of the subnet mask (e.g., 0.0.0.255 for /24).

When to use: Use when configuring Cisco IOS Access Control Lists (ACLs) and OSPF routing areas.

Worked example

Input: CIDR Block: 192.168.1.0/24

Output: Netmask: 255.255.255.0 | Usable Hosts: 254 (192.168.1.1 to 192.168.1.254) | Broadcast: 192.168.1.255

Computed using 32-bit binary bitwise AND masking operations on IPv4 octets.

Tips & limits

A /24 subnet provides 256 total IP addresses and 254 usable host addresses, standard for office local area networks.
Cloud providers like AWS reserve 5 IP addresses per subnet (network, router, DNS, future use, and broadcast).
Point-to-point router links conventionally use /30 subnets (2 usable hosts) or /31 subnets under RFC 3021.

Common problems

Entered host IP shifted the network address: CIDR math automatically clears host bits to find the canonical base network address for the specified prefix.
/31 and /32 show zero or special host counts: A /32 represents a single host route, while /31 is designated for point-to-point links without standard broadcast addresses.

Frequently Asked Questions (FAQ)

What does the slash number (/24) in CIDR notation mean?: The prefix number indicates how many leading bits of the 32-bit IPv4 address are reserved for the network ID, leaving the remaining bits for host devices.
Why are 2 addresses subtracted from total subnet capacity?: The lowest address in any subnet represents the network identifier, and the highest address is reserved for subnet-wide broadcast transmissions.
Are my internal network IP configurations saved on your servers?: No. All bitwise calculations run locally in your browser memory; zero network architecture data is transmitted.

How to use

Step 1: Input IP and CIDR Prefix

Step 2: Review Network Boundaries

Step 3: Copy Subnet Configuration