What does a subnet calculator tell you?

A subnet calculator takes an IP address and a subnet mask or CIDR prefix and returns the complete network breakdown including network address, first and last usable host, broadcast address, total hosts, wildcard mask, and binary mask. It may also display the IP class and whether the address is private or public.

What is the difference between a subnet mask and a CIDR prefix?

A subnet mask and a CIDR prefix represent the same information in different formats. A subnet mask such as 255.255.255.0 uses dotted decimal notation, while a CIDR prefix such as /24 indicates how many leading bits are set to 1. Both formats are interchangeable.

What is the difference between FLSM and VLSM?

Fixed-Length Subnet Masking (FLSM) divides a network into subnets that are all the same size and use the same subnet mask. Variable-Length Subnet Masking (VLSM) creates subnets of different sizes based on host requirements, which makes more efficient use of IP address space.

When should I use FLSM instead of VLSM?

FLSM is useful when all network segments require the same number of hosts, such as in structured lab environments or simple legacy networks. In most modern networks VLSM is preferred because it uses address space more efficiently.

How does VLSM allocate subnets?

VLSM sorts host requirements from largest to smallest and assigns the smallest possible subnet that can support each requirement. For example, if a network needs 100, 50, and 20 hosts, it may allocate a /25, then a /26, then a /27 to minimize wasted addresses.

Does this calculator find free or unused IP addresses?

Yes. After performing FLSM or VLSM calculations, the calculator can generate a Free or Unused IP Network table that shows which address ranges remain unallocated and available for future subnetting.

What is Supernetting (Route Summarization)?

Supernetting, also called route summarization, combines multiple contiguous smaller networks into one larger summary route. This reduces routing table size, improves router efficiency, and simplifies network management.

What are the rules for supernetting to work correctly?

For supernetting to work correctly, the networks must be contiguous with no gaps, the number of networks must be a power of two such as 2, 4, 8, or 16, and the first network must start on the correct boundary for the summarized prefix.

Do I need to create an account or install software?

No. The calculator runs entirely in your browser and does not require account creation, downloads, or installation. All calculations are performed locally.

Can I calculate IPv6 subnets here?

This page focuses on IPv4 subnetting. A separate IPv6 subnet calculator can be used to analyze IPv6 prefixes and address details.

What other tools are available on this site?

The site offers multiple networking tools including subnet calculators, VLSM and FLSM calculators, supernetting tools, subnet overlap checkers, IPv6 calculators, EUI-64 generators, IP range to CIDR converters, wildcard mask converters, MAC address tools, and other utilities.

Are the results accurate enough to use in a real network design?

Yes. The calculations are based on the same binary and bitwise logic used by routers and networking systems, making them suitable for production network planning, certification study, firewall configuration, and cloud network design.

MAC Address Formats Explained: Cisco vs. Windows vs. Linux

While IP addresses get all the glory, the actual physical transfer of data over a local network switch is handled entirely by MAC Addresses (Media Access Control). Every single network interface card (NIC) ever manufactured has a unique, burned-in MAC address.

However, if you work in an environment with different hardware vendors, you will quickly notice that a MAC address copied from a Windows server looks entirely different when pasted into a Cisco switch. Let's explore why this happens and how to read them.

The Structure of a MAC Address

Regardless of how it is formatted on screen, a MAC address is always exactly 48 bits long, written in Hexadecimal (base-16). It is divided into two strict halves:

The First 24 Bits (OUI): The Organizationally Unique Identifier. This is assigned by the IEEE to the hardware manufacturer. For example, any MAC address starting with 00:1A:2B was manufactured by Cisco.
The Last 24 Bits (UAA): The Universally Administered Address. This is the unique serial number the manufacturer assigned to that specific network chip.

Format Compatibility Issues?

If you need to paste a Windows MAC address into a Cisco switchport security configuration, our tool instantly translates the format for you.

Open the Free MAC Converter →

The Three Standard Formats

Even though the 48-bit value is identical, different operating systems separate the hex characters differently for human readability.

1. Standard/Linux Format (Colon-Separated)

Format: 00:1A:2B:3C:4D:5E

This is the standard IEEE 802 format. It breaks the 12 characters into six blocks of two (octets), separated by colons. It is used by Linux, macOS, Android, and most cybersecurity packet sniffers like Wireshark.

2. Windows Format (Hyphen-Separated)

Format: 00-1A-2B-3C-4D-5E

Microsoft Windows utilizes the exact same six-block grouping as Linux, but it uses hyphens (dashes) instead of colons. If you run ipconfig /all in a Windows command prompt, you will see this format listed as the "Physical Address".

3. Cisco Format (Dot-Separated)

Format: 001a.2b3c.4d5e

Cisco operating systems (IOS) group the 12 characters into three blocks of four, separated by periods, and typically format the letters in lowercase. If you are configuring switchport security (port-security) or checking an ARP table on a Cisco catalyst switch, you must input the MAC address in this specific format, or the router will throw an error!