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IP Addresses, IP Ranges, CIDR

Networking involves understanding IP addresses and how they are grouped into networks. This guide explains the basics of IP addresses, ranges, and CIDR notation.

IP Addresses

An IP address is a unique identifier for a device on a network. IPv4 addresses consist of 32 bits and are usually written in dotted decimal format, like:

10.10.10.1

  • Each part separated by dots is called an octet (8 bits).
  • Each octet can have a value from 0 to 255.

Example:

10.10.10.0 → Network address
10.10.10.1 → First usable host
10.10.10.255 → Broadcast address

IP Ranges

An IP range is a set of IP addresses within the same network. Networks are defined by a subnet mask, which separates the network portion from the host portion of the address.

  • A subnet mask can be written in traditional form (e.g., 255.255.255.0) or in CIDR notation (e.g., /24).
  • The subnet mask determines how many IP addresses are in the network.

Calculator Tool: MX Toolbox

CIDR Notation

CIDR (Classless Inter-Domain Routing) is a compact way to represent networks and ranges of IP addresses.

It uses the format:

NetworkAddress/PrefixLength

  • NetworkAddress: Starting IP of the network
  • PrefixLength: Number of bits used for the network

Example: 10.10.10.0/24

  • Network: 10.10.10.0
  • Prefix length: 24 bits
  • Host bits: 32 - 24 = 8 bits

Number of addresses:

  • Total addresses = 2^(host bits) = 2^8 = 256
  • Usable addresses = Total - 2 (network + broadcast) = 254

So, 10.10.10.0/24 contains addresses from 10.10.10.0 to 10.10.10.255.

Calculating CIDR Ranges

To calculate a CIDR range:

  1. Determine the number of host bits: 32 - prefix length
  2. Calculate total addresses: 2^(host bits)
  3. Identify network address (first address)
  4. Identify broadcast address (last address)
  5. Usable IP addresses are all addresses between network and broadcast

Example:

192.168.1.0/26

  • Host bits = 32 - 26 = 6
  • Total addresses = 2^6 = 64
  • Network: 192.168.1.0
  • Broadcast: 192.168.1.63
  • Usable: 192.168.1.1 to 192.168.1.62

Summary

  • IP addresses identify devices on a network
  • IP ranges are groups of addresses defined by a subnet
  • CIDR notation simplifies network representation
  • Calculating ranges helps plan networks and allocate IP addresses efficiently

This guide provides a foundation for understanding IP addressing and network planning.