IP Address

CIDR Notation: What Does /16, /24 Mean in IP Addresses?

Greetings to all tech enthusiasts and server administrators! Today, we’re diving deep into the world of IP addressing, specifically focusing on the CIDR notation, which often appears as /16, /24, etc. If you’ve ever been puzzled by these numbers following IP addresses, this post is for you.

The Basics:

CIDR stands for Classless Inter-Domain Routing. It’s a method used to allocate IP addresses and route IP packets. The numbers you see, like /16 or /24, represent the subnet mask associated with an IP address.

Breaking Down the Notation:

  1. CIDR Notation: When you see an IP address like, the /24 is the CIDR notation. It’s a compact representation of the subnet mask. The number after the slash represents the number of consecutive 1 bits in the subnet mask.
  2. Subnet Mask: A subnet mask is used to specify which portion of an IP address is the network and which part can be used for hosts (devices). For instance, a subnet mask of can be represented as /24 in CIDR notation. This means the first 24 bits are set to 1, representing the network portion, and the remaining 8 bits can be used for hosts.
  3. Hosts: In the context of IP addressing, a host refers to any device on the network, be it a computer, router, smartphone, etc. For a /24 subnet, you can have 256 addresses, but typically only 254 are usable for hosts. The first address denotes the network, and the last is reserved for broadcasting.
  4. Public vs. Private IPs: The CIDR notation and subnetting concepts apply to both public and private IP addresses. The only difference between them is their accessibility. Public IPs are routable on the internet, while private IPs are reserved for internal network use and are not directly accessible from the external internet.

Practical Implications:

Understanding CIDR notation is crucial for network planning, especially when segmenting networks. For instance, a university campus might use a /16 subnet to have a larger address space for its numerous devices. On the other hand, a small office might only need a /24 subnet.

CIDR notation is a fundamental concept in IP networking. It provides a concise way to represent IP addresses and their associated routing information. Whether you’re setting up a new network, planning an expansion, or just curious about those numbers after the slash in IP addresses, I hope this post shed some light on the topic.

Stay tuned for more insights into the world of server administration and networking!


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