Classless Inter-Domain Routing facts for kids

Classless Inter-Domain Routing (CIDR) is a smart way to give out IP addresses and send Internet Protocol packets on the internet. Think of it like organizing house numbers on streets more efficiently. Before CIDR, there were some problems with how IP addresses were used, leading to a lot of wasted addresses. CIDR helps solve these problems by making the system more flexible and allowing for better use of the limited number of available IP addresses.

What is CIDR?

CIDR stands for Classless Inter-Domain Routing. It's a method used in computer networking to manage and assign IP addresses. An IP address is like a unique phone number or house address for every device connected to the internet. It helps computers find each other and send information back and forth.

Before CIDR, IP addresses were given out in fixed "classes" (like Class A, B, or C). This system was not very flexible. CIDR changed this by allowing IP addresses to be grouped in much more flexible ways. This makes it easier to use the internet's addresses without wasting them.

Why do we need CIDR?

In the early days of the internet, IP addresses were given out using a "classful" system. This meant that networks were assigned fixed blocks of addresses. For example, a Class A network had millions of addresses, a Class B had thousands, and a Class C had only 256.

This system caused a lot of problems:

• Wasted Addresses: Many organizations didn't need millions of addresses, but they might get a Class A block anyway. This left many addresses unused.
• Running Out of Addresses: Even with millions of addresses, the internet was growing so fast that we were quickly running out of available IP addresses.
• Large Routing Tables: Every time a new network was added, routers (devices that direct internet traffic) had to remember its exact address. This made the internet's "address book" (routing tables) very large and slow.

CIDR was created in 1993 to fix these issues. It made the internet's address system more flexible and efficient.

How does CIDR work?

CIDR works by getting rid of the old fixed classes for IP addresses. Instead, it uses a system where networks can be any size. This is done by adding a "prefix" to an IP address. This prefix tells you how many bits (parts of the address) are used for the network part and how many are for the device part.

CIDR Blocks and Prefixes

An IP address with a CIDR prefix looks like this: `192.168.1.0/24`.

• `192.168.1.0` is the network address.
• `/24` is the CIDR prefix. It means that the first 24 bits of the IP address identify the network. The remaining bits (32 - 24 = 8 bits) are used to identify individual devices within that network.

The smaller the number after the slash, the larger the network block. For example:

• `/8` means a very large network with millions of addresses.
• `/24` means a smaller network with 256 addresses.
• `/30` means a tiny network with only 4 addresses (often used for links between two routers).

This flexible system allows network administrators to create networks of exactly the right size. They can get a block of addresses that fits their needs, whether it's for a small home network or a large company.

Supernetting and Subnetting

CIDR allows for both "supernetting" and "subnetting":

• Supernetting: This is when multiple smaller networks are grouped together into one larger network. This helps reduce the number of entries in routing tables. Imagine combining several small streets into one big neighborhood for easier navigation.
• Subnetting: This is when a large network block is divided into several smaller subnetworks. This helps organize devices within a large organization. For example, a company might divide its network into separate subnets for different departments like sales, marketing, and engineering.

Benefits of CIDR

CIDR brought many important benefits to the internet:

• Efficient Address Use: It helps save IP addresses by allowing them to be allocated in more precise sizes. This means less waste and more addresses available for new devices.
• Reduced Routing Table Size: By grouping networks (supernetting), CIDR helps keep the internet's "address book" (routing tables) smaller. This makes internet traffic move faster and more efficiently.
• Improved Routing Efficiency: Smaller routing tables mean routers can find the correct path for data packets more quickly. This makes the internet faster and more reliable.
• Flexible Network Design: Organizations can design their networks with much more flexibility, choosing the exact size of address blocks they need.

CIDR is a fundamental part of how the internet works today. It helped ensure that the internet could continue to grow and connect billions of devices worldwide.