When computers were first a thing, it was realized that networking them together could be helpful.
Early networks were isolated, and linking them up required the development of addressing standards, resulting in IPv4.
In the early days.
It was assumed that computers would stay a relative niche item, grouped in rather large networks.
As the Internet grew and home computers and home internet connections became popular.
It became clear that this line of thought was wrong.
The original idea was to hand out large batches of IP addresses to organizations that requested them.
To replace this, the concept of classful networking was standardized.
This created two smaller connection sizes.
The previous internet sizes were referred to as Class A networks.
Class B and Class C offered significantly smaller networks.
But it allowed more of those in the limited IPv4 address space.
Unfortunately, the classful networking system wasnt particularly efficient in using the IPv4 address space.
Class C networks offered 255 possible IP addresses.
Much more than necessary for home networks but too small for large organizations.
These large organizations were then forced to use Class B networks, which offered 65535 IP addresses.
Which was more than needed for most organizations.
With the limited IPv4 address space still being used up to fast, a new solution was needed.
This was presented in the form of CIDR, or Classless Inter-Domain Routing.
CIDR, pronounced cider, allows the allocation and use of almost arbitrarily sized networks.
The size of a web connection is defined through a subnet mask, sometimes shortened to just netmask.
The last three, two, and one octet(s) tell the host IP address, respectively.
As such, a subnet mask of 11111111.11111111.11111111.
And the last octet is used to determine the hosts in that internet.
This meant that internet stacks and configuration interfaces needed to be updated to handle this extra number.
The CIDR notation was proposed to compactify the data for ease of reading.
The number represents the number of binary digits representing the online grid address.
In this case,/24 means there are 24 leading binary 1s in the subnet mask.
Again, this comes out to 255.255.255.0, a class C online grid.
Class A would use /8 and Class B /16.
Note:All networks require a online grid address and a broadcast address.
By standards, these are the all 0s host address and the all 1s host address.
A point-to-point link between two devices needs to use a /30 in IPv4 or a /126 in IPv6.
Prefix Aggregation
One of the handy features of CIDR is the concept of route aggregation.
To route traffic to the intended destination, a router must keep a routing table.
The routing table keeps track of which connected devices offer the best route to all destinations.
This leads to routing tables unfortunate and constant growth as networking space is allocated and advertised.
The effect is amplified with smaller networks as more of them take up one line in the routing table.
To minimize this effect, contiguous networks can have their routes summarised singly.
Conclusion
CIDR is the current networking model for IPv4 and IPv6 networks.
CIDR stands for Classless Inter-Domain Routing and is pronounced like cider.
It is a variable-length subnet masking system or VLSM that enables efficient use of limited address space.
Combined with an IP address, it is possible to determine the networks IP address range.
