1. Subnetting
2. CIDR (Classless Inter Domain Routing)
3. Variable length Subnet Mask (VLSM)
4. Who manages IP addresses?
5. Why we need subnetting?
6. How to assign IP address to device?

Subnetting is a process of dividing large network into the smaller network
based on layer 3 (Network Layer) IP address.
A subnet is a logical subdivision of an IP network. The practice of dividing a
network into two or more networks is called subnetting.
Subnetting provides a method of allocating a part of the host address space to
network addresses, which generate more networks.
Subnetting allows an organization to add sub-networks without the need to
acquire a new IP addresses from ISP.

Benefits of Subnetting
It reduces the network traffic by reducing the size of broadcasts domain.
It enables users to access a work network from their homes.
Subnetting helps in reducing the network traffic and network complexity.
It increase the security options in the network
By using subnetting network addresses can be decentralized it means the
administrator of the network can monitor the subnet.

Classless Inter Domain Routing (CIDR)
Classless Inter-Domain Routing is a method for allocating IP addresses and IP
routing in the Network.
CIDR is introduced in 1993 by Internet Engineering Task Force .
It replace the previous classful addressing method to design a network in the
Its goal was to reduce the rapid exhaustion of IPv4 addresses.

IP address consist of two groups of bits
The most significant bits are the network address or network prefix , which
identifies a whole network or subnet.
The least significant bits are the host address, which specifies a particular
interface of a host on that network.
This division is used in CIDR to perform subnetting.
CIDR allocates address space to ISP and to end users on any address bit
CIDR is based on the variable-length subnet masking (VLSM) technique.

Variable Length Subnet Mask (VLSM)
Variable length subnet mask(VLSM) technique is used in CIDR
VLSM is a process of dividing an IP address space into the subnet of different
sizes without wasting IP addresses. Example
VLSM is closely related to CIDR.
VLSM allows various network subnets to have different subnet masks.
CIDR allows routers to group the various routes together to reduce the amount
of routing information at the core routers whereas VLSM helps how to optimise
the available address space.

Who manages IP addresses?
The Internet Assigned Numbers Authority (IANA) manages the IP address.
It define space allocations globally and form five regional Internet registries
(RIRs) to allocate IP address blocks to ISP such as BSNL, Airtel, Vodafone etc.
Five Regional Internet Registries (RIRs) are:
RIPE (Reseaux IP Europeens) – Europe
APNIC (Asia pacific network information centre) – Asia
AFRINIC (African Network Information Centre) – Africa
ARIN (American registry for internet numbers) – North America
LACNIC (Latin america network information centre) – Latin America

Who manages IP addresses?
If a device wants to connect to internet then that device request the ISP for the
IP address.
ISP get the range of IP addresses from Internet Assigned Numbers Authority
(IANA) through different five Regional Registries according to the location of a
In this way, device get an IP address from the range of IP Addresses.

Why we need Subnetting?
Let take an example, Any Internet Service Provider (ISP) require 150 IP
addresses to install a network. Then ISP request to APNIC for IP addresses.
APNIC provide a IP address to the ISP
As this is Class C address ,and we know class C have 254 valid IP address in
ISP required 150 IP address and APNIC provide 254 IP address. Thus, this led to
the wastage of 104 IP address.
To stop the wastage of IP addresses, a method is introduced known as

IP address are very costly so to stop the wastage of IP addresses we do
Like Class C have 256 IP address in total.

Assigning IP address
IP address can be assign in two ways to the device
1. Static IP address
2. Dynamic IP address

Static IP address
A static IP address is an IP address that are manually configured for a device.
A static IP address is called static because it doesn’t change.
Static IP addresses are also known as fixed IP addresses or dedicated IP addresses.
Dynamic IP address
A dynamic IP address is an IP address that is automatically assigned to each device in a network.
This automatic assignment of IP addresses is done by a DHCP server.
Dynamic IP address is called dynamic because it will change on future connections to the network.


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