Why Subnetting?

Internet Assigned Number Authority (IANA) provides the IP addresses.

**Remember:
Subnet - If mask is more then given mask it called as SUBNET.
eg: 130.20.20.0/26

Supernet - If mask is less then then given mask is called as SUPERNET.
eg: 130.20.20.0/8

SUBNETTING means breaking the network.

Why Subnetting (break the network)?

Reason 1: Organization took an IP block from IANA for connecting there branches. eg: 16.0.0.0/8

All organisations has multiple locations (geographically separated) and they are connected to each other on MAN or WAN (Serial Link), so we have to use ROUTER to connect each other. And, Router routes between the networks. So, each branches will be in different network

Hence, We have to break the IP's into different network (Subnetting).

Reason 2: If organisation is using same subnet ip's throughout the network (Layer 2).

Theoretically, we can design only layer 2 (EoSDH) network to connect each other but practically it will degrade the network performance.

• Flat Layer 2 disadvantage - Broadcast to all the ports on all branch switches (also multiple application are running), Bandwidth issue because of broadcast, Processing (I/O) in computer too high because of the broadcast. 

So, Router is required to block the broadcast and hence, subnetting is necessary.

Reason 3: Out of new IPv4 address, so break (Subnet) one IPv4 into multiple networks.

★CT21

Reference: https://rstforum.net/ (CCNA training)