CCNA 1: CHAPTER 6: BASIC SUBNETTING

Sub netting helps in creating logical networks that are linked together using a network router.These logical networks   are interlinked b...

Sub netting helps in creating logical networks that are linked together using a network router.These logical networks  are interlinked by the use of routers that forward packets to different networks

How is subnetting Important?

Subnetting helps in designating different networks that have different uses.For example let take example of a university network

Student network is separated from the administration network for security purposes

Also subnetting helps in ensuring the  networking is done depending on the number of hosts.

During subnetting,normal bits from the network are borrowed  and are used in subnetting

Formula for calculating Subnets

The formula for calculating subnets is this

2^n=the Number of subnets

N=represents the number of bits borrowed

Let say we want to subnet our network to suit Finance ,Students network,administration and e-learning in a university

We need four subnets

We can determine the number of bits we need to borrow by 

Bits= log 4/ log 2

Formula for calculating the number of hosts

The formula for calculating the number of hosts  in a particular subnet is done this way

2^n=Number of hosts

N=the number of bits that have been left for the hosts

Let say we have 5 bits left for the hosts

The number of hosts here is equal to  2^5=32

See below caption of how subnetting is done

Below is a caption  of how a bits are borrowed and assigning of addresses

Example of subnetting

If a network administrator is given this IP address by the ISP  192.168.1.0/24 .If he want to subnet the address block into 3 subnets.How many bits will he need.He will need  2 bits because 2 raised to power 2=4.He will use the 3 subnets and one subnet will remain unsed

The number of hosts in each subnet will be 62 because only 6 bits are left behind for hosts

2^6 - 2 = 62 hosts per subnet

Let lists all the four subnets

Subnet 0=192.168.1.0/26 Host addresses are from 192.168.1.1-192.168.1.61

Subnet 1=192.168.1.64/26

Subnet 2=192.168.1.128

Subnet 3=192.168.1.192

See below caption for more clarifications

Example of six subnets

Address block given is 192.168.1.0 /24 and we need six subnets

So we need to borrow how many bits??

2^3 = 8

We need to borrow 3 bits and we will leave the hosts bits to be 5 bits

So number of hosts that can be assigned in each

2^5-2= 30

See below caption of subnetting with six subnets

Network addressing

 

Credits:Photo source and content:Cisco Curriculum