CCNA - How to Subnet
CCNA Aspirants, We are starting a set of tutorials for you guys to learn the concepts of CISCO Certification the EASY Way
Today we start with SUBNETTING, one of the easiest if you get the Subject matter, can ruining your CCNA preparation if you dont.
What is subnetting?
“Subnetting is basically breaking down a group of IP addresses in to smaller groups a way of managing IP addresses. With IPv4 we have a limited amount of IP adds that we can use so we have to manage them by subnetting.”
IP address is made up of 4 octects.
192.168.10.1 192.168.10.2…. 192.168.10.250 and so on
Here is why
IP addresses are represented in bit wise pattern
IP address is 32 bits (4 octets)
0. 0. 0. 0
So 0 is the minimum value and 255 is the maximum value.
For every network there should have to be a network ID and Broadcast ID. The first available IP address will be the network ID and the last one will be the broadcast ID
192.168.10.0 :- The first available IP address
192.168.10.255 :- The last available IP address
First one will be the network ID and the last one the broadcast ID.
This rule is valid for every networks.
You are in a situation where you have only one address pool or range and you are to create two networks from that pool. That is wherethe real subnetting test begins…
If we give an IP from the network 192.168.10.0, the default subnetmask will be 255.255.255.0
No. of hosts = ?
For Class C networks, consider only the last octet of the subnetmask.
Last octet 0
Binary of 0 = 00000000
Then from that find the no. of networks and hosts
2 raised to no. of ones in that octet will be the no. of networks
2 raised to no. of zeros -2 will be the no. of hosts (explaination follows)
no.of ones :- 0 0*1= 1
no. of zeros :- 8 2*8-2 = 256-2 = 254
So the network range
So as per our rules
192.168.10.0 – Network ID
192.168.10.1 – First available host
192.168.10.254 – Last available host
192.168.10.255 – Broadcast ID
We all know if we use different Class C networks it is possible to have two networks.
But we don’t want to waste our IP addresses, So what we will do is we are going to create two networks in that range
That is from 192.168.10.0 subnet, we will create 2 networks
192.168.10.0 255.255.255.0 is the mask that we used
For class C the first three parts are network part and the last one is the host part.
We only have the option to change the last part. .ie, the host part
255. 255. 255. 0
we are changing the 0 bit to one (last octet)
255. 255. 255. 128
No. of networks = 2*1 = 2
No. of hosts = 2*7-2 = 128-2 = 126
Block size = 256-128=128
The subnet range
192.168.10.0 :- Network ID
192.168.10.1 :- First host
192.168.10.126 :- Last host
192.168.10.127 :- Broadcast ID
192.168.10.128 :- Network ID
192.168.10.129 :- First host
192.168.10.254 :- Last host
192.168.10.255 :- Broadcast ID