Trancenders Question of the day ?

Irish Man

My Network IP Address is 204.99.99.0/24

I require 3 Subnets
SubNet 1 Requires 10 hosts
SubNet 2 Requires 25 hosts
Subnet 3 Requires 60 hosts

An additional Subnet will be added in the future. I must devide the ip addresses to reserve the max number of ips for the future Subnet.

Seems simple enough.
I break down in to subnetting as follows.
SN1 - 204.99.99.240/29
SN2 - 204.99.99.224/28
SN3 - 204.99.99.192/27

But they tell me the answer is incorrect, am I wrong here ?

Thanks for the help.
Colin

royal

Subnet 1 requires 10 hosts:
2^1-2=0 which is not enough
2^2-2=2 which is not enough
2^3-2=6 which is not enough
2^4-2=14 which gives enough

This means for Subnet 1, we require 4 bits in the client portion of the ip address. Since we are using /24, we have 8 bits available for client ip addresses. Since this is too much, to be efficient, we will change this to a /28 to provide for the 4 bits needed for clients.

Subnet 1 will be 204.99.99.240 /28

The reason it is .240 is because since we are using 4 bits for the client, we will be using the left-most 4 bits for the network. Binary works as 128 64 32 16 8 4 2 1. The 4 left most bits added up = 240. 128+64+32+16=240.


Subnet 2 requires 25 hosts:
2^1-2=0 which is not enough
2^2-2=2 which is not enough
2^3-2=6 which is not enough
2^4-2=14 which is not enough
2^5-2=30 which is enough

This means for Subnet 2, we require 5 bits in the client portion of the ip address. Since we are using /24, we will have 8 bits available for the client ip addresses. Since this is too much, to be efficient, we will change this to a /27 to provide the 5 bits needed for clients.

Subnet 2 will be 204.99.99.224 /27

The reason it is .224 is because since we are using 5 bits for the client, we will be using the left-most 3 bits for the network. Binary works as 128 64 32 16 8 4 2 1. The 3 left most bits added up = 224. 128+64+32=224.


Subnet 3 requires 60 hosts:
2^1-2=0 which is not enough
2^2-2=2 which is not enough
2^3-2=6 which is not enough
2^4-2=14 which is not enough
2^5-2=30 which is not enough
2^6-2=62 which is enough

This means for Subnet 2, we require 6 bits in the client portion of the ip address. Since we are using /24, we will have 8 bits available for the client ip addresses. Since this is too much, to be efficient, we will change this to a /26 to provide the 6 bits needed for clients.

Subnet 3 will be 204.99.99.192 /26

The reason it is .192 is because since we are using 6 bits for the client, we will be using the left-most 2 bits for the network. Binary works as 128 64 32 16 8 4 2 1. The 2 left most bits added up = 192. 128+64=192.


So to sum it all up

Subnet 1 = 204.99.99.240 /28
Subnet 2 = 204.99.99.224 /27
Subnet 3 = 204.99.99.192 /26

Hopefully this helps