Subnetting Question

cgrimaldo

Hello everyone,

I'm doing a CCENT lab/quiz and would like some clarification on this problem if you can.

"An organization is granted a block of classless IP addresses. One of the addresses is 2.2.2.64/20. The organization needs 10 subnets. What is the subnet prefix length?

Now, the logic I have is since we have a slash 20 already, we need 10 subnets. So, we can go in multiples of 2 (2-4-8-16-32, etc) 8 is too small and 32 is too big. So, I choose 16. In order to get 16 subnets, I need 2^4 bits. So, I add the 4 bits to the 20 already and end up with slash 24.

Can anyone tell me if my logic is right? I appreciate everyone's help!

dtlokee

Your logic is correct, you are really re-subnetting an existing subnet into smaller parts.

Netstudent

An organization would not be given a 2.2.2.64/20

It could be given 2.2.0.0/20 which would be 2.2.0.1 - 2.2.15.254. Thats gives you 4094 IP's to play with.

You could break that down into smaller subnets with a /24

2.2.1.0/24

2.2.2.0/24

2.2.3.0/24

ect....