CIDR query

AceAll

I came across this question and I am not able to understand it

which of the summarized subnets is a valid routes according to the main purpose of CIDR ?

1. 200.1.1.0 255.255.255.0
2. 10.0.0.0 255.255.255.0
3. 200.1.0.0 255.255.0.0
4. 10.1.0.0 255.255.0.0

The correct answer is 200.1.0.0. 255.255.0.0

Let me know why did they choose this answer

any help would be appreciated

lordy

Quickly analyzing the question I would say the answer is clear.
It is asking for summarized subnets so you first have to check which of the networks could be summarized.

Answers 2 and 4 obviously aren't summarised as the default netmask for 10.0.0.0 is /8 or 255.0.0.0.

This leaves Answers 1 and 3.

The netmask from answer 1 is again a default netmask (255.255.255.0) so answer 3 is summarized.

Answer 3 summarizes multiple Class C networks and is therefore correct.

HTH,
Lordy

AceAll

This is what I infer ..
to find the summarized subnet the given subnet must be LESS than the default subnet
like in the above case the 200.1.0.0 has the subnet of 255.255.0.0 instead of
255.255.255.0 so it is the summarized subnet

I hope its correct !

lordy

That's what I was trying to say