subneting

i have question

1) im revising for my ccna exam, and come across this question

What is the subnetwork number of a host with an IP Address of 172.16.210.0/22?

a 172.16.42.0
b 172.16.107.0
c 172.16.208.0
d 172.16.252.0
e 172.16.254.0
i know the answer is c 172.16.208.0 but i had to workout starting from 256-252=4 and adding 4 each time till i get to 208 and for broadcast as (208+4)-1 = 211 so valid host will be 209 to 210

but what i want know is that this takes me long time is there easer and quicker way than this?

thanks

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Comments

Netstudent

Well you should automaticaly know that 4 goes evenyl into 200 because it goes evenly into 100. So then just count by fours from 200....That just saved you like 3 minutes and 200,000 brain cells.

You just have to do a lot of subnetting man. You will start to see an increase in your ability to use even numbers in quotients and multiples.

faisal79

im not just asking for this question but for furture in the exam it could be any number, i want know if there is easy to work it out

blackmage439

There should be numerous topics about subnetting tips on the CCNA forum. Just take a few minutes and look around.

Netstudent

You just have to know all the multiples of even numbers that are used in binary.
2,4,8,16,32.....ect..

It's just math. Math is math, there are no shortcuts to computation. you either do the math in your head or you write out a long division problem.

If you do a long division problem and it doesn;t work out evenly, look at the remainder to find how many more numbers you need to make it an even division problem.

once you find an even multiple that is close to the number is question, well you can go from there.