Subnetting question

Ok I'm solid with subnetting but I'm not under 30 seconds like everyone believes I should be.

I get questions where I have to figure out the host range for a subnetwork that is in the 200's or 100's and it takes some time.

For instance I need to find what network 192.168.200.141 /28 is on. Well easy enough I know my increment is 16 because my lowest bit is 16.

Now I am going to count up 192.168.200.0, 16, 32, 48, etc etc etc.

Well that's great and all but if I add these in my head I mistakes and get the question wrong. So I'm rushing through adding these numbers up and I get the answers right but it takes time. Anyone run into this same situation before?

Is there a trick to speed this up?

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Comments

hexem

Yeh, learn to count in 16's !

fowards and backwards, that way you don't have to start from 0 and count up, you can just look at the number and pick out where you should be.

I had trouble at first, but just kept going through it everyday. learn how many bit's are turned on/off for each mask, the slash notation's and everything. Reptition repetition repetition. say it out loud everyday.

bcall64

That's what I thought. Ok I have until Monday until my ICND1 exam.

Now before the exam you have about 10 minutes right in the room with a piece of paper or something? How does that work? Maybe I could write all of them out?

mikem2te

bcall64 wrote: »

That's what I thought. Ok I have until Monday until my ICND1 exam.

Now before the exam you have about 10 minutes right in the room with a piece of paper or something? How does that work? Maybe I could write all of them out?

You have ten minutes or so to check out the exam demo before starting the exam. You can go through the same demo on the internet so you don't have to at the exam. I use the time to write out the following

8      7    6    5    4    3    2    1
128   64   32   16    8    4    2    1
128  192  224  240  248  252  254  255
255  127   61   31   15    7    3    1

It helps me to remember the possible subnet masks, wildcard masks and helps with identifiing the network in these types of questions.

miller811

bcall64 wrote: »

Ok I'm solid with subnetting but I'm not under 30 seconds like everyone believes I should be.

I get questions where I have to figure out the host range for a subnetwork that is in the 200's or 100's and it takes some time.

For instance I need to find what network 192.168.200.141 /28 is on. Well easy enough I know my increment is 16 because my lowest bit is 16.

Now I am going to count up 192.168.200.0, 16, 32, 48, etc etc etc.

Well that's great and all but if I add these in my head I mistakes and get the question wrong. So I'm rushing through adding these numbers up and I get the answers right but it takes time. Anyone run into this same situation before?

Is there a trick to speed this up?

read this
http://www.techexams.net/forums/ccna-ccent/38772-subnetting-made-easy.html

then practice this

IP Subnet Practice

the more you do, the quicker it will become and the easier it will get

daveccna

bcall64 wrote: »

Ok I'm solid with subnetting but I'm not under 30 seconds like everyone believes I should be.

I get questions where I have to figure out the host range for a subnetwork that is in the 200's or 100's and it takes some time.

For instance I need to find what network 192.168.200.141 /28 is on. Well easy enough I know my increment is 16 because my lowest bit is 16.

Now I am going to count up 192.168.200.0, 16, 32, 48, etc etc etc.

Well that's great and all but if I add these in my head I mistakes and get the question wrong. So I'm rushing through adding these numbers up and I get the answers right but it takes time. Anyone run into this same situation before?

Is there a trick to speed this up?

It may well have been on here that I read it but there is a quick way of answering the which subnet is this on question if you have the block size.

Simply divide the presented number by the block size and then cut any fraction off of the result. Then multiply your new whole number by the block size to get the network address.

Are you allowed a calculator in the exam?

miller811

daveccna wrote: »

It may well have been on here that I read it but there is a quick way of answering the which subnet is this on question if you have the block size.

Simply divide the presented number by the block size and then cut any fraction off of the result. Then multiply your new whole number by the block size to get the network address.

Are you allowed a calculator in the exam?

No calculators.... sorry

daveccna

miller811 wrote: »

No calculators.... sorry

Well that being the case I tend to just break down an unmanagable multiplication in to chunks. Maybe do it in 2 steps.

EDIT or use a pencil

johnwest43

If you can get it done in under a minute you shold be fine. There isnt a great need to do it in under 30 seconds like the book says.

thenjduke

I wrote it all down on the board I got. I asked for three of them. Trust me 16 s a good number to learn

bcall64

I just want to thank everyone here for all the help. I laid in bed last night and added by 16's until I fell asleep. It wasn't that hard to get down! As for the chart that looks very very helpful. I will do that as well. I have been practicing subnetting A LOT and this weekend will be full of it. I feel like I should be able to pass this exam on Monday. Wish me luck!

blackninja

This is what I do:

We are looking for network of 192.168.0.125 /28

= 192.168.0.125 255.255.255.255.240

Remember you don't have to count in 16s you can count muliples of 16.

We all know 4 x 16 = 64
then 2 x 64 = 128
128 - 16 = 112

So subnet of 192.168.0.125 /28 =

192.168.0.112 /28

It's that easy

bcall64

blackninja wrote: »

This is what I do:

We are looking for network of 192.168.0.125 /28

= 192.168.0.125 255.255.255.255.240

Remember you don't have to count in 16s you can count muliples of 16.

We all know 4 x 16 = 64
then 2 x 64 = 128
128 - 16 = 112

So subnet of 192.168.0.125 /28 =

192.168.0.112 /28

It's that easy

Now that really makes things easier