Faster subnetting? Tips/Advice/Tricks wanted.

Node Man

Hi Everyone,
Ive been studying for CCENT for about 2 months now. I understood that subnetting is the biggest and toughest part of the CCENT exam, so i hit the subnetting topic real hard.

I feel that I have mastered the subject as I nearly always get the right answer.

However I am very slow. And I use excel to help reach my answers (ip ranges, broadcast address, subnet address, number of subnets and hosts, etc.)

How do you subnet faster, what is your method? for example i use the Excel function "power" for everything, example:

=power(2,5)
= 32 (30 hosts)

Thanks

EV42TMAN

Practice. That is all i can say and just know the powers of 2. The day that I took the CCENT I spent and hour or 2 at work before hand on subnettingquestions.com - Free Subnetting Questions and Answers Randomly Generated Online just going through questions. You won't have a calculator to use on the test. So I'd say get use to working them out with pen and paper.

DoubleNNs

2, 4, 8, 16, 32, 64, 128
Write that at the top of your paper b4 beginning.
Stop using the power function. It's easy to remember powers of 2. Once you stop relying on calculators, your brain will automatically create the pattern for you. Try subnetting with paper only and ween yourself off of excel. An easy fix if that's your only problem area in the CCENT material.

Mrkali

I memorized the powers of 2 up to 2^16, multiples of 16 up to 256 and what subnet masks the various CIDR notations equal out to. I can now subnet most questions in my head.

instant000

I also think memorization tables help, when you already "know" how to do something, and you just want a faster way to reach the solution. (It's the same concept behind the multiplication tables you may have memorized in elementary school.) I can't remember if binary conversions are in there or not, but you might want to make sure you can do binary, hex, and decimal, so you're covered on all sides.

Sett

It's like the multiplication table. After significant experience it'd become a second nature to you.

boredgamelad

Node Man wrote: »

I feel that I have mastered the subject as I nearly always get the right answer.

However I am very slow. And I use excel to help reach my answers

Sorry to be blunt, but if you're using Excel to help reach your 'nearly always right' answers, you aren't close to mastering this topic. You need to do away with the crutches (Excel and even calculators included) and learn it from the ground up. Pencil and paper, writing out your 1s and 0s, manually ANDing, memorizing your powers of 2 (knowing your multiples of 16 is also very helpful); these are the techniques it takes to really learn it, which leads to mastery. Eventually, you can learn the easy ways--the "magic number" method, and other shortcuts--but when you're first starting out you really need to sit down and do it by hand. As others have said, it eventually becomes as natural as doing multiplication in your head. But you can't get there without putting in the work, unless you're just a wiz who understands it all the first time through.

When I took my intro to networking class in 2008 we spent two weeks learning how to subnet, all by hand. Our instructor told us up front that it would suck and not make sense for the first week but by the end of the second week it would all start to come together. Even now I look back and realize that I'm still using the techniques I learned in that two week period today even though my brain has supplanted the need to pick up a pencil and write out my 1s and 0s.

Learn it the hard way and you'll appreciate it in the long run.

Node Man

boredgamelad wrote: »

Sorry to be blunt . . . .Learn it the hard way and you'll appreciate it in the long run.

Thanks for the great advice everyone, and no need to appologize for being blunt. I need to know if I am on the right track!

Ltat42a

Here's a simple chart to help with Block sizes (or range multiples)...

hth

atorven

That table posted by Ltat42a was invaluable to me, memorize it.

WiseWun

Too much memorizing can lead to confusion. Start by practicing on paper and not Excel. The subnet calculator should only be used for verification if you know what your doing. What I normally do is write down these values (128.64.32.16.8.4.2.1) and this helps me figure out the mask, block size, ip range,etc. The left side is network and right is host. So if the question requires 20 hosts, I would borrow 5 bits starting from the right and draw a line. See example.

192.168.10.0, requirement is 20 hosts

128.64.32.|16.8.4.2.1

As you can see from above, my block size/increment is 32 (the # on your left side thats closest to the | character) I can also figure out the subnet mask by adding all the values on the left of the | character, 128+64+32=224. To get the IP range, network and broadcast address, use the block size of 32 starting from network zero.

192.168.10.0 - 192.168.10.31
192.168.10.32 - 192.168.10.63
192.168.10.64 - 192.168.10.95
192.168.10.96 - 192.168.10.127
192.168.10.128 - 192.168.10.159
192.168.10.160 - 192.168.10.191
192.168.10.192 - 192.168.10.223
192.168.10.224 - 192.168.10.255

There are 8 networks above starting with subnet zero. 8 because we borrowed 5 bits for the hosts therefore 3 bits remain for the network portion, 2^3=8. The broadcast address is always the last odd number in the range so .31, .63 are both broadcasts address within their respective networks. The first usable IP address range for subnet 6 is 192.168.10.161 - 192.168.10.190

I hope this was informative. Keep practicing until you nail it and stick to one method for the time being.

Roguetadhg

Paper. Write out the steps you do it. through perfect practice, you'll achieve speed and shortcuts that mean something to you - you'll form shortcuts by doing a lot of them.

Best part about it. You'll also have confidence, and subnetting will be easy peasy. Then you'll be like "Wut, Subnetting? I got this, bro. ...Done."

RoC1909

WiseWun wrote: »

Too much memorizing can lead to confusion. Start by practicing on paper and not Excel. The subnet calculator should only be used for verification if you know what your doing. What I normally do is write down these values (128.64.32.16.8.4.2.1) and this helps me figure out the mask, block size, ip range,etc. The left side is network and right is host. So if the question requires 20 hosts, I would borrow 5 bits starting from the right and draw a line. See example.

192.168.10.0, requirement is 20 hosts

128.64.32.|16.8.4.2.1

As you can see from above, my block size/increment is 32 (the # on your left side thats closest to the | character) I can also figure out the subnet mask by adding all the values on the left of the | character, 128+64+32=224. To get the IP range, network and broadcast address, use the block size of 32 starting from network zero.

192.168.10.0 - 192.168.10.31
192.168.10.32 - 192.168.10.63
192.168.10.64 - 192.168.10.95
192.168.10.96 - 192.168.10.127
192.168.10.128 - 192.168.10.159
192.168.10.160 - 192.168.10.191
192.168.10.192 - 192.168.10.223
192.168.10.224 - 192.168.10.255

There are 8 networks above starting with subnet zero. 8 because we borrowed 5 bits for the hosts therefore 3 bits remain for the network portion, 2^3=8. The broadcast address is always the last odd number in the range so .31, .63 are both broadcasts address within their respective networks. The first usable IP address range for subnet 6 is 192.168.10.161 - 192.168.10.190

I hope this was informative. Keep practicing until you nail it and stick to one method for the time being.

I can subnet fairly quickly using just my head alone, but I found your tip very nice and will add it to my "bag o' tricks!"

Thanks a bunch.

NotHackingYou

Know the powers of 2 all the way up and practice, practice, practice. Honestly when I started studying for the CCNA subnetting was very intimidating for me. I spent over a week on that chapter in Todd Lammle's book, determined to learn it and do it in my head. After lots of practice, it's super easy.