Subnetting

kal#4

I'm struggling with subnetting i get the idea of it and principle's i just can't apply it to different questions. I took my CCNA 10 years ago and passed guessing on the subnet questions sad i know....Now 10 years later working in IT, i wanna renew my ccna and go farther. Now i realize i need to know subnetting i feel like i'm close just can't close the deal. I looked at many websites recommened here but when i see different questions i just can't get it down...i'm at the point now that i may just hire someone to tutor me until i have it down. at this point it;s personal and i'm on a mission to learn and master subnetting/VLSM/summarization, because with out it i don't feel like i can be successful....If anybody can help me with any recommendations i'm all ears. oh and i'm great with a subnet calculator......

Webmaster

http://www.techexams.net/forums/ccna-ccent/71437-new-te-subnetting-test-guide.html

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

Also try a search in our forums for subnetting for many examples - good luck!

Greenmet29

There are some good resources online, including subnettingquestions.com, but a lot of those just ask the questions but don't explain how to get there. If you are struggling with subnetting, I would recommend the cbt nugget videos. That is what I used and I pretty much skipped the subnetting parts in the cisco press books because I felt so confident in my subnetting.

mella060

Have a read through the subnetting chapter in Todd Lammles CCNA study guide. It gives you a heap of examples to do. Do them again and again until you get it. Rinse, repeat... WRITE IT ALL DOWN ON PAPER. That is the key to learning it properly, so it sticks in your brain. It is not good enough to just read from a book or website, write everything down, bit by bit. After you master all the content in that chapter, move on to the CBT Nuggets to make subnetting even easier.

IEWANNABE

kal#4 wrote: »

I'm struggling with subnetting i get the idea of it and principle's i just can't apply it to different questions. I took my CCNA 10 years ago and passed guessing on the subnet questions sad i know....Now 10 years later working in IT, i wanna renew my ccna and go farther. Now i realize i need to know subnetting i feel like i'm close just can't close the deal. I looked at many websites recommened here but when i see different questions i just can't get it down...i'm at the point now that i may just hire someone to tutor me until i have it down. at this point it;s personal and i'm on a mission to learn and master subnetting/VLSM/summarization, because with out it i don't feel like i can be successful....If anybody can help me with any recommendations i'm all ears. oh and i'm great with a subnet calculator......

I know what you mean bro! Sometimes, I feel like I have it down, then depending on how tough the question is, I often feel like I'm at day 1. Often times, all of the many different sites and all of the different ways that subnetting is taught, leaves me even more confused and exhausted. I have the cbt nuggets which is very good. Again, with all of the different styles and techniques, it can be confusing...for example, in cbt nuggets, you're given all of the info needed..IP address, CIDR # and the number of networks and/or hosts needed. With subnettingquestions.com, they don't give you the # of networks or hosts...so that threw me for a loop.

As one of the guys mentioned, practice, practice, practice...and also try and be patient. One of my biggest problems, is not taking the time to read the questions throughly and not paying close attention to the entire address. So many times, when trying to find where a host or network sits, I'm often in the wrong octet. I am getting it, but it's going to take some work. Sorry bro, I didn't mean to hi-jack, but being in the same boat, I know where you're coming from. Just keep pressing forward, It's just a matter of time. I like how you're seeing it as a mission... same here bro

Amjo

Read Todd Lammle CCNA 7th ed. Chapter 3, Its realy helpful, I can subnet in less than 10 sec, he will explain it to you in a way you will never forget.. Good luck

SharkDiver

When I was doing CCNA, I used to sit and play with this site for hours at a time:
subnettingquestions.com - Free Subnetting Questions and Answers Randomly Generated Online
After a few days, subnetting in my head became second nature.

IEWANNABE

SharkDiver wrote: »

When I was doing CCNA, I used to sit and play with this site for hours at a time:
subnettingquestions.com - Free Subnetting Questions and Answers Randomly Generated Online
After a few days, subnetting in my head became second nature.

I go to that site every day, but find that sometimes I'm good and sometimes I feel like I'm at "day 1". Unlike cbt nuggets, where you're given all of the info up front, subnettingquestions.com only gives you the IP address and or/cidr#. Sometimes I find it easy, and sometimes difficult. With just the cidr # or mask, I found a shortcut that easily allows me to find the increment. On class C addresses, I'm a pro, on B and A... I need lots more practice! A big part of my troubles is not being patient and reading the problem throughly and realizing what they're asking for. It's slowly sinking in and I'm recognizing a lot of patterns in the numbers...but I'm not progressing as fast as I'd hoped to.

IEWANNABE

Amjo wrote: »

Read Todd Lammle CCNA 7th ed. Chapter 3, Its realy helpful, I can subnet in less than 10 sec, he will explain it to you in a way you will never forget.. Good luck

Will check that out.. thanks!

thedrama

I do not have any idea if this short thing will assist you but, i'll try. Subnetting was my nightmare at the very beginning of my first CCNA course.
I was having hard times by myself but a friend of mine drew my attention to the critical spot/point. After that, it became the easiest thing for me.

Now, before subnetting you should know default values of IP subnet classes. Class A, B and C at first. Why? Because, the 32-bit IPv4 address is represented differently on each.

I mean

for class A, the default illustration if IP address is considered x.x.x.x , is network.host.host.host
for class B , network.network.host.host
for class C, network.network.network.host

for example by default, 10.0.0.0 is one of the IP addresses belongs to class A. (As you can see above, the first octet is the network portion)
by default, 172.16.0.0 is for the class B(As you can see above, 172.16 is the network portion)
by default, 192.168.1.0 is for the class C(As you can see above, 192.168.1. is the network portion)

Why did i explain this? Because subnetting requires from you to know this.

I'll go on soon.

How subnetting is done? By taking host bits from the IP address and reserving them for to describe the subnet address.
Why subnetting is done? In order to prevent IP address consumption.Creating many subnets from a major network. (Once IPv6 was not developed)

For example lets assume we have 172.16.0.0/24

As you know, by default, 172.16.0.0 is the class B IP address. So it has 255.255.0.0 subnet mask in default.
But here the CIDR notation is 24, i mean its a distinct value than default. What we need to do is substracting first.
24-16(default notation of class = 8. What happened then?

If you remember the default subnet mask for the class B is 255.255.0.0 and it is represented in binary form like
below ; 11111111.11111111.00000000.00000000

then

what was the illustration for class B ? network.network.host.host

We borrowed 8 bits from the third octet(because for the class B, first and the second octet is reserved for the network) by making all zeroes, 1. So, the result is 255.255.255.0(the previous was 255.255.0.0) for the subnet mask

in our example 172.16.0.0/24

we need to do another substraction. 256-255 = 1 (substracted the value we obtained from the result from whole)
What is that "1"? it is the block size which defines that each subnet increases by which number. i mean
if the first subnet is 172.16.0.0, the second will be "here" 172.16.1.0 and the other 172.16.2.0 incremented by 1, up to
256. . 255 is included. Valid subnets in this example are those.

Here, the subnet value is calculated as 2^8= 256 valid subnets. Why? Because, we borrowed 8 bits.
How about how many hosts are there? to learn this, lets get back to illustration for class B. It was network.network.host.host

but, the result : network.network.network.host(because we had borrowed 8 bits from the host portion). Now,
how many host bits remained? 2^8 = 256 bits (bits left other than network portion after subnetting process) - 2 = 254(i can't remember the reason of this substraction)

Here, while the first subnet is 172.16.0.0, the first host will be 172.16.0.1. The next subnet will be 172.16.1.0
but the value before this will be the broadcast address. Thats why, for the first subnet, the valid hosts
usable (can be assigned to the interfaces) are 172.16.0.1 through 172.16.0.254(included).


Now, VLSM.

VLSM is a step further than subnetting to preserve IP addresses. VLSM refers to variable length subnet mask.
What does this mean? By default, class A notation is x.0.0.0.0/8 class B notation is x.x.0.0/16
class C notation is x.x.x.0/24

in VLSM you can assign different numbers other than default. Such as x.0.0.0.0/23

IEWANNABE

thedrama wrote: »

I do not have any idea if this short thing will assist you but, i'll try.

I actually came across something like this last week while doing some searches. This method really works for me, and I'm pretty good when it comes to finding Host & subnet IP addresses/rangess and where they sit. I'm good with class C addresses, and I'm ok with class B...the problem many times for me is not taking the time to read through the problem throughly. Often after finding out I'm wrong, it's easy for me to find my mistakes and then I say to myself, "Why didn't I see that before". The more I practice and work through those mistakes though, the better I get. As I mentioned in an earlier post, I'm coming along,.. just not nearly as fast as I'd like to. Thanks for your input...every little bit helps!

JockVSJock

I'm in the same boat with you. I'm going on 2 years on trying to get my CCNA and subnetting has been a big issue with me.

Here has what really helped me.

-Purchase Chris Bryant's CCNA DVD set from Train Signal. He has a whole DVD chapter dedicated to subnetting. There is another DVD set that gets recommended, can also check that out to. He doesn't cover everything, but I feel he was the only one who explained it to where I got it and could start to do problems on my on, and do them correctly. He explained way better then Odom or Lammle and didn't use tricks like magic number, which even confused me more.

-Use the following websites to do problems:
http://forums.cisco.com/CertCom/game/binary_game_page.htm

http://www.subnettingquestions.com/

subnetting.org - Free Subnetting Questions and Answers Randomly Generated Online

-Download the subnet calculator from this website to review your answers and backwards engineer the answer if you can't figure it out

-If you are still stumped then post here and we'll try to help out

-Also search thru threads on here, inlcuding my user name, to see what others are working on and practice every day