subnet addresses

celtic_tiger

Good day

So i am able to perform the subnet exercises quite quickly and get the correct result, now I just need to interpret the answers im getting.

Currently im stuck looking at my answer to this problem from the cisco book, problem set 5 eg question 5. To analyze

ip 10 150 200 200 mask 255 252 0 0

So I get the correct answer
subnet number: 10 148 0 0
1st usable ip address: 10 148 0 1
last usable ip address: 10 148 255 254
broadcast address: 10 151 255 255

I see ther are 6 subnet bits = 64 subnets, but where do i begin to count upward
eg 10 148 0 1.. 10 148 0 2... etc. goes all the up to 255

10.148.0.1.. 10.149.0.1..... 10.151.0.1 is only 3 addresses

so what do the address of these 64 subnets look like??

please keep the answers nice and layman like for me as Im a relative beginner to IT and my only source of learning is the cisco book.

captobvious

celtic_tiger wrote: »

Good day

So i am able to perform the subnet exercises quite quickly and get the correct result, now I just need to interpret the answers im getting.

Currently im stuck looking at my answer to this problem from the cisco book, problem set 5 eg question 5. To analyze

ip 10 150 200 200 mask 255 252 0 0

So I get the correct answer
subnet number: 10 148 0 0
1st usable ip address: 10 148 0 1
last usable ip address: 10 148 255 254
broadcast address: 10 151 255 255

I see ther are 6 subnet bits = 64 subnets, but where do i begin to count upward
eg 10 148 0 1.. 10 148 0 2... etc. goes all the up to 255

10.148.0.1.. 10.149.0.1..... 10.151.0.1 is only 3 addresses

so what do the address of these 64 subnets look like??

please keep the answers nice and layman like for me as Im a relative beginner to IT and my only source of learning is the cisco book.

actually last usable ip address: 10 151 255 254

you could download the ip subnet calculator to help you IP Subnet Calculator

celtic_tiger

Oh I have the subnet calculator but I don't see where it lists the 64 usable subnet addresses.

captobvious

celtic_tiger wrote: »

Oh I have the subnet calculator but I don't see where it lists the 64 usable subnet addresses.

Maybe the button that says Calculate all Subnets? Just a thought....

motherwolf

With a 255.252.0.0 mask your subnets are going to increment by 4. Your first subnet is going to be:

10.0.0.0---10.4.0.0
10.4.0.0---10.8.0.0
10.8.0.0---10.12.0.0

and so on and so on until you reach the 64th subnet.

celtic_tiger

Many thanks lads I see the light now for the subnets

So see i have 18 host bits for the above yielding 262,162 individual ip addresses and that plays out like

10.148.0.0
10.148.0.1
10.148.0.2
......10.140.0.255 (256 addresses)

then its?

10.149.0.1
10.149.0.2
.....10.49.0.255 (256 addresses)

I cant see where i get the 262,162 hosts from the subnet 10.148.0.0 - 10.151.255.255. Also I often see the books refer eg. class a address yields 16m+ addresses but id like to see how that is played out eg

1.0.0.0
1.0.0.1
1.0.0.2
1.0.0.3
....1.0.0.255

then?

1.0.1.1
1.0.1.2
1.0.0.3

is there a any specific rules?

mella060

celtic_tiger wrote: »

Many thanks lads I see the light now for the subnets

I cant see where i get the 262,162 hosts from the subnet 10.148.0.0 - 10.151.255.255. Also I often see the books refer eg. class a address yields 16m+ addresses but id like to see how that is played out eg

is there a any specific rules?

Well think about it...you have subnets of say:

10.148.0.0
10.152.0.0
10.156.0.0
10.160.0.0

So in each subnet you have two empty octets..0.0...which means you could have 65000 hosts or whatever....256 x 256 gives you that

Multiply that by 4 since the increment is 4 in the second octet

So for example in the 10.148.0.0 subnet you have:

10.148.0.0
10.149.0.0
10.150.0.0
10.151.0.0

Thats how you get that big answer

celtic_tiger

I see, exactly the answer i was looking. thank you.

Do we always move from the right in or i guess if its a host address it dosent matter.

Why do the 64 subnets increment by 4 again arent they 64 independant subnet ranges?

I can see now we multiply 256 for the down 10.148.0.0 has 256 addresses as does 10.148.1.0 through to 10.148.255.254 times 256 addresses each so 10.148.0.0 subnet range has 256 * 256 = 65,536 host address.
given 4 subnets = 65,536* 4 = 262,144 - 2 = 262,142.

so can you/anyone show me the way do i see the class a ip address plays out in the same manner?

eg
1.0.0.0
1.0.0.1
1.0.0.2
1.0.0.3
....1.0.0.255

then?
1.0.1.0
1.0.1.1
1.0.1.2
1.0.1.3
.....1.0.1.255
skip
1.0.2.0
1.0.2.1
1.0.3.0
1.0.4.0
....1.0.2.255

skip many

1.0.255.254

then

1.1.0.0
1.1.0.1
1.1.0.2

tha_dub

motherwolf wrote: »

With a 255.252.0.0 mask your subnets are going to increment by 4. Your first subnet is going to be:

10.0.0.0---10.4.0.0
10.4.0.0---10.8.0.0
10.8.0.0---10.12.0.0

and so on and so on until you reach the 64th subnet.

Just in case I had too many beer.... Should it not be

10.0.0.0---10.3.255.255
10.4.0.0---10.7.255.255
10.8.0.0---10.11.255.255

celtic_tiger

Indeed you are correct.

So does that mean I have 64 separate subnet ranges? meaning

10.0.0.1 - 10.0.0.3 is one subnet range

taking that 10.0.0.0 - 10.0.0.255 is one subnet within that range?

RouteThisWay

celtic_tiger wrote: »

Indeed you are correct.

So does that mean I have 64 separate subnet ranges? meaning

10.0.0.1 - 10.0.0.3 is one subnet range

taking that 10.0.0.0 - 10.0.0.255 is one subnet within that range?

No.


You have 64 subnets.
You already figured out you increment the second octet by 4. It isn't by accident that if you do this 64 times, you reach 256.


10.0.0.0---10.4.0.0 (this is one subnet)
10.4.0.0---10.8.0.0 (this is one subnet)
10.8.0.0---10.12.0.0 (this is one subnet)
etc

You count up in the octet that the remaining bits are in a mask.

i.e, in this case... 255.252.0.0

The last two octets are reserved for hosts, plus however many bits were borrowed from the second.

If the mask was 255.255.255.248, You only count up on the last octet because you have only borrowed a portion of the bits from the last octet for hosts.

If it was 255.255.248.0, you count up in the third octet because the last one is reserved for hosts. You have borrowed some bits from the third octet, so that is the one count up in.

So.. in your example,

10.0.0.0 - 10.3.255.255 = one subnet. Any host that falls within 10.0.x.1 - 10.3.x.254 is part of the 10.0.0.0 subnet. Remember, the first address is the subnet address, the last (255) is the broadcast address.

So your next subnet would be 10.4.0.0
The first host will be 10.4.0.1
You last host will be 10.7.255.254
The broadcast is 10.7.254.255

The next subnet is 10.8.0.0 and so on.



I HIGHLY recommend this thread: http://www.techexams.net/forums/ccna-ccent/38772-subnetting-made-easy.html

It helped me understand subnetting alot better.

celtic_tiger

Thanks i checked out that link.

What then do i call the adresses between 10.0.0.0 and 10.0.3.0

eg. the range 10.0.0.0 - 10.0.0.255 is 256 addresses

Is it that those addresses betwen 10.0.0.0 - 10.0.3.0 are together an "address block" within the subnet?

RouteThisWay

celtic_tiger wrote: »

Thanks i checked out that link.

What then do i call the adresses between 10.0.0.0 and 10.0.3.0

eg. the range 10.0.0.0 - 10.0.0.255 is 256 addresses

Is it that those addresses betwen 10.0.0.0 - 10.0.3.0 are together an "address block" within the subnet?

Any hosts in 10.0.0.1 - 10.0.0.255 are all part of the 10.0.0.0 subnet. As are any hosts up until 10.3.255.254. Those are all part of the 10.0.0.0 subnet.

i.e, 10.18.34.251 is part of the 10.16.0.0 subnet. The next subnet doesn't start until 10.20.0.0.



In your example, the address 10.0.0.0 is the subnet address. And then everything from 10.0.0.1 - 10.0.0.255 are all hosts within the 10.0.0.0 subnet. The next host after 10.0.0.255 is 10.0.1.0, and then 10.0.1.1, and then 10.0.1.2, etc.. and you keep numbering the hosts that way all the way until 10.3.255.254. And 10.3.255.255 is your broadcast address. Then the next subnet (your second subnet) is 10.4.0.0, with the first host being 10.4.0.1

I know this is really confusing at first. Trust me man, I've been there. Just keep practicing and asking questions. Sorry if I am explaining this poorly, never been a teacher. Just trying to explain it how my brain processes it.

celtic_tiger

Ive been my own teacher thus far for any exams and i can do well enough given i have good discipline and am strong with memorisation but maths is my achilles heel and subnetting sems to be a topic where you need some one there to pepper with questions.

saying that your answer clears that question up perfectly mate thanks.

RouteThisWay

Glad I could help. You are absolutely right... it helps to ask questions and have people explain it to you. Especially in different ways, you never know which one will click with you. All of our brains function differently, so one method may work for some, and not others.

If you have any more questions, feel free to post them. TE has a bunch of great people here to help

mella060

celtic_tiger wrote: »

Ive been my own teacher thus far for any exams and i can do well enough given i have good discipline and am strong with memorisation but maths is my achilles heel and subnetting sems to be a topic where you need some one there to pepper with questions.

Have you gone through the subnetting chapter in Todd Lammles CCNA book ? If not, then i highly suggest you do. Thats how i got started with subnetting.

Any octet in a subnet mask that is neither 0 or 255 is what is known as the "interesting" octet". That is where the increment is done. So for example...255.255.240.0..which octet contains a value other then 0 or 255 ?
The 3rd one, right ?...So then the increment in the 3rd octet would be 16..256-240

The second octet which is 255 would just icrement by 1...256-255 but dont worry too much about that octet.

So for example we have the 10.0.0.0 network

Our networks would be

10.0.16.0
10.0.32.0
10.0.48.0
....
....
10.0.224.0
10.0.240.0...what would be the next subnet ?

10.1.0.0
10.1.16.0
10.1.32.0
10.1.48.0

celtic_tiger

No I havent read todd's book. So far i have finished the cisco press chapter 12 on subnetting and Im able do do all the exercises in that, but they dont give you any real life scenarios just how to get the eg subnet / broadcast address etc etc so despite completing the chapter i still have questions that crop up every now and then.

I have completed 70 % of the book but now i realise that the microsoft 203 server exams may expire soon so i have prioritised completing the last exam in the set for systems admin 70-291 but i will use the cisco method for subnetting. then I shall return and complete the ccent.

looking at your last example its the same as the cisco method with the interesting octet.
your example increments the subnets by 16 so looking at prior examples i assumed that we start counting while including the zero, like.

10.0.0.0
10.0.0.15 (subnet 1)

10.0.0.16
10.0.0.31 (subnet 2)

and so on. So what is the rule that applies when incrementing at first you would think it's straight multiples of 16 but its looks like from earlier examples that its 1 less at the end of each subnet, or is it? re: post #9.

mella060

celtic_tiger wrote: »

No I havent read todd's book.

looking at your last example its the same as the cisco method with the interesting octet.
your example increments the subnets by 16 so looking at prior examples i assumed that we start counting while including the zero, like.

10.0.0.0
10.0.0.15 (subnet 1)

10.0.0.16
10.0.0.31 (subnet 2)

and so on. So what is the rule that applies when incrementing at first you would think it's straight multiples of 16 but its looks like from earlier examples that its 1 less at the end of each subnet, or is it? re: post #9.

The increment happens in the interesting octet. So in my example it would increment by 16 in the 3rd octet

10.0.0.0 - 10.0.0.1 - 10.0.15.255 (1st subnet)
10.0.16.0 - 10.0.16.1 - 10.0.31.255 (2nd)
10.0.32.0 - 10.0.32.1 - 10.0.47.255 (3rd)
10.0.48.0 - 10.0.48.1 - 10.0.63.255 (4th)

Something like that

blackninja

Go to subnettingquestions.com

and work out the answer for yourself first, then use the subnetting calc to verify.

Practice, practice & more practice.

That's how you learn how to subnet - there's no easy way I'm afraid.

One day it just all clicks and becomes second nature.