# Questions on how Lammle teaches subnetting

Member Posts: 1,118
So I'm still in the process of teaching myself subnetting with Lammle's material.

I can subnet no problem with Class C addresses, however I still have some questions that he doesn't make clear.

When learning how to subnet the Lammle way, there are five questions to ask:
-How many subnets?
-How many hosts?
-What are the valid subnets?
-What are the valid hosts?

The thing that he never comes out and says is how he gets these numbers in order to figure out the valid subnets?

In all of his examples he is using 256, and I'm not sure where he is getting this number?

For example, his first example uses:

In this example he is taking 256 - 128.

For all Class C examples he is always taking the last octect and subtracting this from 256, I'm just not sure the why behind this? Why not any other octect from the Subnet Address?

Also for the exam, I guess I'm having anxiety trying to do a problem where there 16/34/48/64 subnets.

Is anyone else bothered by this?

Right now I'm doing some of the math by calculator, however on the timed exam, not sure how this is going to go doing this by hand, because I doubt they are going to allow a calculator for this.

Might have more questions as time goes on...
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• Member Posts: 168
JockVSJock wrote: »
The thing that he never comes out and says is how he gets these numbers in order to figure out the valid subnets?

In all of his examples he is using 256, and I'm not sure where he is getting this number?

For example, his first example uses:

In this example he is taking 256 - 128.

I believe 256 comes from the amount of numbers that can be represented using 8 binary digits.

Since each octet contains 8 bits, and each bit can represent a "1" or "0", the amount that is available is 2 to the power of 8, or 256.

For example:
00000000 = 0
11111111 = 255

The range of 0 - 255 represents 256 numbers since we start at 0 and go all the way to 255.

Here's an example:

Suppose we have 199.150.100.0/26
The last octet would look like this for all the subnets.

00000000
01000000
10000000
11000000

When you convert the bold numbers, you get 0, 64, 128, and 192 which are your subnets.
• Member Posts: 897
JockVSJock wrote: »
For all Class C examples he is always taking the last octect and subtracting this from 256, I'm just not sure the why behind this? Why not any other octect from the Subnet Address?

Also for the exam, I guess I'm having anxiety trying to do a problem where there 16/34/48/64 subnets.

Is anyone else bothered by this?

Right now I'm doing some of the math by calculator, however on the timed exam, not sure how this is going to go doing this by hand, because I doubt they are going to allow a calculator for this.

Might have more questions as time goes on...

The first thing you need to do it determine the class of the address....
Then you will know which octet is involved in the host addresses.

There are 3 main classes of IP address that we are concerned with.

Class A Range 0 - 127 in the first octet (0 and 127 are reserved)
Class B Range 128 - 191 in the first octet
Class C Range 192 - 223 in the first octet

Below shows you how, for each class, the address is split in terms of network (N) and host (H) portions.

NNNNNNNN . HHHHHHHH . HHHHHHHH . HHHHHHHH Class A
NNNNNNNN . NNNNNNNN . HHHHHHHH . HHHHHHHH Class B
NNNNNNNN . NNNNNNNN . NNNNNNNN . HHHHHHHH Class C
I don't claim to be an expert, but I sure would like to become one someday.

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• Member Posts: 360
Jock,

Lammle's book doesn't cover is the best IMO, but he is trying to teach you block sizing. If you can master block sizes, you can figure out any subnet question in seconds rather than minutes. Google it
CCNP :study:
• Member Posts: 166
If you're reading Todd's book I'd recommend creating an account on his forums. There is a lot of good information there.
• Member Posts: 1,096 ■■■■■□□□□□
fly351 wrote: »
Jock,

Lammle's book doesn't cover is the best IMO, but he is trying to teach you block sizing. If you can master block sizes, you can figure out any subnet question in seconds rather than minutes. Google it

I can't address Jock's problem, but in response to the above, I found Lammle's teaching of subnetting the best I'd ever seen. I do admit that I nearly had a brain-snap but after getting through it, it all made sense and I now own it forever.

• Member Posts: 196
The reason he is using 256 is because 2^8 = 256. In one octet of a subnet mask there are 8 bits...00000000

But a far easier way to find out the increment/block size is to work out the last bit position where the value is a 1

For example, lets look at the subnet mask 255.255.240.0

In binary that would be 11111111.11111111.11110000.00000000

Notice where the last 1 is ?

128 64 32 16 8 4 2 1

Increment is 16

256 - 240 also = 16
• Member Posts: 54 ■■□□□□□□□□
I'm reading Lammle's book also. And yes, his method of figuring out block sizing bothers me also, even though it works. I just cant make sense of it.

Instead of using his method of calculating block sizes, I divide 256 by 2▲# of network bits. Here's some examples...

In an address with a /26 subnet (aka 255.255.255.192), I take the 'sub-netted' octet of the mask (192), and think about what it looks like in binary (11000000). I note that there is 2 network bits. 2▲2 = 4, which means there are 4 total subnets in this octet. 256/4 = 64. 64 is the block size, so the valid subets would be 0,64,128, & 192. With Lammle's method, 256 -192 = 64 block size.

In a /28 (255.255.255.240), 240 = 11110000, 2▲4 = 16 total subnets, 256/16 = 16 block size, subnets are 0,16,32,48,64,...240. Lammle says 256 - 240 = 16 block size.

In a /19 (255.255.224.0), 224 = 11100000, 2▲3 = 8 total subnets, 256/8 = 32 block size, subnets are 0,32,64,96,128,160,192,224. Lammle says 256-224 = 32 block size

Lammle's method is faster and simpler. I don't understand why it works, but it does. The method I use makes more sense to me, and I still get the right answer, and I can do it fairly quickly in my head, so I use it.
AAS in CS/Networking Technology, A+, Network+, Security+, MCTS Vista Config, MCSA 2003, CCNA
• Member Posts: 54 ■■□□□□□□□□
mella060 wrote: »
The reason he is using 256 is because 2^8 = 256. In one octet of a subnet mask there are 8 bits...00000000

But a far easier way to find out the increment/block size is to work out the last bit position where the value is a 1

For example, lets look at the subnet mask 255.255.240.0

In binary that would be 11111111.11111111.11110000.00000000

Notice where the last 1 is ?

128 64 32 16 8 4 2 1

Increment is 16

256 - 240 also = 16

Wow! I never thought about it like that. That is really simple!!
AAS in CS/Networking Technology, A+, Network+, Security+, MCTS Vista Config, MCSA 2003, CCNA
• Member Posts: 1,118
JSK wrote: »
If you're reading Todd's book I'd recommend creating an account on his forums. There is a lot of good information there.

Thanks for the recommendations, I just did.
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• Member Posts: 196
Deesiel wrote: »
Wow! I never thought about it like that. That is really simple!!
It sure is. I picked this method up from Jeremy C in the cbt nuggets

My advice to JockVSJock would be to check out the cbt nuggets

Basically i got familiar with Lammles method and then watched the nuggets and realised how easy it was
• Member Posts: 933
mella060 wrote: »
The reason he is using 256 is because 2^8 = 256. In one octet of a subnet mask there are 8 bits...00000000

But a far easier way to find out the increment/block size is to work out the last bit position where the value is a 1

For example, lets look at the subnet mask 255.255.240.0

In binary that would be 11111111.11111111.11110000.00000000

Notice where the last 1 is ?

128 64 32 16 8 4 2 1

Increment is 16

256 - 240 also = 16

+1 for this method This is the same method I use and it is SOLID! A friend of mine recommended I do it this way and I can fly through subnetting questions within seconds.
• Member Posts: 723
Lammle's subnetting is easier to understand than Odom's. I love Odom's book, but his subnetting method confused the living heck out of me. I was glad that his ICND1 book comes with subnetting videos explaining the stuff he talked about in his book.
Anyway, I like lammle's method of subnetting, especially the subnetting in your head. Also, the subnetting made easy thread in this forum made subnetting even easier for me. Dude, you need to find that thread.
Studying:
Working on CCNA: Security. Start date: 12.28.10
Microsoft 70-640 - on hold (This is not taking me anywhere. I started this in October, and it is December now, I am still on page 221. WTH!)
Network Warrior - Currently at Part II
Reading IPv6 Essentials 2nd Edition - on hold
• Member Posts: 1,118
miller811 wrote: »

The first thing you need to do it determine the class of the address....
Then you will know which octet is involved in the host addresses.

There are 3 main classes of IP address that we are concerned with.

Class A Range 0 - 127 in the first octet (0 and 127 are reserved)
Class B Range 128 - 191 in the first octet
Class C Range 192 - 223 in the first octet

Below shows you how, for each class, the address is split in terms of network (N) and host (H) portions.

NNNNNNNN . HHHHHHHH . HHHHHHHH . HHHHHHHH Class A
NNNNNNNN . NNNNNNNN . HHHHHHHH . HHHHHHHH Class B
NNNNNNNN . NNNNNNNN . NNNNNNNN . HHHHHHHH Class C

Miller811, nice name...

Ok, I understand how to use this method by Lord Flasheart, however if you compare it Vs Lammle's way, he is also getting us:

-how many subnets
-how many hosts
-what are the valid subnets
-what is the valid hosts

BTW, going back thru Lord Flashearts' thread, looks like I now know how to answer the following questions for this website better:

subnettingquestions.com - Free Subnetting Questions and Answers Randomly Generated Online

thanks
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"Its easier to deceive the masses then to convince the masses that they have been deceived."
-unknown
• Member Posts: 1,118
mella060 wrote: »
It sure is. I picked this method up from Jeremy C in the cbt nuggets

My advice to JockVSJock would be to check out the cbt nuggets

Basically i got familiar with Lammles method and then watched the nuggets and realised how easy it was

One of the things I've noticed that there is no lack of material to study from and I don't want to get overwhelmed with it.
***Freedom of Speech, Just Watch What You Say*** Example, Beware of CompTIA Certs (Deleted From Google Cached)

"Its easier to deceive the masses then to convince the masses that they have been deceived."
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• Member Posts: 897
JockVSJock wrote: »
Miller811, nice name...

Ok, I understand how to use this method by Lord Flasheart, however if you compare it Vs Lammle's way, he is also getting us:

-how many subnets
-how many hosts
-what are the valid subnets
-what is the valid hosts

BTW, going back thru Lord Flashearts' thread, looks like I now know how to answer the following questions for this website better:

subnettingquestions.com - Free Subnetting Questions and Answers Randomly Generated Online

thanks

for practice I prefer this site

IP Subnet Practice
I don't claim to be an expert, but I sure would like to become one someday.

Quest for 11K pages read in 2011
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