What is block size

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Subnetting by using multiples of Block Size

7 320 views | 29 Feb. 2016

Just recorded a quick

Just recorded a quick video with no editing to demonstrate my favorite method to subnet very quickly. In this video I assume that you have already learned subnetting so I leave out a bunch of information about the "why" behind a subnet and just teach you the method. If you do not completely understand subnetting, please watch a longer more in-depth video first!

Fore more networking videos, I highly recommend these two channels as they are what I used to get my CCNA (as well as a website):

1. https://www.youtube.com/user/NetworKingInc

2. https://www.youtube.com/user/ShrikeCast

Website: Networklessons.com (not free, but I love love love this website for learning material)

Looking for a community to join? Reddit has a brilliant subreddit for getting extra help:


I also used Boson to be able to pass my ICND exams on the first try:


Rehum Zondo

It's almost impossible for me to leave comments ... but You are a genius. Thanks a Million....


I see how this would work with Class C. How would you come up with the usuable IP's for Class A & B?

Dean Gough

As you said you are working with a / 11, how did you know that it would be 2nd oxted? Also would this chart work with classes A and B? Thanks

Lahad Israel

@3:30 How did you get 9, 10, 11? I don’t quite get that part.

Ahmad Arafat

Best video for Subnetting. Basic and Simple.

Richard Messi

You saved my life
Thank you


I have another question if it is not too much to ask. In real enterprise environment where this is used , how to they build the physical side the network to accomodate this ? I know that a router has to be employed to route traffic across different subnets but is that the case in real time environments. For example , If I have 4 subnets should I have 4 routers ?


What if the Octet Decimal value of the octet that is being worked has a value less than Block Size.

For example, taking your second example , instead of /29 , what will happen if it is ? Since the block size 8 does not even fit once in in the 4th octet which is "4" , will it be 0 then ?

Like the network ID : ??

Also what if the 4th octet value matches exactly on one of the 8's multiple , say for example, /29.

In this case , will the network ID be ? Or 192.168.18. 56 ?
( in other words should be less than the octet decimal value or lesser or equal to octet decimal value )


Thank you man.

El Dang

What if you are dealing /8

delvon simmons

Thank You so much, this video clears up a lot for me. Well done sir

What is block size

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Classless IP Addressing: Subnet Mask, subnet block size, network address

26 424 views | 18 Feb. 2015

This video lecture is

This video lecture is produced by S. Saurabh. He is B.Tech from IIT and MS from USA.

Slides are from Computer Networks: A Top-Down Approach

Behrouz A. Forouzan

Firouz Mosharraf

It is one of the best books on networking, I like the presentation of the concepts in this book a lot personally.

Understand the concept of classless addressing

1. Be able to find the first and last address given an IP address

2. Be able to find the network address given a classless IP address

3. Be able to create subnets from a block of classless IP addresses

4. Understand address allocation and address aggregation

To study interview questions on Linked List watch http://www.youtube.com/playlist?list=PL3D11462114F778D7&feature=view_all

To prepare for programming Interview Questions on Binary Trees


To study programming Interview questions on Stack, Queues, Arrays visit


To watch all Programming Interview Questions visit


To learn about Pointers in C visit


To learn C programming from IITian S.Saurabh visit


Shahbhaz Alam

didnt understand only..!!

Funny Youtube?

stop fumbling and repeating OKs,jst concentrate on how well u can explain..Your explanation is not at all upto the mark bcaz its confusing,i'm sry to say that but it's true..

Mikel Jonas

sir i hardly trying to understand this pls in 9:20 what the connection between 52 and 12?

Integral Souls



For the people that are confused starting at 5:18:

At this point he is explaining that with a block size of 2^8 the only bits that could possibly not be divisible by 2^8 are the last 8 bits (bits 7-0). What he is doing with a31*2^31+a30*2^30 business is representing the ip address as a binary integer instead of a dotted decimal. For instance a31 represents the left most (most significant) bit in the address. all of the a31...a0 are just bits (0 or 1)

In the example that follows, where we are checking a block that contains 16 addresses the only bits that can't be divisible by 16 are the last 4 bits (16=2^4) so he is checking if the last 4 bits of each address are divisible by 16.

If this is still very confusing you might want to make sure you understand binary integers before continuing.

Ron Borneo

He makes it more complex than it is. During his examples, you can get the intuition behind the problems.


by far the most confusing video on youtube. #redo

Ajit Kumar

@saurabhschool  Hi. can you do a video on an algorithm that checks whether a link list is palindrome or not. I am having trouble understanding it and couldnt find any video tutorial.
the link to the problem is- http://www.geeksforgeeks.org/function-to-check-if-a-singly-linked-list-is-palindrome/

Vineeth Pillai

Saurabh, a quick tip: To check if x is divisible by a number 2^n, we need to make sure that least n bits are zero. You go through the pains of finding the last bits as zero and then verify 0/n = 0 to make sure that it is divisible. You can directly say that without going through the math.

Akshay Saindane

2^8 is 256 not 64 anyways thanks!


as soon as the video reaches 5:18 i get lost smh.

What is block size

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CIS 351 Video 47: Cache Block Size

160 views | 18 Nov. 2020

Discusses a cache's block

Discusses a cache's block size (including benefits and potential costs)