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Learn to Subnet Using Games and Charts

Posted by: admin  :  Category: CCNA, Exam Preps, Routing




Subnet

One of the most intimidating but extremely important subjects on the CCENT/CCNA or ICND1 exam is subnetting. We were all taught to think in decimal but computers think in binary and the idea of all those ones and zeros are just a bit overwhelming for most of us. A subnetwork, or subnet, is a subdivision of an IP network address providing multiple smaller networks. Subnetting is the practice of dividing a network IP address into two or more networks.

 

There are a number of excellent tools available online as well as computer applications to make this task easy and I believe that you should be allowed to use these on the exam, let’s face it if you are configuring a router or switch you are going to have access to a computer, but like grade school students calculators are not allowed on the exam. Therefor we must learn to subnet in our heads or wood brain as it were. Due to a time limit on the exam you do not have a lot of time for wood brain; you need to answer these questions in about 30 sec.

There are a number of methods available to master this subject. There are decimal and binary methods; there is even a Magic Number method it just depends on which method work best for you. Myself I like to spend some time before starting the exam and create a subnet cheat chart. You are not allowed to bring anything with you to an exam but you can request blank paper and a pencil. This chart is easy to create on the fly if you can multiply by 2, just keep doubling the previous number starting with 4 then for the subnet mask subtract the number you are doubling from the previous sub net mask starting with 252 example (252 – 4 = 248).

BITS  

SUBNETTING CHART

1 2¹ = 2  
2 2²  = 4 ID Class  A, B, or C
3 2³  = 8 How many subnets are needed
4 2⁴  = 16 Exit if you need 62 subnets
5 2⁵  = 32  
6 2⁶  = 64 Example:
7 2⁷  = 128 Borrow 6 Bits then you have your block size.
8 2⁸  = 256 Then subtract the block size from 256
9 2⁹  = 512  
10 2¹⁰  = 1024 256 – 64 = 192 = 255.255.255.192
11 2¹¹  = 2048  
12 2¹²  = 4096  
13 2¹³  = 8192  
14 2¹⁴  = 16,384  

MASK

252

248

240

224

192

128

CIDR

/30

/29

/28

/27

/26

/25

 

 

N

E

T

W

O

R

K

 

 

0

0

0

0

0

 

4

8

16

32

64

128

8

16

32

64

128

256

12

24

48

96

192

 

16

32

64

128

256

 

20

40

80

160

 

 

24

48

96

192

 

 

28

56

112

224

 

 

32

64

128

256

 

 

36

72

144

 

 

 

40

80

160

 

 

 

44

88

176

 

 

 

48

96

192

 

 

 

Now that you see how this chart is created try creating it on your own without referring to this example. Use it to practice subnetting also try this Subnetting Game from the Cisco Learning Center using your chart and see how you do.

4 Responses to “Learn to Subnet Using Games and Charts”

  1. dsln9138 Says:

    I can’t fing the subnetting game

  2. admin Says:

    The link is in the article but here it is again, https://learningnetwork.cisco.com/docs/DOC-1802

  3. pcedron Says:

    First time here… so far, so good

  4. mark_praktisero Says:

    tnx

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