Subneting, Reverse engineering **** sheet

sangstar

Hi all

Im sitting my ICND2 in 2 weeks, and realised I need to speed up my sub-netting / reverse engineering, I've come up with the below table that helps so much.




My maths was letting me down on finding networks for IPs, so I made the following chart that has made it so much easier.




Regards,
Sangeeta

cb3dwa

could you explain your diagrams ???

cheers

sangstar

** Diagram 1**


Chart of of CIDR notation, with its corressponding mask, with its corresponding block size & wildcard mask


For example,


172.16.10.3/19 = 172.16.10.3 255.255.224.0
The wildcard for this mask would be 0.0.0.31


The block size = 32, this means the network would increments as follows:


172.16.0.0
172.16.32.0
172.16.64.0
etc...


So you basically look at notation/,mask, and the column give you info about the network.


The additional 256,512... is a reference for hosts required per network
So in our example above 172.16.0.0/19 gives us 1024, of which 1022 are usuable, after taking away your network, and broadcast address.






**Diagram 2**


This is my way of remembering my 16 multiplication table!
The 16's table goes as follows


16
32
48
64
80
96
112
128
144
160
176
192
208
224
240
256


Now i noticed that the last digits goes up in 2, on every alternate multiplication (0,2,4,6,


eg


1 6 - last digit is 6, next alternate is 8


3 2


4 8 - last digit is 8, next alternate is 0


6 4


8 0



For the first digit of the 16's table, you add using sequence 2,1,2,2,1


eg


First digit is 1, add 2 according to sequence, makes first digit of next number 3---->1 6


First digit is 3, add 1 according to sequence, makes first digit of next number 4----> 3 2


First digit is 4, add 2 according to sequence, makes first digit of next number 6----> 4 8


First digit is 6, add 2 according to sequence, makes first digit of next number 8---->6 4


First digit is 8, add 1 according to sequence, makes first digit of next number 9----> 8 0



You are given a white board for notes during the exam.

You given approx 20 mins before exam, this is where I used the cidr chart during my ICND1 exam.

However my let down was my 16 multiplication table (spent too long adding in the exam), so I made Diagram 2 for me to remember, so I can put it on my whiteboard for reference.