IP addresses & subnetting

IP addresses & sub-netting

Classes            Ranges       CIDR (Classless Interlink Routing/Default Mask)

 

A                 1-126                            /8

B                 128-191                    /16

C                 192.223                   /32

D                 224-239                  N/A Multicast

E                 240-255                  N/A Reserved for

 

How to classify is by Octet & not by class i.e in IPv4 we have 4

 

-------- . -------- . -------- . -------- (Each one of them has 8 bits so 8+8+8+8 = 32 Bits, IPv4 is 32 bits address)

So when we classify IP addresses we see the first Octet.

For example:

123.XXX.XXX.XXX (It is Class A and by default the CIDR/Default Mask is 8)

0 is the universal gateway and we use it for default routing. It is not used.

127.0.0.0 is a loopback, we can ping 127.0.0.1 to test the network connection.

Remember the CIDR got nothing to do with the classes.

You can have Class A as /16 or /24. This only means that the Class A is

Now we'll do the Private Class Range: (Private means they are not

Class            Ranges               CIDR (Classless Interlink Routing/Default Mask)

 

A               10.0.0.0 - 10.255.255.255               /8      

B               172.16.0.0 - 172.31.255.255          /12

C               192.168.0.0 - 192.168.255.255         /16

 

192.168 is the Network ID & 0.0 is the Host ID

So there can be changes from 0-255 in the third Octet. 192.168. |0.0 - 192.168. |255.255

Thats why we use NAT (Network Address Transaction) to convert Private IPs to Public IPs

Note: If you know bit values you can answer anything:

128 | 64 | 32 | 16 | 8 | 4 | 2 | 1

Every Octet has these increments because when we see the IPv4 Address its broken down into:

-------- . -------- . -------- . --------

So we got here 4 Octets ( 1 Octet = 8 bits)

Note:

Subnet we count from left to right & host we count from right to left.

 

*        *        *        *        *        *        *        * . ******** . ******** . ********

128     64      32      16       8        4        2        1 . Any so forth.

So if you are give the Mask CIDR /28, what does that mean?

That means:

- - - - - - - - . - - - - - - - - . - - - - - - - - . - - - - - - - - Is from 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

So - - - - - - - - . - - - - - - - - . - - - - - - - - . - - - - | - - - -

Till here its 28 (Network ID)                   Off (Host ID)

So your imaginary line is not at 28:

                 28                   4

- - - - - - - - . - - - - - - - - . - - - - - - - - . - - - - | - - - -

So this last 4 Octet is where our focus should be.

So everything 1-28 is the Network & remaining is the Host

Hence the question arises, how do we use bits?

-  -  -  -  -  -  -  - . -  -  -  -  -  -  -  - . -  -  -  -  -  -  -  - . -  -  -  - | -  -  -  -

 16   8  4  2  1 

 So if you add 1 + 2 + 4 + 8 = 15

 Now the 15 here helps us to calculate the Broadcast Address

 -  -  -  -  -  -  -  - . -  -  -  -  -  -  -  - . -  -  -  -  -  -  -  - . -  -  -  - | -  -  -  -

            X                                X                          X                            16  <-  15  ->

The Xs do not change so:

So now we increment by 16

X.X.X.16

X.X.X.32

X.X.X.48

X.X.X.64 Until it reaches the very last subnet.

(Note: This are all subnet IDs)

The next thing you need to find is the Broadcast Address i.e 0000 or last 4 Octet (8421)

How do we get that?

X.X.X.16

So 16 + 15 (15 is the Broadcast

So what is after X.X.X.16 ? 17

& whats before   X.X.X.31 ? 30

So 17-30 is our range.

What ever X.X.X is it does not matter.It can be 10.0.0 or 192.168.1 it really

Next Network:

X.X.X.32

So 32 + 15 (15 is the Broadcast Calculation) = 47 (You cant use it)

So whats after X.X.X.32 ? 33

& whats before X.X.X.47 ? 46

So 33-46 is our range.

Next Network:

X.X.X.48

So 48 + 15 (15 is the Broadcast

So whats after X.X.X.48 ? 33

& whats before X.X.X.63 ? 46

So 49-62 is our range.

Thank you! 'Happy learning'