IPV4, Class and Subnetting.

 

IPV4, Class and Subnetting.

 

IPV4 which stands for Internet protocol version 4 consists of 32 bits. It is written in four octets (1 octet consists of eight bits) –

xxxxxxxx.xxxxxxxx.xxxxxxxx.xxxxxxxx -----these digits are in binary either 1 or 0 and if written in decimal looks something like this – 10.25.58.65 

The maximum value of 1 octet is 255 that is derived from- lets suppose if an octet is all 1s like 11111111 ---- the decimal value of this equals to 255.

Lets get into few important points:

 

IPV4 class ----

Classes	1st Octet Range	Default Subnet Mask	Finding Formula
A	0-127 (#127 is a loop IP)	255.0.0.0	00000000(0) -011111111(127) (0 constant in the range)
B	128-191	255.255.0.0	10000000(128) – 10111111(191) (10 constant )
C	192 -223	255.255.255.0	11000000(192) – 11011111(223)  (110 constant in the range)
D	224-239	For Multicasting	11100000- 11101111 (1110- constant)
E	240-255	For Research and Future use

 

Just so you know, IP are divided into private and public, and they are broadly relevant to only class A, B and C as D and E are used for multicasting and future purposes respectively.

The table below is used for Private I.P Addresses

Class A	10.x.x.x	10.0.0.0-10.255.255.255
Class B	172.16.x.x – 172.31.x.x	172.16.0.0 – 172.31.255.255
Class C	192.168.x.x	192.168.0.0 – 192.168.255.255

 

 

Lets get few things clear first:

 

·       Every IP address has network portion and the host portion. So, here lets suppose I have an IP address 192.168.5.1 /24 – comparing this to IPV4 class table we know right away --- it falls under C class and its subnet mask is   

255.

255.

255.

0

              Which can be viewed as 

11111111.

11111111.

11111111.

00000000

 Which is essentially    

N.

N.

N.

H

 Meaning 1 bits can be considered as X and can be perceived as the network bits denoted by N in the box. And 0 bits considered as Y and represent the host bits denoted by H in the box.  

 

·       CIDR – I remember by pronouncing it cider just like apple cider , it stands for Classless Inter -Domain Routing my friends.  Lets look at the example below ---

192.168.20.5 /28    ------ the number after the / is called the CIDR and it represents the number of ‘ON” bits in the IP, meaning the number of 1’s –

So, do this way --- you know an IP is 4 octets(meaning 8 digits) separated by a dot after each octet.  So when you see CIDR notations just fill in the 1 digit starting from first,,,, so, In the above case ------ 11111111.11111111.11111111.11110000  -------------------here 3 x 8 = 24 so I filled with 1 digits first 3 octets right away and filled 4 more in the last octets just to make sure I add up to the CIDR notation of 28. 

Also, I am sure you noticed it referencing from the IP class it belongs to Class C and which has a default Subnet mask of 255.255.255.0  but with the CIDR notation of 28 the default mask is

Lets find the decimal value of 11110000 which is 240.  So the subnet mask of  192.168.20.5 /28 is 255.255.255.240

·       A subnet mask my friends is an address of 32 bits and helps as I mentioned above to identify between a network address and a host address.

 

Lets Understand Subnetting by looking at the following table, question may be asked where you have to fill in the IP for all the headings:

 

Target IP	157.168.191.166/26	Fill in the IP for the remaining .
Network IP
First Host IP
Last Host IP
Broadcast IP
Next Subnet IP

 

Network IP is the first IP , broadcast IP is the last IP and host IPs are in the middle.

1

254

1

Network IP                      Host IPs                          Broadcast IP

 

Network IP is calculated by doing the logical ‘AND’ operation of the bits and the subnet mask bits’, so lets find the network IP of 157.168.191.166/26

 

157.168.191.166      157.168.191. 10100110

Subnet Mask – 11111111.11111111.11111111.11000000

10100110 x  11000000 ……………………………..     10000000   ==== 128

Network IP – 157.168.191.128

 

And, subnet mask for above IP is 255.255.255.192 (decimal of 11000000 – since it has a CIDR of 26)

 

       Block Size = 2^y  = 2⁶ = 2x2x2x2x2x2 = 64

       Valid Host =  2^y -2 = 64 – 2 = 62

       Possible Subnets = 2^x = 2² = 2x2 = 4

       Broadcast IP is the last IP –

      So, if network IP is 157.168.191.128,  1^st host is the immediate IP after network IP  --- so it is 157.168.191.129 , and there are 62 valid host --- so last host is  157.168.191.190 (28+62)   and  Next subnet is  128+64(block size) = 192 so 157.168.191.192 and broadcast is the last IP before other network ID begins  and therefore in this case is  157.168.191.191.

 

In this example, four subnets are created so we can do the same starting for another network which is  157168.191.192.

 

 

Thank you my friends,

Hope this helps – if you have any questions, leave me comments and I will ty to get back to you !

 

Cheers !