Partially taken from


Internet Protocol and the Transmission Control Protocol.

IP address is a 32-bit logical number to address a network device. IP are normally represented by decimal numbers, but could be useful sometimes to represent them in binary.

172. 19. 88. 73

An IP address is divided in 4 parts (each 8 bits), these parts are called octets. In the IPV4 there are 5 address classes:

Class A from 1 to 126, in binary the octet start with 0xxx
127 Reserved for loopback, 01111111
Class B from 128 to 191, in binary the octet start with 10xx
Class C from 192 to 223, in binary the octet start with 110x
Class D from 224 to 239, in binary the octet start with 1110 Don’t use. Reserved for the future.
Class E from 240 to 254, in binary the octet start with 1111

IANA reserved 4 address ranges to be used in private networks, these addresses won’t appear on the Internet avoiding IP address conflicts.,, and that means:

– through
– through
– through
– through (reserved for Automatic Private IP Addressing)

The meaning of 8,12 and 16 is

8 =
12 =
16 =

These are subnet mask.

A subnet mask is used to determine which part is the network (n) part and which is the host (H) part.
Default subnet masks:
Class B that is nnnnnnnn.nnnnnnnn.HHHHHHHH.HHHHHHHH
Class C that is nnnnnnnn.nnnnnnnn.nnnnnnnn.HHHHHHHH


Bitwise (logical AND) between IP address and subnet mask to have the IP of the network


To calculate how many subnet in a net mask I can have use the formula (2^n) -2 where n is the number of bits in either field. For example the subnet (11111111.11111111.11110000.00000000 could have (2^4) – 2 = 14 subnets.