An IP address consists of 4 contiguous octets and is generally written in Dotted Decimal Notation in the form:
A.B.C.D
Where:
A represents the most significant octet, D the least significant octet
A,B,C and D are integers between 0 and 255
The 32 bits in an IP address are split between a unique:
Net ID which represents the network to which the host or gateway is attached
Host ID which uniquely identifies a specific host within that network
Note: The Net ID always precedes the Host ID.
Special and Reserved Addresses
There are groups of reserved addresses (RFC 1918: Address Allocation for Private Internets)
10.0.0.0 – 10.255.255.255
This is a Class A address
172.16.0.0 – 172.31.255.255
This is a set of 16 contiguous class B addresses
192.168.0.0 - 192.168.255.255
This is a set of contiguous class C addresses.