IP address: the
unique identifier of the host to ensure normal communication between the hosts;
a network code used to identify a node in the network; the
IP address is composed of 32-bit binary (32bit).
The composition of the IP address: the
network part (NETWORK) and the
host part (HOST)
IP addresses are divided into five categories: A, B, C, D, and E. Each category has different division rules.
A, B, and C three types of IP address composition 
Private address: to
meet the needs of enterprise users in the internal network;
private addresses cannot be used on the Internet;
private addresses include 3 groups:
Class A: 10.0.0.0~10.255.255.255
Class B: 172.16.0.0~172.31.255.255
Class C ：192.168.0.0~192.168.255.255
Subnet mask:
used to determine the IP network address;
32 binary bits;
the network part of the
corresponding IP address is represented by 1; the host part of the corresponding IP address is represented by 0;
IP address and subnet The mask performs logical AND operation to obtain the network address;
0 and any number are equal to 0;
1 and any number are equal to any number itself;
The default subnet masks for the three types of addresses:
A , B, and C Class: 255.0.0.0
Class B: 255.255.0.0
Class C: 255.255.255.0
Configure IP address Configure IP address
under Windows: 
Router configuration IP address
Router(config)#interface fastethernet 0/1
Router(config-if)#ip address ip-address subnet-mask
Router(config-if)#no shutdown
Switch configuration IP Address
Switch(config)#interface vlan 1
Switch(config-if)#ip address ip-address subnet-mask
Switch(config-if)#no shutdown