IPv4 address, subnet mask, gateway

What is? IP Address

IP Address is the Internet address used to identify a network node .
IPv4 Address composition
Address length ：32 position
4 A decimal number （0~255） Express , With . separate （ dotted decimal ）

IP Address classification

By size

Category	network number . Host number	IP Range	scale
A class ：0~127 start	network . Lord . Lord . Lord	0.0.0.0~127.255.255.255	in super-large scale
B class ：128~191 start	network . network . Lord . Lord	128.0.0.0~191.255.255.255	On a large scale
C class ：192~223 start	network . network . network . Lord	192.0.0.0~223.255.255.255	small
D class ：224~239 start			Multicast
E class ：240~254 start			scientific research

Distinguish according to the scope of use

Public address ： Can be legally used on the Internet , You need to NIC Application for payment , The only global
Private address ： Reserved for internal use , There is no need to pay , The LAN is unique

Category	private IP Range
A class	10.0.0.0~10.255.255.255
B class	172.16.0.0~172.31.255.255
C class	192.168.0.0~192.168.255.255

special IP Address

IP Address	effect
127.* .*.*	Local loopback address
169.254 .*.*	Automatically get IP When the address fails
0.0.0.0	All destination hosts in the default route
255.255.255.255	Full broadcast
192.168.10.0/24	network number （ The host is full 0）
192.168.10.255/24	Broadcast address of the network （ The host is full 1）

Subnet mask

• Judge IP Network bit of address , Same network bit IP Can communicate directly
• Cannot exist alone , Must be combined with IP Address used together
• Default subnet mask

Category	Subnet mask	network number . Host number
A Class address	255.0.0.0	network . Lord . Lord . Lord
B Class address	255.255.0.0	network . network . Lord . Lord
C Class address	255.255.255.0	network . network . network . Lord

notes ：192.168.1.1/24, The mask bit is 24, amount to 255.255.255.0（24 individual 1）

gateway

What is a gateway ？

• Connecting one network segment to another “ Gateway ”
• It is usually a router or firewall / The address of the access server

host A
IP/ Mask bit ：192.168.1.1/24
The default gateway ：192.168.1.254

host B
IP/ Mask bit ：192.168.2.1/24
The default gateway ：192.168.2.254