Learn to divide subnets in an article

IP Address and subnet Division

Towards the end of the term , Review computer network , An article teaches you to understand subnet partition .

Basic concepts

• according to TCP/IP agreement , Connected to the Internet Every device on the must have a globally unique IP Address （ The logical address used by the network layer ） 32 The binary number of bits .

• It is generally expressed in dotted decimal system ： Every time 8 One by one , Convert to decimal , use "." separate

• meaning ： network number + Host number

32（bit） The binary number of bits ：

dotted decimal ： Every time 8 Bit to a decimal number , use . separate

IP Address meaning ：

IP Natural classification of addresses

IP Address type	Binary fixed highest	First byte Decimal range	Binary system network number	Binary system Host number
A class	0	0~127	8 position	24 position
B class	1	128~191	16 position	16 position
C class	110	192~223	24 position	8 position
D class	1110	224~239	Multicast uses
E class	11110	240~255	Reserved for trial use

special IP Address

• network address ： The network address is used to represent the network where the device is located . The network number part is not change , The host number part is all “0”（ Binary system ） Of IP The address is called the network address . Such as mainframe 129.5.1.1（B class ） The network address of your network is 129.5.0.0.

• Broadcast address ： The broadcast address is used to broadcast to all devices in the same network . network The network number remains unchanged , The host number part is all “1”（ Binary system ） Of IP Address scale For broadcast address . Such as mainframe 129.5.1.1 （ B class ） the stay network Collateral Of wide seeding The earth site Just yes 129.5.255.255.

• Loopback address ： The device address in the network cannot be decimal 127 As the beginning ,127 open The address of the header is reserved for the system for diagnostic purposes , Called loopback address . If you use instructions ： ping 127.0.0.1 Test whether the local network card works normally （ Loop test ）

subject ： Judge the following IP Classification of addresses

10.2.1.1 128.63.2.100 201.222.5.64 192.6.141.2 256.241.201.10

IP Address	Category	network address	Broadcast address
10.2.1.1	A	10.0.0.0	10.255.255.255
128.63.2.100	B	128.63.0.0	128.63.255.255
201.222.5.64	C	201.222.5.0	201.222.5.255
192.6.141.2	C	192.6.141.0	192.6.141.255

256.241.201.10 non-existent

Subnet mask

• Subnet mask ： Used to identify IP The number of digits of the network number in the address
• 2 There are two ways to express ：
  • 32 Bit binary number , In the subnet mask , Corresponding to the network number part, use binary “1” Express , The host number part is binary “0” Express . Such as IP Address 1.1.1.1 The subnet mask for is 255.0.0.0, Indicates the front of this address 8 Bit is the network number .
  • Network suffix method , namely “IP Address / Number of network numbers ” , Such as 138.96.0.1/18 surface Show that IP The network number of the network where the address is located 18 position , Host number 14 position .

• A network , The host number has x position , Then the network can be assigned to the host IP How many addresses ？
• The network consists of 2 Of x The next address , Remove network address and broadcast address , That can be assigned to a host IP The address is 2 Of x Power -2 individual
  • for example , One C Class network , That can be assigned to a host IP The address is 2 Of 8 Power -2=254 individual

Subnet partition （ Topic actual combat ）

Reasons for dividing subnets ： Improve IP Address utilization .

The core idea of subnet Division ： The network number remains unchanged , Borrowing part of the host number to generate a new network .