1. The role of subnet Division

  ：IP Addresses are like real home addresses , You can identify a node in the network , Data is used to find the destination . His role is Calculate the network number , Select the correct network device through the network number to connect to the terminal device , Subnet division can also be used for LAN ( Intranet ) Network address planning .

2.IP The composition of the address

        IP Address by 32 It's made up of two digits , It can also be expressed as a decimal number with points divided into four segments , this 32 Bit is divided into network bit and host bit （ Network bit + Host bit =32 position ）; Network part （ High ） It is used to determine whether the terminal is in the same network segment , The host part of the （ In the low position ） Used to determine the number of terminals .

2.1 Address protocol

    ipv4： Current mainstream agreements

    ipv6：fe'80::fe7：ca03：81f:2287

3. Subnet mask

Subnet mask ： Distinguish one ip The network part and host part of the address

 192.168.10.1

 255.255.255.0        192.168.10.1 in 192.168.10 It's the network part .1 It's the host part    

4.IP Address classification

The global IP The address is about 43 Billion People put this 43 100 million points 5 class

A B C D E Five categories （ Commonly used ABC class ）

1：A class IP The address is from 1 Byte network address and 3 Byte host address composition , The highest bit of the network address must be “0”.

2：B class IP The address is from 2 Byte network address and 2 Byte host address composition , The highest bit of the network address must be “10”.

3：C class IP The address is from 3 Byte network address and 1 Byte host address composition , The highest bit of the network address must be “110”.

   4：D class IP Address bit multicast address

   5：E Class reserved for future use

4.1 Special address ：

0.0.0.0

Is not a real sense of IP Address . It means all unclear hosts and destination networks

255.255.255.255 

Limit broadcast address . For this machine , This address refers to ( Same broadcast area ) All hosts of

127.0.0.1～127.255.255.254 127.1

Local loopback address , Mainly used for testing . The destination address should never appear on the transmission medium “127.0.0.1” Data packets of

224.0.0.0 To 239.255.255.255

Multicast address ,224.0.0.1 Especially all hosts ,224.0.0.2 Especially all routers .224.0.0.5 finger OSPF Router , Address is used for some specific programs and multimedia programs

169.254.x.x

If Windows The host uses DHCP Automatically assigned IP Address , And can't go from DHCP The server gets the address , The system will be the main

The machine allocates such an address

netmask Subnet mask ：

32 Bit or 128 position （IPv6） The number of , and IP Use in pairs , Used to confirm IP The network in the address ID And host ID, Corresponding network ID The position of is 1,

Corresponding host ID The position of is 0, Example :255.255.255.0 ,

The continuous high level is 1, The continuous low order is 0

5. How to calculate network signal

      The relevant formula ：

The number of hosts available in a network ＝2^ host ID digit -2

The Internet （ paragraph ） Count =2^ The Internet ID The variable number of digits in

The Internet ID=IP And netmask

And operation （ Approximately equal to multiplication ）

subject ：

A:10.0.0.1/8 ping 10.0.0.2

B:10.0.0.2/16

1： Their own IP Address and Subnet mask operation Get the network id

2: take B The address of and A Operate with your own subnet mask obtain b Network of id

3： Judge 1 2 In the middle of step The Internet id Is it consistent Consistent communication

4： If atypism Pass to The gateway helps forward data

host A With the host B Can you communicate ？ You can't ？ It's about who ？ 

192.168.1.00000001

192.168.1.0

33=32+1

192.168.1.001 0 0001

192.168.1.111 00000

192.168.1.00100000

192.168.1.32

Use your own subnet mask and your own IP And the other party's IP Meet each other , Comparison results , The same is the same network , Different network segments