VLSM subnet Division

VLSM Variable length subnet mask   --   Subnet partition

（1） Subnet partition definition ：Internet The organization defines five types of IP Address , Yes A、B、C Three types of address .A There are 126 individual , Every A Such networks may have 16777214 platform host , They are in the same Broadcast area . It is impossible to have so many nodes in the same broadcast domain , The network will be saturated by broadcast communication , Result in 16777214 Most of the addresses are not allocated . Based on each class IP The network is further divided into smaller networks , Each subnet is defined by the router and assigned a new subnet network address , The subnet address is created by borrowing the host part based on each type of network address . After dividing the subnet , By using Mask , Hide the subnet , Make the network unchanged from the outside , This is it. Subnet mask .

（2） Based on the first paragraph, we can distinguish and classify ：

A 1-126

B 128-191

C 192-223

D 224-239

E 240-255

ABC The difference between the three types is that the default subnet mask length is different ：

A  255.0.0.0   B 255.255.0.0   C 255.255.255.0

（3） By extending the length of the subnet mask , From the original host bit to the network bit ; Realize the segmentation of a network number into multiple ; Every new subnet , Fewer hosts ;    Add network number , Reduce the number of users in each network number ;

Bear in mind ： Divide a network segment into multiple subnets , In the network, the master network will not be configured to be available ip;

1> See the subnet division .. I think we should first look at the subnet mask ,（ The role of subnet mask will be a IP The address is divided into network address and host address ） In this way, the network bit and host bit can be distinguished first   Lay a good foundation for the next division

2> Then beginners , You can put it first. 128 64 32 16 8 4 2 1 This string of figures is listed

3> And then ip The address is written in binary   Keep the network in place （ unchanged ） Then divide the network bit and host bit according to the subnet mask

4> See the picture below <1> Because it is divided into four subnets , So there is 00 01 10 11 These four possibilities （ You can imagine it as a permutation ）

Arrange the binary , Division complete , Separate them into 00 01 10 11 Four kinds of , Then start the transformation, as shown in the figure

Because the number of digits of the network address is 24 position , So the number of digits of the host address is 8 position .

And because the number of hosts is 62 platform 、48 Taiwan and 50 platform , therefore ​,

therefore ​,n=6.

Because the number of hosts is 6 position ,8-6=2, So the number of digits of the subnet address is 2 position .

IP Address ：192.168.1. 00   000000

                    chart <1>

The analysis results are shown in the figure . There is another example , You can refer to , Practice, practice , The answer is at the end