Sub-Network Division

In the CIDR representation of the IP address, the value can be used for the 8-30,a class network can use the 8-30,b class network can use the 16-30,c class network only use 24-30.

Answer 5 questions before you divide the subnet:

1. How many subnets to create
2. How many hosts each subnet contains
3. How many legitimate subnets are there?
4. What is the broadcast address for each subnet?
5. Which host addresses each subnet contains

Here are some answers to these questions:

1. 2x each. where x represents different meanings in different types of networks. In Class A networks, X represents the number of 1 in three bytes after the subnet mask, and X in the Class B network represents the number of 1 in the last two bytes of the subnet mask, and the x in the Class C network represents the number of 1 in the subnet mask.
2. A 2y-2. The meaning of y in different types of networks is consistent, representing the number of 0 in the subnet mask. The two minus is the subnet address and broadcast address.
3. The block size (increment) is 256-z. Where z is the last non-0-byte decimal value in the subnet mask, starting with 0 does not add the block size until Z. For example, the subnet mask is 255.255.255.192, then the block size is 256-128=64, and from 0 continuously add 64 to produce 0,64,128,192 four subnets. If the non-0 bytes are not the last byte, then the bytes after the network address are 0.
4. The broadcast address is always the number in front of the next subnet, and the broadcast address of the last subnet is always 255. To continue with the previous step, the broadcast address for subnet 0 is 63, the broadcast address for subnet 64 is 127, and the broadcast address for subnet 192 is 255. As above, if the subnet mask is not the last byte of 0 bytes, then the bytes after the broadcast address are 255.
5. The legitimate host address is between the subnet number and the broadcast address. In the example above, the subnet number is 64 and the broadcast address is 127, then the legitimate host address is 65-126.

Here's a concrete example to illustrate how to divide subnets.

IP Address: 172.16.0.10

Subnet Mask: 255.255.128.0

Let's answer the 5 questions above.

1. This is a Class B network with 2 subnets
2. 215-2=32766 Main Station
3. 256-128=128. There are 0.0,128.0 of two subnets
4. The broadcast address for subnet 0.0 is 127.255, and the broadcast address for subnet 128.0 is 255.255
5. The host in subnet 0.0 has 0.1-127.254, the host within subnet 128.0 has 128.1-255.254

As shown in the following table:

Sub-Network	0.0	128.0
First host Address	0.1	128.1
Last host Address	127.254	255.254
Broadcast Address	127.255	255.255

Sub-Network Division