Relationship between subnet mask and IP address

The subnet mask is used to determine whether the IP addresses of any two computers belong to the same subnetwork.
The simplest understanding is that after the IP address AND subnet mask of the two computers perform the AND operation, if the result is the same, the two computers are on the same sub-network and can communicate directly. That's simple.

See the following example:

Computing Demonstration: aa

IP address 192.168.0.1

Subnet Mask 255.255.255.0

　
Convert to binary for calculation:

IP address 1102.16.10101000.00000000.00000001

Subnet Mask 11111111.111111.1111111111.00000000

AND Operation

111000000.10101000.00000000.00000000
Converted to decimal:

192.168.0.0

Operation demonstration 2:

IP address 192.168.0.254

Subnet Mask 255.255.255.0

Convert to binary for calculation:

IP address 1102.16.10101000.20.2.16.11111110

Subnet Mask 11111111.111111.1111111111.00000000

AND Operation

111000000.10101000.00000000.00000000
Converted to decimal:

192.168.0.0

Computing demonstration 3:

IP address 192.168.0.4

Subnet Mask 255.255.255.0

Convert to binary for calculation:

IP address 1102.16.10101000.00000000.00000100

Subnet Mask 11111111.111111.1111111111.00000000

AND Operation

111000000.10101000.00000000.00000000

Converted to decimal:

192.168.0.0

After the AND operation on the IP addresses AND subnet masks of the three groups of computers, we can see that the operation results are the same. All are 192.168.0.0

Therefore, the computer will regard the three computers as the same sub-network and then communicate with each other. The proxy server used by my current organization is planned as the internal network.

Maybe you have to ask, how many IP addresses are available for such subnet masks? You can calculate this.

According to the above, we can see that the IP address inside the LAN is defined by ourselves, of course, the same as other IP addresses), this is determined by the subnet mask through the analysis of 255.255.255.0. It can be concluded that:
The first three IP addresses can only be fixed to 192.168.0, so only the last one is left. Obviously, the IP address can only be 2 to the power of 8-1 ), that is, 256-1 = 255. Generally, the last digit is 0 or 255.

So you may ask: what if my subnet mask is not 255.255.255.0? You can also do this. Assume that your subnet mask is 255.255.128.0.

So the first two IP addresses in your lan must be fixed. Why is it fixed? Do you understand the above ?)

In this way, you can follow the calculation below to see how many machines can be deployed in the same sub-network.

1. Decimal 128 = binary 1000 0000

2. the IP address AND subnet mask must be used for AND operations.

3. IP address 0001000000001001.1 *******.********

Subnet Mask 11111111.111111.0000000.00000000

AND Operation

000000000001001001.0000000.00000000
Converted to decimal:

16.73.128.0

4. We can see that the available IP addresses on the Intranet are:

000000000001001001.0000000.00000000
To

0001000000001001001.11111111.111111

5. Convert to decimal:

16.73.128.0 to 16.73.20.255

6. 0 and 255 are generally used internally for special purposes. Usually not used.

7. The final result is as follows: all available IP addresses in our unit are:

192.168.128.1-192.168.128.254 192.168.129.1-192.168.129.254 192.168.130.1-192.168.130.254 192.168.131.1-192.168.131.254 . . . . . . . . . . . . . 192.168.139.1-192.168.139.254 192.168.140.1-192.168.140.254 192.168.141.1-192.168.141.254 192.168.142.1-192.168.142.254 192.168.143.1-192.168.143.254 . . . . . . . . . . . . . 192.168.254.1-192.168.254.254 192.168.255.1-192.168.255.254

8. The total number is (255-128 + 1) * (254-1 + 1) = 128*254 = 32512

FAINT !!!! @#! @ We can't buy so many machines after selling all our companies! · ￥! ·#

9. Check whether the result is correct.

(1) set the IP address to 192.168.128.1

Ping 192.168.129.233 and pass the test

Visit http: // 192.168.129.233 to display the Home Page

(2) set the IP address to 192.168.255.254

Ping 192.168.129.233 and pass the test

Visit http: // 192.168.129.233 to display the Home Page

10. Conclusion

The above proves that our conclusion is correct.

Now you can check the number of machines in your subnet.

2017100000000128

Decomposition:

11111111.111111.1111111111.000000

Therefore, the IP address of your internal network can only be

Xxxxxxxx. xxxxxxxx. xxxxxxxx.0 ???????

To

Xxxxxxxx. xxxxxxxx. xxxxxxxx.01111111

Related Articles]

• Two simple subnet mask Algorithms
  

• IP address and subnet mask
  

• Subnet Mask and Its Application