The relationship between the number of subnets, hosts and subnet mask

1. Calculate the subnet mask using the number of subnets

What is the subnet mask for dividing the class B address 172.16.0.0 into 30 subnetworks?

① converts the number of subnetworks 30 to a binary representation of 11110

② calculates that the binary number has five digits.

③ Note: when there is only one 1 in the binary number, the number of digits counted needs to be subtracted by 1 (for example, 10000 should be counted as 4 digits).

④ changes the first five bits of the subnet mask 255.255.0.0 host address portion of a Class B address to 1

⑤ then gets the required subnet mask (11111111.11111111111000.00000000) 255.255.248.0.

2. Use the number of hosts to calculate the subnet mask

The class B address 172.16.0.0 is divided into several subnetworks, each of which can hold 500 hosts. What is its subnet mask?

① converts 500 to binary for 111110100

② calculates that the binary number has 9 digits.

③ changed the subnet mask 255.255.255.255 from 9 bits back to forward to 0

This gives ④ the subnet mask (11111111.11111111.11111110.00000000) 255.255.254.0.

3. Calculate the maximum number of valid subnets using subnet mask

What is the maximum number of valid subnets that can be divided by a Class An IP address with a subnet mask of 255.224.0.0?

① converts the subnet mask to binary representation 11111111.11100000.00000000.00000000

According to the statistics of ②, there are 11 bits in its network.

The base number of network bits for ③ Class An addresses is 8, and the difference between them is 3.

The maximum number of effective subnets of ④ is 2 to the third power, that is, it can be divided into up to 8 subnetworks.

4. Calculate the maximum number of available hosts using the subnet mask

A class An IP address with a subnet mask of 255.252.0.0 is divided into several subnetworks. how many hosts are available in each subnetwork?

① converts the subnet mask to binary for 11111111.11111100.00000000.00000000

According to the statistics of ②, there are 18 host bits.

The maximum number of available hosts for ③ is 2 to the 18th power minus 2 (excluding all zero network addresses and all 1 broadcast addresses), that is, a maximum of 262142 hosts are available per subnet.

5. Use the subnet mask to determine the start and end address of the subnet.

The class B IP address is 172.16.0.0 with a subnet mask of 255.255.192.0. What is the starting and ending address of the subnetwork that it can divide?

① calculates with subnet mask and can be divided into up to 4 subnetworks

② calculates with subnet masks that each subnet can hold 16384 hosts (including network and broadcast addresses)

③ divides 16384 by 256 (all hosts in the network segment, including network and broadcast addresses), and the result is 64

The specific method of dividing the network by ④ is as follows:

172.16.0.05172.16.63.255

172.16.64.0,172.16.127.255

172.16.128.0,172.16.191.255

172.16.192.0,172.16.255.255

6. The following is a table of personal experience.

Class An IP address segment: 1.0.0.0" 126.255.255.255 private address segment: 10.0.0.0" 10.255.255.255

Class B IP address segment: 128.0.0.0" 191.255.255.255 private address segment: 172.16.0.0" 172.31.255.255

Class C IP address segment: 192.0.0.0" 223.255.255.255 private address segment: 192.168.0.0" 192.168.255.255