Subnetting Based On Host

Subnetting Based On Host

Example 1:
You are designing a subnet mask for the 10.0.0.0/8 network. You want 300 hosts on each subnet. What subnet mask should you use?
Example 2:
You have a network ID of 150.160.0.0 and need 600 host IDs per subnet, with the largest number of subnets available. Which subnet mask should you use?
Example 3:
You are designing a subnet mask for the 172.16.0.0/16 network. You want 70 hosts on each subnet. What subnet mask should you use?
Example 4:
You have a Class B network ID and need about 500 IP addresses per subnet. What is the best mask for this network?
Example 5:
Which mask would you assign if you had a class C address with a maximum of 60 hosts per network?
Example 6:
You are designing a subnet mask for the 192.168.10.0/24 network. You want 20 hosts per network. What subnet mask should you use?

Class A

Example 1:

You are designing a subnet mask for the 10.0.0.0/8 network. You want 300 hosts on each subnet. What subnet mask should you use?

Solution:

Class A addresses use a default mask of 255.0.0.0
300 hosts would need  9 bits of host
Subnet mask = 255. 00000000. 00000000. 00000000
For 300 hosts, assign nine 0s from right side.
New subnet mask = 255. 11111111. 11111110. 00000000
                = 255. 255. 254. 0
Host bits = 9 or 9 bits available for host addresses.
Hosts = 2^9 – 2 = 510.
For 300 hosts, we would assign 255. 255. 254. 0  subnet mask.
  

Class B

Example 2:

You have a network ID of 150.160.0.0 and need 600 host IDs per subnet, with the largest number of subnets available. Which subnet mask should you use?

Solution:

Class B addresses use a default mask of 255.255.0.0
600 IP addresses would need  10 bits of host
Subnet mask = 255. 255. 00000000. 00000000
For 600 IP addresses, assign ten 0s from right side.
New subnet mask = 255. 255. 11111100. 00000000
                = 255. 255. 252. 0
Host bits = 10 or 10 bits available for host addresses.
Hosts = 2^10 – 2 = 1022.
For 500 hosts, we would assign 255. 255. 252. 0 subnet mask.
 

Class B

Example 3:

You are designing a subnet mask for the 172.16.0.0/16 network. You want 70 hosts on each subnet. What subnet mask should you use?

Solution:

Class B addresses use a default mask of 255.255.0.0
70 hosts would need  7 bits of host
Subnet mask = 255. 255. 00000000. 00000000
For 70 hosts, assign seven 0s from right side.
New subnet mask = 255. 255. 11111111. 10000000
                = 255. 255. 255. 128
Host bits = 7 or 7 bits available for host addresses.
Hosts = 2^7 – 2 = 126.
The best mask for this network = 255. 255. 255. 128
  

Example 4:

You have a Class B network ID and need about 500 IP addresses per subnet. What is the best mask for this network?

Solution:

Class B addresses use a default mask of 255.255.0.0

500 IP addresses would need  9 bits of host= 23 bits of
network (32–9=23)
Subnet Number would be = 16 – 9 =  7 bits.
Subnet mask = 255. 255. 00000000. 00000000
For 500 IP addresses, assign nine 0s from right side.
New subnet mask = 255. 255. 11111110. 00000000
                = 255. 255. 254. 0
Host bits = 9 or 9 bits available for host addresses.
Hosts = 2^9 – 2 = 510.
For 500 hosts, we would assign 255. 255. 254. 0 subnet mask.
The best mask for this network = 255. 255. 254. 0
  

Class C

Example 5:

Which mask would you assign if you had a class C address with a maximum of 60 hosts per network?

Solution:

Class C addresses use a default mask of 255.255.255.0
60 hosts would need  6 bits of host  =  26 bits of
network  (32 – 6 = 26)
Subnet Number would be = 8 – 6  =  2 bits.
Subnet mask = 255. 255. 255. 00000000
For 60 hosts, assign six 0s from right side.
New subnet mask = 255. 255. 255. 11000000
                = 255. 255. 255. 192
Host bits = 6 or 6 bits available for host addresses.
Hosts = 2^6 – 2 = 62.
The best mask for this network = 255. 255. 255. 192
      

Example 6:

You are designing a subnet mask for the 192.168.10.0/24 network. You want 20 hosts per network. What subnet mask should you use?

Solution:

Class C addresses use a default mask of 255.255.255.0
20 hosts would need 5 bits of host
Subnet mask = 255. 255. 255. 00000000
For 20 hosts, assign five 0s from right side.
New subnet mask = 255. 255. 255. 11100000
                = 255. 255. 255. 224
For 20 hosts, we would assign 255. 255. 255. 224 subnet mask.
The best mask for this network = 255. 255. 255. 224