Subnetting Based On Host and Network

Subnetting Based On Host and Network

Example 1:
You are designing a subnet mask for the 10.0.0.0 network. You want 2300 subnets with up to 2900 hosts on each subnet. What subnet mask should you use?
Example 2:
You are designing a subnet mask for the 10.0.0.0 network. You want 4000 subnets with up to 3700 hosts on each subnet. What subnet mask should you use?
Example 3:
Given a class B network of 155.44.200.0, What mask could be used to provide 15 networks each supporting 120 users ?
Example 4:
You are designing a subnet mask for the 172.16.0.0 network. You want 90 subnets with up to 300 hosts on each subnet. What subnet mask should you use?
Example 5:
What mask would you assign to the network ID of 172.18.0.0 if you needed about 100 subnets with about 500 hosts each?
Example 6:
You are designing a subnet mask for the 172.18.0.0 network. You want 110 subnets with up to 300 hosts on each subnet. What subnet mask should you use?
Example 7:
You are designing a subnet mask for the 172.24.0.0 network. You want 70 subnets with up to 300 hosts on each subnet. What subnet mask should you use?
Example 8:
You are designing a subnet mask for the 172.29.0.0 network. You want 90 subnets with up to 300 hosts on each subnet. What subnet mask should you use?
Example 9:
Your network consists of 120 subnets, with a maximum number of 300 hosts per subnet. With a Class B address, which subnet mask will support this network?
Example 10:
You are designing a subnet mask for the 172.16.0.0 network. You want 300 subnets with up to 100 hosts on each subnet. What subnet mask should you use?
Example 11:
If you had a class B address of 172.19.0.0, which mask would you use to provide a maximum of 220 hosts with more than 190 subnets?
Example 12:
You need to have a Class B network address subnetted into exactly 500 subnets each with about 100 usable host addresses per subnet. What subnet mask would you assign?
Example 13:
You are designing a subnet mask for the 192.168.252.0 network. You want 4 subnets with up to 30 hosts on each subnet. What subnet mask should you use?
Example 14:
You are a network administrator and have been assigned the IP address of 201.100.5.0. You need to have 20 subnets with 5 hosts per subnet. What subnet mask will you use?

Class A

Example 1:

You are designing a subnet mask for the 10.0.0.0 network. You want 2300 subnets with up to 2900 hosts on each subnet. What subnet mask should you use?

Solution:

Class A addresses use a default mask of 255.0.0.0
2900 hosts would need  12 bits of host =  20 bits of
network (32- 12 = 20)
Subnet Number would be = 24 -12  =  12 bits.
Subnet mask = 255. 00000000. 00000000. 00000000
For 2900 hosts, assign twelve 0s from right side.
New subnet mask = 255. 11111111. 11111000. 00000000
                = 255. 255. 240. 0
Subnet bits = 12 or 12 bits available for subnet addresses.
Subnets = 2^12 = 4096.
Host bits = 12 or 12 bits available for host addresses.
Hosts = 2^12 - 2 = 4094.
The best mask for this network = 255. 255. 240. 0
  

Example 2:

You are designing a subnet mask for the 10.0.0.0 network. You want 4000 subnets with up to 3700 hosts on each subnet. What subnet mask should you use?

Solution:

Class A addresses use a default mask of 255.0.0.0
3700 hosts would need  12 bits of host =  20 bits of
network (32 - 12 = 20)
Subnet Number would be = 24 - 12  =  12 bits.
Subnet mask = 255. 00000000. 00000000. 00000000
For 3700 hosts, assign twelve 0s from right side.
New subnet mask = 255. 11111111. 11111000. 00000000
                = 255. 255. 240. 0
Subnet bits = 12 or 12 bits available for subnet addresses.
Subnets = 2^12 = 4096.
Host bits = 12 or 12 bits available for host addresses.
Hosts = 2^12 - 2 = 4094.
The best mask for this network = 255. 255. 240. 0
  

Class B

Example 3:

Given a class B network of 155.44.200.0, What mask could be used to provide 15 networks each supporting 120 users?

Solution:

Class B addresses use a default mask of 255.255.0.0
120 users would need  7 bits of host  =  25 bits of
network  (32 - 7 = 25)
Subnet Number would be = 16 - 7  =  9 bits.
Subnet mask = 255. 255. 00000000. 00000000
For 120 users, assign seven 0s from right side.
New subnet mask = 255. 255. 11111111. 10000000
                = 255. 255. 255. 128
Subnet bits = 9 or 9 bits available for subnet addresses.
Subnets = 2^9 = 512.
Host bits = 7 or 7 bits available for host addresses.
Hosts = 2^7 - 2 = 126.
For 15 networks (subnets) and 120 users (hosts), we
would assign 255. 255. 255. 128 subnet mask.
The best mask for this network = 255. 255. 255. 128

Example 4:

You are designing a subnet mask for the 172.16.0.0 network. You want 90 subnets with up to 300 hosts on each subnet. What subnet mask should you use?

Solution:

Class B addresses use a default mask of 255.255.0.0
300 hosts 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 300 hosts, 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.
Subnet bits = 7 or 7 bits available for subnet addresses.
Subnets = 2^7  = 128.
For 90 subnets and 300 hosts, we would assign 255. 255. 254. 0
subnet mask.
The best mask for this network = 255. 255. 254. 0

Example 5:

What mask would you assign to the network ID of 172.18.0.0 if you needed about 100 subnets with about 500 hosts each?

Solution:

Class B addresses use a default mask of 255.255.0.0
500 hosts 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 hosts, 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.
Subnet bits = 7 or 7 bits available for subnet addresses.
Subnets = 2^7 = 128.
Number of hosts possible = 510.
Number of subnets possible = 128.
For 100 subnets and 500 hosts, we would assign
255. 255. 254. 0 subnet mask.
The best mask for this network = 255. 255. 254. 0
   

Example 6:

You are designing a subnet mask for the 172.18.0.0 network. You want 110 subnets with up to 300 hosts on each subnet. What subnet mask should you use?

Solution:

Class B addresses use a default mask of 255.255.0.0
300 hosts 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 300 hosts, 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.
Subnet bits = 7 or 7 bits available for subnet addresses.
Subnets = 2^7 = 128.
For 110 subnets and 300 hosts, we would assign 255. 255. 254. 0
subnet mask.
The best mask for this network = 255. 255. 254. 0
  

Example 7:

You are designing a subnet mask for the 172.24.0.0 network. You want 70 subnets with up to 300 hosts on each subnet. What subnet mask should you use?

Solution:

Class B addresses use a default mask of 255.255.0.0
300 hosts 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 300 hosts, 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.
Subnet bits = 7 or 7 bits available for subnet addresses.
Subnets = 2^7 = 128.
For 70 subnets and 300 hosts, we would assign 255. 255. 254. 0
subnet mask.
The best mask for this network = 255. 255. 254. 0
  

Example 8:

You are designing a subnet mask for the 172.29.0.0 network. You want 90 subnets with up to 300 hosts on each subnet. What subnet mask should you use?

Solution:

Class B addresses use a default mask of 255.255.0.0
300 hosts 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 300 hosts, 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.
Subnet bits = 7 or 7 bits available for subnet addresses.
Subnets = 2^7 = 128.
For 120 subnets and 300 hosts, we would assign 255. 255. 254. 0
subnet mask.
The best mask for this network = 255. 255. 254. 0

Example 9:

Your network consists of 120 subnets, with a maximum number of 300 hosts per subnet. With a Class B address, which subnet mask will support this network?

Solution:

Class B addresses use a default mask of 255.255.0.0
300 hosts 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 300 hosts, 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.
Subnet bits = 7 or 7 bits available for subnet addresses.
Subnets = 2^7 = 128.
Number of hosts possible = 510.
Number of subnets possible = 128.
For 120 subnets and 300 hosts, we would assign
255. 255. 254. 0 subnet mask.
The best mask for this network = 255. 255. 254. 0

Example 10:

You are designing a subnet mask for the 172.16.0.0 network. You want 300 subnets with up to 100 hosts on each subnet. What subnet mask should you use?

Solution:

Class B addresses use a default mask of 255.255.0.0
100 hosts would need  7 bits of host  =  25 bits of
network  (32 - 7 = 25)
Subnet Number would be = 16 - 7 = 9 bits.
Subnet mask = 255. 255. 00000000. 00000000
For 100 hosts, assign seven 0s from right side.
New subnet mask = 255. 255. 11111111. 10000000
                = 255. 255. 255. 128
Subnet bits = 9 or 9 bits available for subnet addresses.
Subnets = 2^9 = 512.
Host bits = 7 or 7 bits available for host addresses.
Hosts = 2^7 - 2 = 126.
Number of hosts possible = 126.
Number of subnets possible = 512.
For 300 subnets and 100 hosts, we would assign
255. 255. 255. 128 subnet mask.
The best mask for this network = 255. 255. 255. 128

Example 11:

If you had a class B address of 172.19.0.0, which mask would you use to provide a maximum of 220 hosts with more than 190 subnets?

Solution:

Class B addresses use a default mask of 255.255.0.0
220 hosts would need  8 bits of host  =  24 bits of
network  (32 - 8 = 24)
Subnet Number would be = 16 - 8  =  8 bits.
Subnet mask = 255. 255. 00000000. 00000000
For 220 hosts, assign eight 0s from right side.
New subnet mask = 255. 255. 11111111. 00000000
                = 255. 255. 255. 0
Subnet bits = 8 or 8 bits available in the third octet
for subnet addresses.
Subnets = 2^8 = 256.
Host bits = 8 or 8 bits available in the forth octet
for host addresses.
Hosts = 2^8 - 2 = 254.
For 190 subnets and 220 hosts, we would assign
255. 255. 255. 0 subnet mask.
The best mask for this network = 255. 255. 255. 0
  

Example 12:

You need to have a Class B network address subnetted into exactly 500 subnets each with about 100 usable host addresses per subnet. What subnet mask would you assign?

Solution:

Class B addresses use a default mask of 255.255.0.0
100 hosts would need  7 bits of host  =  25 bits of network
(32 - 7 = 25)
Subnet Number would be = 16 - 7 = 9 bits.
Subnet mask = 255. 255. 00000000. 00000000
For 100 hosts, assign seven 0s from right side.
New subnet mask = 255. 255. 11111111. 10000000
                = 255. 255. 255. 128
Subnet bits = 9 or 9 bits available for subnet addresses.
Subnets = 2^9 = 512.
Host bits = 7 or 7 bits available in the forth octet
for host addresses.
Hosts = 2^7 - 2 = 126.
For 100 usable host addresses per subnet, we would assign
255. 255. 255. 128 subnet mask.
  

Class C

Example 13:

You are designing a subnet mask for the 192.168.252.0 network. You want 4 subnets with up to 30 hosts on each subnet. What subnet mask should you use?

Solution:

Class C addresses use a default mask of 255.255.255.0
30 hosts would need 5 bits of host = 27 bits of
network (32 - 5 = 27)
Subnet Number would be = 8 - 5 = 3 bits.
Subnet mask = 255. 255. 255. 00000000
For 30 hosts, assign five 0s from right side.
New subnet mask = 255. 255. 255. 11100000
                = 255. 255. 255. 224
Host bits = 5 or 5 bits available for host addresses.
Hosts = 2^5 - 2 = 30.
Subnet bits = 3 or 3 bits available for subnet addresses.
Subnets = 2^3 = 8.
For 4 subnets and 30 hosts, we would assign 255. 255. 255. 224
subnet mask.
The best mask for this network = 255. 255. 255. 224
  

Example 14:

You are a network administrator and have been assigned the IP address of 201.100.5.0. You need to have 20 subnets with 5 hosts per subnet. What subnet mask will you use?

Solution:

Class C addresses use a default mask of 255.255.255.0
5 hosts would need 3 bits of host = 29 bits of
network (32 - 5 = 27)
Subnet Number would be = 8 - 3 = 5 bits.
Subnet mask = 255. 255. 255. 00000000
For 5 hosts, assign three 0s from right side.
New subnet mask = 255. 255. 255. 11111000
                = 255. 255. 255. 248
Host bits = 3 or 3 bits available for host addresses.
Hosts = 2^3 - 2 = 6.
Subnet bits = 5 or 5 bits available for subnet addresses.
Subnets = 2^5 = 32.
For 20 subnets and 5 hosts, we would assign 255. 255. 255. 248
subnet mask.
The best mask for this network = 255. 255. 255. 248
  

Exercise

Exercise 1:

You need a minimum of 300 sub-networks and a maximum of 50 host addresses per subnet. Working with only one Class B address, which of the subnet masks will support an appropriate addressing scheme?

Answer:

For 300 subnets and 50 hosts, we would assign 255. 255. 255. 192 subnet mask.

Exercise 2:

You are designing a subnet mask for the 172.19.0.0 network. You want 300 subnets with up to 100 hosts on each subnet. What subnet mask should you use?

Answer:

For 300 subnets and 100 hosts, we would assign 255. 255. 255. 128 subnet mask.

Exercise 3:

You are designing a subnet mask for the 172.30.0.0 network. You want 900 subnets with up to 40 hosts on each subnet. What subnet mask should you use?

Answer:

For 900 subnets and 40 hosts, we would assign 255. 255. 255. 192 subnet mask.