subnetting questionsThe good news is that when studying IP subnetting there are only three broad types of questions that seem to crop up. The first type will ask for a network id, a broadcast address or perhaps the first and last valid IP addresses for a given address. This is a very common type question and fortunately there are quick and easy ways to answer them. Another type of question is how many subnets or hosts can be derived from a given network or mask. Again, this is straightforward with a little practice. The third type is more difficult, as this type of question is concerned with the student’s knowledge and ability to transfer that knowledge to a design scenario. This type of question may or may not involve variable length subnet masking. This article will cover all three questions.

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An Introduction to Basic Subnetting

What is the Network ID, Broadcast Address, and first & last valid IP on the subnetwork that the host 192.168.1.15/26 belongs to?

Test A

1.      What is the Network ID, Broadcast Address, and first & last valid IP on the subnetwork that the host 172.30.11.15/26 belong to?

 2.      What is the Network ID, Broadcast Address, and first & last valid IP on the subnetwork that the host 172.19.0.0 255.255.254.0 belong to?

 3.      What is the Network ID, Broadcast Address, and first & last valid IP on the subnetwork that the host 192.168.1.1/30 belong to?

Now, let’s take a look at the second type of question, the one that concerns itself with subnets and hosts. Here is a typical example

How many subnets and hosts per subnet can you get from the network 172.168.21.0 255.255.255.224?

128  64 32  16 8  4  2  1

1    1    1   0  0  0  0  0

Test B

1.      How many subnets and hosts per subnet can you get from the network 192.161.204.0/30?

2.      How many subnets and hosts per subnet can you get from the network 192.16.21.0 255.255.255.128?

3.      How many subnets and hosts per subnet can you get from the network 172.27.0.0 255.255.255.224?

The other type of question is scenario based where a network will require to be addressed using a suitable IP plan, here is a typical example and solution.

You have been asked to design an address plan that will accommodate the 172.16.0.0 network. Your organization requires 1000 subnets, with at least 50 hosts per subnet. What subnet mask should you use?

2^10 = 1024

(Remembering the powers of two, comes in handy),

1   2  3   4    5    6    7      8      9      10      11
2,  4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048 …

64 -2 = 62 valid hosts per subnet, which meets the requirements.

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Test C

1.      You have been asked to design an address plan that will accommodate the 172.16.0.0 network. Your organization requires 400 subnets, with at least 70 hosts per subnet. What subnet mask should you use?

 2.      Find which subnet the host 10.154.124.201 255.255.252.0 belongs?

3.      Enter the last valid host on the network that the host 172.19.197.206/30 is a part off

4.      You have been asked to design an address plan that will accommodate the 172.16.0.0 network. Your organization requires 1500 subnets, with at least 50 hosts per subnet. What subnet mask should you use?

5.      Enter the broadcast address for the network 172.17.168.40 255.255.255.248

6.      What is the shorthand corresponding to a subnet mask of 255.255.128.0?

7.      What is the maximum number of valid subnets and hosts per subnet that you can get from the network 172.28.0.0/22

8.      Which subnet does the host 192.168.137.249 belong?

Take a course at Udemy, and answer all 8 of these questions.

Answers Test A

1 Network ID 172.30.11.0Broadcast Address 172.30.11.63First & Last 172.30.11.1 – 62
2 Network ID 192.168.230.144Broadcast Address 192.168.230.151First & Last 192.168.230.145 – 150
3 Network ID 192.168.1.0/30Broadcast Address 192.168.1.3First & Last 192.168.1.1 – 2

Test B

1 64 subnets2 hosts,
2 128 subnets510 hosts
3 2048 Subnets30 hosts

Test C

1 /25 or 255.255.255.128
2 10.154.124.0
3 172.19.197.206
4 /27 or 255.255.255.224
5 172.17.168.47
6 /17
7 1024 hosts 62 hosts
8 192.168.137.192

 

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