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I'm currently learning about IPv4 and subnetting. As far as I understand, if we want to create 4 small isolated networks with the size 50, we can use subnetting.

If we subnet a Class-C IPv4 network(210.210.210.0) into 4 small networks with the same size (0~63, 64~127, 128~191, 192~255), these small networks are still essential belonged to the big logical network (210.210.210.0) even though we assign subnet masks to them.

If I understand correctly, they can communicate with each other since they share the same network portion. So, in practice, how can we isolate these small networks?

Thanks:)

hackjutsu
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2 Answers2

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If I understand correctly, they can communicate with each other since they share the same network portion.

This part is wrong. The subnets will be their own segment entirely, and will not be able to communicate with eachother - they will only be able to "see" other devices on their own localised smaller subnet.

For example, 210.210.210.0/26 will have a network address of 210.210.210.0 and broadcast address of 210.210.210.63. Any devices will need to sit between 210.210.210.1 and 210.210.210.62.

In addition to this they will need to be separated via either logically separated VLANs or physically separated network hardware. If you need the networks to communicate, you will need to use layer 3 routing.

Connor Low
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Craig Watson
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Your question its not quite right "How to isolate networks when subnetting?" so I will try to clarify things for you .

You have an IP and a Subnet Mask. The IP is the exact interface address, and the subnet mask extract from that IP the network address, for example.

     type      |           Network            HOST    | Hexadecimal
IP addreses    | 11000000.10101000.00000101.00000010  | 192.168.5.2
Subnet mask    | 11111111.11111111.11111111.00000000  | 255.255.255.0
Network address| 11000000.10101000.00000101.00000000  | 192.168.5.0

In order to separate("isolate") your networks, you need different network addresses :

192.168.5.0/24
192.168.10.0/24
192.168.15.0/24

(the 24 stands for 24 bits mask - the binary ones(1))

In order to make those networks communicating to each other, you need a Router that has an interface(physical or virtual) for each network.

Dont get confused by the numbers, look at the binary table! Numbers are separate for better understanding from us(human beings). Look at the binary and the HOST bits are the amount of hosts per network.

So about the question - You separate networks with different Subnet masks

Reference for more detailed explenation - https://en.wikipedia.org/wiki/Subnetwork

Vasil Nikolov
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