How does a mask separate the network from the host?

A subnet mask separates the network from the host using a bitwise comparison (logical AND) - it literally "tells" which bits of the IP address belong to the network and which belong to the device.

More simply: where the mask has 1, that is the network; where it has 0, that is the host.

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#How this works step by step

#1. A mask is a set of 1s and 0s

• 1 → the bit belongs to the network
• 0 → the bit belongs to the host

Example mask:

255.255.255.0

In binary form:

11111111.11111111.11111111.00000000

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#2. An IP address is also translated into bits

IP address:

192.168.1.10

In binary form:

11000000.10101000.00000001.00001010

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#3. The AND operation is applied

The AND rule:

• 1 AND 1 = 1
• 1 AND 0 = 0
• 0 AND 0 = 0

We apply the mask to the IP:

Result:

192.168.1.0

This is the network address.

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#What we got

• Network part:

  192.168.1

• Host part:

  .10

The mask:

• "cut off" the host part
• left only the network

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#The main rule to remember

• IP + mask = network
• same network → devices can communicate directly
• different network → a router is needed

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#Why this matters in practice

A mask lets a device understand:

• whether the destination is on the same network
• or whether the packet needs to be sent to the gateway (router)

Without this:

• normal routing would be impossible
• the network simply would not work

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#In short, for an interview

A subnet mask separates the network from the host by marking network bits with ones and host bits with zeros; a bitwise AND with the IP address lets you extract the network address.