suppose I have three ip addresses

`````` A:172.16.1.1
B:172.16.2.1
C:172.16.3.1
``````

Now, If I want to put B and C in the same network and A in a different network, which subnet mask will i have to use? how will I calculate it?

– user2084
Dec 15, 2015 at 7:49

• `172.16.1.0/24` for A
• `172.16.2.0/23` for B and C

This question will tell you how to calculate it.

IP Address `10.10.15.10/16`

Step 1) Translate the IP address 4 octets into binary:

`00001010.00001010.00001111.00001010`

Step 2) Translate the Subnet mask 4 octets into binary, which is easy using CIDR:

`11111111.11111111.00000000.00000000`

Step 3) Perform the `AND` operation on the two addresses. This will give you the Network Address for the subnet. `AND` rules are:

`1 AND 1 = 1`, `O AND 1 = 0`, `0 AND 0 = 0`, `1 AND 0 = 0`

``````00001010.00001010.00001111.00001010
11111111.11111111.00000000.00000000
===================================
00001010.00001010.00000000.00000000
``````

Step 4) Convert it back to decimal:

`10.10.0.0`