How subnetting works on network design?

Question

Maybe this question is very easy for some people. I know very basic of networking and I am trying to learn more. I have followed tutorials on Microsoft and I read this:

Using a subnet mask of 255.255.255.192, your 192.168.123.0 network then becomes the four networks 192.168.123.0, 192.168.123.64, 192.168.123.128 and 192.168.123.192. These four networks would have as valid host addresses:

   192.168.123.1-62
   192.168.123.65-126
   192.168.123.129-190
   192.168.123.193-254

But when I used online subnet calculator here I got available host adderss range of:

192.168.123.1 - 192.168.123.62

I appreciate if anyone can explain how can I access

   192.168.123.65-126
   192.168.123.129-190
   192.168.123.193-254

by subnet mask of 255.255.255.192, on 192.168.123.0 network or explain if I am doing something wrong. Thanks in advance.

Answer 1

As you said, you have four different networks:
192.168.123.0
192.168.123.64
192.168.123.128
192.168.123.192

You need to put each of those as a separate network into your calculator. Your calculator will only work on one network at a time, and you have four networks.

If you enter 192.168.123.192 as the network with a mask of 255.255.255.192, you should get 192.168.123.193 - 192.168.123.254 as host address range.

Answer 2

With the four defined networks that you want to use:

192.168.123.0/26 (/26 = 255.255.255.192)
192.168.123.64/26
192.168.123.128/26
192.168.123.192/26

You apply these four networks onto router interfaces. Suppose you use the first address as your gateway address, your router interfaces would be assigned these addresses:

!
interface FastEthernet 0/0
 description network-1
 192.168.123.1 255.255.255.192
!
interface FastEthernet 0/1
 description network-2
 192.168.123.65 255.255.255.192
!
interface FastEthernet 0/2
 description network-3
 192.168.123.129 255.255.255.192
!
interface FastEthernet 0/3
 description network-4
 192.168.123.193 255.255.255.192
!

So with a computer on network-1, that computer can have an address of 192.168.123.2 with a default gateway of 192.168.123.1.

A computer on network-2, can have an address 192.168.123.68 with a default gateway of 192.168.123.65.

So on and so forth as long as the address meets the criteria of the range of the respective subnet.