Subnetting IPv4… I think

Until recently, I didn’t really grasp the importance or relevance of subnetting.  After reading this week’s chapter, and watching some videos on YouTube, I realized how it works now and I have a larger understanding of how the IP is restricted based on the subnet (or at least I think I do).  

I had always assumed that the subnet was “another” IP address that you could create many networks from within.  But after this chapter, it has made it more clear to me that the subnet is more of a “locking” mechanism for network addressing.

I get the binary approach, in fact, breaking binary has always been easy for me, it was just the application to subnetting that was confusing.  I think the easiest way for me to remember this now is that the subnet locks the other digits so that your ranges are better defined…

My example is a home network:

IP Address 192.168.1.32/27 or 

1100000.10101000.00000001.00100000

The /27 denotes subnet is locked at 27 characters, so

11111111.11111111.11111111.11100000 or 255.255.255.224

lining them up helped me determine a few things:

                              |
                              V
11000000.10101000.00000001.001 00000  (ip)
11111111.11111111.11111111.111 00000  (subnet)
------------/27---------------^
                              |

Everything to the left of the break can’t change because of the subnet.  So, to find the basic information like network address and broadcast address is as simple as finding the top range and bottom range of the IP. 

Since, in this case, the first 3 digits can’t change in the last octet, the address, you just have to work the numbers that can change:

00100000 (or .32) = Network address

00111111 (or .64) = Broadcast address

That would leave you with 192.168.1.33 through 192.168.1.63 for usable addresses.