This method of expression is known as “CIDR” notation. Subnets are expressed in the form of “masks” or “bits.” Subnets masks look much like IPs (“255.255.255.0”), while bits are just a number, sometimes proceeded by a slash (“/24”). (Subnets are sometimes referred to as “VLANS,” especially in the context of network device configuration.)
To someone who wants to understand subnets at a level that will allow them to provision network address spaces, I would explain it this way:Īn IP address range can be broken up into slices, called “subnets.” These carve out IP address spaces/ranges. That said, I can’t do atypical calculations (ones other than /16, /24, etc.) myself, so I turn to a calculator. Even though I took CCNA classes a while back, part of which was subnet mask and address range calculation, it never fully clicked until I looked into the actual binary math behind it. It was more recently that I got the gist of how the mask works from a binary standpoint. “Understand” as in the effect they have? Fairly quickly once I started went through the process of allocating network spaces. This becomes 62 after the broadcast and gateway are accounted for. Since ther are six host bits, we get 64 total addresses for the hosts. Minus the broadcast and gateway, we can use 4,094 addresses for hosts. We have added three more bits to the network section. Minus the broadcast and the gateway address, you have a range of 1-254 for usable host addresses.
So, the entire last octet is used for hosts, 2 8, or 256. If you convert both sets of numbers into binary values, you can clearly see the separation of network and host sides of the mask. I am afraid I make no sense, but if this helps at all I can try to explain the subnet mask portion.ĮDIT: I will add subnets but am busy at work right now and will try to find time this evening.
The subnet mask is used by the device to know which bits to pay attention to for grouping purposes. So all of our standard addresses are just combinations of which bits are on and off in binaryīinary: 11000000.10101000.00000000.00000001 That is the quick crash course on binary.Īddresses makes a lot more sense (to me) when you understand that the decimal addresses we use are limitations of binary and 32-bit systems, and what those limitations mean.Įach octet is composed of 8 bits which are represented of binary, giving an address size a total of 32 bits. Its the same in binary but you roll over faster because there are less characters to go through. Notice how the 10s place now has a 1 and the 1s place is reset to 0 When you count up you eventually roll over from the 1s place to the 10s place. So in decimal we have 10 number characters. Just like our decimal system has 'places' so does binary, but instead of a 1s place, 10s place, 100s place, and so on each number place is twice that of the last. Binary is a number system composed of only two number characters 0 and 1.
This means at a minimum you need to understand binary. Ip addresses and subnet masks are truly done in binary, we just use decimal format to condense the information so its easier to understand at a glance. What helped me was understanding how the addresses and subnet masks translate from binary to decimal.