Join Lazaro Diaz for an in-depth discussion in this video Understanding the diagram to subnet, part of Cisco Certified Entry Networking Technician Essential Training.
- View Offline
- Okay, in the world of IT subnetting is the kyrptonite of every IT individual out there. It's really not all that difficult and you're gonna see it in just a second how simple it is. So, when we subnet as we mentioned in earlier video that it's taking an address, a network, and dividing it up into smaller networks for better management. So, let's say you're given this particular address right here: the 192.168.100.0 with a sider 28.
That 28 right here means that that is 28 bits in length. That means 28 bits are on. So, what I do is I say, "Okay, well, "8 bits are on here, that's an X, "8 bits are on here, that's an X, "8 bits are on here, that's an X," 'cause I really can't do anything with that. So, my focus is in the last octet which is this one right here. So, we're gonna turn that into its binary format. So, we're gonna go one, two, three four, then we draw a line.
Those are the four bits that are on. The other bits, one, two, three, four, those are the bits that are off, right, because there are eight bits in every octet. So, now all we need to do is put the bit values 1, 2, 4, 8, 16, 32, 64, 128. Now, these bit values stay the same throughout each octet. They all have the same values, all right, but in this instance where we're getting the fourth octet.
We're gonna go ahead and pick a little different color. We're gonna pick blue, all right, and I wanna circle the bit value to the left. Why is that important? Because that number right there is how your network will increment in the fourth octet. If we were to add up these numbers right here it will come out to 15. That number is to help us calculate for the broadcast address. Because there's three things we need to know and let's go ahead and go to black so we can see the difference.
We need to know the network ID. We need to know the usable range, and we need to now the broadcast address. The network ID and the broadcast address are addresses that are not used. They are invalid. The only thing that's valid is what's in the range. So, our network ID is 192.168.100.0 but how do we find out our broadcast? Well, we take this fourth octet right there and we add this 15 right here.
What do we get? 192.168.100.15. So, at that point what's in between 0 and 15? .1 through .14, and then you can start assigning IP addresses starting at 1. Now, what's the next network? Well, we're incrementing by what? 16. So, 192.168.100.16. What's the next network? .32.
What's the next network? .48. What's the next network? .64. And so forth once you get to the last network we should be 240. Now, you can go through the same procedure to find the broadcast. You take this 16 plus this 15 and that will be 31. Are you seeing a pattern anywhere here? 31 is one less 32. 15 is one less 16. So, you don't even have to add. What's one less 48? It's 47.
What's one less 64? It's 63. And then for the last one you can simply just add the 64 and the 15, will give you 79, and then whatever's in between. .17 through .30. .33 to .46. .49 to .62.
And .65 to .78. That's it. That's all there is to subnetting. You just took this address and you subnetted it into one, two, three, four, five different subnets. Now, how many subnets can you have? Now, I'm gonna erase this at the bottom just to get it out of the way so you can see what this little diagram can give you. The diagram is gonna save your life when it comes to subnetting.
When you're counting for subnets you count this way for subnets. 2, 4, 8, 16. So, you have a total of 16 subnets. If you could this way, you're counting for host. How many hosts can you have? 2, 4, 8, 16 -2, 14. On the host side, always -2, always.
Because the two addresses, the network ID, and the broadcast address, are invalid addresses they cannot be used therefore we must subtract two at that point. So, that's all there's to it but this little diagram not only give your network increment which is 16, it gives you the number that you need to calculate your broadcast from, the number of subnets you have, the number of host that you have, but as you can see what mask is this? And we're gonna learn how to do this real quick in the lesson but if you have four consecutive ones that is a 240.
So, you have 255, 255, 255, 240 on the last octet 'cause if you were to add these bit values right here that would be a 240. So, that's what this diagram does for you. Once, the key is a subnet mask. Once you draw that magical line that we have right here, once you draw it, you have the answers to everything they may ever ask you. This will, again, this will save your life. All it takes is just a little bit of practice and believe me, we're gonna do a lot more practice.
- The basics of networking
- The TCP/IP model vs. OSI model
- Understanding the Cisco three-layer model
- Collision and binary domains
- Converting binary to decimal and hexadecimal
- IP addressing
- Diagramming summarization
- Working Cisco IOS
- Managing Cisco internetworks
- IP routing
- Security with ACLs
- Configuring and verifying NAT
- IPv6 addressing