Subtitles of the Movie

OK, welcome to Part 2 of Determining Subnets. In Part 1 we took a look at an address and we have subnetted or we've taken the network ID that we were given and we have subdivided it into 6 more subnets, OK, so go back and watch Part 1 and you'll see how we got here. So we find ourselves now, we have borrowed 3 bits and that has given us 6 subnets. OK, now how many hosts can we have on each one of these 6 networks? Well, we're going to apply our same little magic and you will notice that we have 5 spaces here for host IDs so we take 2 to the 5th power, which comes to 32 - 2 times 2 times 2 times 2, do that 5 times - and you end up at 32. You subtract 2 and you end up with 30. So we now have 6 separate network IDs and they each have 30 host IDs on them. Understand that this right here, this little formula will work both ways. If we took, for example, 27 - 2 times the 27th power minus 2 - you would see how many potential networks are involved in all this, that's what the ISP has to sell. Actually, in our instance it would be from here to here because these belong to us and we just subnetted them, OK? But that formula will work everywhere. Now there's all kinds of tricks you can do here, so we ended up with 6 new subnets, well how do I determine what my network ID's going to be for each one of these, where will it start? Well, if I start from here and look at that I borrowed 3 and move over to the farthest one to the right that position is equal to 32, remember? Here's 1, 2, 4, 8, 16, 32. So the right-most that I borrowed is going to be the number of my subnet network ID, which means here are my 6 networks that I created now, OK? 192.168.2.32 is the first one and that will go all the way up to 63, 64 starts the next one and that goes up to 95, 96 starts the next one and so you can see we've got 6. We can't go any farther than 192 because if you add the 32 to 92 you come up to 224 and it ends on the same one as this so you can't do that. So, all I can tell you to do here is to go over this and over it and over it and the main thing that you want to watch is and you're going to get a lot of questions about this on the exam, so if this doesn't just click with you and look at a lot of practice examples on this and I'm going to show you a couple of tricks here later, but for right now I have to determine how many addresses I need on a Subnet and how many Subnets I need. Well, if I had just taken 2 of these I could take 2 to the 2nd power minus 2 and see how many Subnets I would get and I would have gained another one here for my addresses, so you can see how you're going to have to be able to answer questions about this but use this little 2 to the nth power minus 2 to determine what you need and if you count this way from left to right when you're borrowing it'll tell you how many Subnets you're going to get and if you count this way after you've borrowed it'll tell you how many host addresses you'll have on each network, OK? I hope that make sense to you, alright? Now, let's look at a couple of other things about determining Subnets. In the work files folder I have included a TCP IP memorization chart. Look at that thing and just memorize as much as you can, just go over it until it makes sense to you, OK? You will see all kinds of patterns in these numbers, OK? And what you want to know is a/16 notation means that 16 bits are being used, then that means that 16 bits are available for host IDs and you can just kind of play with that and look at the numbers on that. And let me back up just a second here. I want to show you one more thing here. Right here, notice that when we used these three, the way we got to 224, right, this one is 128, this one is 64 and this is 32 and if you add those three up, right, you get 224. So, I hope you see the way all this is working together, OK, so this turned out to be 224 because 224 of our binary here is being used for Subnets. So anyway, just go through that until it makes sense and it is confusing I know. Always remember this little calculation: 2 to the nth power and this is however many positions you're looking at in an address minus 2 will give you what you're looking for. Now let's look at an example of this. Let's say I've got four positions, so I'm going to take 2 to the 4th power and then subtract 2; that means I'm going to go 2 times 2 times 2 times 2, right, so notice 2 times 2 is 4, times 2 is 8, times 2 equals 16 and that means that I have 14 addresses, hosts, whatever I'm looking at. So use this quite a bit. Now, one tip on this test, you're going to get questions about subnetting and about these bits and how many hosts and how many Subnets and so forth. Play with this until it totally makes sense. Build yourself some sort of chart, memorize it and write it down on your little piece of paper before you start the exam when you first get in there, OK? So anyway, that's Determining Subnets. If this is not making sense to you and I wouldn't be surprised if it doesn't totally, go out and look at some places on Google, go out and read some of the Microsoft books, but you've got enough right here to figure it out, so I hope this helps. That's how to Determine Subnets and answer these questions about subnetting on the exam.