CompTIA Network+ (2009 Objectives) Tutorials
TCP/IP Basics / Subnet Mask
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Subtitles of the Movie (CompTIA Network+ (2009 Objectives) / TCP/IP Basics / Subnet Mask)
The Subnet Mask is considered, for most people, part of the IP address. It really isn't. It's part of the IP configuration, but let's take a look at a Subnet Mask and talk just a little about what it does here. First of all, 192.168.3.14 is our IP address. Now this, we've already talked about, identifies the network and so part of this address identifies the network. And in this instance our network is 192.168.3. And part of this address identifies the particular device on that network, and number 14 is the number of the device on the 192.168.3 network. Now, how do we do that? How do we know that? Well, the Subnet Mask marks the network for us, or it tells us what part of this address is the network ID and what part is the host ID or the device ID. Let's look at how it does that. Here's our IP address again and notice we put the Subnet Mask here. Now you can probably notice something that corresponds to the fact that the first three octets are the network ID. We have 255 that relates to this octet; 255 that relates to this one; and, 255 that relates to this one. We notice something that corresponds there, that is, our network ID, and that's our host ID. Now let's look at it in binary and it starts to make a little more sense. So when we're dealing with the Subnet Mask, anywhere there is a 1 here is indicating to us that it's part of the Subnet Mask, and that's not a totally true statement but it's true enough for now, OK? If any of you are yelling at your screen right now about that's not all really true, then you already are pretty familiar with network IPs and addressing and subnetting and so forth, so we won't worry about that. For now, just notice how the binary works out here and the Subnet Mask, by looking at it, 255.255.255 is telling us this entire, notice they're all set to 1, this entire octet is a network, this entire octet, 168's a network. This entire octet 3 is a network, and none of this octet is a network which means - let me throw something else at you now - this means that all eight of these bits can be used to create unique host ID's or device ID's on this network which means if we add these up 256 possible addresses, right? Because if you remember, 1, 2, 4, 8, 16, 32, 64, 128 - if you add all those up it's 256, alright? However, we have to take off the bottom and the top. We can't use the lowest and the highest for are all kinds of reasons. We won't get into here. And so, if you add them all up all the way across it's 255. Actually, it's zero to 255 and that gives you 256. Nothing like the instructor confusing you. But we're going too deep here, OK? So that's the Subnet Mask. Now one more thing. Go back to our IP address. Now look at this Subnet Mask. What part of this is the network? Well, 255.255 then it's the first two octets and the last two octets are our host ID's. And so the Subnet Mask in binary for this is going to look like this, OK? So the Subnet Mask tells us what part of our IP address is network and what part is host or device ID's that uniquely identify every device on that particular network. That's what the Subnet Mask is there for and that is how it functions. Now the computer in the background looks at the binary on this and we can do all kind of neat binary tricks and we can do subnetting and we'll talk briefly about subnetting a little bit later on in the course but for now, that's the Subnet Mask.
Tutorial Information
| Course: | CompTIA Network+ (2009 Objectives) |
| Author: | Mark Long |
| SKU: | 34216 |
| ISBN: | 1-936334-90-9 |
| Release Date: | 2011-04-29 |
| Duration: | 6 hrs / 91 lessons |
| Work Files: |
Yes |
| Captions: | No |
| Compatibility: |
Vista/XP/2000, OS X, Linux QuickTime 7, Flash 8 |
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