TCP/IP Addressing – CompTIA A+ 220-801: 2.3

If you’re configuring a network connection, then you’ll need to know the fundamentals of TCP/IP addressing. In this video, you’ll learn about the IP address, subnet mask, and default gateway, and you’ll learn how to configuration your system for automatic or manual network settings.

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If you want to be able to communicate out to the internet, then there are a few things you must configure on your work station. The first, obviously, is an IP address. We need to somehow put an IP address configuration that’s specific to the subnet that we happen to be physically connected to.

For example, we might be given an IP version 4 address of And we need to make sure that this IP address is not shared with anybody else on the network. This is something that was unique to our workstation. And no other machine out there will have the same IP address as the one that we have.

Another piece of information that you must assign onto a machine that you are configuring is the subnet mask, for example, This is a set of numbers that helps your computer determine what subnet it happens to be a member of. And it’s going to use this information when it starts to send out information onto the network because the subnet mask helps it understand, should I be sending this information to a device that’s on my local subnet? Or should I be passing it off to a router because this information is located on a separate subnet somewhere outside of my local network?

We don’t usually send this subnet mask across the network. This is something that’s used on our local computer. And if you’re manually configuring a machine, you want to ask for both the IP address and the subnet mask. One of these is not going to work without the other. They are always handed out in pairs.

If you’re just communicating on a local subnet, all you need is an IP address and a subnet mask. But very often, we need to communicate outside of our subnet. We need to communicate onto the internet, for instance. And to be able to do that, we must also configure on our devices a default gateway.

This is used in conjunction with your IP address and the subnet mask to determine where does traffic go when it needs to leave our subnet. We have no idea where it goes after that. That’s really the responsibility of the router or the default gateway. But this is a way that we would tell our configuration of our computer or our device, this is the device you need to talk to if you ever need to communicate outside of this local subnet.

Fortunately, we rarely have to configure an IP address and a subnet mask and a default gateway manually on our computers. We simply plug in, and automatically they get all of these values associated with the machine. The way that occurs is through DHCP. This is the Dynamic Host Configuration Protocol. And DHCP is responsible for configuring IP address, subnet mask, gateway, DNS servers, NTP servers, and very much more of the configuration of your computer.

This way we simply need to plug in, and our computer configures everything on its own. You’ve probably seen this when you’re setting up the IP configuration of your machine. There’s an option where you can use the following IP addresses. And you can manually type in your IP address, and your subnet mask, your default gateway, and your DNS servers.

Or, you simply choose to obtain an IP address automatically, and obtain a DNS server address automatically. Behind the scenes, this is telling your operating system, use DHCP to perform this automatic configuration, ask for a DHCP address. The DHCP server will assign an address to you automatically. And the machine you’re using will automatically fill in all of those blanks for you.

We used to have to do all of our IP addressing manually. We would have to manually type in our IP address, manually type in our subnet mask, manually type in the default gateway. There was no automated way to make this happen. Well, in 1993 we came up with an automated way to do this. We created a protocol and a method called BOOTP. It stands for the Bootstrap Protocol.

And BOOTP made all of this automated. It assigned IP addresses to our workstations. It filled in all of those blanks for us. And we didn’t have to manually type in or keep track of any of that information.

But BOOTP didn’t do everything. Although it did configure quite a bit of this automatically, there were still some sections that manually had to be configured. BOOTP also did not have a built-in mechanism to know when an IP address would be available again. It could hand them out, but it couldn’t take them back. And so we had to have very big pools to pull from. So it wasn’t very efficient in providing those IP addresses. We need a better way to be able to make that happen.

And so we came up with, in 1997, a new updated version of BOOTP that we called DHCP, and that stands for Dynamic Host Configuration Protocol. DHCP gave us a lot more flexibility in being able to automatically assign things on our local computers. And it also was able to determine when a particular IP address has lost its lease. And then it could bring it back into the pool to assign to somebody at a later time.

The way to tell if you computer is set up for this automated DHCP is to look at the IP address configuration of your machine. Then you can see that there is a section where you could manually type in the IP address, the subnet mask, the default gateway, and even manually configure your DNS server information. But if you simply checked Obtain an IP Address Automatically, or Obtain a DNS Server Address Automatically, that means that we’re going to use DHCP. And so your workstation, when it hits the network, will simply send a broadcast out looking for a DHCP server. And that DHCP server is now responsible for assigning the IP address to your machine automatically.