Low Tech Intro to TCP, IP Addresses & Default Gateways.
By Matt Western - part 1.

A default gateway is a location on a network that data is sent to when that data is addressed to a location other than your local network.

For example, let's say you have three computers set up on a small local area network or LAN. Let's say that this LAN is using TCP/IP as its' communication protocol.

Each network that runs TCP/IP has what is known as a network address. The network address is what is used to help identify what PC's or servers are connected to that network or LAN.

In our little example here, we'll say that our network address is 1.2.3.0

Now let's give each PC in the LAN an IP address to uniquely identify it on our network.

Let's say PC1's IP address is 1.2.3.1, PC2's IP address is 1.2.3.2 and PC3's IP address is 1.2.3.3.

Take a close look at those PC IP addresses. Do you notice anything? I know you're pretty clever so I know that you recognised that the IP address of each PC began with the same numbers, 1.2.3. And did you notice that those are the same numbers and in the same sequence that make up our network address?

From that information I can tell you that all of those 3 PC's will be able to talk to one another on their little LAN because they all start with 1.2.3 which means they are all on the same network.

Ok, let's move on a bit.

Each PC has a unique IP address, as they should, so they can pass data between themselves.

Now let's say that these PC's need to get onto the Internet. What they need is some type of access point or conduit that connects the LAN they are connected to the Internet.

Most times this conduit takes the form of a device called a network router or simply just a router. Simply put, a router enables two networks to connect to one another.

In this case, the router will connect the LAN (network 1) to the Internet (network2).

So back to the PC's on our LAN. Whenever one PC wants to communicate with another PC it will talk to the other PC by using its IP address.

For example and this is very simplified, let's say PC1 wants to access a file on PC2. PC1 starts off and says, "Hello out there, this is PC1 and my IP address is 1.2.3.1. I want to speak to PC2 whose IP address is 1.2.3.2." "Can you hear me PC2 at IP address 1.2.3.2?"

PC2 would reply "Yes I can hear you and I can understand you blah blah blah" and so on and so forth and things would go on from there and all would be hunky dory.

As long as any PC connected to this little LAN has an IP address that starts with 1.2.3 it should be able to talk to the other PC's without too much trouble.

But things aren't that easy when you need to talk to another PC on the Internet.

Low Tech Intro to TCP, IP Addresses & Default Gateways. - part 1
Low Tech Intro to TCP, IP Addresses & Default Gateways. - part 2