Default Gateway Explained

Summary

This video explains what a default gateway is and its role in network communication. The default gateway, usually a router, enables devices on one network to communicate with devices on another. Through a demonstration on Windows, the video shows how to check a network’s IP configuration. It also covers how devices use IP addresses and subnet masks to determine whether they are on the same or different networks, and when data needs to be forwarded through the default gateway. The video concludes with examples illustrating these concepts in action.

Takeaways

• 🌐 A default gateway is a device, typically a router, that forwards data from one network to another.
• 💻 On Windows, you can check the default gateway by opening a command prompt and typing 'ipconfig' to view network settings.
• 🚪 The default gateway acts as the doorway or first point of contact for devices on a network that need to communicate with devices on a different network.
• 🔀 Devices on the same network communicate directly through a switch, bypassing the default gateway.
• 🧭 To determine if another device is on the same network, computers use the IP address and subnet mask to identify the network and host portions.
• 🔢 The subnet mask helps distinguish the network portion of an IP address by aligning the '1's in the subnet mask with the corresponding bits in the IP address.
• 🤝 Computers on the same network communicate directly using their MAC addresses, found via ARP broadcasts.
• 🛑 ARP broadcasts are limited to the local network and cannot pass through a router, requiring the use of the default gateway for cross-network communication.
• 🔀 When two devices are on different networks, the default gateway routes the data between them.
• 🌍 Each subnet has its own default gateway, ensuring communication across separate networks through the appropriate routing.

Q & A

What is a default gateway?

A default gateway is a device, typically a router, that forwards data from one network to another.

How do you check the default gateway on a Windows computer?

Open a command prompt, type 'ipconfig', and the output will display the IP address, subnet mask, and default gateway.

Why is a router usually the default gateway?

A router acts as the doorway between networks, allowing data to travel between local networks and the internet.

Can computers on the same network communicate without using a default gateway?

Yes, if the computers are on the same network, they can communicate directly through a switch without using the default gateway.

How do computers determine if another device is on the same or a different network?

They check the IP address and subnet mask. If the network portion of the IP addresses matches, the devices are on the same network.

What role does the subnet mask play in networking?

The subnet mask helps identify which part of the IP address is the network portion and which is the host portion.

What happens if two computers are on different networks?

They must communicate through the default gateway, as devices on different networks cannot directly exchange data.

How does a computer find another device's MAC address on the same network?

The computer sends out an ARP broadcast asking for the MAC address of the device it wants to communicate with.

Why can't ARP broadcasts go past a router?

ARP broadcasts are limited to the local network and cannot cross the router, which separates different networks.

What is the purpose of the default gateway when computers are on different networks?

The default gateway allows communication between devices on different networks by routing data between them.

Outlines

00:00

🌐 Understanding the Default Gateway and Its Role in Networking

This paragraph explains the concept of a default gateway, typically a router that forwards data between different networks. The example provided shows how a router serves as the connection between a local network and the internet. When devices on a local network need to access resources outside their network, the data is routed through the default gateway. This also applies to incoming data from the internet. The paragraph emphasizes that if devices on the same network communicate, they do so directly without involving the default gateway. The explanation highlights the importance of the default gateway in determining the data’s exit path, distinguishing between intra-network communication and external communication through the IP address and subnet mask.

05:06

🔢 Determining Network Boundaries Using IP Addresses and Subnet Masks

This paragraph delves into how computers determine whether they are on the same or different networks, using IP addresses and subnet masks. An IP address is divided into the network and host parts, with the subnet mask helping to identify the boundary. The example demonstrates how the network portion of the IP address (the first three octets) determines if two devices are on the same network, allowing them to communicate directly. The subnet mask works by marking which bits of the IP address correspond to the network part. Devices on the same network communicate without passing through the default gateway, and the host portion of the IP address uniquely identifies each device.

🔗 Subnets and Communication Across Networks

This paragraph introduces the concept of subnets—divisions within a larger network. The example shows two subnets, 192.168.0 and 192.168.1, each with its own default gateway. If a computer on one subnet wants to communicate with another computer on the same subnet, it can do so directly. It identifies the other computer’s IP address to verify they are part of the same network. Communication occurs once it obtains the destination computer's MAC address through an ARP broadcast, allowing data to be transferred within the subnet without involving the gateway.

🚪 Routing Communication Between Different Subnets

This paragraph explores how communication occurs when devices are on different subnets. When computer A from one subnet wants to communicate with computer D on another subnet, it first checks the IP address to determine that they are on different networks. Since they are on different subnets, computer A sends an ARP broadcast to obtain the MAC address of the default gateway, rather than computer D directly. This is because ARP broadcasts cannot cross routers. Once computer A has the MAC address of the gateway, it forwards the data, which is then sent to the correct destination subnet. This demonstrates how routers and gateways facilitate communication across network boundaries.

Keywords

💡Default Gateway

A default gateway is a device that forwards data between networks, usually a router. In the context of the video, it enables communication between devices on different networks. For example, when a computer needs to access a website, the data passes through the default gateway to exit its local network and connect to the internet.

💡Router

A router is a device that connects multiple networks and directs data traffic between them. In this video, the router serves as the default gateway, allowing computers on a local network to communicate with external networks, such as the internet.

💡Local Area Network (LAN)

A Local Area Network (LAN) is a network that connects devices within a specific area, such as a home or office. In the video, it is used as an example where computers can communicate directly with each other through a switch without needing to exit the network through the default gateway.

💡IP Address

An IP address is a unique identifier assigned to each device on a network. It consists of two parts: the network address and the host address. In the video, IP addresses help determine whether a computer is on the same network or a different one, which influences whether the default gateway is needed for communication.

💡Subnet Mask

A subnet mask is a number that helps identify which portion of an IP address is designated for the network and which is for the host. In the video, the subnet mask is used to determine whether devices are on the same network, which in turn decides whether they can communicate directly or need to use the default gateway.

💡MAC Address

A MAC address is a unique identifier assigned to a network interface on a device. In the video, when two devices on the same network communicate, one device sends out an ARP broadcast to request the MAC address of the other device, allowing direct communication without involving the default gateway.

💡ARP Broadcast

An ARP (Address Resolution Protocol) broadcast is a request sent to all devices on a local network asking for the MAC address of a specific IP address. In the video, ARP broadcasts are used by a computer to determine the MAC address of another device, either on the same network or, in some cases, the default gateway.

💡Network Address

The network address is the portion of an IP address that identifies the network to which a device belongs. In the video, the network address is determined by the subnet mask and is used to identify if two computers are on the same network, allowing for direct communication.

💡Host Address

The host address is the portion of an IP address that uniquely identifies a device within a network. In the video, the host address distinguishes individual devices on the same network, allowing them to communicate directly with each other without needing the default gateway.

💡Subnetwork (Subnet)

A subnetwork, or subnet, is a division of a larger network into smaller, more manageable segments. In the video, the example shows two subnets, 192.168.0 and 192.168.1, each with its own default gateway. Devices within the same subnet can communicate directly, while those in different subnets must communicate through the default gateway.

Highlights

A default gateway is a device that forwards data from one network to another, typically a router.

On a Windows computer, you can check the network configuration by typing 'ipconfig' in the command prompt.

The default gateway allows devices to exit their own local network and communicate with devices on another network.

In most cases, the default gateway is a router that forwards data to the internet.

If a device on the internet wants to communicate with a computer in the local network, it must pass through the default gateway.

Devices on the same network can communicate directly with each other without going through the default gateway.

IP addresses consist of two parts: the network address and the host address.

A subnet mask is used to determine which part of an IP address corresponds to the network portion.

If the network portions of two IP addresses are the same, the devices are on the same network and can communicate directly.

A computer sends an ARP broadcast to get the MAC address of another device for communication.

When two devices are on different networks, the default gateway is used to route the data between them.

An ARP broadcast cannot cross a router, so communication between networks involves the default gateway.

The default gateway acts as a bridge for communication between different networks.

Subnetting divides a network into smaller subnets, each with its own default gateway.

If a device on one subnet wants to communicate with a device on another subnet, the communication must go through the respective default gateways.

Transcripts

What is a default gateway? So that is the topic of this video.

Now as a demonstration on a Windows computer, let's  check the network configuration. So if you open up  

a command prompt and then you type in ipconfig  and in the output you'll see the IP address,  

subnet mask, and the default gateway that's  been assigned to this computer. So you might  

be asking yourself, well what is a default gateway? And simply put, a default gateway is a device that  

forwards data from one network to another. And the  majority of the time, this is going to be a router.  

So for example here we have a local area network.  So here is the router, switch, and the computers.  

And on the other side of the router we have the  internet, which is another network. So in order for  

these computers to access another network, such  as a web page out on the internet, the data has  

to exit its own local network by going through the  default gateway, which is the router. And then the  

router will forward the data to the internet. Now  this also works both ways. So if a device on the  

internet wanted to communicate with a computer on  this network, it has to go through this network's  

default gateway and then to the computer. So  in a nutshell, that's what a default gateway is.  

It lets devices from one network communicate with  devices on another network. And as I said before,  

this is typically going to be a router. A router  is the gateway or doorway to every network. And 

the term default means that the designated  device is the first option that's looked upon  

when data needs to exit the network. Now if these  computers here wanted to communicate with each  

other, they can just talk directly to each other  through the switch. And this is because all these  

computers are on the same network. Their data  doesn't have to exit the network and go through  

the default gateway. So this brings us to our next  question. And that is, if these computers wanted to  

communicate with another computer, how do they know whether that computer is on their own network  

or if it's on a different network. Because as I stated  before, if this computer wants to communicate with  

a computer on the same network, it can just talk  directly to it. But if it wants to communicate  

with a computer on a different network, it has  to go through the default gateway. So again how  

does it know? And this is where the IP address and  subnet mask come in. An IP address consists of two  

parts. The first part is the network address and  the second part is the host address. So the way to  

tell which portion belongs to either the network  or the host, is where the subnet mask comes in.  

A subnet mask is a number that resembles an IP  address. And it reveals how many bits in the IP  

address are used for the network by masking the  network portion of the IP address. So here we have  

the IP address and subnet mask in binary form. So the way to tell which portion of this IP address  

is the network portion, is when the subnet mask  binary digit is a 1 it will indicate the position  

of the IP address that defines the network. So   we'll cross out all the digits in the IP address  

that line up with the 1s in the subnet mask. And  when you do this, it will reveal that the first  

three octets or sets are the network portion  and the remaining is the host portion. So any  

computer or device on a network where the first  three numbers of the IP address are 192.168.0  

means that those computers are on the same network. Which means that the computers can talk directly  

to each other without exiting through the default  gateway. And then the host portion is what's  

uniquely assigned to devices, such as computers.  So here we have a private network that has  

been divided into two sub networks or subnets. The  subnet on the left is on the 192.168.0 network and the  

subnet on the right is on the 192.168.1 network.  And each subnet has their own default gateway.  

Now let's say that computer A wanted to  communicate with computer B on this subnet.  

So computer A is going to check computer B's IP  address to see if it's on the same network or not. 

And as you can tell, the two computers are on the  same network because the network portion of the IP  

addresses, which are the first three octets, are the  same. So computer A now knows that computer B is on  

the same network. So now in order for communication to take place, computer A needs computer B's MAC 

address. And it finds this by sending out an ARP  broadcast out on the network asking computer B  

for its MAC address. Then once it has the MAC  address, communication can finally take place.

So in another scenario let's say that computer  A on this subnet here wanted to communicate with  

computer D on this subnet. So again computer  A is going to check computer D's IP address  

to see if it's on the same network or not. And  as you can tell this time, the two computers  

are on different networks because the network  portion of the IP addresses, which are the first  

three octets, are different. And the difference  is the third number. Computer A is using a 0 

and computer D is using a 1. So computer A now  knows that computer D is on a different network.  

So it can't directly communicate with it, it has  to use the default gateway. So computer A will  

send out an ARP broadcast and this time it'll ask  for the MAC address of the default gateway and not  

the computer, because computer D is on a different  network and it won't receive the broadcast because  

ARP broadcasts cannot go past a router. Then once  it has the MAC address, it'll send the data to the  

default gateway and then it'll be forwarded to the  destination. So everyone that concludes this video  

on default gateways. Thank you for watching, please  subscribe, and I'll see you in the next video.