Everything Switches do - Part 1 - Networking Fundamentals - Lesson 4

Summary

In this lesson, we delve into the intricacies of network switches, exploring their role in facilitating data communication within networks. We learn that switches, as layer 2 devices, rely on MAC addresses and operate based on a MAC address table. The video explains the three fundamental actions of switches: learning, flooding, and forwarding. These actions ensure efficient data transfer between devices on the same network. The lesson also touches on how switches handle communication with routers and the role of switch MAC and IP addresses in network management. This foundational knowledge is crucial for understanding network operations and is set to be expanded upon in subsequent lessons.

Takeaways

• 🔌 A switch is a networking device that facilitates communication within a network by moving data.
• 📍 Switches operate based on MAC addresses and are not concerned with IP addresses when making forwarding decisions.
• 📝 The MAC address table is crucial for switches as it maps switch ports to MAC addresses, helping them to direct traffic efficiently.
• 💡 The process of a switch learning the MAC addresses is automatic and begins with an empty table, which gets populated as data flows through the network.
• 🔄 Switches perform three primary actions: learning, flooding, and forwarding, which are fundamental to understanding how they operate.
• 🚀 The learning action occurs when a switch updates its MAC address table with the source MAC address of incoming frames.
• 🌐 Flooding is the process where a switch sends a frame out all ports except the one it came in on, when it doesn't know the destination MAC address.
• 🔄 Forwarding is when a switch sends a frame directly to the port associated with the destination MAC address in its table.
• 🔄 Understanding unicast, broadcast, and multicast are essential for grasping how switches handle different types of network traffic.
• 🌐 VLANs (Virtual Local Area Networks) can affect how switches operate, and understanding them is important for managing network traffic.
• 🔗 The MAC and IP addresses of a switch itself are only used for traffic directed to or from the switch, not for traffic passing through it.

Q & A

What is the primary function of a switch in a network?

The primary function of a switch in a network is to facilitate communication by moving data within the network.

What are the two types of addresses required for hosts to communicate through a switch?

For hosts to communicate through a switch, they each need IP addresses and MAC addresses.

What is the IP network that all devices connected to a switch must belong to?

All devices connected to a switch must belong to the same IP network, in this case, it is the 10.11.x network.

How does a switch determine where to send a frame when it first receives it?

When a switch first receives a frame, it does not know the destination MAC address, so it uses the flooding action to send the frame out all ports except the one it came in on.

What is the purpose of a MAC address table in a switch?

A MAC address table in a switch is a mapping of switch ports to MAC addresses, which helps the switch to learn and forward frames to the correct destination.

What are the three actions a switch performs to facilitate communication?

The three actions a switch performs are learning, flooding, and forwarding. Learning updates the MAC address table, flooding sends a frame out all ports except the incoming one, and forwarding sends a frame directly to the destination port.

Why does a switch not forward a frame back out the port it arrived on?

A switch does not forward a frame back out the port it arrived on because it assumes that if the frame arrived on a particular port, the destination is unlikely to be on the same port.

How does a switch update its MAC address table?

A switch updates its MAC address table by learning the source MAC address of each frame it receives and associating it with the port on which the frame arrived.

What happens when a switch receives a frame with a destination MAC address it knows?

When a switch receives a frame with a destination MAC address it knows, it performs the forwarding action, sending the frame directly out the port associated with that MAC address.

How does the process of a switch facilitating communication apply to a router?

The process of a switch facilitating communication applies to a router in the same way it does to hosts. The switch does not look at the Layer 3 header, so whether the destination is a host or a router, the process remains the same.

Why might a switch's own MAC and IP addresses be involved in network communication?

A switch's own MAC and IP addresses would be involved if you are trying to send traffic directly to or from the switch, such as for management purposes using Telnet or SSH.

Outlines

00:00

🌐 Introduction to Switching and MAC Addressing

This paragraph introduces the fourth lesson of a networking fundamentals course, focusing on switches and their role in facilitating communication within networks. The instructor explains that switches are devices designed to move data and that they operate based on rules of switching. It's emphasized that for hosts to communicate through a switch, they must be on the same IP network. The lesson aims to illustrate how a switch enables communication between two hosts, detailing the process of data transmission and the importance of IP and MAC addresses. The switch's operation is described as being based on a MAC address table, which it uses to learn, flood, and forward frames, which are the three fundamental actions of a switch.

05:01

🔄 The Learning, Flooding, and Forwarding Actions of a Switch

The second paragraph delves into the mechanics of how a switch operates through learning, flooding, and forwarding actions. The learning action involves the switch updating its MAC address table with the source MAC address of incoming frames. Flooding occurs when the switch does not know the destination MAC address and sends the frame out all ports except the one it came in on, ensuring the frame reaches its intended recipient. Forwarding is the process where the switch, now aware of the destination MAC address from its table, sends the frame directly to the appropriate port. The paragraph also discusses how responses are handled once the MAC address table is populated, allowing direct communication between hosts without unnecessary flooding.

10:03

🔗 Switch Communication and MAC Address Table Utilization

The final paragraph wraps up the discussion on switches by emphasizing that they use and maintain a MAC address table for mapping switch ports to MAC addresses. It reiterates that switches perform only three actions: learning, flooding, and forwarding. The paragraph also touches on the applicability of these principles to different network devices, including routers, and explains that the switch's MAC and IP addresses are only relevant when directly communicating with the switch itself, such as for management purposes. The instructor concludes by summarizing the key takeaways and previews the topics for the next lesson, which will cover unicast flooding, VLANs, and communication across multiple switches.

Keywords

💡Switching

Switching refers to the process of moving data within networks. In the context of the video, it is the primary function of a switch, which is a device that facilitates communication between devices on the same network. The script explains that a switch operates based on rules that are common across all switches, regardless of the vendor or platform, making it a foundational concept for understanding network communication.

💡MAC Address

A MAC (Media Access Control) address is a unique identifier assigned to network interfaces for communications on the physical network segment. The video script uses MAC addresses to illustrate how switches recognize and communicate with devices on a network. Each device connected to a switch has a unique MAC address, which the switch uses to forward data to the correct destination.

💡IP Address

An IP (Internet Protocol) address is a numerical label assigned to devices participating in a computer network that uses the Internet Protocol for communication. In the video, IP addresses are mentioned as part of the data packet structure that hosts use to communicate. While switches do not use IP addresses for their operation, they are essential for devices to identify each other across networks.

💡Layer 2 Header

The Layer 2 header is part of the data packet structure used in networking, specifically referring to the data link layer in the OSI model. The video explains that switches operate at this layer, using the information in the Layer 2 header, such as MAC addresses, to make decisions about where to forward data packets. This is a key concept in understanding how switches facilitate communication within a network.

💡ARP (Address Resolution Protocol)

ARP is a protocol used for mapping an IP address to a MAC address on a local network. The video script describes how a host uses ARP to discover the MAC address associated with an IP address before it can communicate with another host. Although ARP is not the focus of the video, it is an essential process that supports the switching actions described.

💡MAC Address Table

A MAC address table is a database used by a switch to keep track of the MAC addresses of devices and their corresponding switch ports. The video script explains that the switch starts with an empty table and populates it as data flows through the network. This table is crucial for the switch to perform its functions of learning, flooding, and forwarding.

💡Learning

In the context of the video, learning refers to the process by which a switch updates its MAC address table with the source MAC address of each frame it receives. This is the first action a switch takes when it encounters new data, allowing it to 'learn' which devices are connected to which ports. The script uses this concept to explain how switches build their knowledge of the network.

💡Flooding

Flooding is an action a switch takes when it receives a frame with a destination MAC address that is not in its MAC address table. The switch sends a copy of the frame out of all ports except the one it came in on. The video script uses flooding to illustrate how switches ensure that frames reach their intended recipients when the destination is initially unknown.

💡Forwarding

Forwarding is the action a switch takes to send a frame directly to the port associated with the destination MAC address in the frame. Once the switch has learned the location of a MAC address through its MAC address table, it can forward frames directly to that port, avoiding unnecessary network traffic. The video script explains forwarding as the final step in the switch's process after learning and flooding.

💡VLANs (Virtual Local Area Networks)

VLANs are not explicitly detailed in the provided script, but they are mentioned as a topic for a future lesson. VLANs are used to divide a physical network into separate broadcast domains, allowing for better organization and security. The script hints that understanding VLANs will provide insight into how switches handle traffic differently when they are used.

Highlights

Introduction to Lesson Four on networking fundamentals focusing on switches.

Switches facilitate communication within networks by moving data.

A switch is a device whose primary purpose is switching.

Devices connected to a switch must belong to the same IP network.

Hosts require IP and MAC addresses to communicate through a switch.

Switches operate based on Layer 2 headers, ignoring Layer 3 headers.

Illustration of how a switch enables communication between Host A and Host D.

Switches use MAC address tables to map switch ports to MAC addresses.

MAC address table starts empty and is populated as data flows through the switch.

Switches perform three actions: learning, flooding, and forwarding.

Learning action updates the MAC address table with the source MAC address of received frames.

Flooding action duplicates frames and sends them out all ports except the receiving port.

Forwarding action delivers frames directly to the appropriate switch port based on the MAC address table.

Once the MAC address table is populated, communication between hosts is direct, bypassing flooding.

The process is the same whether Host A is speaking to another host or sending to a router for external communication.

Switches have MAC and IP addresses, but these are only used for direct communication with the switch itself.

Summary of key takeaways: understanding MAC address tables and the three actions of switches.

Anticipatory teaser for the next lesson covering unicast flooding, VLANs, and communication through multiple switches.

Transcripts

hello welcome to lesson four

of module one of my new course on

networking fundamentals

in this lesson we're going to be picking

apart switches and we're going to show

you

everything a switch does to facilitate

communication

as we discussed in the first lesson

switching is the process of moving data

within networks and a switch is simply a

device whose primary purpose

is switching we're about to show you an

illustration of a switch

and everything it does to funnel

communication between these hosts

but it's important to understand

anything that claims to do switching is

going to operate the way we describe a

switch to operate

we are simply going to be describing the

rules of switching

for these hosts to communicate with one

another they each need ip addresses and

mac addresses

now since a switch only facilitates

communication within a network

this tells us that all of these devices

that are speaking through the switch

must belong to the same ip network in

this case that ip network is the 1011.x

network

in this lesson we can illustrate

everything that the switch does to

enable communication between host a

and host d now in the last lesson we

described the host

role in all this we described that the

host is going to generate some data

to send a host d and then add a layer 3

header to that data which includes the

source of host a

and a destination of hostd's ip address

then host a is going to perform arp

to figure out the mac address which

correlates to that destination ip

address

then host a is going to add a layer 2

header which indicates host a's mac

address and host d's mac address

all of that we described in the last

lesson and all of that still applies

in this lesson we're just going to be

focusing on the switch

and if you recall a switch is a layer 2

device which means they're only going to

be using the layer 2 header to make

their decisions

which means the switch doesn't look at

the layer 3 header at all

in fact everything after the layer 2

header from the perspective of the

switch

is simply considered data you and i know

there's a layer 3 header in here but

from the switches perspective

it doesn't care about that layer 3

header it's just going to make the

decision

based upon the layer 2 header in fact we

can actually get rid of

anything ip related on this topology

because if all we're doing is focusing

on the switch

we don't actually need to consider the

ip addresses that are communicating

we're going to show you everything that

happens to get this data to host d

through the switch now i want to point

out that we are starting from the

position that host

a already knows the mac address it's

trying to speak to normally host a would

have to discover this using arp

but for our illustration we're going to

assume host a

already knows the mac address it's

trying to speak to so we can leave arp

out of this illustration entirely

with that said let's go ahead and

explain how switches facilitate

communication

within networks switches use and

maintain

a mac address table a mac address table

is a mapping of switchboards to mac

addresses

each of the hosts in our topology are

plugged into this switch in a particular

port

for instance host c is plugged into port

6. now every different switch out there

uses different numbering schemes for

their ports for the sake of

illustrations i'm just going to use

these numbers

5 6 7 and 8. a mac address table then is

going to include

the mapping of a particular switch port

and the device that's connected to that

port

meaning it's going to know that out port

7 exists a device with the mac address

b2b2

now this mac address table doesn't start

out populated in fact it starts out

empty and as data is flowing through

this topology the switch will populate

this mac address table

beyond this mac address table the switch

is only ever going to perform

three actions learning flooding

and forwarding if you understand these

three actions

then you'll understand how switching

works every switch you come across

regardless of the platform regardless of

the vendor regardless of the code

version is only going to do

three actions these are actually the

rules of switching in general

so let me show you how they work so host

a is going to start

by putting this information on the wire

that will arrive on the switch on port 5

and this is going to allow the switch to

perform its first

action which is to learn the learning

action

has the switch update its mac address

table with a mapping of the switch port

and the source mac address of the

received frame

meaning on port 5 this switch just

received a frame

with a source mac address of a1a1 which

allows the switch to update its mac

address table

indicating that the device on port 5

owns the mac address a181

that is the learning action and the

switch is going to try to learn

the source mac address for every frame

the switch receives

now the switch has to figure out what

it's going to do with this frame

it's going to look at the destination

address of that frame to determine that

this is meant to be delivered

to the device that has the mac address

d4 d4

you and i know that that device exists

over here but this mac address table

lists everything that the switch knows

so at this point in time the switch does

not know

what port the mac address d4 d4 exists

out of

which means the switch's only option is

to duplicate that frame

and send it out all ports this is the

only way the switch can ensure

that whatever owns that mac address does

get this frame

and notice that the switch did not

forward the frame back out port 5.

when it duplicates the frame and sends

it out all ports it's going to set it

about all ports

except the port that received the frame

initially the idea there is that if this

frame

arrived on port 5 there's a good chance

that the destination does not exist back

out port 5.

so that is the flooding action and all

other hosts in this network are going to

receive a copy

of this frame and when host b and host c

receive this frame

they're going to look at the destination

mac address to determine that they are

not the intended recipient for that

frame they are therefore simply going to

silently discard that frame

host d however will be looking at the

destination mac address to realize it

is destined to host d and host d will

accept that frame for processing

and that is how data will get from host

a to host d

now inevitably host d is going to

generate a response to send back to host

a

this response is going to have a source

mac address of hostd's mac address and a

destination mac address host a's mac

address

host d is going to put this response on

the wire where it'll arrive on the

switch on port 8.

this will allow the switch to once again

perform its learning action

it's going to update its mac address

table indicating that something just

arrived on port 8

with a source mac address of d4 d4 this

allows the switch to create this

mapping now the switch is going to try

and figure out what it's going to do

with this frame

and once again it's going to look at the

destination mac address a1a1 to

determine

where to send this frame next the

difference however

is that now the switch knows how to

deliver a frame

to a1a1 it knows that a1a1

exists out port 5 this will allow the

switch to simply forward

that frame out the appropriate switch

port

that is the third action of the switch

the forwarding action

the forwarding action allows the switch

to deliver a frame directly to the

appropriate switchboard

because the destination mac address

exists in the mac address table

this will allow the switch to send that

frame directly to host a

and that is how the response data will

go from host d

to host a now at this point

anything else that a and d need to send

to each other will simply go

directly to each other now that the mac

address table is populated with either

of those host's mac address

anything a and d send to each other is

going to go directly to each other

without having to do the flooding action

which means host c

and host b will not get a copy of any of

that data

and that wraps up our discussion of how

switches work

again switches use and maintain a mac

address table which is a mapping of a

switchboard to a mac address

and switches perform only these three

actions if you understand these three

actions

you now understand how any switch for

any vendor

on any platform facilitates

communication within

a network but before i let you go

there are two more ideas i want to leave

you with

our illustration involved host a sending

a packet to another host

but everything we just showed you would

still apply if this wasn't actually a

host and it was instead

a router and host a was trying to send

something to the router

in order to speak to something else out

on the internet

the only thing that would be different

would be the layer 3 header and as we

discussed the switch doesn't even look

at the layer 3 header to do its job

which means this process is exactly the

same whether host a is speaking to

a host on the local network or trying to

send something to a router in order to

speak to something on a foreign network

the second idea i want to leave you with

is that we showed you how traffic flows

through the switch we illustrated host a

sending something through the switch

initially to host d

understand that switches have mac

addresses again any nic

has a mac address but you'll notice that

this mac address was completely

uninvolved

for any communication going through the

switch

but what if you wanted to send something

to the switch

well if you're trying to send something

to the switch then this mac address

would be involved

but not only would the switch need a mac

address it would also need an ip address

and at this point if you've configured

an ip address on the switch

and you're trying to send traffic to the

switch the switch is essentially acting

as a host on the local network it's

going to follow

all the rules that we described in the

prior lessons that hosts follow

in order to communicate on a network the

switch's mac address

and also its ip address will only be

used if you're sending traffic to

or receiving traffic from the switch

perhaps you're trying to log into the

switch using telnet or ssh in order to

manage the switch but for any traffic

going

through the switch the switch mac

address and

ip address will be completely uninvolved

in the process

the switch is merely going to perform

these actions over here

in order to facilitate communication

within the network

and that wraps up part one of our lesson

on switches

in the next lesson we're going to unpack

three more ideas

we're going to describe unicast flooding

and explain how that's different from a

broadcast

we're going to briefly define vlans and

show you how these actions are different

or not if vlans are being used and

finally we're going to show you

how communication flows through multiple

switches showing you

how these actions are still the same

regardless of how many switches

data is flowing through either way your

key takeaways from this lesson are

understanding these first two bullets up

here

i hope you enjoyed this video i want to

thank you for watching and we'll see you

in the next one

hey youtube i hope you enjoyed that free

lesson for my new course on networking

fundamentals

i'll be releasing the entire first

module for free here on youtube

i want this course to be the ultimate

networking fundamentals course and since

i'm still scoping out the outline you

could have a say in what topics will be

covered

let me know in the comments below what

subjects you want included in this

course

otherwise remember to like and subscribe

and of course if you learned something

from this video the best way to thank me

is to share this video

it's a small act of gratitude but one i

appreciate greatly

i hope you enjoyed this lesson i want to

thank you for watching and we'll see you

in the next one