Chapter 5 — Session 1: Devices by OSI Layer

This session is foundation material. The main rule from your PDF is:

The OSI layer tells you what address/information the device can understand and what boundary it can break.

📋 Topics to Mark Off

• ⬜ OSI device mapping

• ⬜ Layer 1 — Physical devices

• ⬜ Layer 2 — Data Link devices

• ⬜ Layer 3 — Network devices

• ⬜ Hub

• ⬜ Repeater

• ⬜ Modem

• ⬜ Media converter

• ⬜ NIC

• ⬜ Bridge

• ⬜ Switch

• ⬜ Router

• ⬜ Layer 3 / Multilayer switch

• ⬜ MAC vs. IP addressing

• ⬜ Collision domains

• ⬜ Broadcast domains

📝 Notebook Notes — Quick Review

🏢 The Master OSI Map ⭐ EXAM GOLD

This is the device map given in your Chapter 5 notes.

🧠 MEMORY TRICK

Imagine a 3-story networking building:

🏢 NETWORK BUILDING 3️⃣ Router 📍 IP addresses 🌎 Connects NETWORKS 2️⃣ Switch / Bridge / NIC / AP 🏷️ MAC addresses 💻 Connects DEVICES 1️⃣ Hub / Repeater / Modem 01010101 ⚡ Deals with SIGNALS/BITS

Your PDF uses essentially the same "OSI Building" memory technique.

1⃣ Layer 1 — Physical

Think: BITS & SIGNALS

Layer 1 devices don't make intelligent forwarding decisions based on MAC or IP addresses.

Important L1 devices:

Hub
Repeater
Modem
Media converter

🧠 Memory

L1 = Dumb Muscle 💪

It moves/regenerates signals.

It doesn't care:

❌ Who owns this MAC? ❌ What network is this IP on?

It basically says:

"I got bits. I'm moving bits."

🔌 HUB

Layer:

Layer 1 — Physical

A hub is basically a:

Multiport repeater

When something enters one port, the hub sends it everywhere.

       HUB
        🟦
      /  |  \
     /   |   \
   💻   💻   💻

PC1 sends data
       ↓
      HUB
    ↙  ↓  ↘
   💻  💻  💻
EVERYONE gets it

A hub has:

1 collision domain

and

1 broadcast domain

🧠 Memory

HUB = HEAR U BRO

Everybody hears everything. 😂

📡 REPEATER

Layer:

Layer 1

Its job is to:

Regenerate a weakened signal

Imagine someone yelling:

"HELLOOOOO..."

The signal gets weaker:

HELLOOO → Helloo → hello...

Repeater:

Weak signal
     ↓
📡 REPEATER
     ↓
Strong regenerated signal

🧠 Memory

Repeater = REPEATS the signal.

📞 MODEM

Layer:

Layer 1

Modem means:

MOdulator / DEModulator

It converts signals so information can travel across the transmission medium.

🧠 Memory

MO + DEM

MOdulate
+
DEModulate
=
MODEM

Your PDF groups modems with the Layer 1 devices that work with the physical signal.

🔄 MEDIA CONVERTER

Layer:

Layer 1

A media converter changes one physical media type into another.

Think:

Copper Ethernet
      ↓
🔄 MEDIA CONVERTER
      ↓
Fiber

🧠 Memory

Media Converter = changes the ROAD, not the address.

2⃣ Layer 2 — Data Link

Think:

🏷 MAC ADDRESSES

Important Layer 2 devices:

NIC

Switch

Bridge

AP

🧠 Memory

Layer 2 = MAC name tags 🏷

Imagine every device wearing a MAC-address name tag.

💻🏷 AA:BB:CC:11:22:33

Layer 2 devices can read those tags.

💻 NIC

NIC =

Network Interface Card

Layer:

Layer 2

The NIC provides the computer's connection to the network media and carries its:

⭐ MAC ADDRESS

Your notes also distinguish the NIC lights:

Link light = connection exists

Activity light = traffic is flowing

And importantly:

Link must exist before activity.

🧠 Memory

NIC = Network ID Card 🪪

Think of the MAC address printed on its ID card.

🌉 BRIDGE

Layer:

Layer 2

A bridge connects network segments and uses:

MAC addresses

It also separates:

Collision domains

Your PDF describes a modern switch as essentially a hardware multiport bridge.

🧠 Memory

Think of a real bridge:

LAN A 🌆

|

🌉 BRIDGE

|

LAN B 🌆

It connects two network segments.

🔀 SWITCH ⭐ EXAM GOLD

Layer:

Layer 2

Reads:

MAC addresses

A switch learns MAC addresses and places them into a MAC/filter table.

Imagine:

SWITCH MAC TABLE

MAC                  PORT
AA:AA:AA...           1
BB:BB:BB...           2
CC:CC:CC...           3

Now suppose PC A sends something to PC C.

The switch can say:

"I know where C lives — Port 3."

So instead of sending it everywhere:

PC A
 ↓
SWITCH
 ↓
Port 3
 ↓
PC C

That's much smarter than a hub.

⭐ SWITCH DOMAIN RULE

Each switch port creates its own:

Collision domain

But a normal Layer 2 switch does NOT automatically break broadcast domains.

Example:

       SWITCH
     /   |   \
   💻   💻   💻

Collision domains:

PC1 = 1
PC2 = 1
PC3 = 1

TOTAL = 3

But they're still in:

1 broadcast domain

🚨 EXAM TRAP

"Switches stop broadcasts."

❌ WRONG

A switch normally forwards broadcasts.

What stops broadcasts?

ROUTER

Remember:

Switch splits COLLISIONS.

Router breaks BROADCASTS.

3⃣ Layer 3 — Network

Think:

📍 IP ADDRESSES

The major device here is:

ROUTER

🌎 ROUTER ⭐ EXAM GOLD

Layer:

Layer 3 — Network

Reads:

IP addresses

Job:

Connect:

Different networks

This creates an:

Internetwork

Example:

192.168.1.0/24
      │
      │
   🌎 ROUTER
      │
      │
192.168.2.0/24

The router connects those two networks.

⭐ ROUTERS BREAK BROADCAST DOMAINS

Imagine:

LAN A

💻 💻 💻 | ROUTER | 💻 💻 💻 LAN B

A broadcast from LAN A doesn't automatically cross into LAN B.

🧠 Memory

🧱 Router = Broadcast Wall

Your PDF specifically emphasizes that only a Layer 3 device stops a broadcast storm.

🔀 Layer 3 / Multilayer Switch

This one can confuse people.

A normal switch:

Layer 2

A Layer 3 switch:

Can perform routing

Your notes even warn:

"Layer 3 switch" = router functionality, not a normal Layer 2 switch.

🧠 Memory

Normal Switch
      ↓
MAC
      ↓
Layer 2


Layer 3 Switch
      ↓
MAC + IP
      ↓
Switching + Routing

💻 Knowt Notes — Deep Understanding

🧠 WHY Does the Layer Matter?

This is one of the most important ideas.

The layer determines what information the device can understand.

Imagine receiving three envelopes.

Layer 1

Doesn't read the envelope.

It just carries it.

📨 → 📦 → 📨

That's your:

Hub / Repeater

Layer 2

Looks at the local recipient's:

MAC address

📨 TO: MAC AA:BB:CC:DD

That's your:

Switch / Bridge

Layer 3

Looks at:

IP address

📨 DESTINATION: 192.168.20.50

That's your:

Router

🧠 THE GOLDEN RULE

L1 → BITS
      ↓
L2 → MAC
      ↓
L3 → IP

Memorize that first.

Then device questions become easier.

🆚 Hub vs Switch vs Router ⭐⭐⭐

The collision/broadcast behavior is explicitly emphasized throughout your Chapter 5 notes.

🚨 EXAM TRAPS

Trap #1

Hub = Layer 2

❌ NO.

Hub = Layer 1

Trap #2

Switch = IP

❌ NO.

Normal Layer 2 switch:

MAC

Router:

IP

Trap #3

Switch breaks broadcast domains.

❌ NO.

Switch:

breaks collision domains

Router:

breaks broadcast domains

Trap #4

Layer 3 switch = normal switch

❌ NO.

Layer 3 means it has:

Routing capabilities

Trap #5

Unknown destination MAC arrives at a switch.

Does the switch immediately drop it?

❌ NO.

It:

Floods the frame out all ports except the source port.

🎴 FLASHCARDS

⭐ 1 — EXAM GOLD

At which OSI layer does a hub operate?

A. Layer 1 — Physical
B. Layer 2 — Data Link
C. Layer 3 — Network
D. Layer 4 — Transport

✅ Correct: A

🧠 Hub = dumb repeater = L1.

⭐ 2 — EXAM GOLD

A switch primarily makes forwarding decisions using:

A. IP addresses
B. MAC addresses
C. TCP ports
D. Hostnames

✅ Correct: B

🧠 Switch = L2 = MAC.

⭐ 3 — EXAM GOLD

A router primarily makes forwarding decisions using:

A. MAC addresses only
B. Ethernet preambles
C. IP addresses
D. FCS values

✅ Correct: C

🧠 Router = L3 = IP.

4

Which device is known as a multiport repeater?

A. Switch
B. Hub
C. Router
D. Bridge

✅ Correct: B

🧠 Hub = repeater with lots of ports.

5

Which device regenerates a weakened physical signal?

A. Router
B. Bridge
C. Repeater
D. Layer 3 switch

✅ Correct: C

🧠 Repeater REPEATS.

6

Which device is essentially a hardware-based multiport bridge?

A. Hub
B. Switch
C. Router
D. Modem

✅ Correct: B

🧠 Switch = modern multiport bridge.

⭐ 7 — EXAM GOLD

Each port on a switch represents its own:

A. Broadcast domain
B. Collision domain
C. Autonomous system
D. IP subnet automatically

✅ Correct: B

🧠 Switch Splits Collisions.

⭐ 8 — EXAM GOLD

Which device breaks broadcast domains?

A. Hub
B. Bridge
C. Layer 2 switch
D. Router

✅ Correct: D

🧠 Router = broadcast wall. 🧱

🚨 9 — EXAM TRAP

A switch receives a frame destined for a MAC address it hasn't learned. What happens?

A. It immediately drops it
B. It sends it only to the default gateway
C. It floods it out all ports except the source port
D. It converts the MAC to an IP

✅ Correct: C

🧠 Unknown = Flood.

10

Which device contains the computer's MAC address and provides its network interface?

A. Router
B. Repeater
C. NIC
D. Hub

✅ Correct: C

🧠 NIC = Network ID Card. 🪪

11

What does the link light on a NIC indicate?

A. Frames are currently flowing
B. A network connection exists
C. DHCP succeeded
D. DNS is available

✅ Correct: B

🧠 Link = connected. Activity = traffic.

⭐ 12

Which group contains ONLY Layer 2 devices from your chapter's master map?

A. Hub, switch, router
B. NIC, switch, bridge, AP
C. Router, bridge, repeater
D. Hub, modem, NIC

✅ Correct: B

🧠 L2 devices wear MAC name tags. 🏷

13

Which group contains Layer 1 devices?

A. Hub, repeater, modem, media converter
B. Switch, bridge, router
C. NIC, router, switch
D. Router, firewall, Layer 3 switch

✅ Correct: A

🧠 L1 = dumb muscle moving bits/signals.

⭐ 14 — Scenario

A technician needs a device to connect two different IP networks.

Which device should be used?

A. Hub
B. Bridge
C. Repeater
D. Router

✅ Correct: D

🧠 Different NETWORKS = Router.

⭐ 15 — Scenario

A technician wants each connected Ethernet device to have its own collision domain.

Which device is BEST?

A. Hub
B. Switch
C. Repeater
D. Modem

✅ Correct: B

🧠 Every switch port gets its own collision bubble. 🫧

🚨 16 — EXAM TRAP

Which statement is correct?

A. Switches read IP; routers read MAC
B. Switches read MAC; routers read IP
C. Hubs read MAC; switches read IP
D. Repeaters read IP

✅ Correct: B

🧠

2 = MAC

3 = IP

⭐ 17 — EXAM GOLD

Which device can stop a broadcast storm?

A. Hub
B. Bridge
C. Layer 2 switch
D. Router

✅ Correct: D

🧠 Broadcast storm shelter = ROUTER. 🌪🧱

18

A Layer 3 switch combines:

A. Hub + repeater functionality
B. Firewall + IDS functionality
C. Layer 2 switching + Layer 3 routing
D. DNS + DHCP functionality

✅ Correct: C

🧠 L3 Switch = Switch + Router.

🧠 MEMORY BOARD

Burn this into your head:

🏢 OSI BUILDING 3⃣ NETWORK 🌎 ROUTER 📍 IP 🧱 BREAKS BROADCASTS 2️⃣ DATA LINK 🔀 SWITCH 🌉 BRIDGE 💻 NIC 📡 AP 🏷️ MAC 💥 BREAKS COLLISIONS 1️⃣ PHYSICAL 🔌 HUB 📡 REPEATER 📞 MODEM 🔄 MEDIA CONVERTER 010101 BITS

🎯 Network+ Summary

The three associations you absolutely want memorized are:

L1 → Hub/Repeater/Modem → Bits

L2 → Switch/Bridge/NIC/AP → MAC

L3 → Router/L3 Switch → IP

And:

💥 Switch splits collision domains.

📢 Router breaks broadcast domains.

🌪 Only Layer 3 stops a broadcast storm.

Those relationships are specifically highlighted as Chapter 5 exam priorities in your PDF.

⭐ Network+ Exam Priorities

For Session 1, make sure you can answer these instantly:

Hub → L1

Repeater → L1

Modem → L1

NIC → L2

Bridge → L2

Switch → L2 → MAC

Router → L3 → IP

Layer 3 switch → routing

Switch → breaks collision domains

Router → breaks broadcast domains

Unknown MAC → switch floods

Link light → connection

Activity light → traffic

Once those feel easy, Session 2 gets deeper into NICs, hubs, bridges, switches, routers, managed vs. unmanaged switches, and their configuration.

📚 Your End-of-Test Review

Final Score: 14/20 (70%)

📌 Router — 2 missed

Router = Layer 3/IP. It breaks broadcast domains and stops broadcast storms.

Missed: Which device can stop a broadcast storm?
Correct: Router
🧠 Broadcast storm shelter = router.

Missed: Which device breaks broadcast domains?
Correct: Router
🧠 Router = broadcast wall.

📌 Hub — 1 missed

Hub = Layer 1 multiport repeater; one collision domain and one broadcast domain.

Missed: How many collision and broadcast domains does a basic hub segment create?
Correct: 1 collision, 1 broadcast
🧠 Hub = one big shared room.

📌 Bridge — 1 missed

Bridge = Layer 2 and breaks collision domains.

Missed: Which statement best describes a bridge?
Correct: L2 device that connects segments and breaks collision domains
🧠 Bridge = L2, MAC-based, splits collisions.

📌 Switch — 2 missed

Switch = Layer 2/MAC. Each port is its own collision domain. Unknown MAC = flood except source.

Missed: Each port on a switch is its own:
Correct: Collision domain
🧠 Switch splits collisions.

Missed: A switch receives a frame for an unknown destination MAC. What does it do?
Correct: Floods all ports except source
🧠 Unknown MAC = flood except source.

🧠 Switch splits collisions

🧠 Unknown MAC = flood except source.

🧠 Bridge = L2, MAC-based, splits collisions.

🧠 Hub = one big shared room.

🧠 Broadcast storm shelter = router.'

With a hub, all devices share one collision domain.

🔀 A switch fixes this

A switch gives each port its own separate "lane":

💻 ───┐ │ 💻 ───┤ 🔀 SWITCH 💻 ───┤ │ 💻 ───┘ Each connection = separate collision domain