Chapter 5 — Session 2: Core Networking Devices

Now we’ll go deeper into the devices from Session 1 and focus on how they actually behave on a network.

📋 Topics to Mark Off

⬜ NIC
⬜ Link light
⬜ Activity light
⬜ Hub
⬜ Bridge
⬜ Switch
⬜ MAC address table
⬜ MAC learning
⬜ Unknown unicast flooding
⬜ Router
⬜ Routing table
⬜ Managed switch
⬜ Unmanaged switch
⬜ Switch interface configuration
⬜ Collision domains
⬜ Broadcast domains

📝 Notebook Notes — Quick Review

💻 NIC — Network Interface Card

A NIC connects a device to the network.

Think:

💻 Computer → NIC → 🌐 Network

The NIC operates primarily at:

Layer 2 — Data Link

And is associated with the device's:

🏷 MAC address

🧠 Memory Trick

NIC = Network ID Card

💡 NIC Lights

You'll commonly see:

🔗 Link Light

Means:

A physical/network connection exists.

⚡ Activity Light

Means:

Network traffic is occurring.

⭐ EXAM GOLD

LINK = Connected 🔗

ACTIVITY = Talking 💬

If there is no link, you wouldn't expect normal network activity.

🔌 Hub

A hub operates at:

Layer 1 — Physical

It doesn't understand MAC addresses.

If PC1 sends something:

        HUB
       / | \
      /  |  \
    💻  💻  💻
     ↑
   Sender

The hub repeats it to:

EVERY port

⭐ Collision Domain

All devices connected to the hub share:

ONE collision domain

🧠 Remember what we just covered:

Hub = everyone driving on the same road. 🚗💥🚗

🌉 Bridge

A bridge operates at:

Layer 2

It uses:

MAC addresses

A bridge can connect two LAN segments:

LAN A             LAN B
💻 💻             💻 💻
  │                 │
  └──── 🌉 BRIDGE ──┘

It can determine whether traffic needs to cross from one segment to another.

🧠 Memory

Bridge connects network segments just like a real bridge connects two areas.

🔀 Switch ⭐ EXAM GOLD

A switch is essentially a:

Multiport bridge

It operates normally at:

Layer 2

And makes forwarding decisions using:

MAC addresses

📋 MAC Address Table

A switch learns where devices are located.

Example:

MAC TABLE

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

If the switch needs to reach:

BB:BB:BB...

It knows:

Send the frame through Port 2.

🧠 How Does a Switch Learn MAC Addresses?

This is VERY important.

A switch learns from the:

⭐ SOURCE MAC ADDRESS

Suppose:

PC-A
MAC = AAAA

   ↓ Frame

🔀 Switch
Port 3

The switch sees:

"This frame came INTO Port 3 from MAC AAAA."

So it learns:

AAAA → Port 3

🚨 EXAM TRAP

What address does a switch use to LEARN its MAC table?

❌ Destination MAC

✅ SOURCE MAC

🧠 Memory

SOURCE teaches. DESTINATION tells.

Source MAC teaches the switch where a device lives.

Destination MAC tells the switch where the frame needs to go.

🌊 Unknown Unicast Flooding ⭐ EXAM GOLD

What happens if the destination MAC isn't in the switch's MAC table?

The switch doesn't know which port to use.

So it:

Floods the frame.

Meaning it sends the frame out:

Every port except the port it came from.

Example:

            PC-B
              ↑
              │
PC-A → 🔀 SWITCH → PC-C
              │
              ↓
            PC-D

Eventually, the correct device responds.

Then the switch learns more MAC information.

🧠 Memory

Unknown = Flood 🌊

🌎 Router

A router operates at:

Layer 3 — Network

Instead of MAC addresses, its main forwarding decisions use:

📍 IP addresses

Its job is to connect:

Different IP networks

Example:

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

🗺️ Routing Table

A router needs to know:

Where networks are located.

That's what the routing table helps with.

Think of it like GPS:

Destination Network     Go This Way

192.168.10.0/24   →     Interface 1
192.168.20.0/24   →     Interface 2
10.0.0.0/8        →     Router B

🧠 Memory

Routing Table = Router's GPS 🗺

🆚 MAC Table vs. Routing Table ⭐

This is an excellent exam distinction.

Device	Table	Looks For
Switch	MAC table	MAC addresses
Router	Routing table	IP networks

🧠 Memory

🔀 Switch → MAC Map

🌎 Router → Network Map

🔧 Managed Switch

A managed switch allows administrators to configure and monitor it.

Depending on the switch, you may configure things such as:

VLANs
Port settings
Security features
Monitoring
Management settings

Think:

Managed = I CONTROL IT. 🎮

📦 Unmanaged Switch

An unmanaged switch is basically:

Plug and play

You connect devices and it starts switching traffic.

Much less configuration is available.

🧠 Memory

UNmanaged = UNcomplicated

🆚 Managed vs. Unmanaged

Managed	Unmanaged
Configurable	Plug-and-play
VLAN support commonly available	Little/no configuration
Monitoring	Minimal management
Enterprise/business use	Simple networks

⭐ EXAM CLUE

Question says:

"Administrator needs to configure VLANs."

Think:

✅ MANAGED SWITCH

💥 Collision Domains

Remember:

A switch creates:

One collision domain per port

       SWITCH
      /  |  \

💻 💻 💻 3 connected ports ↓ 3 collision domains

📢 Broadcast Domains

A regular Layer 2 switch generally keeps connected devices in:

ONE broadcast domain

💻 ─┐ 💻 ─┼─ 🔀 SWITCH 💻 ─┘ 📢 Broadcast can reach everyone

But:

🌎 Router

separates broadcast domains.

⭐ GOLDEN DOMAIN RULE

HUB
↓
ONE collision domain
ONE broadcast domain


SWITCH
↓
Each port = collision domain
Normally ONE broadcast domain


ROUTER
↓
Breaks broadcast domains

🧠 Memory Trick

Switch Splits Collisions.

Router Restricts Broadcasts.

💻 Knowt Notes — Deep Understanding

🔀 What Actually Happens When PC-A Sends to PC-B?

Imagine:

PC-A
MAC: AAAA
   │
   │ Port 1
   ▼
┌──────────────┐
│    SWITCH    │
└──────────────┘
   │
   │ Port 4
   ▼
PC-B
MAC: BBBB

PC-A sends:

SOURCE MAC:
AAAA

DESTINATION MAC:
BBBB

The switch first looks at:

SOURCE

It learns:

AAAA → Port 1

Then it looks at:

DESTINATION

It asks:

"Do I know where BBBB lives?"

If yes:

BBBB → Port 4

Send only through Port 4.

If no:

🌊 FLOOD

Send it everywhere except Port 1.

⭐ The Entire Switching Process

Think:

FRAME ARRIVES
     ↓

👀 Read SOURCE MAC ↓ 🧠 Learn source port ↓ 👀 Read DESTINATION MAC ↓ Do I know it? / \ YES NO ↓ ↓ FORWARD FLOOD 🌊

This is a great mental model for Network+ questions.

🚨 Exam Traps

Trap #1

Switch learns destination MAC addresses.

❌ Wrong.

It learns from:

SOURCE MAC addresses

Trap #2

Unknown MAC means drop.

❌ Wrong.

Unknown destination:

FLOOD

Trap #3

Router uses MAC table for routing.

❌ Wrong.

Router:

Routing table + IP networks

Switch:

MAC table + MAC addresses

Trap #4

Unmanaged switch is better when you need VLAN configuration.

❌ Wrong.

You generally need:

Managed switch

Trap #5

One switch = one collision domain.

❌ Wrong.

Each switch port = separate collision domain.

✅ Correct: D

🧠 One switch port = one collision domain.

⭐ 11 — EXAM GOLD

A normal Layer 2 switch with no VLAN segmentation generally represents how many broadcast domains?

A. One
B. One per port
C. Two per port
D. Zero

✅ Correct: A

🧠 Switch splits collisions—not broadcasts.

⭐ 12

Which device separates broadcast domains?

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

✅ Correct: D

🧠 Router Restricts Broadcasts.

🧠 Memory Board

🔀 SWITCH SOURCE MAC ↓ 🧠 LEARN DESTINATION MAC ↓ 🗺️ LOOK UP Known? ↓ FORWARD Unknown? ↓ 🌊 FLOOD 🌎 ROUTER IP ADDRESS ↓ ROUTING TABLE ↓ Different Network 💥 DOMAINS HUB 1 collision domain SWITCH 1 collision domain PER PORT ROUTER BREAKS broadcast domains

🎯 Network+ Summary

The biggest concept from this session is how switches think:

Source MAC = learn

Destination MAC = forward

Unknown destination MAC = flood

And remember the two different maps:

🔀 Switch → MAC table

🌎 Router → Routing table

Finally:

💥 Switch separates collision domains.

📢 Router separates broadcast domains.

⭐ Network+ Exam Priorities

Memorize these cold:

NIC → MAC address

Link light → connection

Activity light → traffic

Hub → Layer 1

Bridge → Layer 2

Switch → Layer 2

Switch → MAC table

Source MAC → learning

Destination MAC → forwarding

Unknown MAC → flooding

Router → Layer 3

Router → IP addresses

Router → routing table

Managed switch → configurable/VLANs

Unmanaged switch → plug-and-play

Switch port → separate collision domain

Router → separates broadcast domains