CCNA 200-301 v1.1 (Full Course)

1.1.b Layer 2 and Layer 3 Switches

🔹 What is a Switch (basic recap)?

A switch is a networking device that connects devices in a LAN.
It works at Layer 2 (Data Link Layer) of the OSI model (but some switches also work at Layer 3 (Network Layer)).
Main job: Forward frames based on MAC addresses.

🔹 Layer 2 Switch

Works at OSI Layer 2 (Data Link Layer).
Makes decisions based on MAC addresses.
Functions:
- Builds a MAC address table (switching table).
- Forwards frames within the same VLAN.
- Supports VLANs (but cannot route between them).
Limitation:
- Cannot understand IP addresses.
- Cannot route between different subnets/VLANs.
Example Use Case:
- Inside an office LAN where devices are on the same network.

👉 Think of it as a traffic controller for local devices.

🔹 Layer 3 Switch

Works at both Layer 2 & Layer 3.
Can perform all Layer 2 switch functions, plus routing (Layer 3) functions.
Functions:
- Routes packets between different VLANs/subnets (Inter-VLAN routing).
- Uses IP routing protocols (like OSPF, EIGRP, RIP, static routes).
- Often faster than routers for internal LAN routing (since switching hardware is optimized).
Limitation:
- Usually used inside LANs (not for WAN edge like routers).

👉 Think of it as a switch + router combined.

🔹 Key Differences (Layer 2 vs Layer 3 Switch)

Feature	Layer 2 Switch	Layer 3 Switch
OSI Layer	Layer 2 (Data Link)	Layer 2 & 3
Forwards using	MAC Address	MAC + IP Address
Inter-VLAN routing	❌ Not possible	✅ Possible
Routing protocols	❌ No	✅ Yes (OSPF, EIGRP, RIP, Static)
Typical Use	Basic LAN switching	Large LAN, VLAN-to-VLAN routing
Speed	High (hardware switching)	High (hardware + routing)

🔹 Real Life Example

Layer 2 Switch Example: Cisco Catalyst 2960 (only does switching).
Layer 3 Switch Example: Cisco Catalyst 3560/3850 (does both switching and routing).

🔹 Exam Tips (CCNA)

✅ Remember: Layer 2 switch = MAC only, Layer 3 switch = MAC + IP.
✅ Routers vs Layer 3 switches: Both route between subnets, but routers are for WAN edge (internet, branch connections), while Layer 3 switches are for LAN inter-VLAN routing.
✅ Inter-VLAN routing can be done either:

Using a router-on-a-stick (router + trunk link), OR
Using a Layer 3 switch (SVIs = Switch Virtual Interfaces).

🔹 Unmanaged Switch

Very basic switch.
Just plug it in and it works.
It only lets devices talk to each other on the same network.
No settings, no VLANs, no security.
Example: small cheap switch for home use.

👉 Think of it like a basic power strip: you just plug things in, no control.

🔹 Managed Switch

A smart switch that you can configure.
You can log in using CLI (commands), web page, or software.
Supports:
- VLANs → separate groups of devices.
- Security → block or allow devices.
- Monitoring → check traffic, errors, logs.
- Quality of Service (QoS) → give priority to voice/video.
Used in schools, companies, data centers.

👉 Think of it like a traffic light system: you control and manage the flow.

🔹 Quick Summary Table

Type of Switch	Main Job	Can it do VLANs?	Can it route (connect VLANs)?	Who uses it?
Unmanaged	Just connects devices	❌ No	❌ No	Home, small office
Managed (L2)	Smart switch using MAC	✅ Yes	❌ No	Schools, offices
Managed (L3)	Switch + Router	✅ Yes	✅ Yes	Large LAN, enterprises