Switch
Switch
A switch is a networking device that connects computers, printers, servers, and other devices within a network and forwards data to the correct destination.
What is an L2 (Layer 2) Switch?
A Layer 2 Switch operates at Layer 2 (Data Link Layer) of the OSI model.
It forwards traffic using MAC addresses.
How It Works
When a device sends data:
The switch reads the source MAC address.
The switch learns which port that MAC address is connected to.
The switch stores it in a MAC Address Table (CAM Table).
Future traffic is sent only to the correct port.
Example
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PC-A ------+
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Switch
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PC-B ------+
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If PC-A wants to communicate with PC-B:
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Destination MAC = PC-B
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The switch forwards the frame only to PC-B's port.
Main Functions of an L2 Switch
MAC address learning
Frame forwarding
Flooding unknown traffic
VLAN support
Reducing network collisions
L2 Switch Characteristics
✅ Uses MAC addresses
✅ Operates at OSI Layer 2
✅ Connects devices within the same network
✅ Supports VLANs
❌ Cannot route between different IP networks by itself
Example VLANs on an L2 Switch
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VLAN 10 = HR
VLAN 20 = Sales
VLAN 30 = IT
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Devices in different VLANs cannot communicate unless a router or Layer 3 device is used.
What is a Multilayer Switch?
A Multilayer Switch (also called a Layer 3 Switch) combines:
Layer 2 switching
Layer 3 routing
into a single device.
It can make forwarding decisions using:
MAC addresses (Layer 2)
IP addresses (Layer 3)
How It Works
A multilayer switch performs normal switching:
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PC-A → PC-B
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and can also route traffic:
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VLAN 10 → VLAN 20
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without needing a separate router.
Example
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HR VLAN (10)
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Multilayer Switch
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IT VLAN (20)
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The multilayer switch routes traffic between VLANs internally.
Inter-VLAN Routing
One of the most common uses of a multilayer switch is Inter-VLAN Routing.
Example:
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192.168.10.0/24 (HR)
192.168.20.0/24 (Sales)
192.168.30.0/24 (IT)
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A Layer 2 switch cannot route between these networks.
A multilayer switch can.
L2 Switch vs Multilayer Switch
Feature L2 Switch Multilayer SwitchOSI Layer Layer 2 Layer 2 & 3
Uses MAC Addresses Yes Yes
Uses IP Addresses No Yes
VLAN Support Yes Yes
Inter-VLAN Routing No Yes
Routing Tables No Yes
Static Routes No Yes
Dynamic Routing No Yes (many models)
Real-World Example
Layer 2 Network
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PCs
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L2 Switch
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Router
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Internet
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The router performs all routing.
Multilayer Switch Network
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PCs
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Multilayer Switch
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Internet Router
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The multilayer switch handles routing between internal networks, reducing the workload on the router.
Advantages of a Multilayer Switch
✅ Faster routing
✅ Inter-VLAN communication
✅ Reduced router load
✅ Better scalability
✅ Enterprise-ready
✅ Supports routing protocols
Examples:
OSPF
EIGRP
RIP
Static Routing
Network+ Exam Tip
Remember:
Layer 2 Switch
Uses MAC addresses
Forwards frames
Operates at OSI Layer 2
Connects devices in the same network
Multilayer (Layer 3) Switch
Uses MAC and IP addresses
Forwards frames and packets
Operates at Layers 2 and 3
Performs routing between VLANs
Quick Memory Trick
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L2 Switch = Switching
L3 (Multilayer) Switch = Switching + Routing
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Simple definition: An L2 switch forwards traffic based on MAC addresses and operates at the Data Link layer, while a multilayer switch can both switch traffic using MAC addresses and route traffic using IP addresses, allowing communication between different VLANs and networks.
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