Lecture Notes: Local Area Networks (LANs) and VLANs

Local Area Networks (LANs)

• Definition: A group of devices in the same broadcast domain.
• Configuration: Devices connected to a switch are in the same broadcast domain.
• Example: Red and blue networks, each on separate switches.

Challenges with Separate Switches

• Each switch requires:
  • Separate power sources
  • Space in a rack
  • Individual management
• Inefficiencies: Managing multiple switches separately is less efficient.

Virtual Local Area Networks (VLANs)

• Purpose: Allows for multiple broadcast domains on a single switch.
• Configuration:
  • Each interface on a switch can belong to a specific VLAN.
  • Devices on the same VLAN can communicate with each other.
• Numbering: VLANs are defined by numbers (e.g., VLAN 1, VLAN 2, VLAN 3).

VLAN Trunking

• Problem: Need to connect the same VLANs across different switches.
• Solution: Use a VLAN trunk (802.1Q trunk).
  • Allows multiple VLANs to share a single physical connection between switches.
  • Tags are added to Ethernet frames to identify VLAN membership.
  • VLAN Tag: 12 bits long, allowing up to 4,094 VLANs.

Native VLAN

• Definition: A VLAN that does not add a tag over a trunk connection.
• Purpose: Useful for devices and admin functions that do not support 802.1Q.
• Configuration: Ensure the native VLAN is the same on connected switches to avoid errors.

Layer 2 vs. Layer 3 Switches

• Layer 2 Switch: Makes forwarding decisions based on MAC addresses.
• Layer 3 Switch: Combines switch and router functionality.
  • Uses IP addresses for routing decisions.
  • Configures Switched Virtual Interfaces (SVIs) for routing.
• Advantages: Combines routing and switching in one device, saving space and power.

Combining Voice and Data

• Historical Setup: Separate cables for Ethernet and telephones.
• Current Setup: Voice over IP allows voice and data on the same network.
• Challenge: Contention between voice and data traffic.
• Solution: Assign voice and data to separate VLANs using trunking technology.
  • Requires compatible switching equipment.
  • Ensures seamless simultaneous use of voice and data.

Conclusion

• VLANs provide efficient management and separation of network traffic on a single switch.
• Trunking and VLAN configurations enhance connectivity and communication across networks.
• Layer 3 switches integrate routing and switching, optimizing network functionality.