CCNA | VLANS

Overview

• The video covers foundational concepts of Local Area Networks (LANs) and Virtual Local Area Networks (VLANs).

• It emphasizes understanding LANs, broadcast domains, VLAN basics, and VLAN configuration on Cisco switches.

• The next video will continue to delve into VLANs.

What is a LAN?

• Definition: A LAN (Local Area Network) is a group of connected devices such as PCs, servers, routers, switches in a single geographic area like a home or office.

• Broadcast Domain: A LAN operates as a single broadcast domain, meaning all devices will receive broadcast frames sent by any member within that domain.

Understanding Broadcast Domains

• Broadcast Frame: A frame sent with a destination MAC address of 'all F's' that any member of the broadcast domain can send.

• Example:

  • If PC1 sends a broadcast frame:

    • The frame is received by switch 1, which floods it to all interfaces except the one it came from.

    • Devices receiving it include PC2 and Router 1 (R1).

  • R1, when it receives the broadcast, does not forward it.

• Multiple Broadcast Domains: The concept of broadcast domains is illustrated through several examples within a network diagram:

  • First Broadcast Domain: Includes PC1, PC2, switch1, and R1's interface.

  • Second Broadcast Domain: Includes PC3, PC4, PC5, switch2, and R1’s interface.

  • Third Broadcast Domain: Includes PC6, PC7, PC8, switch3, and R2.

  • Fourth Broadcast Domain: The connection between R1 and R2.

Issues with a Single LAN

• With departments (like engineering, HR, sales) in the same LAN:

  • A broadcast from one department (engineering) can flood other departments, leading to security risks and performance degradation (unnecessary broadcast traffic).

• Solution: Subnetting departments into separate subnets:

  • For example:

    • Engineering: 192.168.1.0/26

    • HR: 192.168.1.64/26

    • Sales: 192.168.1.128/26

• Router Requirement: Each subnet requires an interface on the router.

• Inter-subnet communication: Traffic from one subnet to another must go through the router, enforcing security policies.

Introduction to VLANs

• Purpose of VLANs: Introduces separation of devices logically at Layer 2 while physically being on the same switch:

  • Helps with network performance by reducing broadcast traffic.

  • Enhances security by isolating broadcast domains.

• VLAN Assignment: VLANs are assigned to switch interfaces:

  • Each VLAN behaves like a separate LAN; broadcast frames sent from one VLAN do not reach other VLANs.

VLAN Configuration Basics

• Access Ports vs. Trunk Ports:

  • Access Ports: Connect to end hosts and belong to a single VLAN.

  • Trunk Ports: Carry multiple VLANs—covered in future videos.

• Interface Configuration:

  • Example commands:

    • interface range g1/0 to g1/3 for VLAN 10.

    • switchport mode access to configure it as an access port.

    • switchport access vlan 10 assigns the VLAN.

• Default VLANs: VLAN 1 is created by default, along with a range of others that cannot be deleted.

• Renaming VLANs: Names of VLANs can be defined for clarity (e.g., engineering, HR, sales).

Summary of Key Concepts

• LAN: Defined as a broadcast domain.

• VLAN: Logically separates devices in a network to create multiple broadcast domains at Layer 2.

• Configuration: Basic understanding of commands used for VLAN configuration on Cisco switches has been introduced, especially focusing on access ports.

Review Questions

1. How many broadcast domains exist without VLANs? Answer: Six.

2. How many broadcast domains exist with configured VLANs? Answer: Five.

3. What happens when assigning an interface to a non-existent VLAN? Answer: The switch creates the VLAN automatically.

4. How many devices will receive a broadcast from PC3 in a configured VLAN? Answer: Three.

5. Total VLANs after creating three new VLANs on the switch? Answer: Eight (includes default VLANs).

Conclusion

• This video provides foundational knowledge about LANs and VLANs, setting the stage for deeper exploration in future lessons.