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04 - Day 16 - VLANs Part 1.md

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Day 16 - VLANs Part 1

Reviewed: No

What is a LAN?

  • Definition: A LAN (Local Area Network) is a single broadcast domain where all devices receive a broadcast frame.
  • Broadcast Domain: A group of devices receiving a broadcast frame (destination MAC of all Fs).
  • LAN Composition: Includes PCs, servers, routers, switches, etc., typically in a single location (home, office).

Understanding Broadcast Domains

  1. Behavior of Broadcast Frames:
    • Sent by a device (e.g., PC) and flooded by switches.
    • Routers do not forward broadcast frames, thus ending the domain.
  2. Example Network Analysis:
    • Scenario: Multiple PCs connected through switches and routers.
    • Broadcast Domain Count: Four distinct domains identified based on the propagation of broadcast frames.

Introduction to VLANs

  • Definition: VLANs are logical subdivisions within a LAN that segment the network into multiple broadcast domains at Layer 2.
  • Purpose: Improve network performance and security by controlling broadcast traffic and access.

Benefits of VLANs

  1. Performance: Reduces unnecessary broadcast traffic, improving overall network efficiency.
  2. Security: Limits access and controls traffic between different parts of the network.

VLAN Configuration Basics

  • Assigning VLANs: Configured on switch interfaces to assign devices to specific VLANs.
  • Separation: VLANs create separate broadcast domains, preventing traffic from crossing VLAN boundaries without routing.

Scenario: Company Network

  • Departments: Engineering, Sales, and Human Resources.
  • Network Segmentation: Initially all in one subnet (192.168.1.0/24), causing security and performance issues.
  • Solution: Separate departments into distinct subnets (e.g., Engineering - 192.168.1.0/26, HR - 192.168.1.64/26, Sales - 192.168.1.128/26) and assign VLANs (VLAN10, VLAN20, VLAN30).

Detailed VLAN Configuration on Cisco Switches

  1. Default VLANs: VLAN1 and VLANs 1002-1005 exist by default and cannot be deleted.
  2. Access Ports: Configured to connect end hosts; belong to a single VLAN.
  3. Trunk Ports: Carry multiple VLANs; discussed in detail in Day 17.
  4. Commands:
    • interface range G1/0 - G1/3: Select interfaces.
    • switchport mode access: Set interfaces to access mode.
    • switchport access vlan [VLAN_ID]: Assign VLAN to interfaces.
    • show vlan brief: Display VLAN information on the switch.

VLAN Name Customization

  • VLAN Naming: Assign meaningful names (e.g., Engineering, HR, Sales) for clarity.
  • Command: vlan [VLAN_ID] followed by name [NAME].

Review and Summary

  • LAN vs. VLAN: A LAN is a broadcast domain, while a VLAN is a virtual segment of a LAN creating multiple broadcast domains.
  • Purpose of VLANs: Enhances network performance and security by limiting broadcast domains and controlling access.
  • VLAN Configuration: Focus on access ports, with trunk ports to be covered later.

Commands Used in Day 16

  • VLAN Creation and Assignment:
    • show vlan brief
    • interface range [INTERFACES]
    • switchport mode access
    • switchport access vlan [VLAN_ID]
    • vlan [VLAN_ID]
    • name [NAME]