Free CCNA | QoS (Part 2) | Day 47 | CCNA 200-301 Complete Course

Introduction

This tutorial is designed to provide a comprehensive understanding of Quality of Service (QoS) as covered in the CCNA 200-301 course by Jeremy's IT Lab. By the end of this guide, you will have a solid grasp of QoS mechanisms, including classification, prioritization, and congestion management, which are essential for managing network traffic effectively.

Step 1: Understand Classification

Classification is the process of identifying and defining traffic types on a network. This step is crucial for implementing QoS since it allows network devices to apply specific policies based on the traffic type.

• Key Methods of Classification:
  • PCP (Priority Code Point) / CoS (Class of Service): Used in VLANs to prioritize traffic.
  • IP ToS Byte: The Type of Service byte in the IP header that specifies how packets should be handled.
  • IP Precedence: An older method of prioritizing IP packets, utilizing the first three bits of the ToS byte.
  • DSCP (Differentiated Services Code Point): A more modern and flexible method to classify packets, replacing IP Precedence.

Step 2: Explore PCP and CoS

PCP and CoS are essential for identifying and managing VLAN traffic.

• Understanding PCP:
  • It is a 3-bit field in the Ethernet frame that indicates the priority level (0-7).
• CoS:
  • Works with VLANs to provide priority for different types of traffic.

Step 3: Delve into the IP ToS Byte

The IP ToS byte is an important component in IP packet headers that allows for traffic prioritization.

• Components of the ToS Byte:
  • Precedence: The first three bits indicate the priority level.
  • Delay, Throughput, Reliability: The next three bits define the desired service characteristics.

Step 4: Learn about IP Precedence and DSCP

Understanding IP Precedence and DSCP is crucial for effective traffic classification.

• IP Precedence:
  • Utilizes the first three bits of the ToS byte for prioritization.
• DSCP:
  • Allows for a greater range of priority settings by using the first six bits of the ToS byte.

Step 5: Differentiate Between DF, EF, and AF

These are specific QoS categories used for different traffic types.

• DF (Default Forwarding): Used for best-effort traffic.
• EF (Expedited Forwarding): Designed for low-loss, low-latency traffic, often used for voice.
• AF (Assured Forwarding): Provides different levels of assurance for delivery.

Step 6: Review the AF Summary Chart

This chart provides a visual representation of the different classes under the AF category and their characteristics.

• Key Classes:
  • Each AF class has a designated drop precedence level (low, medium, high).

Step 7: Understand Congestion Management

Congestion management is critical for maintaining service quality during high traffic volumes.

• Techniques:
  • Queuing: Manages how packets are queued for processing.
  • Congestion Avoidance: Techniques like Random Early Detection (RED).

Step 8: Explore Shaping and Policing

Shaping and policing are essential for controlling bandwidth and traffic flow.

• Traffic Shaping:
  • Smooths out traffic bursts to ensure consistent flow.
• Traffic Policing:
  • Drops or marks packets that exceed defined bandwidth limits.

Conclusion

This tutorial has provided an overview of Quality of Service (QoS) principles, essential for CCNA certification and effective network management. Key concepts included classification methods, prioritization techniques, congestion management, and traffic shaping. To further your understanding, consider revisiting the video for visual explanations and engaging with practical labs.