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Difficulty: MediumIPv6 Addressing Concepts and Header Structure

A network technician is configuring Quality of Service (QoS) for real-time VoIP traffic across an IPv6 enterprise network. The technician needs to tag IPv6 packet headers at Layer 3 so that intermediate routers can classify and prioritize voice packets. Which IPv6 header field is specifically used to carry Differentiated Services Code Point (DSCP) and Explicit Congestion Notification (ECN) information?

  1. Traffic ClassAnswer
  2. B
    Flow Label
  3. C
    Next Header
  4. D
    Hop Limit

Answer

The Traffic Class field is the IPv6 header component designed to carry DSCP and ECN values for packet classification and QoS enforcement.
The Traffic Class field in the fixed 40-byte IPv6 header is an 8-bit field designed specifically for packet classification and traffic prioritization. It directly corresponds to the IPv4 Type of Service (ToS) / Differentiated Services (DiffServ) byte, carrying 6 bits of DSCP data and 2 bits of ECN data.

Step-by-Step Solution

1
Identify the QoS requirement in the scenario
The requirement is to mark Layer 3 IPv6 headers with DSCP and ECN values for traffic prioritization.
Quality of Service relies on standardized header fields to inform intermediate network devices how to queue and handle traffic.
2
Evaluate the function of IPv6 header fields
The 8-bit Traffic Class field stores 6 bits for DSCP (Differentiated Services Code Point) and 2 bits for ECN (Explicit Congestion Notification).
This field mirrors the IPv4 DiffServ/ToS byte structure, enabling compatible QoS policy enforcement across IPv6 routers.

Key Concept

IPv6 Base Header Structure and Traffic Class Field
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Topics

IPv6 Addressing Concepts and Header Structure

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