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400-007 · Question #56

You are designing a network running both IPv4 and IPv6 to deploy QoS. Which consideration is correct about the QoS for IPv4 and IPv6?

The correct answer is C. IPv6 and IB/4 traffic types can use a single QoS policy to match both protocols. When deploying QoS in a dual-stack IPv4/IPv6 network, Cisco MQC allows a single service policy to classify and manage traffic from both protocol families simultaneously.

Designing Network Services

Question

You are designing a network running both IPv4 and IPv6 to deploy QoS. Which consideration is correct about the QoS for IPv4 and IPv6?

Options

  • AIPv4 and IPv6 traffic types can use use queuing mechanisms such as LLQ, PQ and CQ.
  • BIPv6 packet classification is only available with process switching, whereas IPv4 packet
  • CIPv6 and IB/4 traffic types can use a single QoS policy to match both protocols
  • DDifferent congestion management mechanisms need to be used for IPv4 and IPv6 traffic types

How the community answered

(22 responses)
  • A
    5% (1)
  • C
    91% (20)
  • D
    5% (1)

Why each option

When deploying QoS in a dual-stack IPv4/IPv6 network, Cisco MQC allows a single service policy to classify and manage traffic from both protocol families simultaneously.

AIPv4 and IPv6 traffic types can use use queuing mechanisms such as LLQ, PQ and CQ.

PQ (Priority Queuing) and CQ (Custom Queuing) are legacy IOS interface-level queuing mechanisms that have largely been superseded by MQC-based tools, and claiming they apply equivalently to IPv6 in modern dual-stack deployments is inaccurate.

BIPv6 packet classification is only available with process switching, whereas IPv4 packet

IPv6 packet classification fully supports Cisco Express Forwarding (CEF) switching, so restricting it to process switching only is factually incorrect and would represent a severe performance limitation that does not exist in modern IOS.

CIPv6 and IB/4 traffic types can use a single QoS policy to match both protocolsCorrect

Cisco's Modular QoS CLI (MQC) supports class-maps and policy-maps that can match both IPv4 and IPv6 traffic within the same service policy using protocol-agnostic match criteria such as DSCP or protocol type. This means a single policy-map applied to a dual-stack interface handles both protocol families without requiring separate policies. This unified approach simplifies QoS configuration and ensures consistent treatment of traffic regardless of IP version.

DDifferent congestion management mechanisms need to be used for IPv4 and IPv6 traffic types

The same congestion management mechanisms such as CBWFQ and LLQ apply equally to IPv4 and IPv6 traffic within a single MQC policy, so requiring different mechanisms per protocol type is incorrect.

Concept tested: Dual-stack QoS single MQC policy support

Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/qos_mqc/configuration/xe-16/qos-mqc-xe-16-book/qos-mqc.html

Topics

#QoS#IPv4 IPv6 dual-stack#LLQ#unified QoS policy

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