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352-001 · Question #304

The Service Provider you work for wants to deploy CoS functionality on the P routers of the MPLS core, to provide a complete CoS solution to all customers that purchase services such as dedicated…

The correct answer is A. Control plane 10%, Real Time 30%, Business Critical 40%, Best Effort 20% D. Control plane 20%, Real Time 40%, Business Critical 30%, Best Effort 10%. A valid MPLS core CoS bandwidth allocation must reserve a small portion for SP-managed control traffic while giving customers the majority across real-time, business-critical, and best-effort queues. Options A and D both meet this requirement with proportionally sound…

Design Considerations

Question

The Service Provider you work for wants to deploy CoS functionality on the P routers of the MPLS core, to provide a complete CoS solution to all customers that purchase services such as dedicated Internet access, MPLS Layer 3 VPN, and Layer 2 VPN (pseudowire). The design requirements are:

  • The network supports four service queues with equal treatment for

delay, jitter, and packet loss.

  • Queues are numbered 0-3, where 0 is the default queue.
  • Three queues have one treatment, whereas the other queue has either

one or two treatments.

  • The Service Provider manages control traffic, whereas the customers

manage business critical and best effort. Which two statements could you recommend to allow for the appropriate level of bandwidth allocation? (Choose two.)

Options

  • AControl plane 10%, Real Time 30%, Business Critical 40%, Best Effort 20%
  • BControl plane 80%. Real Time 10%, Business Critical 5%, Best Effort 5%
  • CControl plane 90%, Real Time 5%, Business Critical 5%, Best Effort 0%
  • DControl plane 20%, Real Time 40%, Business Critical 30%, Best Effort 10%

How the community answered

(31 responses)
  • A
    58% (18)
  • B
    10% (3)
  • C
    32% (10)

Why each option

A valid MPLS core CoS bandwidth allocation must reserve a small portion for SP-managed control traffic while giving customers the majority across real-time, business-critical, and best-effort queues. Options A and D both meet this requirement with proportionally sound distributions.

AControl plane 10%, Real Time 30%, Business Critical 40%, Best Effort 20%Correct

Allocating 10% to control plane, 30% to real-time, 40% to business-critical, and 20% to best-effort satisfies all design requirements - the SP retains a small but protected control queue, and all four queues receive a non-zero meaningful share of bandwidth.

BControl plane 80%. Real Time 10%, Business Critical 5%, Best Effort 5%

Assigning 80% to the control plane is disproportionate for a live SP network and leaves only 20% split across all customer service queues, effectively starving real-time and business-critical traffic.

CControl plane 90%, Real Time 5%, Business Critical 5%, Best Effort 0%

Assigning 90% to control plane is operationally unreasonable, and allocating 0% to the best-effort queue violates the requirement that all four queues numbered 0-3 be provisioned.

DControl plane 20%, Real Time 40%, Business Critical 30%, Best Effort 10%Correct

Allocating 20% to control plane, 40% to real-time, 30% to business-critical, and 10% to best-effort also meets the requirements - control traffic is modest, and customers receive 80% of total bandwidth distributed across three distinct service queues.

Concept tested: MPLS core CoS bandwidth allocation per service queue

Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/qos_classn/configuration/xe-16/qos-classn-xe-16-book/qos-classn-mrkng-opt-clsif.html

Topics

#CoS#QoS queuing#MPLS core#bandwidth allocation

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