352-001 · Question #564
352-001 Question #564: Real Exam Question with Answer & Explanation
The correct answer is B: Applying hierarchical QoS with parent policy for the overall circuit and child policy for the spokes. In this DMVPN design, hierarchical QoS (HQoS) at HQ is required to enforce the 20 Mb/s aggregate limit as a parent policy while applying per-spoke child policies that match each branch's 1.5 Mb/s ADSL constraint.
Question
Options
- ARate-limiting the 100 Mb/s circuit to 20 Mb/s
- BApplying hierarchical QoS with parent policy for the overall circuit and child policy for the spokes
- CTraffic shaping the 100 Mb/s circuit to 20 Mb/s
- DQoS is not required in this instance due to maximum traffic being received by the branches being
Explanation
In this DMVPN design, hierarchical QoS (HQoS) at HQ is required to enforce the 20 Mb/s aggregate limit as a parent policy while applying per-spoke child policies that match each branch's 1.5 Mb/s ADSL constraint.
Common mistakes.
- A. Rate-limiting (policing) discards excess packets rather than buffering and scheduling them, causing unnecessary drops and providing no ability to prioritize critical traffic within the constrained bandwidth.
- C. A flat shaping policy applied only to the 20 Mb/s aggregate does not address per-spoke fairness or the 1.5 Mb/s branch constraint, leaving individual spokes vulnerable to starvation or over-subscription.
- D. QoS is required because the aggregate HQ uplink (20 Mb/s) can easily overwhelm individual branch ADSL lines (1.5 Mb/s each), and without per-spoke shaping critical traffic will be dropped at the branch access loop.
Concept tested. Hierarchical QoS for DMVPN hub spoke bandwidth management
Reference. https://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/WAN_and_MAN/DMVPN_2_Phase2/DMVPN_QoS.html
Community Discussion
No community discussion yet for this question.