350-501 Automation and Quality of Service Practice Question
Which THREE statements about implementing QoS in an MPLS VPN environment are correct? (Choose three.)
⚠ Common exam trap
Cisco often tests the misconception that MPLS encapsulation prevents QoS application, when in fact QoS policies are fully supported on MPLS interfaces, and the trap is that 802.1p CoS is not automatically preserved across the MPLS backbone—it must be explicitly mapped to MPLS EXP bits.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
DSCP values can be set at the PE router to classify customer traffic into different classes.
On a PE router, DSCP values can be set or remarked to classify incoming customer traffic into distinct service classes. This classification is performed at the ingress edge of the MPLS VPN network, allowing the provider to apply appropriate per-hop behaviors (PHBs) before the traffic is label-switched.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
DSCP values can be set at the PE router to classify customer traffic into different classes.
Why this is correct
PE routers can mark DSCP for customer traffic before entering the MPLS backbone.
- ✓
MPLS EXP bits can be used to prioritize traffic across the service provider backbone.
Why this is correct
EXP bits are the standard way to carry QoS across MPLS.
- ✗
QoS policies cannot be applied to MPLS interfaces due to label encapsulation.
Why it's wrong here
QoS policies can be applied to MPLS interfaces, often using EXP-based classification.
- ✗
802.1p CoS marking is preserved across the MPLS backbone by default.
Why it's wrong here
802.1p is typically not preserved across MPLS backbone without explicit mapping.
- ✓
Hierarchical QoS (HQoS) can be used to apply per-VPN QoS policies on a PE router.
Why this is correct
HQoS allows separate policies for different VPNs on the same interface.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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