350-501 Automation and Quality of Service Practice Question
A network operator deploys a QoS policy on a route reflector to classify traffic based on BGP community values. However, the policy is not matching the intended traffic. Which is the most likely cause?
⚠ Common exam trap
Cisco often tests the distinction between control-plane attributes (like BGP communities) and data-plane packet headers, leading candidates to incorrectly assume that any attribute visible in the routing table can be used for QoS classification.
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
✓
The class-map uses a match statement referencing BGP community values, which are not visible at the QoS classification stage.
BGP community values are exchanged as part of the BGP routing update and are stored in the BGP table, but they are not carried in the IP packet header. QoS classification in Cisco IOS operates on fields within the Layer 2 or Layer 3 packet header (e.g., DSCP, IP precedence, CoS) and cannot inspect BGP attributes like community values. Therefore, a class-map using a match statement for BGP communities will never match traffic at the QoS classification stage, making this the most likely cause of the policy not working.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The policy-map is applied to the wrong interface.
Why it's wrong here
Interface application affects where the policy is processed, but the match condition itself is invalid.
- ✓
The class-map uses a match statement referencing BGP community values, which are not visible at the QoS classification stage.
Why this is correct
BGP communities are control-plane attributes; QoS uses packet headers.
- ✗
The service-policy is applied in the wrong direction (input vs output).
Why it's wrong here
Direction affects when the policy is applied, but the match is still invalid.
- ✗
The class-default class is consuming all traffic.
Why it's wrong here
Class-default matches unclassified traffic; if a match existed it would work.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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