350-501 Automation and Quality of Service Practice Question
A network engineer is troubleshooting QoS on a Cisco ASR 1000 router. The router has a service-policy applied on the ingress interface GigabitEthernet0/0/0. The policy uses a class-map to match traffic based on NBAR protocol discovery for 'cisco-jabber'. The goal is to mark the traffic with DSCP AF41. However, when the engineer checks the policy statistics, the class 'jabber' shows zero matches, even though the users are actively using Cisco Jabber. The NBAR protocol discovery is enabled globally and on the interface. The engineer verifies that the NBAR protocol pack is up-to-date. What is the most likely reason for the class-map not matching?
⚠ Common exam trap
Cisco often tests the limitation that NBAR cannot classify encrypted or obfuscated traffic, leading candidates to incorrectly assume the issue is with policy direction, match method, or protocol pack activation.
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
✓
Cisco Jabber traffic is encrypted, so NBAR cannot identify it
Cisco Jabber uses encrypted signaling and media (SRTP/TLS), which prevents NBAR from performing deep packet inspection to identify the application. Even with an up-to-date protocol pack, NBAR cannot match encrypted traffic unless decryption is performed elsewhere. Therefore, the class-map matching 'cisco-jabber' via NBAR protocol discovery will show zero matches.
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 service-policy should be applied on the egress interface instead
Why it's wrong here
Classification must happen on ingress to mark before routing.
- ✓
Cisco Jabber traffic is encrypted, so NBAR cannot identify it
Why this is correct
NBAR relies on deep packet inspection; encryption hides application signatures.
- ✗
The class-map is using 'match access-group' instead of 'match protocol'
Why it's wrong here
If using access-group, it might not match NBAR signatures.
- ✗
The NBAR protocol pack is not activated on this interface
Why it's wrong here
Protocol pack is global; activation is not per-interface.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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