mediumMultiple Choice
350-401 Practice Question: Given the following configuration: policy-map…
Given the following configuration:
policy-map MARKING_POLICY
class CRITICAL_DATA
set dscp af31
class BULK_DATA
set dscp af11
class class-default
set dscp default
What is the effect of the set dscp default command in the class-default?
⚠ Common exam trap
Cisco often tests the misconception that 'default' means 'leave the original value unchanged' or that it refers to a specific high-priority default like voice, rather than the actual DSCP value of 0 for best-effort traffic.
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
✓
It sets the DSCP value to 0, which is the default best-effort marking.
The 'set dscp default' command explicitly sets the DSCP field to a value of 0, which corresponds to the default best-effort per-hop behavior (PHB) as defined in RFC 2474. This ensures that any traffic not matching the user-defined classes (CRITICAL_DATA or BULK_DATA) is marked with the lowest priority, which is the standard behavior for class-default in a marking policy.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
It sets the DSCP value to 0, which is the default best-effort marking.
Why this is correct
The `set dscp 0` command explicitly overwrites the Differentiated Services Code Point bits with binary 000000. DSCP 0, also known as CS0 or default PHB, is the standard best-effort marking applied to normal IP traffic. Because this is an explicit action in a policy-map, it always results in DSCP 0 regardless of any original marking.
- ✗
It sets the DSCP value to the original value of the packet, effectively not changing it.
Why it's wrong here
This option confuses an explicit marking instruction with a 'copy' or 'preserve' behavior. The `set dscp 0` action does not read the packet's current DSCP value; it writes the constant value 0 into the DSCP field. If the original packet already carried, say, DSCP 34, it would be changed down to 0, so the marking is definitely not left unchanged.
- ✗
It sets the DSCP value to 46, which is the default for voice.
Why it's wrong here
DSCP 46 equates to EF (Expedited Forwarding), which is the recommended per-hop behavior for interactive voice RTP traffic, but it is not a default marking and is not the value used here. The command in question hard-codes DSCP 0, not 46. Standard default behavior for IP packets uses DSCP 0/CS0, while EF must be explicitly configured.
- ✗
It is invalid because class-default cannot have a set action.
Why it's wrong here
The class-default class is a special, mandatory class in any policy-map that matches all traffic not matched by other classes, and it fully supports marking actions. There is no restriction preventing a `set dscp` action inside class-default; in fact, it is commonly used to assign a default best-effort mark. The command is valid as long as the policy-map is correctly referenced on an interface.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-401 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-401 exam.