The answer is label 0, which is reserved for the Explicit NULL label in MPLS. This label value is used to signal the penultimate hop router to pop the MPLS label stack and forward the packet based solely on the IP header, rather than performing a full label lookup at the egress router. The purpose of Explicit NULL is to avoid two label lookups at the edge of the MPLS domain, improving efficiency by having the penultimate hop remove the label before the packet reaches its final destination. On the Cisco CCNP ENARSI 300-410 exam, this concept often appears in questions about MPLS forwarding behavior and label operations, testing your understanding of when and why Explicit NULL is used instead of Implicit NULL. A common trap is confusing Explicit NULL (label 0) with Implicit NULL (label 3); remember that Explicit NULL explicitly tells the penultimate hop to pop the label, while Implicit NULL is a signal to do the same but without a label value. For a memory tip, think of “Explicit 0” as “expressly pop to zero labels left.”
300-410 MPLS Operations Practice Question
This 300-410 practice question tests your understanding of mpls operations. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Which MPLS label value is reserved for the Explicit NULL label and what is its purpose?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Label 0; used for the Explicit NULL label to indicate that the penultimate hop should pop the label.
Label value 0 is the IPv4 Explicit NULL label, used to signal the penultimate hop to pop the label stack and forward the packet based on the IP header.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Label 0; used for the Explicit NULL label to indicate that the penultimate hop should pop the label.
Why this is correct
Label 0 is the IPv4 Explicit NULL per RFC 3032.
Related concept
Read the scenario before looking for a memorised answer.
✗
Label 1; used for the Router Alert label.
Why it's wrong here
Label 1 is the Router Alert label, not Explicit NULL.
✗
Label 2; used for the Implicit NULL label.
Why it's wrong here
Label 3 is the Implicit NULL label; label 2 is the IPv6 Explicit NULL.
✗
Label 3; used for the Implicit NULL label.
Why it's wrong here
Label 3 is the Implicit NULL, not Explicit NULL.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 300-410 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
Identify which 300-410 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
MPLS Operations — This question tests MPLS Operations — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Label 0; used for the Explicit NULL label to indicate that the penultimate hop should pop the label. — Label value 0 is the IPv4 Explicit NULL label, used to signal the penultimate hop to pop the label stack and forward the packet based on the IP header.
What should I do if I get this 300-410 question wrong?
Identify which 300-410 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This 300-410 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 300-410 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.