The answer is 10.4.4.0/24, as this prefix shows a status of 'No Label' in the MPLS forwarding table, indicating a missing MPLS label binding. When a router has not received a label from the next-hop router for that specific Forwarding Equivalence Class (FEC), it cannot impose the correct label on outgoing packets, causing labeled traffic toward that destination to be dropped. On the Cisco SPCOR / CCNP Service Provider Core 350-501 exam, this scenario tests your ability to interpret show mpls forwarding-table output and identify label allocation failures, often caused by misconfigured LDP sessions or missing route targets. A common trap is confusing 'No Label' with 'Untagged'—remember that 'No Label' means the router lacks a label from the next hop, while 'Untagged' means the router itself is the penultimate hop. Keep this memory tip handy: if you see 'No Label', think "no label from the neighbor," and check LDP neighbor adjacency or IGP reachability first.
350-501 MPLS and Segment Routing Practice Question
This 350-501 practice question tests your understanding of mpls and segment routing. 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.
Exhibit
Refer to the exhibit. The output below is from a Cisco router.
R1# show mpls forwarding-table
Local Outgoing Prefix Bytes Label Outgoing Next Hop
Label Label or Tunnel Id Switched interface
16 27 10.1.1.0/24 0 Gi0/0 172.16.1.2
17 31 10.2.2.0/24 0 Gi0/0 172.16.1.2
18 Pop Label 10.3.3.0/24 0 Gi0/1 172.16.2.2
19 No Label 10.4.4.0/24 no vif Gi0/2 172.16.3.2
20 35 10.5.5.0/24 0 Gi0/0 172.16.1.2
Based on the exhibit, which prefix is missing a label binding and likely causing traffic to be dropped?
Refer to the exhibit. The output below is from a Cisco router.
R1# show mpls forwarding-table
Local Outgoing Prefix Bytes Label Outgoing Next Hop
Label Label or Tunnel Id Switched interface
16 27 10.1.1.0/24 0 Gi0/0 172.16.1.2
17 31 10.2.2.0/24 0 Gi0/0 172.16.1.2
18 Pop Label 10.3.3.0/24 0 Gi0/1 172.16.2.2
19 No Label 10.4.4.0/24 no vif Gi0/2 172.16.3.2
20 35 10.5.5.0/24 0 Gi0/0 172.16.1.2
A
10.2.2.0/24
Why wrong: This prefix has an outgoing label (31), so it is working.
B
10.1.1.0/24
Why wrong: This prefix has an outgoing label (27), so it is working.
C
10.4.4.0/24
'No Label' means no label binding exists; traffic to this prefix will be dropped.
D
10.3.3.0/24
Why wrong: 'Pop Label' is a valid operation (PHP), so traffic can still be forwarded.
E
10.5.5.0/24
Why wrong: This prefix has an outgoing label (35), so it is working.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
10.4.4.0/24
The prefix 10.4.4.0/24 has 'No Label', indicating the router has not learned a label from the next-hop for that FEC. This can cause labeled packets to that prefix to be dropped.
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.
✗
10.2.2.0/24
Why it's wrong here
This prefix has an outgoing label (31), so it is working.
✗
10.1.1.0/24
Why it's wrong here
This prefix has an outgoing label (27), so it is working.
✓
10.4.4.0/24
Why this is correct
'No Label' means no label binding exists; traffic to this prefix will be dropped.
Related concept
Read the scenario before looking for a memorised answer.
✗
10.3.3.0/24
Why it's wrong here
'Pop Label' is a valid operation (PHP), so traffic can still be forwarded.
✗
10.5.5.0/24
Why it's wrong here
This prefix has an outgoing label (35), so it is working.
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 350-501 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.
What to study next
Got this wrong? Here's your next step.
Identify which 350-501 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 and Segment Routing — This question tests MPLS and Segment Routing — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: 10.4.4.0/24 — The prefix 10.4.4.0/24 has 'No Label', indicating the router has not learned a label from the next-hop for that FEC. This can cause labeled packets to that prefix to be dropped.
What should I do if I get this 350-501 question wrong?
Identify which 350-501 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.
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Question Discussion
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