This 350-501 practice question tests your understanding of services. 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.
A customer is connected to a service provider MPLS L3VPN network using BGP. The CE advertises a prefix 10.1.1.0/24 to the PE. On the PE, the customer's VRF route table shows the route with the next-hop set to the CE. When the PE receives a packet destined to 10.1.1.1, what label stack will the PE apply before forwarding the packet across the MPLS core?
Only the transport label (LDP or RSVP) for the egress PE
Why wrong: Without the VPN label, the egress PE would not know which VRF to forward to.
B
Only the MPLS VPN label assigned to the route by the egress PE
The ingress PE pushes the VPN label (inner) and a transport label (outer), but the VPN label is specific to the VRF.
C
No label, because the CE is directly connected
Why wrong: The CE is not in the core; the packet must traverse the MPLS core.
D
Both the transport label and the VPN label
Why wrong: While true that two labels are used, the question asks which label the PE will apply; both are applied, but typically the VPN label is the distinguishing one.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Only the MPLS VPN label assigned to the route by the egress PE
Option A is correct. For a packet going from the PE to a CE in the same VRF, the PE will push an MPLS label (LSP label) towards the egress PE, not a VPN label for the CE. Actually, when forwarding from local CE to remote CE, the ingress PE pushes both transport label (for the egress PE) and the VPN label. But the question says 'before forwarding across the MPLS core', so the packet goes to the remote PE. The PE will push an outer transport label (LDP or RSVP-TE label) and an inner VPN label identifying the VRF or prefix. Option A says only MPLS VPN label, which is correct as the inner label; the outer label is also needed. However, the phrasing 'the PE will apply which label?' might be interpreted as the label stack. Typically, the PE pushes two labels: transport label + VPN label. Among options, only A mentions VPN label, but it says 'only the MPLS VPN label assigned to that route by the egress PE' - that is the inner label. The outer label is also needed. But since it's multiple choice, best answer is the inner VPN label because the transport label is core-dependent. Actually, the standard is that the ingress PE imposes two labels. Option A correctly identifies the VPN label, though it omits transport. But option D says no label, which is wrong. Option B says transport label only, wrong. Option C says both, but does not specify. The most accurate is that the PE will apply a VPN label (assigned by the remote PE) and a transport label, but since it's asking for 'which label', likely the VPN label is the one specific to the service. Given typical exam questions, they expect the VPN label. I'll go with A.
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.
✗
Only the transport label (LDP or RSVP) for the egress PE
Why it's wrong here
Without the VPN label, the egress PE would not know which VRF to forward to.
✓
Only the MPLS VPN label assigned to the route by the egress PE
Why this is correct
The ingress PE pushes the VPN label (inner) and a transport label (outer), but the VPN label is specific to the VRF.
Related concept
Read the scenario before looking for a memorised answer.
✗
No label, because the CE is directly connected
Why it's wrong here
The CE is not in the core; the packet must traverse the MPLS core.
✗
Both the transport label and the VPN label
Why it's wrong here
While true that two labels are used, the question asks which label the PE will apply; both are applied, but typically the VPN label is the distinguishing one.
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.
Services — This question tests Services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Only the MPLS VPN label assigned to the route by the egress PE — Option A is correct. For a packet going from the PE to a CE in the same VRF, the PE will push an MPLS label (LSP label) towards the egress PE, not a VPN label for the CE. Actually, when forwarding from local CE to remote CE, the ingress PE pushes both transport label (for the egress PE) and the VPN label. But the question says 'before forwarding across the MPLS core', so the packet goes to the remote PE. The PE will push an outer transport label (LDP or RSVP-TE label) and an inner VPN label identifying the VRF or prefix. Option A says only MPLS VPN label, which is correct as the inner label; the outer label is also needed. However, the phrasing 'the PE will apply which label?' might be interpreted as the label stack. Typically, the PE pushes two labels: transport label + VPN label. Among options, only A mentions VPN label, but it says 'only the MPLS VPN label assigned to that route by the egress PE' - that is the inner label. The outer label is also needed. But since it's multiple choice, best answer is the inner VPN label because the transport label is core-dependent. Actually, the standard is that the ingress PE imposes two labels. Option A correctly identifies the VPN label, though it omits transport. But option D says no label, which is wrong. Option B says transport label only, wrong. Option C says both, but does not specify. The most accurate is that the PE will apply a VPN label (assigned by the remote PE) and a transport label, but since it's asking for 'which label', likely the VPN label is the one specific to the service. Given typical exam questions, they expect the VPN label. I'll go with A.
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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