Question 1,492 of 2,152

MPLS L3VPN →mediumMultiple ChoiceObjective-mapped

MPLS L3VPN Label Stack: Ingress Pushes Two Labels

This 300-410 practice question tests your understanding of mpls l3vpn. 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 of the following statements about MPLS L3VPN label operations is true?

A
The ingress PE pushes two labels: the outer IGP label and the inner VPN label.
The outer label is used to reach the egress PE, and the inner label identifies the VRF and the specific prefix.
B
The egress PE uses the IGP label to determine the VRF.
Why wrong: The IGP label is used for transport; the VPN label is used for VRF identification.
C
The P routers swap the VPN label as they forward the packet.
Why wrong: P routers only swap the outer IGP label; they do not look at the VPN label.
D
The ingress PE pushes only one label (the VPN label) and uses the IP destination for forwarding.
Why wrong: Without an IGP label, the packet would not be label-switched across the core; two labels are needed.

Full breakdown with real-world context →

Quick Answer

The answer is that the ingress PE pushes two labels: the outer IGP label and the inner VPN label. This is correct because in MPLS L3VPN, the provider edge router must first encapsulate the customer packet with a VPN label that identifies the specific VRF and destination prefix on the egress PE, then stack an outer IGP label that routes the packet across the MPLS core to that egress PE. The egress PE pops the IGP label and uses the inner VPN label to determine the correct VRF and forward the packet to the appropriate CE. On the Cisco CCNP ENARSI 300-410 exam, this concept tests your understanding of the MPLS L3VPN label stack operations, often appearing in questions about label imposition and disposition. A common trap is confusing the direction of label operations—remember that the ingress PE always pushes two labels, while the egress PE pops the outer label and uses the inner VPN label. A helpful memory tip: think of the IGP label as the "envelope" that gets the packet to the right post office (egress PE), and the VPN label as the "room number" that delivers it to the correct tenant (CE).

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

✓

The ingress PE pushes two labels: the outer IGP label and the inner VPN label.

In MPLS L3VPN, the PE router assigns a per-VRF label (VPN label) for each prefix in the VRF. When forwarding a packet from the CE, the ingress PE pushes an IGP label (for the egress PE) and the VPN label. The egress PE pops the IGP label and uses the VPN label to identify the VRF and forward to the correct CE.

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.

✓
The ingress PE pushes two labels: the outer IGP label and the inner VPN label.
Why this is correct
The outer label is used to reach the egress PE, and the inner label identifies the VRF and the specific prefix.
Related concept
Read the scenario before looking for a memorised answer.
✗
The egress PE uses the IGP label to determine the VRF.
Why it's wrong here
The IGP label is used for transport; the VPN label is used for VRF identification.
✗
The P routers swap the VPN label as they forward the packet.
Why it's wrong here
P routers only swap the outer IGP label; they do not look at the VPN label.
✗
The ingress PE pushes only one label (the VPN label) and uses the IP destination for forwarding.
Why it's wrong here
Without an IGP label, the packet would not be label-switched across the core; two labels are needed.

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.

What to study next

Got this wrong? Here's your next step.

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.

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FAQ

Questions learners often ask

What does this 300-410 question test?

MPLS L3VPN — This question tests MPLS L3VPN — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The ingress PE pushes two labels: the outer IGP label and the inner VPN label. — In MPLS L3VPN, the PE router assigns a per-VRF label (VPN label) for each prefix in the VRF. When forwarding a packet from the CE, the ingress PE pushes an IGP label (for the egress PE) and the VPN label. The egress PE pops the IGP label and uses the VPN label to identify the VRF and forward to the correct CE.

What should I do if I get this 300-410 question wrong?

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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