Question 1,519 of 2,015

WAN Technologies →mediumMultiple ChoiceObjective-mapped

Quick Answer

The answer is that the PE router is not disabling BGP next-hop-self for the VRF, causing the routes advertised to the CE to retain the remote CE’s IP as the next-hop, which is unreachable from the local CE. In MPLS L3VPN, when a PE receives a route from a remote CE via BGP, it must change the next-hop to its own interface address before advertising it to the local CE; otherwise, the local CE will try to reach the remote CE’s loopback directly, which fails because the MPLS core hides those addresses. On the ENCOR 350-401 exam, this scenario tests your understanding of BGP next-hop processing in a VRF context—a common trap is assuming that an established BGP session and received routes guarantee reachability, when the real issue is that the next-hop is not resolved in the global routing table. A quick memory tip: if the CE can ping the PE loopback but not the remote CE loopback, think “next-hop-self missing” to fix the path.

350-401 WAN Technologies Practice Question

This 350-401 practice question tests your understanding of wan technologies. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.

An enterprise is replacing its legacy Frame Relay WAN with MPLS L3VPN. The new MPLS provider assigns a single VRF to the customer. The customer's CE routers are running BGP with the provider's PE routers. The engineer notices that the CE routers can ping the PE loopback addresses but cannot reach remote CE loopbacks. The BGP sessions are established and routes are received. What is the most likely cause?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

Question 1mediummultiple choice

Open the full BGP breakdown →

A
The CE router is not configured with 'no bgp default ipv4-unicast'.
Why wrong: Incorrect. This command prevents the BGP process from automatically advertising IPv4 unicast routes, but it would not cause the specific symptom of being able to ping the PE but not the remote CE.
B
The PE router is not sending the customer routes to the remote CE because the next-hop is set to the local PE's loopback, which is reachable, but the remote PE is not advertising the routes due to route-target mismatch.
Why wrong: Incorrect. Route-target mismatch would prevent routes from being imported into the VRF, but the scenario says routes are received on the CE, so route-targets are likely correct.
C
The CE router is not advertising its own loopback into BGP, so the remote CE does not have a route to it.
Why wrong: Incorrect. The question states that routes are received, so the remote CE should have the route. The issue is that the CE can ping the PE but not the remote CE, indicating a problem with the route's next-hop reachability.
D
The PE router is not disabling BGP next-hop-self for the VRF, so the routes advertised to the CE have the remote CE's IP as the next-hop, which is not reachable from the local CE.
Correct. In MPLS L3VPN, the PE should set next-hop-self when advertising routes to the CE so that the CE uses the PE as the next hop. If not, the CE will try to reach the remote CE directly, which is not possible over the MPLS network.

Full breakdown with real-world context →

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 PE router is not disabling BGP next-hop-self for the VRF, so the routes advertised to the CE have the remote CE's IP as the next-hop, which is not reachable from the local CE.

In MPLS L3VPN, the PE router must advertise the customer routes with the correct next-hop (usually the PE's own address) and the MPLS labels must be properly distributed. However, the most common issue when CE can ping PE but not remote CE is that the PE is not advertising the customer routes back to the remote CE because of BGP next-hop processing or route-target filtering.

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 CE router is not configured with 'no bgp default ipv4-unicast'.
Why it's wrong here
Incorrect. This command prevents the BGP process from automatically advertising IPv4 unicast routes, but it would not cause the specific symptom of being able to ping the PE but not the remote CE.
✗
The PE router is not sending the customer routes to the remote CE because the next-hop is set to the local PE's loopback, which is reachable, but the remote PE is not advertising the routes due to route-target mismatch.
Why it's wrong here
Incorrect. Route-target mismatch would prevent routes from being imported into the VRF, but the scenario says routes are received on the CE, so route-targets are likely correct.
✗
The CE router is not advertising its own loopback into BGP, so the remote CE does not have a route to it.
Why it's wrong here
Incorrect. The question states that routes are received, so the remote CE should have the route. The issue is that the CE can ping the PE but not the remote CE, indicating a problem with the route's next-hop reachability.
✓
The PE router is not disabling BGP next-hop-self for the VRF, so the routes advertised to the CE have the remote CE's IP as the next-hop, which is not reachable from the local CE.
Why this is correct
Correct. In MPLS L3VPN, the PE should set next-hop-self when advertising routes to the CE so that the CE uses the PE as the next hop. If not, the CE will try to reach the remote CE directly, which is not possible over the MPLS network.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.

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.

Trap categories for this question

Command / output trap
Incorrect. This command prevents the BGP process from automatically advertising IPv4 unicast routes, but it would not cause the specific symptom of being able to ping the PE but not the remote CE.
Scenario analysis trap
Incorrect. Route-target mismatch would prevent routes from being imported into the VRF, but the scenario says routes are received on the CE, so route-targets are likely correct.

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 350-401 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 350-401 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.

Related 350-401 practice-question pages

Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.

Architecture practice questions

Practise 350-401 questions linked to Architecture.

Enterprise Network Design practice questions

Practise 350-401 questions linked to Enterprise Network Design.

SD-Access Architecture practice questions

Practise 350-401 questions linked to SD-Access Architecture.

SD-WAN Architecture practice questions

Practise 350-401 questions linked to SD-WAN Architecture.

QoS Architecture practice questions

Practise 350-401 questions linked to QoS Architecture.

Virtualization practice questions

Practise 350-401 questions linked to Virtualization.

Network Function Virtualization practice questions

Practise 350-401 questions linked to Network Function Virtualization.

Virtual Machines and Hypervisors practice questions

Practise 350-401 questions linked to Virtual Machines and Hypervisors.

VRF and Path Isolation practice questions

Practise 350-401 questions linked to VRF and Path Isolation.

Infrastructure practice questions

Practise 350-401 questions linked to Infrastructure.

OSPF practice questions

Practise 350-401 questions linked to OSPF.

BGP practice questions

Practise 350-401 questions linked to BGP.

Practice this exam

Start a free 350-401 practice session

Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.

10 questions 20 questions 30 questions 50 questions Timed 30

350-401 practice-test guide →Study guide →Browse all practice tests

FAQ

Questions learners often ask

What does this 350-401 question test?

WAN Technologies — This question tests WAN Technologies — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The PE router is not disabling BGP next-hop-self for the VRF, so the routes advertised to the CE have the remote CE's IP as the next-hop, which is not reachable from the local CE. — In MPLS L3VPN, the PE router must advertise the customer routes with the correct next-hop (usually the PE's own address) and the MPLS labels must be properly distributed. However, the most common issue when CE can ping PE but not remote CE is that the PE is not advertising the customer routes back to the remote CE because of BGP next-hop processing or route-target filtering.

What should I do if I get this 350-401 question wrong?

Are there clue words in this question I should notice?

Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

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 →

How Courseiva writes practice questions · Editorial policy

Keep practising

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.

Loading comments…

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.