The answer is that the CE router lacks a default route pointing to the PE’s VRF interface. While the PE can ping remote sites from within the VRF—proving that the VPNv4 routes are correctly imported and the MPLS L3VPN backbone is functional—the CE itself has no path to forward traffic out of its local subnet. In an MPLS L3VPN, the CE must have either a static default route or a dynamic routing protocol pointing to the PE’s VRF-facing IP as its next hop; without it, packets from the CE never reach the PE to be label-switched across the provider core. On the ENCOR 350-401 exam, this scenario tests your understanding of the separation between the PE’s VRF routing table and the CE’s routing table—a common trap is assuming that because the PE can reach remote sites, the CE automatically can too. Remember the “CE default route” check: if the CE can’t ping, but the PE can from the VRF, the missing piece is always the CE’s next-hop route toward the PE.
350-401 VRF and Path Isolation Practice Question
This 350-401 practice question tests your understanding of vrf and path isolation. 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.
A network engineer is configuring MPLS L3VPN on a Cisco IOS-XE router. The VRF CUSTOMER_C has route-target import 300:1 and export 300:1. The PE receives VPNv4 routes from the route reflector, but the CE router connected to the PE cannot ping any remote site IP addresses. The PE can ping the remote site IP addresses from the VRF. 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The CE router does not have a default route pointing to the PE's VRF interface.
The PE can ping remote site IP addresses from within the VRF, confirming that the VRF has the correct route-target import/export configuration and that VPNv4 routes are being received and installed in the VRF routing table. However, the CE router cannot ping remote sites, which indicates that the CE does not have a route pointing to the PE’s VRF interface as its next hop. Without a default route or a specific route pointing to the PE’s VRF-facing interface, the CE has no path to forward traffic to remote VPN destinations, even though the PE can reach them.
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 does not have a default route pointing to the PE's VRF interface.
Why this is correct
Correct because if the CE does not have a route to remote sites, it cannot send traffic. The PE can ping because it has the routes in the VRF.
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.
✗
The VRF is missing the route-target export command.
Why it's wrong here
Incorrect because the PE can reach remote sites, meaning VPNv4 routes are imported correctly, so export is working.
✗
The PE router is not running a routing protocol with the CE router.
Why it's wrong here
Incorrect because even without a routing protocol, static routes can be used; the issue is the CE's lack of a route.
✗
The MPLS LDP is not enabled on the PE-CE link.
Why it's wrong here
Incorrect because MPLS is not required on the PE-CE link for L3VPN.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that if the PE can reach remote sites from the VRF, the CE must also be able to reach them, but the trap is that the CE’s routing table is independent and requires explicit route injection or a default route pointing to the PE.
Detailed technical explanation
How to think about this question
In MPLS L3VPN, the CE router must have a route (typically a default route or a specific prefix) pointing to the PE’s VRF interface as the next hop to reach remote VPN sites. The PE installs remote VPN prefixes into the VRF via BGP VPNv4 route import, but the CE is unaware of these routes unless the PE redistributes them into the CE-PE routing protocol or the CE has a static default. A common real-world scenario is when the PE uses BGP with the CE and forgets to redistribute VRF routes into the CE-facing BGP session, leaving the CE without any remote prefixes.
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.
TExam Day Tips
→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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 350-401 question in full detail.
VRF and Path Isolation — This question tests VRF and Path Isolation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The CE router does not have a default route pointing to the PE's VRF interface. — The PE can ping remote site IP addresses from within the VRF, confirming that the VRF has the correct route-target import/export configuration and that VPNv4 routes are being received and installed in the VRF routing table. However, the CE router cannot ping remote sites, which indicates that the CE does not have a route pointing to the PE’s VRF interface as its next hop. Without a default route or a specific route pointing to the PE’s VRF-facing interface, the CE has no path to forward traffic to remote VPN destinations, even though the PE can reach them.
What should I do if I get this 350-401 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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.
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