- A
Ensure that the IGP operating in the core has propagated the loopback interface address of PE1 to all P routers.
Why wrong: VPNv4 routes use BGP next-hop, and IGP propagation of loopbacks is not directly related to VRF reachability.
- B
Verify that the BGP session between PE4 and the route reflector is using the correct update source.
Why wrong: The BGP session is already established, so update source is not the issue.
- C
Verify that the CE router at Site4 is configured with the correct VRF name and default gateway.
Why wrong: Since Site4 can send traffic to the PE, the CE configuration is likely correct.
- D
Check the VRF route target import on PE1 to ensure it includes the route target exported by PE4 for Site4's subnet.
Even if the remote prefix is in the VRF, return traffic requires the local prefix to be imported by the remote PE.
350-501 Services Practice Question
This 350-501 practice question tests your understanding of services. 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 service provider recently deployed MPLS L3VPN for a customer with four sites (Site1, Site2, Site3, Site4) connected to PE1, PE2, PE3, and PE4 respectively. All sites are in VRF CUST-A with route targets 100:1 import and 100:1 export on all PEs. The customer reports that Site4 cannot ping the loopback interface (10.1.1.1/32) of Site1, but Site2 and Site3 can reach it. The provider verifies that BGP sessions between all PEs and the route reflector are up and that VPNv4 routes are advertised. The VRF on PE4 shows the route 10.1.1.1/32 with next-hop 192.0.2.1 (PE1's loopback) but when Site4 initiates a ping, it fails. What should the provider check next?
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
Check the VRF route target import on PE1 to ensure it includes the route target exported by PE4 for Site4's subnet.
Option B is correct because the ping failure is likely due to return path routing; the VRF on PE4 has the route, but the ping echo reply must be routed back to Site4. The VRF on PE1 must have a route for Site4's subnet. Typically, the import and export RTs are symmetric, but if PE1 is not importing the RT that PE4 exports (e.g., Site4's prefix), the return traffic will be dropped. Checking the RT import on PE1 for the route from Site4 is the most common cause. Option A is incorrect because BGP sessions are already up. Option C is incorrect because IGP propagation of loopbacks is not needed for VPNv4. Option D is incorrect because CE configuration is likely fine since Site2 and Site3 work.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Ensure that the IGP operating in the core has propagated the loopback interface address of PE1 to all P routers.
Why it's wrong here
VPNv4 routes use BGP next-hop, and IGP propagation of loopbacks is not directly related to VRF reachability.
- ✗
Verify that the BGP session between PE4 and the route reflector is using the correct update source.
Why it's wrong here
The BGP session is already established, so update source is not the issue.
- ✗
Verify that the CE router at Site4 is configured with the correct VRF name and default gateway.
Why it's wrong here
Since Site4 can send traffic to the PE, the CE configuration is likely correct.
- ✓
Check the VRF route target import on PE1 to ensure it includes the route target exported by PE4 for Site4's subnet.
Why this is correct
Even if the remote prefix is in the VRF, return traffic requires the local prefix to be imported by the remote PE.
Related concept
CIDR notation defines the prefix length.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
- CIDR notation defines the prefix length.
- Block size helps identify subnet boundaries.
- Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
- The required host count determines the smallest suitable subnet.
TExam Day Tips
- Write the block size before choosing the subnet.
- Check whether the question asks for hosts, subnets or a specific address range.
- Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 350-501 subnetting questions on CIDR, address ranges, and subnet selection.
- →
Services — study guide chapter
Learn the concepts, then practise the questions
- →
Services practice questions
Targeted practice on this topic area only
- →
All 350-501 questions
500 questions across all exam domains
- →
Cisco SPCOR / CCNP Service Provider Core 350-501 study guide
Full concept coverage aligned to exam objectives
- →
350-501 practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Related 350-501 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 350-501 questions linked to Architecture.
Networking practice questions
Practise 350-501 questions linked to Networking.
MPLS and Segment Routing practice questions
Practise 350-501 questions linked to MPLS and Segment Routing.
Automation and Quality of Service practice questions
Practise 350-501 questions linked to Automation and Quality of Service.
Services practice questions
Practise 350-501 questions linked to Services.
Automation and Assurance practice questions
Practise 350-501 questions linked to Automation and Assurance.
350-501 fundamentals practice questions
Practise 350-501 questions linked to 350-501 fundamentals.
350-501 scenario practice questions
Practise 350-501 questions linked to 350-501 scenario.
350-501 troubleshooting practice questions
Practise 350-501 questions linked to 350-501 troubleshooting.
Practice this exam
Start a free 350-501 practice session
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
FAQ
Questions learners often ask
What does this 350-501 question test?
Services — This question tests Services — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Check the VRF route target import on PE1 to ensure it includes the route target exported by PE4 for Site4's subnet. — Option B is correct because the ping failure is likely due to return path routing; the VRF on PE4 has the route, but the ping echo reply must be routed back to Site4. The VRF on PE1 must have a route for Site4's subnet. Typically, the import and export RTs are symmetric, but if PE1 is not importing the RT that PE4 exports (e.g., Site4's prefix), the return traffic will be dropped. Checking the RT import on PE1 for the route from Site4 is the most common cause. Option A is incorrect because BGP sessions are already up. Option C is incorrect because IGP propagation of loopbacks is not needed for VPNv4. Option D is incorrect because CE configuration is likely fine since Site2 and Site3 work.
What should I do if I get this 350-501 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 350-501 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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 →
Last reviewed: Jun 24, 2026
This 350-501 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 350-501 exam.
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.
Sign in to join the discussion.