The answer is to enable BFD on the PE-CE interface and associate it with the static route. This is correct because BFD provides sub-second failure detection on the PE-CE link, and when tied to a static route, it allows the PE to immediately remove the failed route from the routing table, triggering fast convergence without waiting for any routing protocol timers. On the Cisco SPCOR 350-501 exam, this scenario tests your understanding that static routes lack dynamic failure detection, so BFD fills that gap to prevent traffic drops in MPLS L3VPNs. A common trap is assuming that simply enabling BFD on the interface is enough—you must explicitly associate it with the static route using the `bfd` parameter in the static route configuration. Remember the memory tip: “Static routes sleep without BFD; wake them up with a BFD handshake.”
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 is deploying MPLS Layer 3 VPNs and wants to ensure that customer traffic is not dropped when a PE-CE link fails. The CE router is using static routing. Which design should be implemented to provide fast convergence?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Enable BFD on the PE-CE interface and associate it with the static route.
Option D is correct because BFD (Bidirectional Forwarding Detection) provides sub-second failure detection on the PE-CE link, and when associated with a static route, it allows the PE to quickly remove the failed route from the routing table. This triggers fast convergence without waiting for routing protocol timers, which is critical for MPLS Layer 3 VPNs using static routing on the CE side.
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.
✗
Configure OSPF on the PE-CE link and set hello timers to 1 second.
Why it's wrong here
OSPF hello timers improve convergence but OSPF is not used for static routes; also, BFD is faster.
✗
Use IP SLA tracking to monitor the CE and adjust the static route.
Why it's wrong here
IP SLA is slower than BFD and adds configuration complexity.
✗
Increase the administrative distance of the static route to 255.
Why it's wrong here
Changing AD does not affect failure detection speed.
✓
Enable BFD on the PE-CE interface and associate it with the static route.
Why this is correct
BFD provides sub-second failure detection, triggering fast route withdrawal.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often choose IP SLA (Option B) thinking it provides fast failure detection, but they overlook that IP SLA is poll-based and slower than BFD, which is the Cisco-recommended mechanism for sub-second convergence with static routes.
Detailed technical explanation
How to think about this question
BFD operates independently of routing protocols, sending rapid hello packets (as fast as 50 ms) to detect link failures. When associated with a static route via the 'bfd' keyword under the static route configuration, the router immediately withdraws the route upon BFD session down, enabling convergence in under a second. In real-world MPLS VPN deployments, this is essential for meeting SLA requirements for voice or video traffic over static-routed CE links.
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 network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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: Enable BFD on the PE-CE interface and associate it with the static route. — Option D is correct because BFD (Bidirectional Forwarding Detection) provides sub-second failure detection on the PE-CE link, and when associated with a static route, it allows the PE to quickly remove the failed route from the routing table. This triggers fast convergence without waiting for routing protocol timers, which is critical for MPLS Layer 3 VPNs using static routing on the CE side.
What should I do if I get this 350-501 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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