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 customer's MPLS L3VPN has two CE routers connected to two different PEs, but the PEs are not receiving the customer's routes from each other. The PE-CE routing protocol is OSPF. The PEs have the VRF configured with OSPF process, and the routes from CE are in the VRF routing table. The MP-BGP session between PEs is up and the VPNv4 address family is working. On the source PE, the routes show as not advertised to BGP. What is the likely issue?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The OSPF process on the PE is not redistributed into BGP VPNv4 under the VRF
The correct answer is C because in an MPLS L3VPN with OSPF as the PE-CE protocol, the VRF OSPF process must be explicitly redistributed into the MP-BGP VPNv4 address family using the `redistribute ospf <process-id> match internal external` command under the VRF address-family IPv4. Without this redistribution, the OSPF routes learned from the CE remain in the VRF routing table but are never injected into BGP, so they are not advertised to the remote PE, even though the MP-BGP session is up and the VPNv4 address family is working.
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 route-target export on the source PE does not match the import on the remote PE
Why it's wrong here
Incorrect. If route-target mismatched, routes would be advertised but not imported by the remote PE.
✗
The OSPF network type is not set to broadcast
Why it's wrong here
Incorrect. OSPF network type does not affect redistribution into BGP.
✓
The OSPF process on the PE is not redistributed into BGP VPNv4 under the VRF
Why this is correct
Correct. The 'redistribute ospf process-id' command under the VRF address-family is missing, so OSPF routes are not injected into MP-BGP.
Related concept
Read the scenario before looking for a memorised answer.
✗
The next-hop-self is not configured under the VRF OSPF process
Why it's wrong here
Incorrect. Next-hop-self is used for BGP advertisement to other PEs; it does not affect route advertisement from OSPF to BGP.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that simply enabling OSPF under a VRF and having a working MP-BGP session is sufficient for route exchange, when in fact explicit redistribution from OSPF into BGP VPNv4 is required.
Detailed technical explanation
How to think about this question
In MPLS L3VPN, the VRF OSPF process runs as a separate OSPF instance with its own RIB, and redistribution into BGP is mandatory because BGP is the only protocol that carries VPNv4 routes with route distinguishers and route targets across the MPLS core. A common real-world scenario is when an engineer configures OSPF under the VRF and sees CE routes in the VRF table but forgets the `redistribute ospf` command under the BGP VRF address-family, leading to silent route non-advertisement; this is often missed because the MP-BGP session appears healthy and the VRF OSPF adjacency is up.
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: The OSPF process on the PE is not redistributed into BGP VPNv4 under the VRF — The correct answer is C because in an MPLS L3VPN with OSPF as the PE-CE protocol, the VRF OSPF process must be explicitly redistributed into the MP-BGP VPNv4 address family using the `redistribute ospf <process-id> match internal external` command under the VRF address-family IPv4. Without this redistribution, the OSPF routes learned from the CE remain in the VRF routing table but are never injected into BGP, so they are not advertised to the remote PE, even though the MP-BGP session is up and the VPNv4 address family is working.
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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