The correct answer is to verify that the BGP VPNv4 neighbor relationship is established between the new PE and the RR, and to confirm that the VRF import/export policies using route targets match the community values expected by other PEs. When troubleshooting missing VPN routes in a route reflector setup, the RR must have an active MP-BGP session to the new PE to receive and redistribute VPNv4 prefixes; without this session, no routes can be reflected. Additionally, even if the session is up, the route targets defined in the VRF import and export policies on the new PE must align with those on the existing PEs, as the RR simply reflects routes without modifying RTs—mismatched RTs cause the receiving PE to discard the routes. On the Cisco SPCOR 350-501 exam, this scenario tests your understanding of MPLS L3VPN control plane operations, specifically how route reflectors handle VPNv4 updates and the critical role of RT filtering. A common trap is assuming OSPF or route refresh can fix missing routes, but the core issue is always session state or policy alignment. Memory tip: “Session first, then RTs match—no session, no routes; no match, no import.”
350-501 MPLS and Segment Routing Practice Question
This 350-501 practice question tests your understanding of mpls and segment routing. 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.
In an MPLS L3VPN network, a route reflector (RR) is used to distribute VPNv4 routes between PE routers. After a new PE router (PE4) is added, some VPN routes are not being received by other PEs. Which TWO actions should be investigated to resolve the issue? (Choose two.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Ensure the VRF route-target import/export values are correctly configured on the new PE.
Option B is correct because the RR must have BGP MP-BGP session to the new PE. Option D is correct because VRF import/export policies using route targets must match the community values expected by other PEs. Option A is unnecessary if underlay connectivity exists. Option C is incorrect because route refresh does not fix missing policy. Option E is incorrect because OSPF is not used in the core for VPN route exchange.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
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 the VRF route-target import/export values are correctly configured on the new PE.
Why this is correct
Mismatched RTs prevent routes from being imported into the VRF.
Check physical connectivity and IGP adjacency between the new PE and the RR.
Why it's wrong here
Physical connectivity is assumed; the issue is at the BGP layer.
✗
Issue a 'clear ip bgp * refresh' on the RR.
Why it's wrong here
Route refresh only requests a resend, but does not fix missing policies.
Common exam traps
Common exam trap: OSPF can fail even when IP connectivity looks correct
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
Detailed technical explanation
How to think about this question
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
KKey Concepts to Remember
OSPF neighbours must agree on key parameters.
Router ID selection can affect neighbour relationships and LSDB output.
OSPF cost influences the preferred path.
A route can appear in OSPF information but not become the installed route.
TExam Day Tips
→Check area mismatch first when OSPF adjacency fails.
→Review passive interfaces when a network is advertised but no neighbour forms.
→Use show ip ospf neighbor and show ip route clues carefully.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
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.
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 350-501 OSPF questions on adjacency and route selection.
MPLS and Segment Routing — This question tests MPLS and Segment Routing — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: Ensure the VRF route-target import/export values are correctly configured on the new PE. — Option B is correct because the RR must have BGP MP-BGP session to the new PE. Option D is correct because VRF import/export policies using route targets must match the community values expected by other PEs. Option A is unnecessary if underlay connectivity exists. Option C is incorrect because route refresh does not fix missing policy. Option E is incorrect because OSPF is not used in the core for VPN route exchange.
What should I do if I get this 350-501 question wrong?
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 350-501 OSPF questions on adjacency and route selection.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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Question Discussion
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