The correct answer is that route targets (RTs) are used to control the import and export of VPNv4 routes between VRFs. This is because in an MPLS VPN environment, when multiple customers use overlapping IP addresses, the PE router must segregate traffic by associating each VRF with specific RT values; the RT attached to a VPNv4 route during export tells other PE routers which VRFs should import that route, ensuring that only the correct customer’s VRF receives the route despite identical IPs. On the Cisco SPCOR 350-501 exam, this concept tests your understanding of how MPLS VPNs scale across service provider networks—a common trap is confusing route distinguishers (RDs) with RTs, but remember that RDs make prefixes unique globally, while RTs control the actual import/export policy for overlapping addresses. A useful memory tip: think of RTs as the “routing tags” that decide who gets the route, while RDs are just unique labels to avoid ambiguity.
350-501 Architecture Practice Question
This 350-501 practice question tests your understanding of architecture. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 needs to offer L3VPN services to multiple customers, each with overlapping IP addresses. The provider plans to use MPLS VPNs with VRFs. Which statement is TRUE regarding the configuration of VRFs on the PE routers?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Route targets (RTs) are used to control the import and export of VPNv4 routes between VRFs
Option D is correct because route targets (RTs) are used to control the import/export of VPNv4 routes between PE routers, ensuring proper segregation and connectivity. Option A is wrong because RD must match within a VPN to avoid route ambiguity, but it can differ if RTs are properly configured; however, the question asks for TRUE statement. Option B is wrong because MPLS label allocation per VRF is automatic. Option C is wrong because OSPF is not required; any IGP or BGP can be used.
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.
✗
The VRF must run OSPF to exchange routes with the CE router
Why it's wrong here
VRF can use static, BGP, or OSPF; OSPF is optional.
✓
Route targets (RTs) are used to control the import and export of VPNv4 routes between VRFs
Why this is correct
RTs determine which VRFs receive which routes, allowing overlapping addresses.
MPLS labels are assigned per prefix inside a VRF by manual configuration
Why it's wrong here
Labels are automatically assigned by LDP or SR, not manually per prefix.
✗
Each VRF must have a unique route distinguisher across the entire provider network
Why it's wrong here
RDs need to be unique locally to a PE, but duplicate RDs across different PEs are allowed if VPN route targets handle separation.
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.
Architecture — This question tests Architecture — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: Route targets (RTs) are used to control the import and export of VPNv4 routes between VRFs — Option D is correct because route targets (RTs) are used to control the import/export of VPNv4 routes between PE routers, ensuring proper segregation and connectivity. Option A is wrong because RD must match within a VPN to avoid route ambiguity, but it can differ if RTs are properly configured; however, the question asks for TRUE statement. Option B is wrong because MPLS label allocation per VRF is automatic. Option C is wrong because OSPF is not required; any IGP or BGP can be used.
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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