The answer is that the VRF on PE2 does not have the CE2 route in its routing table, which prevents the route from being advertised via BGP VRF. This is correct because for a BGP VRF route to be advertised to a BGP neighbor, the prefix must first exist in the VRF’s IP routing table on the advertising PE; without a network statement or a redistribute command under the BGP VRF address family on PE2, the CE2 route (10.2.2.0/24) never enters the BGP table for that VRF, so it cannot be sent to PE1. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of the MPLS L3VPN control plane flow—specifically that a missing network statement under the VRF address family is a common misconfiguration, even when the route appears in the global routing table. A frequent trap is assuming that a directly connected CE route is automatically injected into BGP, but it must be explicitly matched. Memory tip: “No network, no advertise—check the VRF table first.”
300-410 MPLS L3VPN Practice Question
This 300-410 practice question tests your understanding of mpls l3vpn. 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 network engineer is troubleshooting an MPLS L3VPN where CE1 (10.1.1.0/24) cannot reach CE2 (10.2.2.0/24). The PE routers are using eBGP with the CEs. On PE1, the show ip bgp vpnv4 vrf CUSTOMER command shows the route for 10.2.2.0/24 with a next-hop of 192.168.1.2, and the show ip route vrf CUSTOMER command shows the route. However, traffic from CE1 to CE2 fails. The show ip bgp vpnv4 vrf CUSTOMER 10.2.2.0/24 command on PE1 shows the route is received and best, but the show ip bgp vpnv4 vrf CUSTOMER 10.2.2.0/24 neighbors 192.168.1.2 advertised-routes command on PE2 shows the route is not advertised. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The VRF on PE2 does not have the CE2 route in its routing table.
The route is not being advertised from PE2 to PE1. This could be due to a missing network statement or redistribute command under the BGP VRF address family on PE2, or the route is not in the VRF routing table on PE2. The engineer should check PE2's VRF routing table for the CE2 route.
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 on PE2 does not have the CE2 route in its routing table.
Why this is correct
Correct: If the route is not in the VRF routing table on PE2, it cannot be advertised via BGP.
Clue confirmation
The clue words "best", "most likely" in the question point toward this answer.
Incorrect because the route is received on PE1, so the session is up.
✗
The route-target export on PE2 is misconfigured.
Why it's wrong here
Incorrect because the route is received, so export is working.
✗
The VRF on PE1 has the wrong route-target import.
Why it's wrong here
Incorrect because the route is received on PE1.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
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 300-410 OSPF questions on adjacency and route selection.
MPLS L3VPN — This question tests MPLS L3VPN — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: The VRF on PE2 does not have the CE2 route in its routing table. — The route is not being advertised from PE2 to PE1. This could be due to a missing network statement or redistribute command under the BGP VRF address family on PE2, or the route is not in the VRF routing table on PE2. The engineer should check PE2's VRF routing table for the CE2 route.
What should I do if I get this 300-410 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 300-410 OSPF questions on adjacency and route selection.
Are there clue words in this question I should notice?
Yes — watch for: "best", "most likely". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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