Question 237 of 2,152

MPLS Operations →hardMultiple ChoiceObjective-mapped

Quick Answer

The answer is a VRF export route-map filter. This is correct because when a route exists in the VRF routing table on PE1 but is missing from the BGP VPNv4 advertised-routes to the remote PE, the issue lies in the export direction—the route is present locally but is being blocked before it can be redistributed into MP-BGP. Since the BGP session between PE1 and PE2 is established, the problem is not connectivity or session state, but rather a policy that prevents the route from being advertised. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of VRF route leaking and BGP policy filtering, often disguised as a redistribution or next-hop issue. A common trap is to suspect the import side or a missing network command, but the key clue is that the route is in the VRF but not in the BGP table. Memory tip: “Export blocks out, import blocks in”—if the route is in the VRF but not advertised, check the export route-map first.

300-410 MPLS Operations Practice Question

This 300-410 practice question tests your understanding of mpls operations. 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 can ping the PE1 interface but cannot ping CE2. On PE1, show ip route vrf CUSTOMER shows the route to CE2's subnet, but show bgp vpnv4 unicast all neighbors 10.0.0.2 advertised-routes does not show the route. The BGP session between PE1 and PE2 is established. 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: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

Question 1hardmultiple choice

Open the full BGP breakdown →

A
The VRF export route-target does not match the import route-target on the remote PE.
Why wrong: Incorrect because route-target mismatch would affect import on the remote PE, not advertisement from the local PE; the route would still be advertised.
B
A route-map applied to the VRF export is filtering the route.
Correct because a route-map on VRF export can filter routes before they are advertised to BGP, preventing the route from being sent to the remote PE.
C
The BGP session is not using the correct update-source.
Why wrong: Incorrect because the BGP session is established, so the update-source is correct; the issue is with route advertisement, not session establishment.
D
The next-hop-self command is missing under the VRF address-family.
Why wrong: Incorrect because next-hop-self affects the next-hop attribute, not whether the route is advertised; the route would still be sent.

Full breakdown with real-world context →

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

A route-map applied to the VRF export is filtering the route.

The route is present in the VRF but not advertised to the remote PE, indicating a BGP policy issue. Since the BGP session is up, the most likely cause is that the route is not being redistributed into BGP or is being filtered by a route-map or prefix-list on the VRF export.

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 export route-target does not match the import route-target on the remote PE.
Why it's wrong here
Incorrect because route-target mismatch would affect import on the remote PE, not advertisement from the local PE; the route would still be advertised.
✓
A route-map applied to the VRF export is filtering the route.
Why this is correct
Correct because a route-map on VRF export can filter routes before they are advertised to BGP, preventing the route from being sent to the remote PE.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
OSPF neighbours must agree on key parameters.
✗
The BGP session is not using the correct update-source.
Why it's wrong here
Incorrect because the BGP session is established, so the update-source is correct; the issue is with route advertisement, not session establishment.
✗
The next-hop-self command is missing under the VRF address-family.
Why it's wrong here
Incorrect because next-hop-self affects the next-hop attribute, not whether the route is advertised; the route would still be sent.

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 300-410 OSPF questions on adjacency and route selection.

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FAQ

Questions learners often ask

What does this 300-410 question test?

MPLS Operations — This question tests MPLS Operations — OSPF neighbours must agree on key parameters..

What is the correct answer to this question?

The correct answer is: A route-map applied to the VRF export is filtering the route. — The route is present in the VRF but not advertised to the remote PE, indicating a BGP policy issue. Since the BGP session is up, the most likely cause is that the route is not being redistributed into BGP or is being filtered by a route-map or prefix-list on the VRF export.

What should I do if I get this 300-410 question wrong?

Are there clue words in this question I should notice?

Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

What is the key concept behind this question?

OSPF neighbours must agree on key parameters.

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