The answer is to change the IGP to IS-IS with wide metrics and enable MPLS-TE on all IS-IS levels. This resolves the issue because in a multi-area OSPF network, the Traffic Engineering Database (TEDB) is not flooded across area boundaries by default, meaning the headend router PE-New lacks the TE topology information needed to compute paths to inter-area destinations. Since MPLS-TE relies on a complete TEDB for path calculation, tunnels to remote areas fail with the "TEDB lookup failed" error, while intra-area tunnels succeed. On the Cisco SPCOR 350-501 exam, this scenario tests your understanding that OSPF’s area-based flooding limitation breaks inter-area TE, whereas IS-IS inherently floods TE information across all levels when wide metrics and MPLS-TE are enabled. A common trap is assuming static routes or priority adjustments can populate the TEDB, but only a protocol that floods TE LSAs across the entire domain works. Memory tip: "OSPF areas block TE; IS-IS levels share it freely."
350-501 Architecture Practice Question
This 350-501 practice question tests your understanding of architecture. 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 service provider operates an MPLS-TE network using RSVP-TE with a full mesh of tunnels between core routers. The network uses OSPF as IGP with traffic engineering extensions. Recently, a new headend router PE-New was added and configured with several TE tunnels to remote destinations. However, some tunnels repeatedly go down after a few minutes and show in the 'down' state with the error 'Tunnel path option 0: no path to destination (TEDB lookup failed)'. The TE tunnels that remain up are those to destinations that are directly connected to the same OSPF area. The network has multiple OSPF areas (area 0, 1, 2) with inter-area routes redistributed. The operator suspects the issue is related to the TEDB (Traffic Engineering Database) not having complete information. Which action is MOST likely to resolve the issue?
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Change the IGP to IS-IS with wide metrics and enable MPLS-TE on all IS-IS levels
Option D is correct: In multi-area OSPF, the TEDB is not flooded across area boundaries by default. To have TE information for inter-area destinations, IS-IS is preferred; but if OSPF is used, enabling 'flooding' of TE LSAs across areas requires configuring 'mpls traffic-eng inter-area' or similar (on Cisco IOS XR, the command is 'mpls traffic-eng inter-area [level-2]' but for OSPF, it's 'mpls traffic-eng area X' with redistribution; however, the simplest fix is to use a single area or IS-IS. Option A: Static routes do not provide TE information. Option B: Adding IP routes does not populate the TEDB. Option C: Increasing hold-priority does not fix missing TEDB entries.
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.
✗
Increase the tunnel hold-priority and setup-priority values
Why it's wrong here
Priorities affect preemption, not path computation due to missing TEDB.
✗
Add the remote loopbacks to OSPF using network statements in area 0
Why it's wrong here
Adding to area 0 helps reachability but not TE; TEDB still limited to area.
✓
Change the IGP to IS-IS with wide metrics and enable MPLS-TE on all IS-IS levels
Why this is correct
IS-IS natively propagates TE information across all levels, ensuring TEDB completeness for inter-area tunnels.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Configure static routes for the remote destinations on PE-New
Why it's wrong here
Static routes do not add TE information to the TEDB.
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: Change the IGP to IS-IS with wide metrics and enable MPLS-TE on all IS-IS levels — Option D is correct: In multi-area OSPF, the TEDB is not flooded across area boundaries by default. To have TE information for inter-area destinations, IS-IS is preferred; but if OSPF is used, enabling 'flooding' of TE LSAs across areas requires configuring 'mpls traffic-eng inter-area' or similar (on Cisco IOS XR, the command is 'mpls traffic-eng inter-area [level-2]' but for OSPF, it's 'mpls traffic-eng area X' with redistribution; however, the simplest fix is to use a single area or IS-IS. Option A: Static routes do not provide TE information. Option B: Adding IP routes does not populate the TEDB. Option C: Increasing hold-priority does not fix missing TEDB entries.
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.
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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