The answer is that the route was redistributed into OSPF by router 3.3.3.3 with a metric of 20. This is correct because the Type 5 LSA output explicitly shows the Advertising Router as 3.3.3.3, the Metric Type as 2 (E2), and the Metric value as 20, which together confirm that the external prefix 5.5.5.5/32 was injected into OSPF through redistribution rather than learned via an OSPF neighbor. On the Cisco CCNP ENARSI 300-410 exam, this tests your ability to interpret OSPF external LSAs, specifically distinguishing between E1 and E2 metrics—a common trap is forgetting that E2 metrics do not add internal path cost, so the advertised metric remains 20 regardless of how far the route travels. A key memory tip is that a Forward Address of 0.0.0.0 means the next hop is the advertising router itself, simplifying path selection. Remember: “E2 stays true, E1 adds the view.”
300-410 OSPF Troubleshooting (v2/v3) Practice Question
This 300-410 practice question tests your understanding of ospf troubleshooting (v2/v3). 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 runs the following command to troubleshoot OSPF route redistribution:
R1# show ip ospf database external 5.5.5.5
OSPF Router with ID (1.1.1.1) (Process ID 1)
Type-5 AS External Link States
LS age: 120
Options: (No TOS-capability, DC, Upward)
LS Type: AS External Link
Link State ID: 5.5.5.5 (External Network Number)
Advertising Router: 3.3.3.3
LS Seq Number: 80000001
Checksum: 0xABCD
Length: 36
Network Mask: /32
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
Forward Address: 0.0.0.0
External Route Tag: 0
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The route was redistributed into OSPF by router 3.3.3.3 with a metric of 20.
The output shows an OSPF Type 5 External LSA for prefix 5.5.5.5/32, advertised by router 3.3.3.3 with a metric type E2 and metric 20.
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 prefix 5.5.5.5/32 is a network inside the OSPF domain.
Why it's wrong here
Type 5 LSAs are for external routes redistributed into OSPF.
✓
The route was redistributed into OSPF by router 3.3.3.3 with a metric of 20.
Why this is correct
The LSA is Type-5, advertising router is 3.3.3.3, metric type E2 with metric 20.
The forward address indicates the next-hop is 5.5.5.5.
Why it's wrong here
The forward address is 0.0.0.0, meaning the next-hop is the advertising router.
✗
This is a Type 4 Summary ASBR LSA.
Why it's wrong here
The LS Type is AS External Link, which is Type 5.
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.
OSPF Troubleshooting (v2/v3) — This question tests OSPF Troubleshooting (v2/v3) — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: The route was redistributed into OSPF by router 3.3.3.3 with a metric of 20. — The output shows an OSPF Type 5 External LSA for prefix 5.5.5.5/32, advertised by router 3.3.3.3 with a metric type E2 and metric 20.
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.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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