mediumMultiple Choice
300-410 Practice Question: Runs the following command to troubleshoot a…
A network engineer runs the following command to troubleshoot a Route Summarization issue:
R1# show ip ospf database summary 10.0.0.0
OSPF Router with ID (1.1.1.1) (Process ID 1)
Summary Net Link States (Area 0)
LS age: 100 Options: (No TOS-capability, DC) LS Type: Summary Links(Network) Link State ID: 10.0.0.0 (summary Network Number) Advertising Router: 2.2.2.2 LS Seq Number: 80000001 Checksum: 0x1234 Length: 28 Network Mask: /16 TOS: 0 Metric: 20
What does this output indicate?
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
✓
The summary route 10.0.0.0/16 is being advertised by router 2.2.2.2 as a Type 3 LSA into Area 0.
This output shows the OSPF database entry for a summary route 10.0.0.0/16. The LS Type is Summary Links, indicating it is a Type 3 LSA generated by an ABR (advertising router 2.2.2.2). The metric of 20 suggests it is a summary route injected into Area 0.
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 summary route 10.0.0.0/16 is being advertised by router 2.2.2.2 as a Type 3 LSA into Area 0.
Why this is correct
The output shows a Summary Net Link State advertisement, which is a Type 3 LSA, with Link State ID 10.0.0.0 and mask /16, originated by Advertising Router 2.2.2.2 and flooded into Area 0. This confirms the summarised inter-area route.
- ✗
The summary route is a Type 5 external LSA from an ASBR.
Why it's wrong here
The output shows LS Type 'Summary Links(Network)' within 'Summary Net Link States (Area 0)', which is a Type 3 summary LSA generated by an ABR, not a Type 5 external LSA originated by an ASBR. Type 5 LSAs appear under 'AS External Link States' and carry an external metric type; this option confuses inter-area summarisation with redistribution.
- ✗
The summary route is a Type 1 router LSA from router 2.2.2.2.
Why it's wrong here
The output shows a Summary Net Link State (Type 3 LSA) with network mask /16, not a Type 1 router LSA. Type 1 LSAs advertise router interfaces within an area, whereas Type 3 LSAs are generated by an ABR to summarise routes between areas. This option is tempting because the advertising router (2.2.2.2) is a router, so one might assume it originates a router LSA, but the LS Type field explicitly identifies it as a summary link.
- ✗
The summary route is not installed because the metric is too high.
Why it's wrong here
Nothing in the output indicates the route was rejected; the LSA exists in the link-state database with Metric 20 and a valid sequence number. OSPF installs summary routes regardless of metric magnitude, since metric only influences path preference. This option misreads a normal database entry as a failure condition.
Visual reference
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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