Quick Answer
The answer is that a route-map filtering OSPF routes is the likely cause of the missing routes. This is correct because the OSPF database clearly contains two router link states (from 10.1.1.1 and 10.2.2.2) and a net link state, indicating that OSPF adjacencies are fully formed and LSAs are being exchanged, yet the routing table shows only a single OSPF route. When the database is complete but the routing table is incomplete, the issue is almost always a filtering mechanism—such as a distribute-list or route-map applied under the OSPF process—that prevents certain prefixes from being installed. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your ability to distinguish between OSPF database issues (like missing LSAs) and route installation issues, a common trap where candidates mistakenly suspect neighbor problems. Remember the key diagnostic: if the database looks healthy but the routing table is sparse, think filter, not adjacency. A useful memory tip is “DB full, RIB empty? Check the route-map entry.”
This 300-410 practice question tests your understanding of route maps and route filtering. 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 on Router R1:
R1# show ip ospf database
OSPF Router with ID (10.1.1.1) (Process ID 1)
Router Link States (Area 0)
Link ID ADV Router Age Seq# Checksum Link count
10.1.1.1 10.1.1.1 100 0x80000001 0x00A0B0 1 10.2.2.2 10.2.2.2 200 0x80000003 0x00C0D0 2
Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
10.1.1.2 10.1.1.2 150 0x80000001 0x00E0F0
R1# show ip route ospf
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
O 10.2.2.0/24 [110/20] via 10.1.1.2, 00:10:00, FastEthernet0/0Based on this output, what is a likely issue?
A route-map is filtering OSPF routes, causing only one route to be installed.
The database has more routes than the routing table, indicating filtering.
OSPF is not running on any interface.
Why wrong: The database shows OSPF is running.
The router ID is misconfigured.
Why wrong: Router ID 10.1.1.1 is valid.
The area is not configured correctly.
Why wrong: Area 0 is standard.
Answer choices
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 is filtering OSPF routes, causing only one route to be installed.
The OSPF database shows two routers and a net link, but only one OSPF route is in the routing table. This could be due to a route-map filtering OSPF routes. The correct answer is that a route-map may be filtering some OSPF routes from being installed.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
A route-map is filtering OSPF routes, causing only one route to be installed.
Why this is correct
The database has more routes than the routing table, indicating filtering.
Related concept
OSPF neighbours must agree on key parameters.
OSPF is not running on any interface.
Why it's wrong here
The database shows OSPF is running.
The router ID is misconfigured.
Why it's wrong here
Router ID 10.1.1.1 is valid.
The area is not configured correctly.
Why it's wrong here
Area 0 is standard.
Common exam traps
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.
Trap categories for this question
Command / output trap
The database shows OSPF is running.
Detailed technical explanation
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.
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
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
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.
Route Maps and Route Filtering — study guide chapter
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FAQ
Route Maps and Route Filtering — This question tests Route Maps and Route Filtering — OSPF neighbours must agree on key parameters..
The correct answer is: A route-map is filtering OSPF routes, causing only one route to be installed. — The OSPF database shows two routers and a net link, but only one OSPF route is in the routing table. This could be due to a route-map filtering OSPF routes. The correct answer is that a route-map may be filtering some OSPF routes from being installed.
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 neighbours must agree on key parameters.
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Last reviewed: Jun 18, 2026
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