The root cause is that the ABR R1 is missing the `area 1 range 10.1.48.0 255.255.240.0` command, so the route to 10.1.48.0/20 is not advertised. When OSPF route summarization is configured on an ABR using the `area range` command, the router suppresses the advertisement of all more specific Type 3 LSAs within that range and instead advertises only the summary. However, any subnets that fall outside the configured summary ranges—like 10.1.48.0/20 here—are neither summarized nor forwarded as individual routes, because the ABR discards them by default. This is a classic trap on the Cisco CCNP ENARSI 300-410 exam: candidates often assume that missing summary ranges still allow individual routes to leak through, but OSPF’s default behavior is to suppress all routes not explicitly covered by a `range` statement. The fix is to either add the missing range or use a broader summary that encompasses all subnets. Memory tip: “If it’s not in the range, it’s out of the exchange.”
300-410 Network Logging and Syslog Practice Question
This 300-410 practice question tests your understanding of network logging and syslog. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 network uses OSPF with route summarization on Area Border Routers (ABRs). Router R1 (ABR) has the configuration:
router ospf 1
area 1 range 10.1.0.0 255.255.240.0
area 1 range 10.1.16.0 255.255.240.0
Router R2 (internal to area 1) shows:
R2# show ip route ospf
10.1.0.0/20 is subnetted, 1 subnets
O IA 10.1.0.0/20 [110/2] via 10.2.1.1, 00:00:15, Serial0/0/0
10.1.16.0/20 is subnetted, 1 subnets
O IA 10.1.16.0/20 [110/2] via 10.2.1.1, 00:00:10, Serial0/0/0
10.1.32.0/20 [110/3] via 10.2.1.2, 00:00:05, Serial0/0/1
R2 is missing a route to 10.1.48.0/20. What is the root cause?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The ABR R1 has a missing 'area 1 range 10.1.48.0 255.255.240.0' command.
The ABR R1 configured two summary ranges for area 1, but the missing route 10.1.48.0/20 is not covered by either summary. OSPF summarization on the ABR creates Type 3 LSAs for the configured ranges, but any routes not falling within those ranges are not advertised as summaries and are also not advertised as individual routes (unless the 'no discard-route' option is used). This causes the missing route. The correct fix is to add an additional summary range covering 10.1.48.0/20 or use a broader summary.
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 ABR R1 has a missing 'area 1 range 10.1.48.0 255.255.240.0' command.
Why this is correct
The summary range for 10.1.48.0/20 is not configured, so that route is not advertised into area 0.
R2 has a routing table limit that prevents installation of the route.
Why it's wrong here
There is no indication of a routing table limit; R2 receives other routes.
✗
R1's OSPF process has a distribute-list blocking the route.
Why it's wrong here
No distribute-list is shown in the configuration.
✗
The missing route is a result of OSPF route filtering at the area boundary.
Why it's wrong here
Route filtering is not configured; the issue is incomplete summarization.
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.
Trap categories for this question
Command / output trap
No distribute-list is shown in the configuration.
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.
Network Logging and Syslog — This question tests Network Logging and Syslog — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: The ABR R1 has a missing 'area 1 range 10.1.48.0 255.255.240.0' command. — The ABR R1 configured two summary ranges for area 1, but the missing route 10.1.48.0/20 is not covered by either summary. OSPF summarization on the ABR creates Type 3 LSAs for the configured ranges, but any routes not falling within those ranges are not advertised as summaries and are also not advertised as individual routes (unless the 'no discard-route' option is used). This causes the missing route. The correct fix is to add an additional summary range covering 10.1.48.0/20 or use a broader summary.
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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