The answer is that the OSPF summary-address command on R1 is blocking the redistribution of the specific 10.1.1.0/24 route. This occurs because the OSPF summary-address 10.0.0.0/16 creates a local summary route that suppresses more specific prefixes during redistribution into OSPF, while the EIGRP interface summary-address further aggregates the route into a /16, causing the /24 to be discarded as a less specific match. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of how summary-address commands interact with redistribution—a common trap is assuming both summaries are independent, when in fact the OSPF summary blocks the specific prefix from being injected at all. To troubleshoot missing routes due to summary addresses in redistribution, always check both protocol-level and interface-level summaries for overlapping aggregates. Memory tip: “Summaries swallow specifics—if you see a missing route, look for a bigger prefix eating it.”
300-410 Route Redistribution Practice Question
This 300-410 practice question tests your understanding of route redistribution. 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 large enterprise network is experiencing intermittent reachability to a subnet 10.1.1.0/24 from the rest of the network. Router R1 has the following relevant configuration:
interface GigabitEthernet0/0
ip summary-address eigrp 100 10.0.0.0 255.255.0.0 5
Router R2 shows:
R2# show ip route 10.1.1.0
Routing entry for 10.0.0.0/16, supernet
Known via "eigrp 100", distance 90, metric 128256
Redistributing via eigrp 100
Last update from 10.10.10.1 on GigabitEthernet0/1
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The OSPF summary-address command on R1 is blocking the redistribution of the specific /24 route.
The issue is that R1 has both an OSPF summary-address and an EIGRP interface summary-address, causing the more specific /24 route to be suppressed by the /16 summary. The EIGRP summary-address command on the interface creates a null0 summary route, and the OSPF redistribution of the EIGRP summary further aggregates, losing the specific prefix. The fix is to remove the interface summary-address or adjust the summary to include the specific subnet.
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 OSPF summary-address command on R1 is blocking the redistribution of the specific /24 route.
Why this is correct
The OSPF summary-address creates an aggregate route, and combined with the EIGRP interface summary, the specific /24 is suppressed.
The EIGRP metric values are too high, causing the route to be unreachable.
Why it's wrong here
The metric values are valid; the issue is summarization, not metric.
✗
The redistribute ospf command under EIGRP is missing the subnets keyword.
Why it's wrong here
The subnets keyword is present under OSPF redistribution, not needed under EIGRP.
✗
The route is being filtered by a distribute-list on R2.
Why it's wrong here
No distribute-list is configured; the issue is 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
Keyword trap
The subnets keyword is present under OSPF redistribution, not needed under EIGRP.
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.
Route Redistribution — This question tests Route Redistribution — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: The OSPF summary-address command on R1 is blocking the redistribution of the specific /24 route. — The issue is that R1 has both an OSPF summary-address and an EIGRP interface summary-address, causing the more specific /24 route to be suppressed by the /16 summary. The EIGRP summary-address command on the interface creates a null0 summary route, and the OSPF redistribution of the EIGRP summary further aggregates, losing the specific prefix. The fix is to remove the interface summary-address or adjust the summary to include the specific subnet.
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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