The root cause is the ACL implicit deny blocking all routes not matching 10.0.0.0/8, which includes the management traffic’s route. When an ACL is applied in a route-map for redistribution, any prefix not explicitly permitted is denied by the implicit deny statement at the end of the ACL, even if the route-map itself is configured as permit. In this scenario, the management route (10.1.1.1/32) is a connected route that does not fall under the 10.0.0.0/8 range, so it gets filtered out, causing traffic loss. On the Cisco CCNP ENARSI 300-410 exam, this tests your understanding of how ACL and route-map redistribution interact, specifically the often-overlooked implicit deny that can silently break connectivity. A common trap is assuming a permit route-map alone allows all routes, forgetting that the ACL’s implicit deny overrides it. Memory tip: “ACL deny is final—if it’s not permitted, it’s not redistributed.”
300-410 Route Redistribution Practice Question
This 300-410 practice question tests your understanding of route redistribution. 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 network administrator configures an ACL to filter routes during redistribution, but management traffic stops working. Router R1 config:
access-list 100 permit ip 10.0.0.0 0.255.255.255 any
!
router eigrp 100
redistribute ospf 1 route-map FILTER
!
route-map FILTER permit 10
match ip address 100
R1# show ip route 10.1.1.1
Routing entry for 10.1.1.1/32
Known via "connected", distance 0, metric 0
Redistributing via eigrp 100
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The ACL implicit deny blocks all routes not matching 10.0.0.0/8, including management routes.
The ACL only permits 10.0.0.0/8, but the management traffic may use a different source or destination. The implicit deny at the end of the ACL blocks all other routes, including management prefixes. The fix is to add a permit statement for the management network or use a more specific ACL.
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 ACL implicit deny blocks all routes not matching 10.0.0.0/8, including management routes.
Why this is correct
The implicit deny at the end of the ACL filters out management routes, causing them not to be redistributed.
The route-map is missing the set metric command, causing routes to be unreachable.
Why it's wrong here
Missing set metric does not block routes; the ACL is the issue.
✗
The access-list is applied in the wrong direction.
Why it's wrong here
The ACL is used in a route-map, which does not have direction; it matches prefixes.
✗
The redistribute command is missing the subnets keyword.
Why it's wrong here
Missing subnets would affect classful behavior, but the ACL is the primary issue.
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.
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 ACL implicit deny blocks all routes not matching 10.0.0.0/8, including management routes. — The ACL only permits 10.0.0.0/8, but the management traffic may use a different source or destination. The implicit deny at the end of the ACL blocks all other routes, including management prefixes. The fix is to add a permit statement for the management network or use a more specific ACL.
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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