The answer is that Router R9 has three PIM neighbors, one operating in Dense mode and two in Sparse mode. This is correct because the "Mode" column in the show ip pim neighbor output directly reflects the PIM mode configured on each neighbor interface; the neighbor at 192.168.1.10 shows "Dense," while 192.168.1.11 and 192.168.1.12 both show "Sparse." On the ENCOR 350-401 exam, this command tests your ability to interpret PIM neighbor table output and understand that a single router can have neighbors in different modes if its interfaces are configured for sparse-dense mode or if different interfaces use different PIM modes. A common trap is assuming all neighbors must share the same mode, but the table clearly shows mixed modes are possible. Remember the memory tip: "Dense floods, Sparse joins"—Dense mode forwards traffic everywhere unless pruned, while Sparse mode requires explicit joins, and the neighbor table tells you which mode each peer is using.
CCNP WAN Technologies Practice Question
This 350-401 practice question tests your understanding of wan technologies. 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 engineer runs the following command on Router R9:
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Router R9 has three PIM neighbors, one in Dense mode and two in Sparse mode.
The output shows PIM neighbors with different modes (Dense and Sparse). The mode indicates the PIM mode configured on the interface.
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.
✗
All PIM neighbors are operating in Sparse mode.
Why it's wrong here
One neighbor is in Dense mode.
✓
Router R9 has three PIM neighbors, one in Dense mode and two in Sparse mode.
Why this is correct
The output lists three neighbors with modes: Dense, Sparse, Sparse.
The PIM neighbor 192.168.1.12 is on the same interface as the others.
Why it's wrong here
192.168.1.12 is on GigabitEthernet0/1, while the others are on GigabitEthernet0/0.
✗
All PIM neighbors are in the 'Expires' state.
Why it's wrong here
The Expires column shows remaining time, not a state.
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
The Expires column shows remaining time, not a state.
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.
What to study next
Got this wrong? Here's your next step.
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 350-401 OSPF questions on adjacency and route selection.
WAN Technologies — This question tests WAN Technologies — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: Router R9 has three PIM neighbors, one in Dense mode and two in Sparse mode. — The output shows PIM neighbors with different modes (Dense and Sparse). The mode indicates the PIM mode configured on the interface.
What should I do if I get this 350-401 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 350-401 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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