Quick Answer
The answer is NBMA. By default, a multipoint GRE tunnel interface in DMVPN Phase 3 inherits the OSPF network type of Non-Broadcast Multi-Access (NBMA), meaning the router will not send multicast Hellos and requires manual neighbor configuration to form OSPF adjacencies. This default behavior stems from the fact that mGRE tunnels emulate a non-broadcast multi-access medium, unlike physical Ethernet links which default to broadcast. On the Cisco CCNP ENARSI 300-410 exam, this concept tests your understanding of how DMVPN interacts with OSPF, often appearing in questions about neighbor discovery failures or misconfigured interfaces. A common trap is assuming mGRE tunnels behave like point-to-point links, but the NBMA default forces you to either configure the neighbor statement or change the network type to broadcast or point-to-multipoint. Remember the memory tip: "mGRE means NBMA—no multicast, manual adjacency."
This 300-410 practice question tests your understanding of dmvpn. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
In DMVPN Phase 3 using OSPF, what is the default network type on a multipoint GRE tunnel interface?
broadcast
Why wrong: Incorrect. Broadcast is not the default; it must be explicitly configured.
point-to-multipoint
Why wrong: Incorrect. Point-to-multipoint is not the default for mGRE; it is an option for non-broadcast environments.
NBMA
Correct. The default OSPF network type for mGRE is NBMA.
point-to-point
Why wrong: Incorrect. Point-to-point is used on physical serial links or point-to-point GRE tunnels, not on mGRE.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
NBMA
By default, a multipoint GRE tunnel interface is treated as an OSPF NBMA network type. This requires manual neighbor configuration unless the interface is set to broadcast or point-to-multipoint.
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.
broadcast
Why it's wrong here
Incorrect. Broadcast is not the default; it must be explicitly configured.
point-to-multipoint
Why it's wrong here
Incorrect. Point-to-multipoint is not the default for mGRE; it is an option for non-broadcast environments.
NBMA
point-to-point
Why it's wrong here
Incorrect. Point-to-point is used on physical serial links or point-to-point GRE tunnels, not on mGRE.
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.
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.
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FAQ
DMVPN — This question tests DMVPN — OSPF neighbours must agree on key parameters..
The correct answer is: NBMA — By default, a multipoint GRE tunnel interface is treated as an OSPF NBMA network type. This requires manual neighbor configuration unless the interface is set to broadcast or point-to-multipoint.
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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