The correct answer is point-to-point. On Cisco routers, a serial interface using HDLC or PPP encapsulation defaults to the OSPF network type point-to-point because these encapsulations inherently imply a direct, single-hop link between exactly two routers, eliminating the need for a designated router election. This concept is frequently tested on the Cisco CCNP ENARSI 300-410 exam, often as a distractor where candidates mistakenly assume a broadcast or non-broadcast type applies to all serial links. A common trap is forgetting that Frame Relay or ATM encapsulations change the default to non-broadcast or point-to-multipoint, while HDLC and PPP remain strictly point-to-point. For the exam, remember the mnemonic: "HDLC and PPP? Point-to-Point for me."
300-410 Device Management Practice Question
This 300-410 practice question tests your understanding of device management. 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.
What is the default OSPF network type for a serial interface configured with HDLC encapsulation on Cisco routers?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Point-to-point
By default, Cisco IOS sets serial interfaces with HDLC or PPP encapsulation to OSPF network type point-to-point. This is because these encapsulations typically indicate a direct link between two routers.
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.
✗
Broadcast
Why it's wrong here
Broadcast is the default for Ethernet interfaces, not serial HDLC.
✗
Non-broadcast (NBMA)
Why it's wrong here
NBMA is the default for Frame Relay multipoint interfaces, not HDLC.
✓
Point-to-point
Why this is correct
Correct: Serial HDLC defaults to point-to-point, enabling faster convergence without DR/BDR election.
Point-to-multipoint is not a default network type for any interface; it must be configured manually.
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.
Device Management — This question tests Device Management — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: Point-to-point — By default, Cisco IOS sets serial interfaces with HDLC or PPP encapsulation to OSPF network type point-to-point. This is because these encapsulations typically indicate a direct link between two routers.
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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