- A
Broadcast
Why wrong: Broadcast is the default for Ethernet interfaces, not serial HDLC.
- B
Non-broadcast (NBMA)
Why wrong: NBMA is the default for Frame Relay multipoint interfaces, not HDLC.
- C
Point-to-point
Correct: Serial HDLC defaults to point-to-point, enabling faster convergence without DR/BDR election.
- D
Point-to-multipoint
Why wrong: Point-to-multipoint is not a default network type for any interface; it must be configured manually.
Question 1,332 of 2,152
Default OSPF Network Type on Serial HDLC: Point-to-Point
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?
Quick Answer
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."
Answer choices
Why each option matters
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
On Cisco routers, a serial interface using HDLC encapsulation defaults to the OSPF network type point-to-point. This is because HDLC is a synchronous framing protocol that inherently implies a direct, single-neighbor link, so OSPF automatically sets the network type to point-to-point, which requires no DR/BDR election and uses multicast Hello packets (224.0.0.5).
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Point-to-multipoint
Why it's wrong here
Point-to-multipoint is not a default network type for any interface; it must be configured manually.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse the default OSPF network type for serial interfaces with the default for Ethernet (broadcast) or Frame Relay (NBMA), forgetting that HDLC encapsulation forces a point-to-point OSPF network type.
Detailed technical explanation
How to think about this question
Under the hood, OSPF determines its network type based on the underlying Layer 2 media and encapsulation; for serial interfaces, the default is point-to-point when the encapsulation is HDLC or PPP, meaning OSPF sends Hellos every 10 seconds (default) and does not elect a DR/BDR, simplifying convergence. A real-world scenario where this matters is when migrating from Frame Relay to HDLC on a serial link—engineers must remember that OSPF adjacency behavior changes from NBMA (requiring neighbor statements) to point-to-point (automatic adjacency), or they may misconfigure the network type and break routing.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Visual reference
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this 300-410 question test?
Device Management — This question tests Device Management — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Point-to-point — On Cisco routers, a serial interface using HDLC encapsulation defaults to the OSPF network type point-to-point. This is because HDLC is a synchronous framing protocol that inherently implies a direct, single-neighbor link, so OSPF automatically sets the network type to point-to-point, which requires no DR/BDR election and uses multicast Hello packets (224.0.0.5).
What should I do if I get this 300-410 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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