CCNA IP Routing Practice Question
A router advertises its LAN network into OSPF, but no OSPF Hellos should be sent toward end-user devices on that LAN. Which configuration approach solves this cleanly?
⚠ Common exam trap
A frequent exam trap is selecting the option to increase the OSPF cost on the LAN interface to prevent Hello packets. While adjusting the cost changes the metric used for route selection, it does not stop the router from sending or receiving OSPF Hellos. Another common mistake is to disable OSPF globally and redistribute connected routes, which is unnecessarily complex and does not address the problem of suppressing Hellos on a specific interface. Additionally, converting the LAN interface to a loopback is irrelevant because loopbacks are logical interfaces used for router IDs and testing, not for controlling OSPF Hello behavior on physical LAN interfaces.
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
✓
Configure the LAN interface as a passive interface in OSPF
A passive interface advertises the connected subnet into OSPF without sending or processing Hellos on that interface. That is exactly what you want for user-facing LANs with no OSPF neighbors.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use ip ospf cost 65535 on the LAN interface
Why it's wrong here
`ip ospf cost 65535` sets the maximum OSPF interface cost, which only influences SPF path selection by making that link appear extremely expensive. It does not suppress Hello packets, so the router will still send OSPF Hellos and may form adjacencies, and the LAN network will still be advertised. Cost tuning cannot replace passive-interface; it assumes the interface is already an active OSPF participant.
When this WOULD be correct
In a scenario where the question asks for a method to influence OSPF path selection without needing to suppress Hello packets, setting the OSPF cost to 65535 could be correct. For example, if the question specifies that the goal is to manipulate OSPF metrics for routing decisions without affecting neighbor relationships.
- ✓
Configure the LAN interface as a passive interface in OSPF
Why this is correct
The `passive-interface` command under the OSPF process tells OSPF to stop transmitting Hello packets on that interface while still injecting the interface's subnet as an OSPF route. This preserves full route reachability into the LAN without forming neighbor adjacencies, cutting unnecessary protocol overhead. It is the standard, purpose-built mechanism for LAN-facing OSPF interfaces.
- ✗
Disable OSPF globally and redistribute connected routes
Why it's wrong here
Disabling OSPF in favour of redistributing connected routes is not equivalent: OSPF would no longer run, so the router loses all neighbor adjacency state and dynamic topology awareness. Redistribution from the connected table into a non-existent OSPF process is contradictory, and re-injecting routes normally requires metric and tagging tuning. A single passive-interface statement prevents Hellos while keeping OSPF fully operational, making this approach both needless and disruptive.
When this WOULD be correct
If a question asked how to completely eliminate OSPF from a router while still allowing connected routes to be advertised through another routing protocol, then disabling OSPF globally would be the correct approach.
- ✗
Convert the LAN interface to a loopback
Why it's wrong here
A physical LAN interface cannot be changed into a loopback; loopbacks are logical interfaces with no physical layer behavior, so "converting" it would eliminate actual LAN connectivity. Even if a loopback were used, OSPF treats it as a stub /32 host route, not as the original LAN subnet, and the required command is still passive-interface. Thus, this option replaces a simple configuration change with an invalid and symptomatically different approach.
When this WOULD be correct
If the question asked for a method to isolate OSPF routing from a specific segment of the network while still allowing the interface to function normally for other purposes, converting the LAN interface to a loopback could be a valid solution, as loopbacks are often used for management or routing purposes without direct user connectivity.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓Configure the LAN interface as a passive interface in OSPFCorrect answer▾
Why this is correct
The `passive-interface` command under the OSPF process tells OSPF to stop transmitting Hello packets on that interface while still injecting the interface's subnet as an OSPF route. This preserves full route reachability into the LAN without forming neighbor adjacencies, cutting unnecessary protocol overhead. It is the standard, purpose-built mechanism for LAN-facing OSPF interfaces.
✗Use ip ospf cost 65535 on the LAN interfaceWrong answer — click to see why▾
Why this is wrong here
The 'ip ospf cost' command only modifies the OSPF metric for the interface, not the transmission of Hello packets. OSPF Hellos are still sent regardless of the cost value, so this does not prevent Hellos from reaching end-user devices.
★ When this WOULD be the correct answer
In a scenario where the question asks for a method to influence OSPF path selection without needing to suppress Hello packets, setting the OSPF cost to 65535 could be correct. For example, if the question specifies that the goal is to manipulate OSPF metrics for routing decisions without affecting neighbor relationships.
Why candidates choose this
Students might think that setting a very high cost could effectively suppress OSPF operations on the interface, but cost only affects route selection, not protocol behavior like Hello transmission.
✗Disable OSPF globally and redistribute connected routesWrong answer — click to see why▾
Why this is wrong here
Disabling OSPF globally and redistributing connected routes is an overly complex and messy approach. It removes OSPF entirely from the router, requiring redistribution of all connected routes, which can lead to suboptimal routing and administrative overhead. The passive-interface command achieves the goal cleanly without disabling OSPF.
★ When this WOULD be the correct answer
If a question asked how to completely eliminate OSPF from a router while still allowing connected routes to be advertised through another routing protocol, then disabling OSPF globally would be the correct approach.
Why candidates choose this
A test-taker might consider this option because redistribution can advertise routes without running OSPF on the interface, but they overlook that disabling OSPF globally affects all interfaces and requires additional configuration to re-advertise routes.
✗Convert the LAN interface to a loopbackWrong answer — click to see why▾
Why this is wrong here
Converting a LAN interface to a loopback interface changes its fundamental characteristics (e.g., it becomes a virtual interface that is always up) and is not a standard or clean solution for preventing OSPF Hellos. Loopback interfaces are typically used for router IDs or management, not for connecting end-user devices.
★ When this WOULD be the correct answer
If the question asked for a method to isolate OSPF routing from a specific segment of the network while still allowing the interface to function normally for other purposes, converting the LAN interface to a loopback could be a valid solution, as loopbacks are often used for management or routing purposes without direct user connectivity.
Why candidates choose this
Students might confuse the passive-interface concept with loopback interfaces, thinking that loopbacks do not send Hellos (which is true), but this approach is impractical and alters the network design unnecessarily.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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.
Go deeper
Related to this question
Learn chapter
OSPFv3 Single-Area Configuration for IPv6
Key term
Interface
An interface is a point of connection or interaction between two systems, devices, or software components that allows them to exchange information or signals.
Key term
LAN
Local Area Network — a network confined to a single physical location such as an office, building, or campus.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.