The answer is to apply the `ip ospf authentication message-digest` command under the specific interface. This is correct because OSPF MD5 authentication is configured at the interface level, not globally under the OSPF routing process; the `message-digest` keyword tells the router to use MD5 hashing for OSPF packets on that link, and it must be paired with an `ip ospf message-digest-key` command to define the actual key and key ID. On the Cisco SCOR / CCNP Security Core 350-701 exam, this tests your understanding that OSPF authentication is an interface-level security feature, and a common trap is trying to configure it with the `area authentication message-digest` command under the OSPF process, which only enables authentication for the area but still requires the interface-level command to activate it on a specific link. Remember the mnemonic: "Interface first, key second" — always apply `ip ospf authentication message-digest` on the interface before defining the key.
350-701 Network Security Practice Question
This 350-701 practice question tests your understanding of network security. 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.
A network engineer is configuring OSPF on a Cisco router and needs to enable authentication between neighbors. The authentication type should be MD5. Which configuration step is required?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
ip ospf authentication message-digest under the interface
Option B is correct because to enable OSPF MD5 authentication on a Cisco router, the 'ip ospf authentication message-digest' command must be applied under the specific interface. This command tells OSPF to use MD5 (message-digest) authentication for that interface, and it must be paired with an 'ip ospf message-digest-key' command to define the actual key. The authentication type is configured at the interface level, not globally under the OSPF routing process.
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.
✗
ospf authentication-key under router ospf
Why it's wrong here
The authentication-key command is used in interface mode, not router mode in modern IOS.
✓
ip ospf authentication message-digest under the interface
Why this is correct
This interface command enables MD5 authentication.
Related concept
Read the scenario before looking for a memorised answer.
✗
area 0 authentication command in router configuration
Why it's wrong here
This command enables authentication for the area but does not specify the key; the interface command is still needed.
✗
ip ospf authentication null
Why it's wrong here
This disables authentication.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between area-level authentication (which defaults to simple) and interface-level MD5 authentication, causing candidates to mistakenly choose 'area 0 authentication' thinking it covers MD5.
Trap categories for this question
Command / output trap
The authentication-key command is used in interface mode, not router mode in modern IOS.
Detailed technical explanation
How to think about this question
OSPF authentication uses a shared key and a hash algorithm to verify neighbor packets. MD5 (type 2) creates a 128-bit hash appended to each OSPF packet, preventing replay attacks via a monotonically increasing sequence number. In a real-world scenario, if you only configure 'area 0 authentication' without 'message-digest', the router defaults to simple text authentication (type 1), which sends the key in plaintext and is insecure.
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.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Network Security — This question tests Network Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: ip ospf authentication message-digest under the interface — Option B is correct because to enable OSPF MD5 authentication on a Cisco router, the 'ip ospf authentication message-digest' command must be applied under the specific interface. This command tells OSPF to use MD5 (message-digest) authentication for that interface, and it must be paired with an 'ip ospf message-digest-key' command to define the actual key. The authentication type is configured at the interface level, not globally under the OSPF routing process.
What should I do if I get this 350-701 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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Question Discussion
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