Quick Answer
The answer is strict mode (rx). When you configure the command 'ipv6 verify unicast source reachable-via' without any keyword, the router defaults to strict mode, meaning it checks that the source address of an incoming IPv6 packet is reachable via the exact interface on which the packet arrived. This is the most secure uRPF behavior because it drops any traffic whose return path does not match the ingress interface, preventing spoofed packets from being forwarded. On the Cisco CCNP ENARSI 300-410 exam, this default behavior is a common trap—candidates often assume they must specify a keyword, but the router applies strict mode automatically. The exam tests your understanding that omitting the keyword does not leave the feature disabled; it activates the strictest verification. A reliable memory tip is to think of the word “strict” as the default stance: if you do not explicitly choose a looser option like 'any', the router enforces the tightest possible check on the receiving interface.
This 300-410 practice question tests your understanding of ipv6 traffic filtering and urpf. 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 uRPF mode when 'ipv6 verify unicast source reachable-via' is configured without any keyword?
Loose mode (any)
Why wrong: Loose mode requires the 'any' keyword; the default is strict.
Strict mode (rx)
Without keywords, the router uses strict uRPF, checking the source is reachable via the receiving interface.
No uRPF is applied
Why wrong: The command itself enables uRPF; the default mode is strict.
Only default routes are allowed
Why wrong: That would be 'allow-default', which is not the default.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Strict mode (rx)
If no keyword is specified, the default is strict mode (rx).
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Loose mode (any)
Why it's wrong here
Loose mode requires the 'any' keyword; the default is strict.
Strict mode (rx)
Why this is correct
Without keywords, the router uses strict uRPF, checking the source is reachable via the receiving interface.
Related concept
Read the scenario before looking for a memorised answer.
No uRPF is applied
Why it's wrong here
The command itself enables uRPF; the default mode is strict.
Only default routes are allowed
Why it's wrong here
That would be 'allow-default', which is not the default.
Common exam traps
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Trap categories for this question
Keyword trap
Loose mode requires the 'any' keyword; the default is strict.
Command / output trap
The command itself enables uRPF; the default mode is strict.
Detailed technical explanation
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the 300-410 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Identify which 300-410 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
IPv6 Traffic Filtering and uRPF — study guide chapter
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FAQ
IPv6 Traffic Filtering and uRPF — This question tests IPv6 Traffic Filtering and uRPF — Read the scenario before looking for a memorised answer..
The correct answer is: Strict mode (rx) — If no keyword is specified, the default is strict mode (rx).
Identify which 300-410 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 18, 2026
This 300-410 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 300-410 exam.
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