This 300-410 practice question tests your understanding of ipv6 traffic filtering and urpf. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 runs the following command on Router R1:
R1# show ipv6 interface gigabitethernet 0/0 | include uRPF
IPv6 uRPF: loose mode
Based on this output, what is the operational state of uRPF on this interface?
uRPF is disabled
Why wrong: The output shows uRPF is enabled.
uRPF is enabled in strict mode
Why wrong: The output specifies loose mode.
uRPF is enabled in loose mode
The output confirms loose mode uRPF.
uRPF is enabled but only for IPv4
Why wrong: This is an IPv6 interface, and uRPF is configured for IPv6.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
uRPF is enabled in loose mode
The command 'show ipv6 interface gigabitethernet 0/0 | include uRPF' returns 'IPv6 uRPF: loose mode', which directly indicates that unicast Reverse Path Forwarding (uRPF) is enabled and operating in loose mode on this interface. Loose mode checks only that a source address exists in the routing table, without requiring that the incoming interface matches the best return path.
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.
uRPF is disabled
Why it's wrong here
The output shows uRPF is enabled.
uRPF is enabled in strict mode
Why it's wrong here
The output specifies loose mode.
uRPF is enabled in loose mode
Why this is correct
The output confirms loose mode uRPF.
Related concept
Read the scenario before looking for a memorised answer.
uRPF is enabled but only for IPv4
Why it's wrong here
This is an IPv6 interface, and uRPF is configured for IPv6.
Common exam traps
Cisco often tests the distinction between 'loose mode' and 'strict mode' by presenting output that clearly states the mode, but candidates may confuse 'loose' with 'disabled' or incorrectly assume that any uRPF output implies strict mode.
Trap categories for this question
Command / output trap
The output shows uRPF is enabled.
Detailed technical explanation
uRPF loose mode (RFC 3704) is often used in asymmetric routing environments where traffic from a valid source may arrive on an interface different from the best return path; it only verifies that the source prefix is reachable via any route in the FIB. In contrast, strict mode requires the incoming interface to match the RIB's best path, which can drop legitimate traffic in multihomed or load-balanced topologies. The 'show ipv6 interface' output is the primary method to confirm the operational uRPF mode for IPv6, as there is no separate 'show ipv6 uRPF' command.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
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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: uRPF is enabled in loose mode — The command 'show ipv6 interface gigabitethernet 0/0 | include uRPF' returns 'IPv6 uRPF: loose mode', which directly indicates that unicast Reverse Path Forwarding (uRPF) is enabled and operating in loose mode on this interface. Loose mode checks only that a source address exists in the routing table, without requiring that the incoming interface matches the best return path.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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