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: strict mode
Based on this output, which statement is true?
uRPF is disabled
Why wrong: The output clearly shows uRPF is enabled.
uRPF is enabled in strict mode
The output confirms strict mode uRPF.
uRPF is enabled in loose mode
Why wrong: The output specifies strict mode.
uRPF is enabled but only for multicast
Why wrong: uRPF applies to unicast traffic.
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 strict mode
The command output explicitly shows 'IPv6 uRPF: strict mode', which confirms that unicast Reverse Path Forwarding (uRPF) is enabled and operating in strict mode. In strict mode, the router verifies that the source address of an incoming packet matches a route in the FIB and that the incoming interface is the same as the outgoing interface for that route. This prevents spoofed traffic from entering the network.
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 clearly shows uRPF is enabled.
uRPF is enabled in strict mode
Why this is correct
The output confirms strict mode uRPF.
Related concept
Read the scenario before looking for a memorised answer.
uRPF is enabled in loose mode
Why it's wrong here
The output specifies strict mode.
uRPF is enabled but only for multicast
Why it's wrong here
uRPF applies to unicast traffic.
Common exam traps
Cisco often tests the distinction between strict and loose uRPF modes, and the trap here is that candidates might confuse the 'strict mode' output with 'loose mode' or assume uRPF is disabled when the output line is present.
Trap categories for this question
Command / output trap
The output clearly shows uRPF is enabled.
Detailed technical explanation
uRPF strict mode relies on the Forwarding Information Base (FIB) to perform a two-part check: the source address must have a reachable route, and the incoming interface must be the best return path to that source. This is defined in RFC 3704 and is commonly deployed at network edges to mitigate source IP address spoofing. A subtle behavior is that uRPF strict mode can drop legitimate traffic if asymmetric routing is present, which is why loose mode or allow-default option may be used in such topologies.
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 strict mode — The command output explicitly shows 'IPv6 uRPF: strict mode', which confirms that unicast Reverse Path Forwarding (uRPF) is enabled and operating in strict mode. In strict mode, the router verifies that the source address of an incoming packet matches a route in the FIB and that the incoming interface is the same as the outgoing interface for that route. This prevents spoofed traffic from entering the network.
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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