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
GigabitEthernet0/0 is up, line protocol is up IPv6 is enabled, link-local address is FE80::1 Global unicast address(es): 2001:DB8:1:1::1, subnet is 2001:DB8:1:1::/64 Joined group address(es): FF02::1 FF02::2 ICMP redirects are enabled ICMP unreachables are enabled ND DAD is enabled, number of DAD attempts: 1 ND reachable time is 30000 milliseconds ND advertised reachable time is 0 milliseconds ND advertised retransmit interval is 1000 milliseconds ND router advertisements are sent every 200 seconds ND router advertisements live for 1800 seconds Hosts use stateless autoconfig for addresses. IPv6 uRPF: strict mode (drop invalid packets)
Based on this output, what is the operational state of uRPF on this interface?
uRPF is disabled
Why wrong: The output explicitly shows uRPF is enabled.
uRPF is enabled in strict mode
The output confirms strict mode uRPF is active.
uRPF is enabled in loose mode
Why wrong: The output specifies strict mode, not loose.
uRPF is enabled but only for multicast
Why wrong: uRPF applies to unicast traffic, not specifically multicast.
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 output explicitly states 'IPv6 uRPF: strict mode (drop invalid packets)', which confirms that unicast Reverse Path Forwarding (uRPF) is enabled on the interface 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 pointing back to the same interface; if not, the packet is dropped. This is a direct read of the operational state from the show command.
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 explicitly shows uRPF is enabled.
uRPF is enabled in strict mode
Why this is correct
The output confirms strict mode uRPF is active.
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, not loose.
uRPF is enabled but only for multicast
Why it's wrong here
uRPF applies to unicast traffic, not specifically multicast.
Common exam traps
Cisco often tests the ability to read the exact operational state from the 'show ipv6 interface' output, where candidates may overlook the explicit 'strict mode' line and instead assume uRPF is disabled or confuse it with loose mode based on incomplete knowledge of the command syntax.
Trap categories for this question
Command / output trap
The output explicitly shows uRPF is enabled.
Detailed technical explanation
uRPF in strict mode is commonly used to mitigate source address spoofing by ensuring that packets arriving on an interface have a source address that is reachable via that same interface in the routing table. This is particularly important in IPv6 due to the larger address space and potential for spoofing in stateless autoconfiguration environments. The command 'ipv6 verify unicast source reachable-via any' enables loose mode, while 'ipv6 verify unicast source reachable-via rx' enables strict mode; the output confirms the latter.
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 output explicitly states 'IPv6 uRPF: strict mode (drop invalid packets)', which confirms that unicast Reverse Path Forwarding (uRPF) is enabled on the interface 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 pointing back to the same interface; if not, the packet is dropped. This is a direct read of the operational state from the show command.
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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