Question 83 of 2,152

IPv6 Traffic Filtering and uRPF →mediumMultiple ChoiceObjective-mapped

IPv6 uRPF Strict Mode Verification — Suppress Feature

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 to verify IPv6 uRPF on an interface:

R1# show ipv6 interface GigabitEthernet0/0 | include verify|suppress

IPv6 verify source: strict IPv6 verify source suppress: disabled

What does this output indicate?

A
Strict uRPF is enabled, and no suppression is configured, so all incoming packets are subject to strict verification.
Correct. Strict uRPF is active and no exceptions are configured.
B
Loose uRPF is enabled with suppression.
Why wrong: Incorrect. It says strict, not loose.
C
uRPF is disabled on this interface.
Why wrong: Incorrect. It shows enabled.
D
Suppression is enabled, so uRPF checks are bypassed.
Why wrong: Incorrect. Suppression is disabled.

Full breakdown with real-world context →

Quick Answer

The answer is that strict uRPF is enabled with the suppress feature disabled, meaning all incoming IPv6 packets on GigabitEthernet0/0 are subject to strict reverse path forwarding verification. This is correct because the command output explicitly shows "IPv6 verify source: strict" and "IPv6 verify source suppress: disabled," indicating no traffic is bypassing the verification process. The suppress feature, when enabled, allows uRPF to be skipped for packets from known or trusted sources, but here its disabled state forces every packet to be checked for a matching source address in the routing table and a valid return path. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your ability to interpret the show ipv6 interface uRPF strict suppress status output, often appearing in a multiple-choice or simulation question where the trap is confusing "suppress disabled" with a misconfiguration. Remember the key memory tip: "Strict means check every path; suppress disabled means no shortcuts allowed."

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

Strict uRPF is enabled, and no suppression is configured, so all incoming packets are subject to strict verification.

The output shows 'IPv6 verify source: strict' and 'IPv6 verify source suppress: disabled'. This confirms that strict unicast Reverse Path Forwarding (uRPF) is enabled on the interface, meaning every incoming packet's source address is checked against the routing table to ensure the best return route uses the same incoming interface. Because suppression is disabled, no packets bypass this verification, so all incoming packets are subject to strict uRPF checks.

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.

✓
Strict uRPF is enabled, and no suppression is configured, so all incoming packets are subject to strict verification.
Why this is correct
Correct. Strict uRPF is active and no exceptions are configured.
Related concept
Read the scenario before looking for a memorised answer.
✗
Loose uRPF is enabled with suppression.
Why it's wrong here
Incorrect. It says strict, not loose.
✗
uRPF is disabled on this interface.
Why it's wrong here
Incorrect. It shows enabled.
✗
Suppression is enabled, so uRPF checks are bypassed.
Why it's wrong here
Incorrect. Suppression is disabled.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the distinction between 'strict' and 'loose' uRPF modes, and the trap here is that candidates may confuse the 'suppress' keyword with disabling uRPF entirely, when in fact it only controls whether certain packets are exempt from the check.

Trap categories for this question

Command / output trap
Incorrect. It shows enabled.

Detailed technical explanation

How to think about this question

Strict uRPF verifies that the source address of an incoming packet has a route in the FIB pointing back out the same interface it arrived on, which is critical for mitigating spoofed traffic in IPv6 networks. The 'suppress' feature, when enabled, allows bypassing uRPF checks for packets sourced from certain prefixes (e.g., those learned via routing protocols), but here it is disabled, ensuring full verification. In real-world scenarios, strict uRPF is often used on customer-facing interfaces to prevent source address spoofing, while loose uRPF (which only checks for any route to the source) is used on upstream links.

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 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

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.

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FAQ

Questions learners often ask

What does this 300-410 question test?

IPv6 Traffic Filtering and uRPF — This question tests IPv6 Traffic Filtering and uRPF — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: Strict uRPF is enabled, and no suppression is configured, so all incoming packets are subject to strict verification. — The output shows 'IPv6 verify source: strict' and 'IPv6 verify source suppress: disabled'. This confirms that strict unicast Reverse Path Forwarding (uRPF) is enabled on the interface, meaning every incoming packet's source address is checked against the routing table to ensure the best return route uses the same incoming interface. Because suppression is disabled, no packets bypass this verification, so all incoming packets are subject to strict uRPF checks.

What should I do if I get this 300-410 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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Same concept, more angles

1 more ways this is tested on 300-410

These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.

Variation 1. A network engineer runs the following command to verify IPv6 uRPF operation: R1# show ipv6 interface GigabitEthernet0/0 | include verify IPv6 verify source: strict What does this output indicate?

medium

✓ A.Strict uRPF is enabled, so the router will drop packets if the source address is not in the routing table or if the best return path is not through the receiving interface.
B.Strict uRPF is enabled, but it only checks if the source address is in the routing table, regardless of interface.
C.Loose uRPF is enabled, which only checks if the source address is in the routing table.
D.uRPF is disabled on this interface.

Why A: The output 'IPv6 verify source: strict' indicates that strict unicast Reverse Path Forwarding (uRPF) is enabled on the interface. Strict uRPF verifies that the source IPv6 address of an incoming packet is reachable via the routing table AND that the best return path to that source uses the same interface on which the packet was received. If either condition fails, the packet is dropped. This matches option A exactly.

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