Question 1,634 of 2,152

DHCP (IPv4 and IPv6) →hardMultiple ChoiceObjective-mapped

DHCPv6 Client Address Not Used for Outgoing Traffic

This 300-410 practice question tests your understanding of dhcp (ipv4 and ipv6). 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.

A router is configured as a DHCPv6 client on an interface using 'ipv6 address dhcp'. The router receives a valid IPv6 address from the server, but the address is not used for outgoing traffic. Which is the most likely explanation?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

A
The router has a static IPv6 address configured on the same interface, and the DHCP-assigned address is not preferred for source selection.
Correct: If a static address is present, the router may use it as the source, especially if it is in the same subnet as the destination.
B
The DHCPv6 server assigned a temporary address (IA_TA) instead of a non-temporary address (IA_NA).
Why wrong: Incorrect: The 'ipv6 address dhcp' command requests IA_NA, not IA_TA.
C
The router's 'ipv6 unicast-routing' is disabled.
Why wrong: Incorrect: Unicast routing is needed for forwarding, but the address would still be used.
D
The DHCP-assigned address is in a different subnet than the default gateway.
Why wrong: Incorrect: The DHCP server typically assigns an address from the same subnet as the client.

Full breakdown with real-world context →

Quick Answer

The answer is that a static IPv6 address configured on the same interface is preferred over the DHCPv6-assigned address for outgoing traffic. This occurs because the router’s source address selection logic prioritizes manually configured static addresses over dynamically learned ones, even when the DHCPv6 client successfully obtains a valid non-temporary address via the `ipv6 address dhcp` command. On the Cisco CCNP ENARSI 300-410 exam, this tests your understanding of IPv6 source address selection rules and the interaction between static and dynamic addressing on a single interface. A common trap is assuming the DHCPv6 client address is automatically used for all outbound packets, but the router will only use it if no static global unicast address is present or if the static address is removed. Remember the memory tip: “Static beats dynamic for source selection”—the router always favors the manually configured address unless explicitly overridden.

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

✓

The router has a static IPv6 address configured on the same interface, and the DHCP-assigned address is not preferred for source selection.

When a router has both a static IPv6 address and a DHCPv6-assigned address on the same interface, the static address is typically preferred as the source address for outgoing traffic because it is manually configured and considered more stable. The DHCPv6-assigned address, while valid, is not selected as the source unless explicitly preferred via source-interface selection rules or policy. This explains why the address is received but not used.

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.

✓
The router has a static IPv6 address configured on the same interface, and the DHCP-assigned address is not preferred for source selection.
Why this is correct
Correct: If a static address is present, the router may use it as the source, especially if it is in the same subnet as the destination.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The DHCPv6 server assigned a temporary address (IA_TA) instead of a non-temporary address (IA_NA).
Why it's wrong here
Incorrect: The 'ipv6 address dhcp' command requests IA_NA, not IA_TA.
✗
The router's 'ipv6 unicast-routing' is disabled.
Why it's wrong here
Incorrect: Unicast routing is needed for forwarding, but the address would still be used.
✗
The DHCP-assigned address is in a different subnet than the default gateway.
Why it's wrong here
Incorrect: The DHCP server typically assigns an address from the same subnet as the client.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the subtlety that a DHCPv6 client can receive an address but not use it if a static address is present, leading candidates to incorrectly suspect DHCPv6 configuration issues or routing problems.

Trap categories for this question

Command / output trap
Incorrect: The 'ipv6 address dhcp' command requests IA_NA, not IA_TA.

Detailed technical explanation

How to think about this question

IPv6 source address selection follows RFC 6724 rules, which prefer addresses that are assigned to the outgoing interface and are not deprecated. A static IPv6 address is considered 'preferred' and typically has a higher priority than a DHCPv6-assigned address because it is manually configured and has a longer lifetime. In real-world scenarios, this behavior can cause troubleshooting confusion when an administrator expects the DHCPv6 address to be used for traffic, but the router silently uses the static address instead.

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 network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.

Visual reference

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?

DHCP (IPv4 and IPv6) — This question tests DHCP (IPv4 and IPv6) — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The router has a static IPv6 address configured on the same interface, and the DHCP-assigned address is not preferred for source selection. — When a router has both a static IPv6 address and a DHCPv6-assigned address on the same interface, the static address is typically preferred as the source address for outgoing traffic because it is manually configured and considered more stable. The DHCPv6-assigned address, while valid, is not selected as the source unless explicitly preferred via source-interface selection rules or policy. This explains why the address is received but not used.

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.

Are there clue words in this question I should notice?

Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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