Question 287 of 2,152

DHCP (IPv4 and IPv6) →hardMultiple SelectObjective-mapped

DHCPv6 Prefix Delegation: Delegating vs Requesting Router

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.

Which TWO statements about DHCPv6 prefix delegation are true? (Choose TWO.)

A
The requesting router uses the IA_NA option to request a prefix.
Why wrong: Incorrect. The requesting router uses the IA_PD (Identity Association for Prefix Delegation) option, not IA_NA (non-temporary address).
B
The delegating router must have a DHCPv6 pool configured with a prefix-delegation statement.
Correct. The delegating router uses a DHCPv6 pool with the 'prefix-delegation' command to define the prefix to be delegated.
C
The requesting router uses the 'ipv6 dhcp client pd' command on its upstream interface to request a prefix.
Correct. This command enables the requesting router to act as a DHCPv6 prefix delegation client on that interface.
D
The delegating router must be configured with 'ipv6 dhcp server' under the downstream interface facing the requesting router.
Why wrong: Incorrect. The 'ipv6 dhcp server' command is used on the delegating router's interface facing the requesting router, but the statement is misleading because the delegating router enables DHCPv6 server functionality on the interface connected to the requesting router, not 'downstream' in the sense of LAN clients.
E
The requesting router can only use the delegated prefix on the interface that received it.
Why wrong: Incorrect. The requesting router can sub-delegate the prefix to downstream interfaces, typically using the 'ipv6 address prefix-from-provider' or similar command to assign /64 subnets from the delegated prefix.

Full breakdown with real-world context →

Quick Answer

The correct answer is that the requesting router uses the 'ipv6 dhcp client pd' command on its upstream interface to request a prefix. This is because DHCPv6 prefix delegation separates the roles of a delegating router, which assigns a larger prefix (e.g., a /48) from a configured pool, and a requesting router, which receives that prefix and sub-delegates smaller /64 prefixes to its downstream interfaces. On the Cisco CCNP ENARSI 300-410 exam, this concept tests your understanding of the IA_PD option—distinct from IA_NA for address assignment—and the correct command placement: the delegating router uses 'ipv6 dhcp server' referencing the pool, while the requesting router uses 'ipv6 dhcp client pd' on the upstream interface. A common trap is confusing the requesting router with the delegating router or misapplying the IA_NA option. Memory tip: think "PD for Prefix Delegation, client on the upstream side."

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 delegating router must have a DHCPv6 pool configured with a prefix-delegation statement.

Option B is correct because the delegating router (DHCPv6 server) must have a DHCPv6 pool configured with a prefix-delegation statement to define the prefix pool from which it can assign prefixes to requesting routers. This is a mandatory configuration for the server to provide prefix delegation as per RFC 3633.

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 requesting router uses the IA_NA option to request a prefix.
Why it's wrong here
Incorrect. The requesting router uses the IA_PD (Identity Association for Prefix Delegation) option, not IA_NA (non-temporary address).
✓
The delegating router must have a DHCPv6 pool configured with a prefix-delegation statement.
Why this is correct
Correct. The delegating router uses a DHCPv6 pool with the 'prefix-delegation' command to define the prefix to be delegated.
Related concept
Read the scenario before looking for a memorised answer.
✓
The requesting router uses the 'ipv6 dhcp client pd' command on its upstream interface to request a prefix.
Why this is correct
Correct. This command enables the requesting router to act as a DHCPv6 prefix delegation client on that interface.
Related concept
Read the scenario before looking for a memorised answer.
✗
The delegating router must be configured with 'ipv6 dhcp server' under the downstream interface facing the requesting router.
Why it's wrong here
Incorrect. The 'ipv6 dhcp server' command is used on the delegating router's interface facing the requesting router, but the statement is misleading because the delegating router enables DHCPv6 server functionality on the interface connected to the requesting router, not 'downstream' in the sense of LAN clients.
✗
The requesting router can only use the delegated prefix on the interface that received it.
Why it's wrong here
Incorrect. The requesting router can sub-delegate the prefix to downstream interfaces, typically using the 'ipv6 address prefix-from-provider' or similar command to assign /64 subnets from the delegated prefix.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the distinction between IA_NA (for addresses) and IA_PD (for prefixes), and the correct placement of the 'ipv6 dhcp server' command on the upstream interface of the delegating router, not the downstream.

Trap categories for this question

Similar concept trap
Incorrect. The requesting router can sub-delegate the prefix to downstream interfaces, typically using the 'ipv6 address prefix-from-provider' or similar command to assign /64 subnets from the delegated prefix.
Command / output trap
Incorrect. The 'ipv6 dhcp server' command is used on the delegating router's interface facing the requesting router, but the statement is misleading because the delegating router enables DHCPv6 server functionality on the interface connected to the requesting router, not 'downstream' in the sense of LAN clients.

Detailed technical explanation

How to think about this question

DHCPv6 prefix delegation (RFC 3633) allows a delegating router to assign a prefix (e.g., /48 or /56) to a requesting router, which then sub-delegates it to downstream networks. The requesting router uses the 'ipv6 dhcp client pd prefix-name' command on its upstream interface to request the prefix, and the delegated prefix can be applied to other interfaces using 'ipv6 address prefix-name sub-bits'. This is commonly used in ISP environments where a CPE router receives a prefix for its LAN segments.

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?

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 delegating router must have a DHCPv6 pool configured with a prefix-delegation statement. — Option B is correct because the delegating router (DHCPv6 server) must have a DHCPv6 pool configured with a prefix-delegation statement to define the prefix pool from which it can assign prefixes to requesting routers. This is a mandatory configuration for the server to provide prefix delegation as per RFC 3633.

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

2 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. An engineer configures DHCPv6 prefix delegation on a Cisco router acting as a requesting client. The router receives a valid IA_PD prefix from the server, but no route for the delegated prefix appears in the routing table. Which is the most likely explanation?

hard

A.DHCPv6 prefix delegation automatically installs a connected route; the issue is a missing 'ipv6 route' command to point the prefix to the DHCP-learned next-hop.
✓ B.The router's 'ipv6 dhcp client pd' command does not install a route; the engineer must manually configure a static route for the delegated prefix.
C.The DHCPv6 server must also send a route option; the requesting client cannot install a route without it.
D.The router's 'ipv6 unicast-routing' is disabled, preventing route installation.

Why B: Option B is correct because the `ipv6 dhcp client pd` command on a Cisco router acting as a DHCPv6 prefix delegation client does not automatically install a route for the delegated prefix into the routing table. The command only assigns the prefix to an interface for use (e.g., with `ipv6 address` commands), but the engineer must manually configure a static route pointing to the DHCP-learned next-hop address to populate the routing table.

Variation 2. A network engineer runs the following command to troubleshoot DHCPv6 address assignment on router R1: R1# show ipv6 dhcp binding Output: Client: FE80::21A:2BFF:FE3C:4D01 DUID: 0003000121A2B3C4D5E6 Username: unassigned VRF: default IA NA: IA ID 0x00040001, T1 302400, T2 483840 Address: 2001:DB8:1::100 Preferred lifetime 604800, valid lifetime 2592000 Expires at Mar 01 2025 12:00 PM (2592000 seconds) IA PD: IA ID 0x00040002, T1 302400, T2 483840 Prefix: 2001:DB8:1::/48 Preferred lifetime 604800, valid lifetime 2592000 Expires at Mar 01 2025 12:00 PM (2592000 seconds) What does this output indicate?

medium

A.The DHCPv6 server has assigned only an IPv6 address to the client.
✓ B.The DHCPv6 server has assigned both an IPv6 address and a prefix delegation to the client.
C.The DHCPv6 client is using stateless autoconfiguration (SLAAC) because no address is shown.
D.The DHCPv6 server has a pool with only one prefix available.

Why B: The output shows both an IA_NA (Identity Association for Non-temporary Address) with an IPv6 address (2001:DB8:1::100) and an IA_PD (Identity Association for Prefix Delegation) with a prefix (2001:DB8:1::/48). This confirms that the DHCPv6 server has assigned both a global unicast address and a delegated prefix to the client, making option B correct.

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