mediumMultiple Choice
DHCPv6 Prefix Delegation: Delegating vs Requesting Router
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?
⚠ Common exam trap
Cisco often tests the distinction between IA_NA (address assignment) and IA_PD (prefix delegation), and candidates may overlook the IA_PD section, assuming only an address was assigned.
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 DHCPv6 server has assigned both an IPv6 address and a prefix delegation to the client.
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.
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 DHCPv6 server has assigned only an IPv6 address to the client.
Why it's wrong here
The binding shows both an IA NA address (2001:DB8:1::100) and an IA PD delegated prefix (2001:DB8:1::/48), so address-only assignment is contradicted by the prefix entry. It is tempting because IA NA alone is the common case for hosts; prefix delegation applies when the client is a requesting router needing downstream subnets.
- ✓
The DHCPv6 server has assigned both an IPv6 address and a prefix delegation to the client.
Why this is correct
The binding shows an IA NA entry with an assigned address (2001:DB8:1::100) plus an IA PD entry with a delegated prefix (2001:DB8:1::/48), confirming the server provided both address assignment and prefix delegation to the same client.
- ✗
The DHCPv6 client is using stateless autoconfiguration (SLAAC) because no address is shown.
Why it's wrong here
An address is present (2001:DB8:1::100), and SLAAC bypasses DHCPv6 binding state entirely, so no binding would appear. It is tempting because SLAAC also autoconfigures addresses, but it uses router advertisements, not the DHCPv6 server's binding table shown here.
- ✗
The DHCPv6 server has a pool with only one prefix available.
Why it's wrong here
The binding shows one client holding one IA_NA address and one IA_PD prefix; it says nothing about pool size or remaining prefixes, since bindings list active leases only. It tempts because a single prefix appears, but pool exhaustion would require checking pool configuration or statistics, not this per-client binding table.
Visual reference
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Related to this question
Learn chapter
Device Management and Network Monitoring (SNMP, Syslog, NetFlow)
Key term
MPLS Layer 3 VPN
A technology that uses Multiprotocol Label Switching to create secure, scalable virtual private networks that connect multiple sites at the network layer, where the service provider manages routing between customer sites.
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