100-150 Practice Question: A network engineer is configuring IPv6 on a Cisco router interface
A network engineer is configuring IPv6 on a Cisco router interface. The engineer wants to ensure that the interface can automatically generate a link-local address and participate in neighbor discovery without manual configuration. Which IPv6 address type is automatically generated on the interface when IPv6 is enabled?
⚠ Common exam trap
The trap here is assuming that a global unicast address is automatically configured, when in fact only the link-local address is generated without external input.
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
✓
Link-local address
Enabling IPv6 on an interface automatically creates a link-local address, which is essential for neighbor discovery and local link communication. Global unicast and unique local addresses require additional configuration or router advertisements. Multicast addresses are not unicast addresses assigned to the interface.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
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Unique local address
Why it's wrong here
Unique local addresses, in FC00::/7 and in practice FD00::/8, are private IPv6 addresses for use inside an organisation, similar in purpose to RFC 1918 IPv4 ranges. They are not created automatically when IPv6 is enabled; they must be configured manually, through SLAAC from an advertised ULA prefix, or by DHCPv6. Only the link-local address is always generated automatically.
- ✓
Link-local address
Why this is correct
Enabling IPv6 on an interface, with 'ipv6 enable' or by configuring any IPv6 address, automatically creates a link-local address in FE80::/10, on Cisco routers usually from the MAC address using modified EUI-64. Link-local addresses are used for neighbour discovery, router advertisements and routing protocol neighbours, and are never routed. Many engineers set them manually, such as FE80::1, to make gateways easier to read.
- ✗
Multicast address
Why it's wrong here
Interfaces do not get a multicast address as their own address; instead, they join multicast groups. An IPv6 interface automatically joins FF02::1 (all nodes) and, on routers, FF02::2 (all routers), plus a solicited-node group for each unicast address, used by neighbour discovery. These memberships appear in 'show ipv6 interface', but the automatically generated address is the link-local one.
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Global unicast address
Why it's wrong here
Global unicast addresses are routable on the public internet and are typically assigned manually or via DHCPv6 or SLAAC. They are not automatically generated solely by enabling IPv6 on an interface. While SLAAC can create a global address if a router advertisement is received, the link-local address is the one that is always auto-generated.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Security Systems Architect · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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