Cisco Certified Network Associate (CCNA) 200-301 · Free study guide

Objective 1.9 — Distinguish IPv6 address types

IPv6 address types describe delivery scope and behavior. Identify them from the prefix and use case, then distinguish an address type from the method used to form an interface identifier.

Unicast scopes

Global unicast addresses are intended for ordinary routed unicast reachability. The documentation prefix 2001:db8::/32 appears in examples but should not be treated as production global allocation. Unique-local addresses use fc00::/7 with locally assigned designs commonly under fd00::/8; they support internal routing but are not meant as ordinary global Internet space.

Link-local unicast uses fe80::/10 and is valid only on the local link. Every IPv6-enabled interface has link-local significance, so the same address can appear on different links. A command using a link-local next hop may need an exit interface to remove ambiguity.

Multicast and anycast

Multicast begins with ff00::/8 and delivers to members of a group. IPv6 uses multicast for functions that IPv4 might have used broadcast for. Scope fields limit how far a group applies.

Anycast uses a unicast-format address assigned to more than one interface. The routing system leads a sender to one instance, commonly the nearest under routing policy. There is no special visible anycast prefix that tells you by inspection; the assignment and routing design create the behavior.

Modified EUI-64

Modified EUI-64 can derive a 64-bit interface identifier from a 48-bit MAC address by inserting fffe and toggling the universal/local bit. This is an identifier-formation technique, not an address scope. The resulting address's type still comes from its prefix. Privacy and operational concerns mean many hosts use other identifier methods.

Worked classification

fe80::7 is link-local, fd12:3456:789a::20 is unique-local, and an address beginning ff02 is multicast with link-local scope. A globally routed unicast address could also be configured on several service nodes as anycast; the text alone would look like unicast.

Operational evidence

Inspect interface addresses with their prefixes and scopes. Check multicast membership where relevant. For anycast, inspect repeated assignment and routing advertisements. For modified EUI-64, reconstruct the interface identifier rather than assuming every recognizable MAC-derived pattern is currently used.

Common traps

• Calling unique-local addresses link-local.
• Inventing an IPv6 broadcast type.
• Expecting anycast to have a unique prefix.
• Treating modified EUI-64 as an address scope.
• Assuming link-local addresses are globally unique.

Readiness checklist

• I can recognize link-local, unique-local, global, and multicast prefixes.
• I can explain anycast through routing behavior.
• I can derive the modified EUI-64 steps.
• I include interface context when using link-local addresses.