Use the 128-bit space.
Read the prefix.

Read and abbreviate IPv6 addresses

An IPv6 address is 128 bits, written as eight 16-bit hextets in hexadecimal separated by colons. Leading zeros in a hextet may be omitted. One contiguous sequence of all-zero hextets may be compressed with :: once in an address. The prefix length identifies the network portion, commonly /64 on LANs.

Recognize IPv6 address types

Global unicast addresses are globally routable and come from 2000::/3. Link-local addresses use FE80::/10 and are valid only on the local link. Multicast addresses use FF00::/8. The loopback address is ::1 and the unspecified address is ::. IPv6 does not use broadcast; multicast performs many group-delivery functions.

Configure IPv6 dynamically

A host can use static configuration or learn network information dynamically. SLAAC uses Router Advertisements to help a host create its own global unicast address when the advertised prefix has the Autonomous flag set. With RA flags M=0/O=0, hosts use SLAAC only; M=0/O=1 means SLAAC plus stateless DHCPv6 for other settings; M=1 indicates stateful DHCPv6 address assignment. A link-local address is required on every IPv6-enabled interface for local communication and Neighbor Discovery.

Configure global and link-local addresses

An IPv6-enabled interface needs a link-local address as well as any global unicast address used for routed communication. A link-local address can be generated automatically or assigned manually with the link-local keyword. Modified EUI-64 can derive a 64-bit interface ID by inserting FFFE between the MAC halves and flipping the universal/local bit, but modern systems often use stable or temporary privacy identifiers instead. Do not assume an IPv6 interface ID reveals its hardware MAC.

interface gigabitEthernet 0/0/0
 ipv6 address 2001:db8:acad:1::1/64
 ipv6 address fe80::1 link-local
 no shutdown
show ipv6 interface brief

Use Duplicate Address Detection (DAD) before an address is used. DAD sends a Neighbor Solicitation for the tentative address; if another node responds, the address must not be assigned.

Use Neighbor Discovery and IPv6 multicast

IPv6 uses ICMPv6 Neighbor Discovery rather than ARP. Neighbor Solicitation (NS) and Neighbor Advertisement (NA) resolve neighbors and support DAD. Router Solicitation (RS) asks routers to send Router Advertisements (RA); Redirect tells a host that a better first hop exists. Common link-local multicast groups include FF02::1 (all nodes) and FF02::2 (all routers). Neighbor Solicitation uses a solicited-node multicast address derived from the target address’s low-order 24 bits. This is more selective than sending every solicitation to all nodes.

Plan IPv6 /64 subnets from a /48

With a /48 global routing prefix and /64 LAN prefixes, the 16 bits between them form the subnet ID. This provides 65,536 possible /64 LAN prefixes. For example, 2001:DB8:ACAD:00A2::/64 uses subnet ID 00A2 within 2001:DB8:ACAD::/48. A hierarchical plan may split those 16 bits into site, sub-site, and subnet fields. Concatenate the allocated bit fields to form the fourth hextet, then append ::/64. Keep the /48-to-/64 boundary clear: the interface identifier begins after the first 64 bits.

Choose an IPv4/IPv6 coexistence method

Dual stack runs IPv4 and IPv6 side by side. Tunneling encapsulates one protocol inside the other to cross an incompatible transit network. Translation, such as NAT64, enables communication between IPv6-only and IPv4-only systems. These methods solve different migration constraints; they are not interchangeable and do not replace native end-to-end IPv6 where it is available.

Separate addressing from routing configuration

The main objective of this module is IPv6 addressing. Commands such as ipv6 unicast-routing and ipv6 route ::/0 are useful operational extensions: the first enables a router to forward IPv6 unicast packets, and the second configures an IPv6 default static route. Treat these as routing/configuration enrichment rather than a substitute for mastering address types, GUA/LLA configuration, SLAAC/DHCPv6 behavior, multicast, and subnet IDs.