2.9.1. Unicast Addresses

Global Unicast Address (GUA): Routable on the internet (like public IPv4)

• Structure: 48-bit Global Routing Prefix + 16-bit Subnet ID + 64-bit Interface ID
• ISPs assign the prefix; organizations assign subnets; hosts get interface IDs
• Hosts can build their own GUA with SLAAC (Stateless Address Autoconfiguration): they take the /64 prefix from a router's Router Advertisement and generate the interface ID themselves (modified EUI-64 or a random value), so no DHCP server is needed. Stateful DHCPv6 instead has a server assign and track each address.

Unique Local Address (ULA): Private addressing (like RFC 1918)

• FD00::/8 is commonly used
• Not routable on the internet

Link-Local Address: Automatically configured on every IPv6 interface

• Required for IPv6 to function
• Only valid on the local link (not routed)
• Used for neighbor discovery, routing protocols

Loopback (::1/128): the IPv6 equivalent of 127.0.0.1—valid only inside the local host, never sent on a link.