2.9. IPv6 Address Types

💡 First Principle: IPv6 eliminates broadcast and replaces it with multicast for efficiency. Every IPv6 device has multiple addresses: at least one link-local (for local communication) and typically one global unicast (for internet communication). The prefix tells you the address type—and knowing prefixes is how you'll solve exam questions.

Consider this troubleshooting scenario: A user reports their IPv6 connection doesn't work. You check their interface and see only FE80::1234:5678:abcd:ef01. That's a link-local address—it works for talking to neighbors but can't reach the internet. The device either isn't getting a global address from SLAAC/DHCPv6 or it's misconfigured. Without knowing address types, you might chase DNS or routing issues instead.

What happens without proper IPv6 addressing: Link-local addresses (FE80::) can't cross routers—traffic dies at the first hop. Global addresses from the wrong prefix won't route correctly. Configuring ULA addresses (FD00::) when you need internet access means packets get dropped. Each address type has specific capabilities and limitations.

Why multiple addresses per interface?

• Link-local handles neighbor discovery and local routing—always works, even without a global address
• Global unicast enables internet connectivity—assigned by DHCP or autoconfiguration
• Multicast replaces broadcast—more efficient because devices only process traffic for groups they've joined

Address Types and Prefixes