Just like IPv4, a host can be addressed a number of different ways in IPv6. Typically, an IPv4 host is numbered either statically or via DHCP. Besides assigning IP addresses, DHCP can also provide domain names and DNS server information to hosts.
Dynamic addressing in IPv6 uses the same methods as IPv4 as well as a few others. They are:
Static addressing
Static addressing with stateless DHCPv6
Dynamic addressing via stateful DHCPv6
SLAAC
SLAAC with stateless DHCPv6
Static addressing in IPv6 works exactly the same as in IPv4. DHCP in IPv6 is handled by two different methods – stateful and stateless. Stateful addressing means the DHCP server tracks addresses that are given out. Stateless addressing means the DHCP server does not track information given to clients nor does it assign addresses. Instead, it just assigns other information that is typically assigned with DHCP like DNS servers or domain names. If a host receives stateless DHCP information, the address must be assigned with another method such as via static assignment or SLAAC.
So, what is SLAAC? Stateless Address Autoconfiguration, that’s what (pronounced like slack).
According to Cisco:
SLAAC provides the ability to address a host based on a network prefix that is advertised from a local network router via Router Advertisements (RA). RA messages are sent by default by most IPV6 routers; these messages are sent out periodically by the router and include information including:
- One or more IPv6 prefixes (Link-local scope)
- Prefix lifetime information
- Flag information
- Default device information (Default router to use and its lifetime)
Basically, SLAAC provides the ability for a client to dynamically form the host identifier which is suffixed to the advertised prefix. The advertised prefix must be 64 bits in order for SLAAC to work. The host identifier can either be configured with EUI-64 (same as link local addresses) or with privacy extensions as defined in RFC4941.