EMZETT.IPv6: SLAAC and DHCPv6
In short: In IPv6, devices mostly assign their own address via SLAAC, without a DHCP server. DHCPv6 exists in addition for central management.
In more detail: SLAAC (“stateless address autoconfiguration”) uses router advertisements: the router sends the network prefix, the device appends its own identifier and so forms its address.
In Depth
- Router advertisement (RA): The router announces periodically or on request (router solicitation) the prefix (usually /64), gateway and hints.
- Device identifier: Formerly derived from the MAC address (EUI-64), today from random values (privacy addresses) that change regularly.
- Duplicate check: Before use the device checks via duplicate address detection whether the address is taken.
- DHCPv6: Hands out addresses with bookkeeping (“stateful”) or supplies only extra data such as DNS servers (“stateless”). Android does not support DHCPv6 for addresses, so SLAAC stays important.
- Prefix delegation: The provider gives the router a larger prefix (for example /56 or /60) from which it derives networks for the home.
- Advantage: No NAT needed, every device is in principle directly reachable. A firewall on the router is therefore important.