In IPv6 they redid the whole relationship between layer 3 IP stuff and layer 2 link stuff such as ethernet.
* There is no gateway address option in DHCPv6; the only way to find your upstream gateways is by listening to the link-local (fe80::/64) addresses of the senders of the ICMPv6 Router Advertisements.
* IPv4 ARP is replaced by ICMPv6 Neighbor Discovery. You multicast Solicitations to a group based on the last 24 bits of the IPv6 address, and receive a unicast Advertisement response linking the IPv6 address with the ethernet MAC.
Also, in IPv6, client DHCP and address selection strategies are controlled by flags in the router advertisement.
Ole is right that IPv6 doesn't have broadcast, though multicasting to group ff02::1 (link-local all hosts) comes close. Even in IPv4 broadcast is only a link layer concept; it never extended across routing hops.
The minimum number of IPv6 addresses for a host with 1 interface is 5:
1) an fe80:://64 link-local scope address, usually with host part mapped from an ethernet MAC (EUI-64 mapping)
2) an 2::/3 series global-scope address, ditto on the host part
3) ::1 node-scope loopback address
4) listening on link-scope ff02::1 all hosts
5) listening on link-scope ff02::1:ffXX:YYZZ, the neighbor solicitation group corresponding to (1) and (2)
But there could be a lot more addresses, what with the temporary (privacy) versus permanent, deprecated versus preferred, multiple on-link prefixes, different strategies for picking hosts parts (static? DHCPv6? SLAAC? privacy? cryptographic?) etc.
-- James Leinweber, WI State Lab of Hygiene
