DHCP servers have been around for a long time, and they're a pretty common practice in medium to large networks. The purpose for DHCP servers is to allocate IPv4 addresses, DSN addresses, gateway addresses, WINs, and a lot more options if needed. In DHCPv6 there is no difference; it works just like an IPv4 DHCP, but with obvious differences, such as the addresses and the way clients advertise to them.
In IPv4, clients send a discover message, which is in the form of a broadcast looking for a DHCP server to allocate an IP address. In IPv6, RA, and RS processes happens first, so if it finds a DHCP server for use, the RA will come back with the DHCP information to the client, but if does not find a DHCP server, all clients will respond with a DHCP solicit message, which is the following multicast address: ff02::1::2. This looks for all DHCP severs or relay agents...