Internet Protocol version 6 (IPv6) is the next-generation Internet Layer protocol for packet-switched internetworks and the Internet. IPv4 is currently[update] the dominant Internet Protocol version, and was the first to receive widespread use. In December 1998, the Internet Engineering Task Force (IETF) designated IPv6 as the successor to version 4 by the publication of a Standards Track specification, RFC 2460.
IPv6 has a much larger address space than IPv4. This results from the use of a 128-bit address, whereas IPv4 uses only 32 bits. The new address space thus supports 2128 (about 3.4×1038) addresses.
Router ADVertisment Daemon (RADVD): IPv6 has a lot more support for autoconfiguration than IPv4. But for this autoconfiguration to work on the hosts of a network, the routers of the local network have to run a program which answers the autoconfiguration requests of the hosts. On Linux this program is called radvd, which stands for Router ADVertisement Daemon. This daemon listens to router solicitations (RS) and answers with router advertisement (RA). Furthermore unsolicited RAs are also send from time to time.
These RAs contain information, which is used by hosts to configure their interfaces. This information includes address prefixes, the MTU of the link and information about default routers.
Of course the routers can't autoconfigure themself, so the information on the routers has to be provided by the administrator of the system. This is done by manually configuring the interfaces and routes and by configuring the router advertisement daemon.