What has been learned from experience with IPv4? First and foremost, more than 32 bits are needed for addresses; the primary motive in developing IPv6 was the specter of running out of IPv4 addresses (something which, at the highest level, has already happened; see the discussion at the end of 1.10 IP - Internet Protocol). Another important issue is that IPv4 requires (or used to require) a modest amount of effort at configuration; IPv6 was supposed to improve this.
- 8.8: IPv6 Host Address Assignment
- IPv6 provides two competing ways for hosts to obtain their full IP addresses. One is DHCPv6, based on IPv4’s DHCP, in which the entire address is handed out by a DHCPv6 server. The other is StateLess Address AutoConfiguration, or SLAAC, in which the interface-identifier part of the address is generated locally, and the network prefix is obtained via prefix discovery.
- 8.15: IPv6-to-IPv4 Connectivity
- What happens if you switch to IPv6 completely, perhaps because your ISP (or phone provider) has run out of IPv4 addresses? Some of the time – hopefully more and more of the time – you will only need to talk to IPv6 servers. For example, the DNS names facebook.com and google.com each correspond to an IPv4 address, but also to an IPv6 address (above). But what do you do if you want to reach an IPv4-only server? Such servers are expected to continue operating for a long time to come.