Address Selection
Both IPv4 and IPv6 have standard methods for address autoconfiguration. For link-local addressing IPv4 uses the special block 169.254.0.0/16 as described in RFC 3927 while IPv6 hosts use the prefix fe80::/10.
Most IPv4 hosts use link-local addressing (IPv4LL) only as a last resort when a DHCP server is unavailable. An IPv4 host otherwise uses its DHCP-assigned address for all communications, global or link-local. One reason is that IPv4 hosts are not required to support multiple addresses per interface, although many do. Another is that not every IPv4 host implements distributed name resolution (e.g., multicast DNS), so discovering the autoconfigured link-local address of another host on the network can be difficult. However, discovering the DHCP-assigned address of another host also requires either distributed name resolution or a unicast DNS server with this information, and some networks feature DNS servers that are automatically updated with DHCP-assigned host and address information.
IPv6 hosts are required to support multiple addresses per interface; moreover, every IPv6 host is required to configure a link-local address even when global addresses are available. IPv6 hosts may additionally self-configure one or more global addresses on receipt of one or more router advertisement messages, thus eliminating the need for a DHCP6 server; see RFC 4862.
Both IPv4 and IPv6 hosts may randomly generate the host-specific part of an autoconfigured address. IPv6 hosts generally combine a prefix of up to 64 bits with a 64-bit EUI-64 derived from the factory-assigned 48-bit IEEE MAC address. The MAC address have the advantage of being globally unique, a property inherited by the EUI-64. The host is normally required to ensure, through broadcast queries, that the addresses it generates are not in use by any other host on the local network.
The technique is called Link-Local address assignment in RFC 3927. However, Microsoft refers to this as Automatic Private IP Addressing (APIPA) or Internet Protocol Automatic Configuration (IPAC) (supported since at least Windows 98).
Read more about this topic: Zero Configuration Networking
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