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|Internet protocol suite|
IPv6 hosts can acquire IP addresses using stateless address autoconfiguration, or by using DHCPv6. DHCP tends to be preferred at sites where central management of hosts is valued; stateless autoconfiguration does not require any sort of central management, and is therefore preferable in networks where no management is readily available, such as a typical home network.
IPv6 hosts that use stateless autoconfiguration may require information other than an IP address. DHCPv6 can be used to acquire this information, even though it is not being used to configure IP addresses. DHCPv6 is not necessary for configuring Domain Name System servers—they can be configured using Neighbor Discovery Protocol, which is needed anyway for stateless autoconfiguration.
IPv6 routers, such as home routers, must be configured automatically with no operator intervention. Such routers require not only an IPv6 address for use in communicating with upstream routers, but also an IPv6 prefix for use in configuring devices on the downstream side of the router. DHCPv6 Prefix delegation provides a mechanism for configuring such routers.
DHCPv6 uses UDP port number 546 for clients and port number 547 for servers.
The DHCP Unique Identifier (DUID) is used by a client to get an IP address from a DHCPv6 server. It has a minimum length of 12 bytes (96 bits) and a maximum length of 20 bytes (160 bits). Its actual length depends on its type. The server compares the DUID with its database and delivers configuration data (address, lease times, DNS servers, etc.) to the client. The first 16 bits of a DUID contain the DUID type, of which there are three types. The meaning of the remaining 96 bits depend on the DUID type.
In this example, the server's link-local address is
fe80::0011:22ff:fe33:5566 and the client's link-local address is
[ff02::1:2]:547. (All client messages are sent to the multicast address, per section 13 of RFC 3315.)
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