DHCPv6

DHCPv6 is a network protocol that is used for configuring IPv6 hosts with IP addresses, IP prefixes and/or other configuration required to operate on an IPv6 network.

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.

Operation

Port numbers

DHCPv6 uses UDP port number 546 for clients and port number 547 for servers.

DHCP Unique Identifier

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.

Example

In this example, the server's link-local address is fe80::0011:22ff:fe33:5566 and the client's link-local address is fe80::aabb:ccff:fedd:eeff.

• DHCPv6 client sends a Solicit from [fe80::aabb:ccff:fedd:eeff]:546 for [ff02::1:2]:547.
• DHCPv6 server replies with an Advertise from [fe80::0011:22ff:fe33:5566]:547 for [fe80::aabb:ccff:fedd:eeff]:546.
• DHCPv6 client replies with a Request from [fe80::aabb:ccff:fedd:eeff]:546 for [ff02::1:2]:547. (All client messages are sent to the multicast address). 
• DHCPv6 server finishes with a Reply from [fe80::0011:22ff:fe33:5566]:547 for [fe80::aabb:ccff:fedd:eeff]:546.