DHCPv6

DHCPv6, the Dynamic Host Configuration Protocol for IPv6, is the protocol used to automatically assign IPv6 addresses and provide other network configuration parameters to IPv6-enabled devices. Defined in RFC 3315 and updated by subsequent documents, DHCPv6 complements SLAAC by enabling stateful address management and distribution of information such as DNS servers, domain search lists, and other options.

DHCPv6 can operate in two primary modes. In stateful DHCPv6, a server assigns IPv6 addresses to clients and maintains state about each assignment using Identity Associations (IAs) such as IA_NA for addresses and IA_PD for prefixes delegated to the client. In stateless DHCPv6, a client can obtain non-address configuration data from a DHCPv6 server while using SLAAC to configure its own addresses.

DHCPv6 identifies clients with a DUID (DHCP Unique Identifier) and uses servers identified by their DUID. The typical exchange is Solicit, Advertise, Request, and Reply to acquire configuration. Additional message types exist for lease renewal (Renew, Rebind), release, and address confirmation (Confirm). The Information-Request message allows a client to retrieve configuration without obtaining an address. Prefix delegation with IA_PD enables a network to obtain subnets from an upstream provider.

DHCPv6 operates over UDP using client port 546 and server port 547 (servers respond from 547 to 546). Relay agents may forward DHCPv6 messages using Relay-Forward and Relay-Reply, optionally carrying Relay Agent Information (Option 82).

In practice, many networks use DHCPv6 in conjunction with SLAAC, while others rely on DHCPv6 for full stateful configuration or for essential options such as DNS. Security considerations include optional DHCPv6 authentication mechanisms, and deployment boundaries are typically governed by network administration and policy.