Both of the stateless and stateful DHCPv6 operations are started with an ICMPv6 RA message from the router. The RA message may have been periodic or solicited by the device using an RS message. The devices start client and server communication when stateless or stateful DHCPv6 is indicated in the RA message. The DHCPv6 operation is started when an RA message indicates stateful or stateless DHCPv6.
The DHCPv6 messages are sent in user datagram protocol (UDP). Messages from the server to the client use UDP destination port 546, and messages from the client to the server use UDP destination port 547.
The DHCPv6 client needs to discover a DHCPv6 server. The client sends a Router SOLICIT (RS) message to the reserved IPv6 multicast all-DHCPv6-servers address FF02::1:2. This multicast address has a link-local scope, which means routers do not forward the messages to other networks.
The available DHCPv6 servers respond with a DHCPv6 ADVERTISE message, which tells the client that the server is available for DHCPv6 service. The client responds with a DHCPv6 REQUEST in case of stateful DHCPv6 and an Information-request in case of stateless DHCPv6 to the server. The figure below illustrates the DHCPv6 operation.
- Stateless DHCPv6 client—The client sends a DHCPv6 INFORMATION-REQUEST message to the DHCPv6 server. The message includes a request only for configuration parameters, such as DNS address. The client generated its IPv6 address with the help of the RA message and a self-generated interface ID. The server replies with the information requested.
- Stateful DHCPv6 client—The client sends a DHCPv6 REQUEST to the DHCPv6 server to get IPv6 address information, including all other configuration parameters.
FAQs
What triggers the start of DHCPv6 operation?
An ICMPv6 Router Advertisement (RA) from the router—either periodic or solicited via RS—indicates stateless or stateful DHCPv6, prompting the client to begin SOLICIT to all servers on FF02::1:2.
How does a stateless DHCPv6 client obtain configuration?
After self-generating its address from RA prefix + interface ID, the client sends an INFORMATION-REQUEST unicast to the server, which replies only with options like DNS—no address is assigned.
What UDP ports are used in DHCPv6 communication?
The client multicasts SOLICIT to the link-local all-DHCPv6-servers address FF02::1:2 so every available server on the same link can respond with ADVERTISE; routers do not forward it.
What is the difference between DHCPv6 REQUEST and INFORMATION-REQUEST?
REQUEST (stateful) asks for IPv6 address + options; INFORMATION-REQUEST (stateless) asks only for options like DNS after the client has already formed its address via SLAAC.
