The message type field of 1 byte indicates the type of DHCPv6 message. The 3-byte "Transaction ID" field is determined by the client and used to group messages exchanged with DHCPv6 messages. The DHCPv6 option after the transaction ID field is used to indicate the identity, address and other configuration settings of the client and server. For a list of defined DHCPv6 options, please refer to RFC 33 15 quoted in the sidebar "DHCPv6 RFC resources". The format of the DHCPv6 option is the type length value (TLV) format. Figure 2 shows the structure of the DHCPv6 option.
The 2-byte option code field indicates a specific option. The 2-byte option length field indicates the length of the option data field, in bytes. The option data field contains data for the option.
It provides a separate message structure for various messages exchanged between the relay agent and the server to record other information.
Figure 3 shows the structure of various types of messages.
The "hop count" field of 1 byte indicates the number of relay agents that have received the message. If the configured maximum hop count is exceeded, the receiving relay agent can discard the message. The "Link Address" field of 16 bytes contains the unlinked local address assigned to the interface connected to the client subnet. In the Link Address field, the server can determine the appropriate address range for the assigned address. The Peer Address field of 16 bytes contains the IPv6 address of the client that originally sent the message or the relay agent that previously relayed the message. Outside the peer address field is the DHCPv6 option, which includes the relay message option, which contains messages to be relayed and other options. The relay message option provides encapsulation of messages to be exchanged between the client and the server.
There is no broadcast address defined for IPv6. Therefore, for DHCPv6, all _ DHCP _ relay _ agents _ and _ servers address of FF02:: 1:2 is used to replace the restricted broadcast address for some DHCPv4 messages. For example, a DHCPv6 client tries to find the location of a DHCPv6 server on the network and sends a "Request" message to FF02:: 1:2 from its link local address. If there is a DHCPv6 server on the host subnet, it will receive this "request" message and send an appropriate reply. More typically, the DHCPv6 relay agent on the host subnet receives this "request" message and forwards it to the DHCPv6 server to obtain the IPv6 address and configuration settings. DHCPv6 stateful message exchange (when the M and O flags in the receiving router announcement are both set to 1) usually consists of the following messages:
The request message sent by the client to locate the server.
The server sends a notification message, indicating that it can provide the address and configuration settings.
A "request" message sent by a client requesting an address and configuration settings in a specific server.
"Reply" message with address and configuration settings sent by the requesting server.
If there is a relay agent between the client and the server, the relay agent will send a "relay forwarding" message to the server, which contains encapsulated "request" and "request" messages from the client. The server sends the relay agent "relay reply" message, which contains the "announcement" and "reply" messages encapsulated for the client. For a complete list of DHCPv6 messages, please refer to the following table. DHCPv6 message describes that the client needs to send a peer-to-peer DHCP for IPv4 message to locate the server. A DHCPDiscover announcement is sent by the server in response to a request message indicating availability. A client sends a DHCPOffer request to request an address or configuration settings from a specific server. The client sends a DHCPRequest confirmation to all servers to determine whether the configuration of the connected linked client is valid. DHCPReply updates are sent by the client to a specific server to extend the life of the allocated address and obtain updated configuration settings. When no response to the "Update" message is received, the client sends DHCPRequest rebinding to any server. DHCPRequest reply is sent by the server to a specific client when responding to a request, request, update, rebinding, information request, confirmation, publication or rejection message. The client sends a DHCPAck announcement to indicate that the client no longer uses the assigned address. DHCPRelease refuses to be sent by the client to a specific server to indicate that the assigned address is already in use. DHCPDecline reconfiguration is sent by the server to the client to indicate that the server has new or updated configuration settings. Then, the client sends an "update" or "information request" message. Not applicable to the information request sent by the client, which is used to request configuration settings (but does not include the address). DHCPInform relay forwarding is sent by the relay agent to forward the mail to the server. Relay forwards client messages that contain the option to relay messages encapsulated as DHCPv6. The "Not Applicable" relay reply is sent by the server to send a message to the client through the relay proxy. The relay reply contains the server message encapsulated as the DHCPv6 relay message option. The N/A DHCPv6 stateless message exchange (when the M flag is set to 0 and the O flag is set to 1 in the announcement of the receiving router) usually consists of the following messages: an "information request" message sent by the DHCPv6 client requesting configuration settings from the server, and a "reply" message sent by the server containing the requested configuration settings.
For IPv6 networks where routers are configured to assign stateless address prefixes to IPv6 hosts, dual message DHCPv6 exchange can be used to assign DNS servers, DNS domain names and other configuration settings that are not included in router advertisement messages.