8. Client/Server Message Formats

This section preserves the RFC text for DHCPv6, including message exchanges, relay behavior, DUIDs, IA_NA, IA_TA, IA_PD, DHCP options, RKAP authentication, IANA registries, normative requirements, and appendix option-appearance matrices.

Original RFC Text

8.  Client/Server Message Formats

   All DHCP messages sent between clients and servers share an identical
   fixed-format header and a variable-format area for options.

   All values in the message header and in options are in network byte
   order.

   Options are stored serially in the "options" field, with no padding
   between the options.  Options are byte-aligned but are not aligned in
   any other way (such as on 2-byte or 4-byte boundaries).

   The following diagram illustrates the format of DHCP messages sent
   between clients and servers:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    msg-type   |               transaction-id                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   .                            options                            .
   .                 (variable number and length)                  .
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 2: Client/Server Message Format

   msg-type:  Identifies the DHCP message type; the available message
      types are listed in Section 7.3.  A 1-octet field.

   transaction-id:  The transaction ID for this message exchange.  A
      3-octet field.

   options:  Options carried in this message; options are described in
      Section 21.  A variable-length field (4 octets less than the size
      of the message).