This file contains notes that cannot be stored in source code but developer
should know.

## RFC 8415

Clients and servers exchange DHCP messages using UDP (see [RFC768]
and BCP 145 [RFC8085]).  The client uses a link-local address or
addresses determined through other mechanisms for transmitting and
receiving DHCP messages.

`All_DHCP_Relay_Agents_and_Servers`: ff02::1:2
`All_DHCP_Servers`: ff05::1:3

Clients listen for DHCP messages on UDP port 546.  Servers and relay
agents listen for DHCP messages on UDP port 547.



                Server                          Server
            (not selected)      Client        (selected)

                  v               v               v
                  |               |               |
                  |     Begins initialization     |
                  |               |               |
     start of     | _____________/|\_____________ |
     4-message    |/ Solicit      | Solicit      \|
     exchange     |               |               |
              Determines          |          Determines
             configuration        |         configuration
                  |               |               |
                  |\              |  ____________/|
                  | \________     | /Advertise    |
                  | Advertise\    |/              |
                  |           \   |               |
                  |      Collects Advertises      |
                  |             \ |               |
                  |     Selects configuration     |
                  |               |               |
                  | _____________/|\_____________ |
                  |/ Request      |  Request     \|
                  |               |               |
                  |               |     Commits configuration
                  |               |               |
     end of       |               | _____________/|
     4-message    |               |/ Reply        |
     exchange     |               |               |
                  |    Initialization complete    |
                  |               |               |
                  .               .               .
                  .               .               .
                  |   T1 (renewal) timer expires  |
                  |               |               |
     2-message    | _____________/|\_____________ |
     exchange     |/ Renew        |  Renew       \|
                  |               |               |
                  |               | Commits extended lease(s)
                  |               |               |
                  |               | _____________/|
                  |               |/ Reply        |
                  .               .               .
                  .               .               .
                  |               |               |
                  |      Graceful shutdown        |
                  |               |               |
     2-message    | _____________/|\_____________ |
     exchange     |/ Release      |  Release     \|
                  |               |               |
                  |               |         Discards lease(s)
                  |               |               |
                  |               | _____________/|
                  |               |/ Reply        |
                  |               |               |
                  v               v               v


The IAID uniquely identifies the IA and MUST be chosen to be unique
among the IAIDs for that IA type on the client (e.g., an IA_NA with
an IAID of 0 and an IA_PD with an IAID of 0 are each considered
unique).  The IAID is chosen by the client.  For any given use of an
IA by the client, the IAID for that IA MUST be consistent across
restarts of the DHCP client.



       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


### RFC 8415: 16. Message Validation


A server MUST discard any Solicit, Confirm, Rebind, or
Information-request messages it receives with a Layer 3 unicast
destination address.