DHCPv6 prefix delegation
========================

| DHCPv6 prefix delegation client implementation is split between
  Control Plane and Data Plane.
| Data Plane can also be used alone by external application (external
  Control Plane) using Data Plane Binary API.

| Number of different IA_PDs managed by VPP is currently limited to 1
  (and corresponding IAID has value 1).
| Client ID is of type DUID-LLT (Link Layer address plus time) and is
  created on VPP startup from avaliable interfaces (or chosen at random
  for debugging purposes).
| Server ID is only visible to Data Plane. Control Plane identifies
  servers by a 32-bit handle (server_index) mapped to Server ID by Data
  Plane.

Control Plane
-------------

| DHCPv6 PD clients are configured per interface.
| When configuring a PD client we have to choose a name of a prefix
  group for that client.
| Each prefix obtained through this client will be flagged as belonging
  to specified prefix group.
| The prefix groups are used as a filter by prefix consumers.

| To enable client on particular interface call Binary API function
  dhcp6_pd_client_enable_disable with param ‘sw_if_index’ set to that
  interface, ‘prefix_group’ set to prefix group name and ‘enable’ set to
  true.
| Format of corresponding Debug CLI command is: “dhcp6 pd client
  [disable]”

To add/delete IPv6 address potentially using available prefix from
specified prefix group call Binary API command
ip6_add_del_address_using_prefix with parameters:
> sw_if_index - software interface index of interface to add/delete
address to/from > prefix_group - name of prefix group, prefix_group[0]
== ‘\\0’ means no prefix should be used > address - address or suffix to
be used with a prefix from selected group > prefix_length - subnet
prefix for the address > is_add - 1 for add, 0 for remove or Debug CLI
command with format: “set ip6 addresses [prefix group ]

.. raw:: html

   <address>

[del]”

| When no prefix is avaliable, no address is physically added, but is
  added once a prefix becomes avaliable.
| Address is removed when all available prefixes are removed.
| When a used prefix is removed and there is other available prefix, the
  address that used the prefix is reconfigured using the available
  prefix.

| There are three debug CLI commands (with no parameters) used to show
  the state of clients, prefixes and addresses:
| show ip6 pd clients
| show ip6 prefixes
| show ip6 addresses

Example configuration
~~~~~~~~~~~~~~~~~~~~~

set int state GigabitEthernet0/8/0 up dhcp6 pd client
GigabitEthernet0/8/0 prefix group my-dhcp6-pd-group set ip6 address
GigabitEthernet0/8/0 prefix group my-dhcp6-pd-group ::7/64

Data Plane
----------

| First API message to be called is dhcp6_clients_enable_disable with
  enable parameter set to 1.
| It enables DHCPv6 client subsystem to receive UDP messages containing
  DHCPv6 client port (sets the router to DHCPv6 client mode).
| This is to ensure client subsystem gets the messages instead of DHCPv6
  proxy subsystem.

| There is one common Binary API call for sending DHCPv6 client messages
  (dhcp6_pd_send_client_message) with these fields:
| > msg_type - message type (e.g. Solicit) > sw_if_index - index of TX
  interface > server_index - used to dentify DHCPv6 server, unique for
  each DHCPv6 server on the link, value obrtained from
  dhcp6_pd_reply_event API message, use ~0 to send message to all DHCPv6
  servers > param irt - initial retransmission time > param mrt -
  maximum retransmission time > param mrc - maximum retransmission count
  > param mrd - maximum retransmission duration for sending the message
  > stop - if non-zero then stop resending the message, otherwise start
  sending the message > T1 - value of T1 in IA_PD option > T2 - value of
  T2 in IA_PD option > prefixes - list of prefixes in IA_PD option

| The message is automatically resent by Data Plane based on parameters
  ‘irt’, ‘mrt’, ‘mrc’ and ‘mrd’.
| To stop the resending call the same function (same msg_type is
  sufficient) with ‘stop’ set to 1.

| To subscribe for notifications of DHCPv6 messages from server call
  Binary API function
| want_dhcp6_pd_reply_events with enable_disable set to 1
| Notification (dhcp6_pd_reply_event) fileds are:
| > sw_if_index - index of RX interface > server_index - used to dentify
  DHCPv6 server, unique for each DHCPv6 server on the link > msg_type -
  message type > T1 - value of T1 in IA_PD option > T2 - value of T2 in
  IA_PD option > inner_status_code - value of status code inside IA_PD
  option > status_code - value of status code > preference - value of
  preference option in reply message > prefixes - list of prefixes in
  IA_PD option

| Prefix is a struct with with these fields:
| > prefix - prefix bytes > prefix_length - prefix length > valid_time -
  valid lifetime > preferred_time - preferred lifetime