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+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