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Internet Engineering Task Force                               C. Perkins
INTERNET DRAFT                                          Sun Microsystems
                                                            30 July 1997


    Extensions for the Dynamic Host Configuration Protocol for IPv6
                      draft-ietf-dhc-v6exts-07.txt


Status of This Memo

   This document is a submission by the Dynamic Host Configuration
   Working Group of the Internet Engineering Task Force (IETF).
   Comments should be submitted to the dhcp-v6@bucknell.edu mailing
   list.

   Distribution of this memo is unlimited.

   This document is an Internet-Draft.  Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups.  Note that other groups may also distribute
   working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at
   any time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as ``work in progress.''

   To learn the current status of any Internet-Draft, please check
   the ``1id-abstracts.txt'' listing contained in the Internet-Drafts
   Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net (North
   Europe), ftp.nis.garr.it (South Europe), munnari.oz.au (Pacific Rim),
   ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast).


Abstract

   The Dynamic Host Configuration Protocol for IPv6 [4] (DHCPv6)
   provides a framework for passing configuration information to hosts
   on a TCP/IP network.  Configuration parameters and other control
   information are carried in typed data items that are stored in the
   'extensions' field of the DHCPv6 message.  The data items themselves
   are also called 'extensions.'

   This document specifies the current set of DHCPv6 extensions.  This
   document will be periodically updated as new extensions are defined.
   Each superseding document will include the entire current list of
   valid extensions.






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                                Contents



Status of This Memo                                                    i

Abstract                                                               i

 1. Introduction                                                       1

 2. DHCPv6 Extension Field Format                                      2
     2.1. Character Encoding and String Issues  . . . . . . . . . .    2

 3. IP Address Extension                                               3
     3.1. Client Considerations for the IP Address extension  . . .    6
           3.1.1. Address Lifetimes . . . . . . . . . . . . . . . .    6
           3.1.2. Use with the DHCP Request message . . . . . . . .    7
           3.1.3. Receiving as part of the DHCP Reply message . . .    8
           3.1.4. Use with the DHCP Release message . . . . . . . .    9
     3.2. Server Considerations for the IP Address extension  . . .    9
           3.2.1. Use with the DHCP Advertise message . . . . . . .    9
           3.2.2. Receiving a DHCP Request with the IP Address
                          Extension  . . . . . . . . . . . . . . . .   9
           3.2.3. Use with the DHCP Reply message . . . . . . . . .   10
           3.2.4. Use with the DHCP Reconfigure message . . . . . .   11
           3.2.5. Receiving a DHCP Release with the IP Address
                          Extension  . . . . . . . . . . . . . . . .  11
     3.3. DHCP Relay Considerations . . . . . . . . . . . . . . . .   11

 4. General Extensions                                                11
     4.1. Time Offset . . . . . . . . . . . . . . . . . . . . . . .   12
     4.2. IEEE 1003.1 POSIX Timezone extension  . . . . . . . . . .   12
           4.2.1. IEEE 1003.1 POSIX Timezone specifier  . . . . . .   12
           4.2.2. An Example  . . . . . . . . . . . . . . . . . . .   14
           4.2.3. Timezone 0ption Precedence  . . . . . . . . . . .   14
     4.3. Domain Name Server Extension  . . . . . . . . . . . . . .   15
     4.4. Domain Name . . . . . . . . . . . . . . . . . . . . . . .   15

 5. Application and Service Parameters                                15
     5.1. Directory Agent Extension . . . . . . . . . . . . . . . .   16
     5.2. Service Scope Extension . . . . . . . . . . . . . . . . .   17
     5.3. Network Time Protocol Servers Extension . . . . . . . . .   18
     5.4. Network Information Service Domain Extension  . . . . . .   19
     5.5. Network Information Servers Extension . . . . . . . . . .   19
     5.6. Network Information Service+ Domain Extension . . . . . .   19
     5.7. Network Information Service+ Servers Extension  . . . . .   20



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     5.8. Vendor Specific Information . . . . . . . . . . . . . . .   20

 6. TCP Parameters                                                    21
     6.1. TCP Keepalive Interval Extension  . . . . . . . . . . . .   21

 7. DHCPv6 Extensions                                                 22
     7.1. Maximum DHCPv6 Message Size Extension . . . . . . . . . .   22
     7.2. Class Identifier  . . . . . . . . . . . . . . . . . . . .   22
     7.3. Reconfigure Multicast Address . . . . . . . . . . . . . .   23
     7.4. Renumber DHCPv6 Server Address  . . . . . . . . . . . . .   23
     7.5. Client-Server Authentication Extension  . . . . . . . . .   24
     7.6. Client Key Selection Extension  . . . . . . . . . . . . .   25

 8. End extension specification                                       26

 9. Security Considerations                                           26
     9.1. Replay Protection . . . . . . . . . . . . . . . . . . . .   26
     9.2. Default Authentication Algorithm  . . . . . . . . . . . .   26

10. Defining New Extensions                                           27

11. Acknowledgements                                                  29

Chair's Address                                                       31

Author's Address                                                      31

























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1. Introduction

   This document specifies extensions for use with the Dynamic
   Host Configuration Protocol for IP version 6, DHVPv6.  The full
   description of DHCPv6 message formats may be found in the DHCPv6
   specification document [4].  In this document, several words are used
   to signify the requirements of the specification, in accordance with
   RFC 2119 [5].  These words (MUST, SHOULD, MAY, MUST NOT, etc) are
   often capitalized.

   This document defines the format of information in the last field
   of DHCPv6 messages ('extensions').  The extensions defined within
   this document specify a generalized use of this area for giving
   information useful to a wide class of machines, operating systems
   and configurations.  Sites with a single DHCPv6 server that is
   shared among heterogeneous clients may choose to define other, site-
   specific formats for the use of the 'extensions' field.

   Section 2 of this memo describes the formats of DHCPv6 extensions.
   Information on registering new extensions is contained in section 10.
   The other sections organize the format descriptions of various
   extensions according to their general type, as follows:

    -  IP Address extension

    -  Miscellaneous host configuration

    -  Service Location configuration

    -  Miscellaneous network layer

    -  TCP

    -  Vendor Specific

    -  DHCPv6

   Future applications will make extensive use of an ever-increasing
   number and variety of network services.  It is expected that client
   needs for creating connections with these future network services
   will be satisfied by the Service Location Protocol [21], and not
   DHCPv6.  DHCP is expected to be used for the kinds of configuration
   that enable clients to become fully functional as self-contained
   network entities, but not the kinds of configuration that might be
   required by applications running above the network or transport layer
   protocol levels.





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2. DHCPv6 Extension Field Format

   DHCPv6 extensions have the same format as the BOOTP "vendor
   extensions" [2].  Extensions may be fixed length or variable length.
   All extensions begin with a type field, which is two octets long and
   uniquely identifies the extension.  Fixed length extensions without
   data consist of only the two octet type field.  Only extension 65535
   is fixed length.  All other extensions are variable length with a two
   octet unsigned integer Length field following the type octets.  The
   value of the Length field does not include the four octets specifying
   the type and length.  The Length field is followed by "length" octets
   of data.  In the case of some extensions the length field is a
   constant but MUST still be specified.  In each case, unless otherwise
   specified, the length field specifies the length of the extension in
   octets.  Any extensions defined subsequent to this document should
   contain a Length field even if the length is fixed or zero.  There
   is no particular requirement for alignment of the data fields within
   existing DHCPv6 extensions.

   Unrecognized extensions SHOULD be skipped by ignoring the number of
   octets specified in the length field, and processing continued for
   subsequent extensions.  Unless and until specified otherwise by use
   of extension type 64 (see section 7.1), DHCP entities MUST assume
   that the maximum DHCP message size including extensions is 1500
   octets.

   All multi-octet quantities are in network byte-order.

   Extension types 32768 to 65534 (decimal) are reserved for
   site-specific extensions.

   All of the extensions described in this document will also have their
   default values specified, if any.  Whenever an extension is received
   as part of a DHCP message, any reserved fields of the message MUST
   be ignored, and processing continued as if the reserved fields were
   zero.


2.1. Character Encoding and String Issues

   Certain extensions (e.g., type 16 described in section 5.1) have
   fields which can use various character encodings.  Values for
   character encoding can be found in the Internet Assigned Numbers
   Authority's (IANA) database
         http://www.isi.edu/in-notes/iana/assignments/character-sets
   and have the values referred by the MIBEnum value.  Note that in some
   character sets, each character may require two or more octets of data
   for its representation.



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   The encoding will determine the interpretation of all character data
   in the corresponding fields of particular extensions.  There is no
   way to mix US-ASCII and UNICODE, for example.  All responses MUST be
   in the character set of the request or use US-ASCII. If a request is
   sent to a DHCP server, which is unable to manipulate or store the
   character set of the incoming message, the request will fail.  The
   server returns a status code of 24in a DHCP Reply message in this
   case.  Requests using US-ASCII (MIBEnum value == 3) will never fail
   for this reason, since all DHCP entities MUST be able to accept this
   character set.  All DNS-related strings are presumed to be encoded in
   US-ASCII.


3. IP Address Extension

   The IP Address extension is the most essential of all the DHCPv6
   extensions.  It can be used by both client and server in various
   ways.  Since the IP Address extension can be used more than once in
   the same DHCP message, all information relevant to a particular IPv6
   allocation has to be collected together in the same extension.  Some
   of the fields within the IP Address extension can specify how DNS may
   be updated [22].

   To ask for an IP address in a DHCP Request message, a client includes
   an IP Address Extension.  To renew or extend the lifetime of a
   particular IP address, the client puts that address in the client
   address field.  To request the allocation of a new but unspecified IP
   address, the client omits the client address field.  The IP address
   returned by the server in the latter case will be compatible with a
   subnet prefix of the link to which the client is currently attached.





















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   An IP Address Extension can contain at most one IP address.  To
   specify more than one IP address, multiple extensions are used.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   pfx-size    |    status     |C|L|Q|A|P|      reserved       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         (if present)                          |
   |                    client address (16 octets)                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          (if present) preferred lifetime (4 octets)           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            (if present) valid lifetime (4 octets)             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         (if present) DNS name (variable length)  ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type     1

      Length   (unsigned integer, variable) The length of the Extension
               in octets.

      pfx-size
               If the client address is present (the 'C' bit is set), a
               nonzero pfx-size is the number of leftmost bits of the
               client's IPv6 address which make up the routing prefix.
               Otherwise, if the 'C' bit is not set, pfx-size MUST be
               zero.

      status   If the server is unable to honor the client's request,
               the reason is indicated in the status.

      C        If the 'C' bit is set, the field containing the IP
               address for the client is present in the extension.

      L        If the 'L' bit is set, the preferred and valid lifetimes
               are present in the extension.

      Q        If the 'Q' bit is set, the fields included by the client
               are required, and must be made available by the server or
               else the extension must be rejected.

      A        If the 'A' bit is set, the client requests that that
               the the server updates DNS with a new AAAA record, as
               specified by the client's FQDN.



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      P        If the 'P' bit is set, the client requests that that
               the the server updates DNS with a new PTR record, as
               specified by the client's FQDN.

      reserved MUST be zero.

      client address
               The IP address to be allocated by the server for use by
               the client (16 octets long).

      preferred lifetime
               The preferred lifetime of the IP address in seconds

      valid lifetime
               The valid lifetime of the IP address in seconds

      DNS name
               The DNS name (a null-terminated string of ASCII octets)
               to be used by the client (variable length).

   The following values for the status field are defined within this
   document:

        0   request granted, no errors
       18   Security parameters failed for this client
       20   Resource AAAA Record Parameter Problem
       21   Resource PTR Record Parameter Problem
       22   Unable to honor required extension parameters
       23   DNS name string error
       33   The name server was unable to interpret the request
          due to a format error.
       34   dynDNS Not Available at this time
       35   Some name that ought to exist, does not exist.
       36   The name server does not support the specified Opcode.
       36   dynDNS Not Implemented
       37   The name server refuses to perform the specified
          operation for policy or security reasons.
       38   Some name that ought not to exist, does exist.
       39   Some RRset that ought not to exist, does exist.
       40   Some RRset that ought to exist, does not exist.
       41   The server is not authoritative for the zone named in
          the Zone Section.
       42   A name used in the Prerequisite or Update Section is
          not within the zone denoted by the Zone Section.
       34   Authoritative DNS Server could not be found

   Status values 34through 21are described more fully within RFC
   2136 [22].  Up-to-date values for the values of the status field are



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   specified in the most recent "Assigned Numbers" [17].  To inform the
   client of the DYNDNS [22] error return codes (i.e., nonzero return
   codes) received by the DHCPv6 server the client MUST assume the
   status codes 32 through 42 are formed as follows:

      status code = 32 + DYNDNS Error Code

   The DNS name can be a host name, which does not contain the '.'
   ASCII character as a separator between DNS hierarchy components.  Any
   name containing the '.'  is treated as a Fully Qualified Domain Name
   (FQDN). The length of the DNS name may be determined by subtracting,
   from the Length, the length of those fixed length fields which are
   present.  If the last octet of the DNS name is not zero, the IP
   Address Extension MUST be rejected, with status 23.

   If the 'Q' bit is set, the values or actions requested by the C, L,
   A, and P bits are required, and MUST be provided, or the extension
   MUST be rejected with status code 22.

   If the 'Q' bit is set, and if the 'A' bit is set, the server MUST
   ensure that the DNS is updated with a new AAAA record, as specified
   by the client's FQDN, before responding with the corresponding DHCP
   Reply.  Likewise, if the 'Q' bit is set, and if the 'P' bit is
   set, the server MUST ensure that the DNS is updated with a new PTR
   record, as specified by the client's FQDN, before responding with the
   corresponding DHCP Reply.

   A DHCP client can include an IP address in its IP Address extension
   and set the 'A' bit and/or 'P' bit to ask the DHCP Server to use that
   address for updating DNS. This can be done even with IP addresses
   obtained by Stateless Address Autoconfiguration [20].


3.1. Client Considerations for the IP Address extension

3.1.1. Address Lifetimes

   An IP address returned to a client has a preferred and valid
   lifetime.  The valid lifetime represents the lease for addresses
   provided to the client, from the server.

   The client SHOULD make a new Request for any address that is about
   to expire, or request a new address or the same address before the
   lease actually expires.  If the client does not make a new Request
   for an address, the server SHOULD assume the client does not want
   that address.  The server MAY provide that address to another client
   requesting an address.




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   The client MAY request values for the lifetimes, but the client MUST
   use the lifetimes provided by the server response.

   When the preferred lifetime of an IP address expires, the client's
   address becomes a deprecated address.  See [8] for required handling
   of deprecated IP addresses.  Before an address for a DHCPv6 client's
   interface becomes deprecated, the client SHOULD request a new address
   for that interface, or make a new DHCP Request for the existing
   address (which can result in the address receiving an updated
   preferred lifetime).

   When the client requests an IP address from the DHCPv6 server, the
   client MUST keep track of when the request was issued.  When the
   client receives a successful reply from the DHCPv6 server, it MUST
   decrement the received Lifetimes by the amount of time between the
   transmission of the DHCP Request and the reception of the DHCP Reply.
   In this way, the client is best assured that its address lifetimes
   will not expire at the DHCP Server before they expire at the client.


3.1.2. Use with the DHCP Request message

   In a DHCP Request (for each address extension), a client MUST set the
   status code to zero.

   In a DHCP Request (for each address extension), a client MAY:

    -  include an IP address and/or a DNS name (which may be a host name
       or a FQDN).

    -  set the 'A' bit to request that the server update DNS with a new
       AAAA record, as specified by the client's FQDN; if the 'Q' bit is
       also set, this update MUST be completed before responding with
       the corresponding DHCP Reply.

    -  set the 'P' bit to request that the server update DNS with a new
       PTR record, as specified by the client's FQDN; if the 'Q' bit is
       also set, this update MUST be completed before responding with
       the corresponding DHCP Reply.

    -  indicate the minimum preferred (and/or valid) lifetime, by
       supplying a value for the field(s).

    -  specify whether address, name and lifetimes (if present) are
       advisory -or- mandatory, by setting the 'Q' bit.

   If the Request is advisory, a server may send different parameters
   than requested in the DHCP Reply.  Otherwise, if the Request is



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   mandatory, the server MUST reject the Request if it cannot be
   fulfilled.  A server can always supply a greater value for the
   lifetimes than that requested by the client, even if the 'Q' bit is
   set.  If the client wishes to have a smaller lifetime than the server
   supplies, the client MAY use the DHCP Release mechanism to relinquish
   it.

   A client may include multiple IP Address extensions in a single DHCP
   Request.  The server that receives the Request is not absolutely
   required to honor the client's Request.  A DHCP client indicates that
   it cannot accept anything other than the configuration information
   (e.g., IP address) listed in the IP Address extension to the DHCP
   Request, by specifying the 'Q' (Required) bit.

   When a client requests an IP address, it MUST maintain a record for
   the server which allocates that address, so that the client can (if
   necessary) in the future

    -  Extend the lifetime with the same server, or

    -  Release the address, using DHCP Release.

   Note that if a client wishes to specify a lifetime for its IP
   address, it normally only needs to specify a value for the preferred
   lifetime, not the valid lifetime.


3.1.3. Receiving as part of the DHCP Reply message

   When the client receives an IP address extension as part of a DHCP
   Reply which it accepts (see [4]), it first inspects the status to see
   whether the requested information has been granted.  If the status is
   nonzero, the client should log the error, display the error condition
   for action by the user and/or the network administrator.  Nonzero
   status almost always indicates that the client will be need to modify
   its request before it could be satisfied by the replying DHCP server,
   or alternatively that the replying DHCP server will need to be given
   updated configuration information for the client.

   Upon reception of a new IP address with a lifetime, the client MUST
   perform Duplicate Address Detection (DAD) [20]; however, if the
   address has already been allocated to the client and it is merely
   renewing the lifetime of the address, the client does not have to
   perform DAD each time.  If the client receives an IP address with
   zero valid lifetime, the client MUST immediately discontinue using
   that IP address.





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3.1.4. Use with the DHCP Release message

   In DHCP Release (for each address extension):

    -  the client may include an IP address and/or a DNS name (which may
       be a host name or a FQDN).

    -  the server MUST update DNS to delete the AAAA record or records
       that the server originally used when updating DNS when the
       address was allocated to the client, and likewise for the PTR
       record (regardless of the setting of the 'A' or 'P' bits in the
       address extension).

    -  If the client, on the other hand, took charge of the DNS updates,
       it MUST perform the corresponding deletions before issuing the
       DHCP Release.

   If the DNS name is provided ONLY all client AAAA records for that
   name will be deleted.


3.2. Server Considerations for the IP Address extension

3.2.1. Use with the DHCP Advertise message

   In DHCP Advertise (for each address extension), the Server can
   indicate:

    -  the cllient's FQDN or host name

    -  the preferred lifetime

    -  whether DNS will accept new names for the address (via the 'A'
       bit)

   If the server sets the 'A' bit, it is willing to perform DNS updates
   to AAAA records on behalf of the client.  Likewise, if the server
   sets the 'P' bit, it is willing to perform DNS updates to PTR records
   on behalf of the client.


3.2.2. Receiving a DHCP Request with the IP Address Extension

   When a server receives a request for an IP address, it consults its
   allocation tables and determines an IP address appropriate for the
   requesting client and the subnet to which the client is attached.
   The subnet can be determined by the Agent address in the DHCP Request
   message header, or, when there is no relay, by the subnet of the



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   interface on which the request was received.  This is true in the
   latter case because the client and the server have to be on the same
   subnet when there is no Agent address included in the message header.

   If the client has requested that the server perform DNS updates as
   part of the IP address allocation and configuration, the server
   MUST maintain this fact as part of the client's binding.  Then, if
   the client eventually releases the IP address (see the DHCP Releas
   message in [4]), the server MUST perform the reverse service by
   updating DNS again as needed.


3.2.3. Use with the DHCP Reply message

   In a DHCP Reply message (for each address extension) the server MUST
   indicate in the IP address extension

    -  the preferred lifetime

    -  the valid lifetime

    -  the status of the request

   If the Reply is a response to a DHCP Release, the lifetimes MUST both
   be zero.

   In a DHCP Reply message, for each address extension) the server MAY
   indicate

    -  the DNS name

    -  whether AAAA has been DNS updated (by setting the 'A' bit)

    -  whether PTR has been DNS updated (by setting the 'P' bit)

   If the client requests updates, and sets the 'Q' bit, the server MUST
   NOT issue the DHCP Reply until after receiving positive indication
   that the DNS update has indeed been performed.  If the 'Q' bit has
   been set, and the server cannot honor the IP address extension, it
   MUST return a DHCP reply with the status 22.

   Otherwise, the client can subsequently update DNS if needed (i.e.,
   the server didn't do it).

   If the server receives a DHCP Request from one of its clients
   whose address it wishes to invalidate, it can cause the client to
   discontinue use of the old address by including valid and preferred
   lifetimes with a value of zero.



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   To perform renumbering, the server will include two IP address
   extensions, one to reduce the zero out the preferred lifetime and
   reduce the valid lifetime for the old address, and another to give
   the client its new address.

   On a practical note, note also that if the DHCP administrator uses
   site-local addresses for IP address allocation to clients, there will
   be less need for renumbering whenever the site moves to a new site
   prefix or set of site prefixes.


3.2.4. Use with the DHCP Reconfigure message

   In DHCP Reconfigure (for each address extension) the server MAY
   indicate the DNS name.


3.2.5. Receiving a DHCP Release with the IP Address Extension

   When a DHCP client releases its IP address, by including an
   appropriate IP Address Extension with the DHCP Release message, the
   server determines whether or not it was originally responsible for
   updating the DNS AAAA record or PTR record for the client.  If so,
   then the server must also perform the reverse service by updating DNS
   again to delete the client records.


3.3. DHCP Relay Considerations

   The DHCP Relay MUST NOT change any information in any DHCPv6
   Extension fields.  All Extension information flows between DHCPv6
   Server and DHCPv6 Client without modification by any Relay.


4. General Extensions

   The following extensions are important for many DHCPv6 clients, and
   are not specific to any upper-level protocol.













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4.1. Time Offset

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Type              |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Time Offset                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Type for the time offset extension is 2, and its Length is 4
   octets.  The time offset field specifies the offset of the client's
   clock in seconds from Coordinated Universal Time (UTC). The offset is
   expressed as a signed (two's complement) 32-bit integer.


4.2. IEEE 1003.1 POSIX Timezone extension

   DHCP includes an extension for the specification of the Universal
   Coordinated Time Offset (type 2, defined in section 4.1), which is
   defined as a two's complement 32-bit integer representing the offset
   in seconds from UTC. Unfortunately, the UTC offset extension does not
   provide enough information for an Internet client to determine such
   timezone-related details as the timezone names, daylight savings time
   start and end times in addition to the timezone UTC offsets.  This
   extension (analogous to that proposed for DHCPv4 [6]) allows delivery
   of timezone information in the form of a IEEE 1003.1 POSIX Timezone
   specifier [10].

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Type              |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    IEEE 1003.1 POSIX Timezone string (variable length) ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The extension type is 3.  This IEEE 1003.1 POSIX Timezone is detailed
   next, in section 4.2.1.


4.2.1. IEEE 1003.1 POSIX Timezone specifier

   .

   The format of the IEEE 1003.1 POSIX timezone string is specified as

      StdOffset[Dst[Offset],[Start[/Time],End[/Time]]]



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   where '[' and ']' enclose optional fields, '|' indicates choice
   of exactly one of the alternatives, ',' and '/' represent literal
   characters present in the string, and:

      Std      three or more octets for the standard timezone (Std).
               Any characters (or case) except a leading colon, digits,
               comma, minus or plus sign are allowed.

      Offset   Indicates the value one must add to local time to
               arrive at UTC, of the form:  [+|-]hh[:mm[:ss]].  Offset
               following Std is required.  Digits are always interpreted
               as decimal number.  If preceded by a '-', the timezone is
               east of the Prime Meridian, otherwise it is west ('+' is
               optional) The permissible values for hh[:mm[:ss]] are as
               follows:

                  hh       0 <= hh <= 23

                  mm       0 <= mm <= 60

                  ss       0 <= ss <= 60

               Offset has no default value.

      Dst      three or more octets for the daylight savings timezone.
               If Dst is missing, then daylight savings time does not
               apply in this locale.  If no Offset follows Dst, then
               Dst is assumed to be one hour ahead of standard time.
               Any characters (or case) except a leading colon, digits,
               comma, minus or plus sign are allowed.

      Start    Indicates the day of the year, in one of the formats
               indicated below, when to change to daylight savings time.
               The 'Time' field (which follows immediately after a '/'
               character, if present) indicates when the change is made,
               in local time.

      End      Indicate the day of the year, in one of the formats
               indicated below, when to change back from daylight
               savings time.  The 'Time' field (which follows
               immediately after a '/' character, if present) indicates
               when the change is made, in local time.

      Time     Time has the same format as Offset, except that no
               leading '-' or '+' is permitted.  The default is
               02:00:00.

   The day of the year can be given in one of the following formats:



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      Jn       The julian day n, (1 <= n <= 365).  Leap days are not
               counted.

      n        zero-based julian day, (0 <= n <= 365).  Leap days are
               counted so it is possible to refer to Feb 29.

      Mm.n.d   The 'd'th day, (0 <= d <= 6) of week 'n' of month 'm' of
               the year (1 <= n <= 5, 1 <= m <= 12, where week 5 means
               last 'd' day in month 'm' which may occur in either the
               fourth or the fifth week.  Week '1' is the first week in
               which the 'd' day occurs.


4.2.2. An Example

   For Eastern USA time zone, 1986, the Posix timezone string is as
   follows:

      EST5EDT4,116/02:00:00,298/02:00:00


4.2.3. Timezone 0ption Precedence

   If a DHCP client receives both the Time Offset (type 2) and the POSIX
   Timezone (type 3) extension in a DHCP reply message, the client MUST
   discard the value of the Time Offset (type 2) extension and utilize
   the POSIX Timezone Option.  The DHCP client MAY notify the user that
   it is resolving the conflict by discarding the Time Offset (type 2)
   extension.

   If a DHCP client finds that the POSIX Timezone extension value is
   misformatted, it SHOULD notify the the user of the problem and MUST
   discard the entire extension value.


















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4.3. Domain Name Server Extension

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Type              |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Domain Name System server addresses              |
   |                       (16 octets each)                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The domain name server extension specifies a list of Domain Name
   System [16] name servers available to the client.  Servers SHOULD be
   listed in order of preference.

   The Type for the domain name server extension is 6.  The minimum
   Length for this extension is 16 octets, and the Length MUST always be
   a multiple of 16.


4.4. Domain Name

   This extension specifies the default domain name that client should
   use when resolving hostnames via the Domain Name System.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Domain Name (variable length)  ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Type for this extension is 10.  Its minimum Length is 1.

   The domain name is a null-terminated ASCII string, Length octets in
   size, including the terminating zero octet.

   If the Domain Name extension is not specified, and the IP Address
   extension received by a client contains a FQDN, then the client may
   take the part of the FQDN after the first '.'  octet as the Domain
   Name.


5. Application and Service Parameters

   This section details some miscellaneous extensions used to configure
   miscellaneous applications and services.



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5.1. Directory Agent Extension

   Entities using the Service Location Protocol [21] need to find out
   the address of Directory Agents in order to transact messages.  They
   may need to discover the correct scope to be used in conjunction with
   the service attributes which are exchanged using the Service Location
   Protocol.  The scope MAY be denoted in any standardized character
   set.

   This extension requests or specifies a Directory Agent (DA), along
   with zero or more scopes supported by that DA. Note that this
   extension MAY be included multiple times in the same DHCP Request or
   DHCP Reply.  If so, then the extensions SHOULD be included in order
   of decreasing preference.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Char Encoding         |   DA length   |D|M|F|S|  rsv  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Directory Agent (variable length) ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        (if present) Service Scope (variable length) ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type     16

      Length   (unsigned integer, variable) The length of the Extension
               in octets.

      Char Encoding
               The standardized encoding for the characters denoting the
               scope.

      DA Length (unsigned integer, variable) The length of the Directory
               Agent field in octets.

      D        If the 'D' bit is set, the Directory Agent field is
               present.

      M        If the 'M' bit is set, the Directory Agent address is
               the only one that may be used, and multicast methods for
               discovering Directory Agents MUST NOT be used.

      F        If the 'F' bit is set, the Directory Agent is indicated
               by including its variable length host name or Fully



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               Qualified Domain Name (FQDN) instead of its 16 octet IP
               address.

      S        If the 'S' bit is set, the scope is present, encoded in
               the indicated character set.

      rsv      reserved; ignored upon reception; MUST be sent as zero

      Directory Agent
               The Fully Qualified Domain Name (FQDN), host name,
               or IP address of the Directory Agent (see following
               description).

      Service Scope
               The characters denoting the scope.  The length of the
               scope is only indicated implicitly by the overall length
               of the extension.

   In order to simplify administration of the configuration of Directory
   Agents for Service Location Protocol clients, the Directory Agent
   can be indicated by presenting its FQDN or host name instead of its
   IP address.  This allows renumbering to proceed more smoothly [7].
   When the FQDN or host name is used, the server sets the 'F' bit.  The
   host name can be distinguished from the FQDN by the presence of a '.'
   character.  In any case, the DA length field is set to be the length
   of the Directory Agent field.  When the 'F' bit is not set, the DA
   Length MUST be 16.

   Note that more than one Directory Agent extension may be present in
   a DHCP message.  Each such extension may have the same or different
   scope.  The client may request any Directory Agent with a particular
   scope, by including the Directory Agent extension in a DHCP Request
   message with no Directory Agent address included (the 'D' bit set to
   zero), and the characters denoting the scope.


5.2. Service Scope Extension

   This extension indicates a scope that should be used by a Service
   Agent (SA) [21], when responding to Service Request messages as











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   specified by the Service Location Protocol.  This extension MAY be
   included multiple times in the same DHCP Request or DHCP Reply.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Char Encoding         |         Service Scope ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type     17

      Length   (unsigned integer, variable) The length of the Extension
               in octets.

      Char Encoding
               The standardized encoding for the characters denoting the
               scope.

      Service Scope
               the characters denoting the scope.

   Note that more than one Service Scope extension may be present in a
   DHCP message.  The length of the scope is only indicated implicitly
   by the overall length of the extension.


5.3. Network Time Protocol Servers Extension

   This extension specifies a list of IP addresses indicating NTP [14]
   servers available to the client.  Servers SHOULD be listed in order
   of preference.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     NTP server addresses                      |
   |                       (16 octets each)                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The type for this extension is 18.  Its minimum Length is 16, and the
   Length MUST be a multiple of 16.






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5.4. Network Information Service Domain Extension

   This extension specifies the name of the client's NIS [13] domain.
   The domain is formatted as a character string consisting of
   characters from the US-ASCII character set.

   The type for this extension is 19.  Its minimum Length is 1.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              NIS Domain Name (variable length)  ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


5.5. Network Information Servers Extension

   This extension specifies a list of IP addresses indicating NIS [13]
   servers available to the client.  Servers SHOULD be listed in order
   of preference.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     NIS server addresses                      |
   |                       (16 octets each)                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The type for this extension is 20.  Its minimum Length is 16, and the
   Length MUST be a multiple of 16.


5.6. Network Information Service+ Domain Extension

   This extension specifies the name of the client's NIS+ [13]
   domain.  The domain is formatted as a character string consisting of
   characters from the US-ASCII character set.










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   The type for this extension is 21.  Its minimum Length is 1.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              NIS+ Client Domain Name (variable length)  ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


5.7. Network Information Service+ Servers Extension

   This extension specifies a list of IP addresses indicating NIS+ [13]
   servers available to the client.  Servers SHOULD be listed in order
   of preference.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     NIS+ server addresses                     |
   |                       (16 octets each)                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The code for this extension is 22.  Its minimum Length is 16, and the
   Length MUST be a multiple of 16.


5.8. Vendor Specific Information

   This extension is used by clients and servers to exchange vendor-
   specific information.  The information is an opaque collection of
   data, presumably interpreted by vendor-specific code on the clients
   and servers.  The definition of this information is vendor specific.
   The vendor is indicated in the class-identifier extension.  Servers
   not equipped to interpret the vendor-specific information sent by a
   client MUST ignore it (although it may be reported).  Clients which
   do not receive desired vendor-specific information SHOULD make an
   attempt to operate without it, although they may do so (and announce
   they are doing so) in a degraded mode.

   If a vendor encodes more than one item of information in this
   extension, then the vendor MUST encode the extension using
   "Encapsulated vendor-specific extensions" as described below:





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   The Encapsulated vendor-specific extensions field MUST be encoded
   as a sequence of type/length/value fields of identical syntax to
   the fields defined in every other DHCPv6 extension.  Extension
   65535 (END), if present, signifies the end of the encapsulated
   vendor extensions, not the end of the vendor extensions field.
   If no extension 65535 is present, then the end of the enclosing
   vendor-specific information field is taken as the end of the
   encapsulated vendor-specific extensions field.

   The Type for this extension is 31 and its minimum Length is 4.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Vendor-specific extension information  ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   When encapsulated vendor-specific extensions are used, each one has
   the same format as just shown.  In other words, all vendor-specific
   extensions are encoded in Type-Length-Value (TLV) format.  More than
   one vendor-specific extension can, therefore, be included in the same
   DHCP "Vendor Specific Information" extension.


6. TCP Parameters

   This section lists the extensions that affect the operation of the
   TCP layer on a per-interface basis.


6.1. TCP Keepalive Interval Extension

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Keepalive Time Interval                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This extension specifies the interval (in seconds) that the
   client TCP should wait before sending a keepalive message on a TCP
   connection.  The time is specified as a 32-bit unsigned integer.
   A value of zero indicates that the client should not generate
   keepalive messages on connections unless specifically requested by an
   application.



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   The Type for this extension is 32, and its Length is 4.


7. DHCPv6 Extensions

   This section details the extensions that are specific to DHCPv6.


7.1. Maximum DHCPv6 Message Size Extension

   This extension specifies the maximum size in octets of any DHCPv6
   message that the sender of the extension is willing to accept.  The
   size is specified as an unsigned 16-bit integer.  A client may use
   the maximum DHCPv6 message size extension in DHCP Request messages,
   but SHOULD NOT use the extension in DHCP Solicit messages (see [4]),
   and MUST NOT use the extension in other DHCP messages.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Max DHCPv6 Message Length   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Type for this extension is 64, and its Length is 2.  The minimum
   permissible value is 1500.


7.2. Class Identifier

   This extension is used by a DHCP client to optionally identify the
   type or category of user or applications it represents.

   DHCP administrators may define specific class identifiers to convey
   information about a client's software configuration or about its
   user's preferences.  For example, an identifier may specify that
   a particular DHCP client is a member of the class "accounting
   auditors", which have special service needs such as a particular
   database server.  Alternatively, the identifier may encode the
   client's hardware configuration.

   Servers not equipped to interpret the class identifier specified by
   a client MUST ignore it (although it may be reported).  Otherwise,
   servers SHOULD respond with the set of extensions corresponding to
   the class identifier specified by the client.  Further, if the server
   responds with the set of extensions corresponding to the given class




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   identifier, it MUST return this extension (with the given class
   identifier value) to the 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Char Encoding         |        Class Identifier ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The class identifier is a string of characters in the character
   set specified by the Char Encoding field (see section 2.1), of
   length "Length"-2 octets.  The class identifier represents the class
   identifier of which the client is a member.


7.3. Reconfigure Multicast Address

   A DHCPv6 server can instruct its clients to join a multicast group
   for the purposes of receiving DHCPv6 Reconfigure messages.  This will
   allow a server to reconfigure all of its clients at once; such a
   feature will be useful when renumbering becomes necessary.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Reconfigure Multicast Address                |
   |                          (16 octets)                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Type of the Reconfigure Multicast Address is 66, and the Length
   is 16.


7.4. Renumber DHCPv6 Server Address

   A DHCPv6 server can instruct its clients to change their internal
   records to reflect the server's newly renumbered IP address, by using
   the "Renumber DHCPv6 Server Address" extension.  This extension may
   be sent with the DHCP Reconfigure message, and thus can be multicast








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   to all of the server's clients instead of being unicast to each one
   individually.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   New DHCPv6 Server Address                   |
   |                          (16 octets)                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Type of the Renumber DHCPv6 Server Address is 67, and the Length
   is 16.


7.5. Client-Server Authentication Extension

   Exactly one Client-Server Authentication Extension MAY be present
   in any DHCPv6 message transmitted between a client and server (or
   vice-versa).  If present, it MUST be the last extension.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Security Parameters Index (SPI)               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Replay Protection                      |
   |                           (8 octets)                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Authenticator (variable length) ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type     84

      Length   (unsigned integer, variable) 4 for the SPI, plus 8 for
               the replay protection, plus the number of octets in the
               Authenticator.

      SPI      A Security Parameters index [3] identifying which
               security context among those available between the DHCPv6
               client and server.

      Replay Protection
               A 64-bit timestamp (in Network Time Protocol [15](NTP)
               format) (see section 9.1).



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      Authenticator
               (variable length) (See Section 9.2.)

   This authentication extension remedies the inability of IPsec to
   provide for non end-to-end authentication, since authentication is
   needed even when the client has no IPv6 address of large enough scope
   to reach the DHCP server.  The extension can be originated by either
   the DHCPv6 Client or DHCPv6 server to authenticate the rest of the
   data in the DHCPv6 message.  The default authentication algorithm is
   defined in section 9.2.

   Note that SPI values 0 through 255 are reserved and, if used, MUST
   conform to the security context defined by that value in the most
   recent Assigned Numbers RFC (e.g., [18]).


7.6. Client Key Selection Extension

   A DHCPv6 server may wish to indicate to a prospective client which
   SPI it must use to authenticate subsequent messages, using the
   Client-Server Authentication Extension.  In such cases, the server
   includes the Client Key Selection Extension in its DHCP Advertise
   message.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Security Parameters Index (SPI)               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type     85

      Length   4

      SPI      A Security Parameters index [3] identifying a security
               context between a pair of nodes among the contexts
               available in the security association defined between
               the DHCPv6 client and server.  SPI values 0 through 255
               are reserved and, if used, MUST conform to the security
               context defined by that value as defined in the most
               recent Assigned Numbers RFC (e.g., [9]).








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8. End extension specification

   The end extension marks the end of valid information in the vendor
   field.  The Type for the end extension is 65535, and its Length is 2
   octets; there is no Length field for the end extension.

    0                   1
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             65535             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


9. Security Considerations

   There is an urgent need to define some security protocol for use
   with DHCPv6, since otherwise malicious parties could create numerous
   denial-of-service style attacks based on depleting available server
   resources or providing corrupted or infected data to unsuspecting
   clients.  The following sections discuss aspects of security relevant
   for users of the Client-Server Authentication extension 7.5.  See
   also the Security Considerations in the companion specification [4].


9.1. Replay Protection

   A 64-bit timestamp, in Network Time Protocol [15](NTP) format, is
   used to protect against replay of previous authenticated messages
   by malicious agents.  The NTP timestamp value used in the extension
   MUST be chosen, and verified, to be larger than values used by the
   originator in previous Client-Server Authentication extensions.
   On the other hand, the timestamp value MUST also be chosen (and
   verified) to be no greater than one year more than the last known
   value (if any) used by the originator.


9.2. Default Authentication Algorithm

   The default authentication algorithm is HMAC [12], using
   keyed-MD5 [19].  Given a secret key K, and "data" the information to
   be authenticated, HMAC_result is computed as follows:

    1. opad := 0x36363636363636363636363636363636 (128 bits)

    2. ipad := 0x5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C5C (128 bits)

    3. zero_extended_key := K extended by zeroes to be 128 bits long




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    4. opadded_key := zero_extended_key XOR opad

    5. ipadded_key := zero_extended_key XOR ipad

    6. HMAC_result := MD5 (opadded_key , MD5 (ipadded_key, data))

   The key K is the shared secret defined by the security association
   between the client and server and by the SPI value specified in
   the Authentication Extension.  The "data" is the stream of octets
   in all previous fields in the DHCPv6 message and extensions.  The
   authenticator is the 128-bit value HMAC_result.


10. Defining New Extensions

   Implementation specific use of undefined extensions (including those
   in the range 86-32767) may conflict with other implementations, and
   registration is required.

   The author of a new DHCP extension MUST follow these steps to obtain
   acceptance of the extension as a part of the DHCP Internet Standard:

    1. The author devises the new extension.

    2. The author requests a number for the new extension from IANA by
       contacting:

          Internet Assigned Numbers Authority (IANA)
          USC/Information Sciences Institute
          4676 Admiralty Way
          Marina del Rey, California 90292-6695
          or by email as:  iana@isi.edu

    3. The author documents the new extension, using the newly obtained
       extension number, as an Internet Draft.

    4. The author submits the Internet Draft for review through the
       IETF standards process as defined in "Internet Official Protocol
       Standards" [11].  The new extension will be submitted for
       eventual acceptance as an Internet Standard.

    5. The new extension progresses through the IETF standards
       process; the new extension will be reviewed by the Dynamic Host
       Configuration Working Group (if that group still exists), or as
       an Internet Draft not submitted by an IETF working group.






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    6. If the new extension fails to gain acceptance as an Internet
       Standard, the assigned extension number will be returned to IANA
       for reassignment.

   This procedure for defining new extensions will ensure that:

     * allocation of new extension numbers is coordinated from a single
       authority,

     * new extensions are reviewed for technical correctness and
       appropriateness, and

     * documentation for new extensions is complete and published.






































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11. Acknowledgements

   Thanks to Jim Bound for his frequent review, helpful suggestions, and
   design assistance.  Ralph Droms has also made many, many suggestions
   which have been incorporated into this draft.  The original form of
   this internet draft was copied directly from RFC1533 [1], written
   by Steve Alexander and Ralph Droms.  Thanks to Erik Guttman for his
   helpful suggestions for the Service Location extensions.  Thanks to
   Matt Crawford and Erik Nordmark for their careful review as part of
   the Last Call process.


References

    [1] S. Alexander and R. Droms.  DHCP Options and BOOTP Vendor
        Extensions.  RFC 1533, October 1993.

    [2] S. Alexander and R. Droms.  DHCP Options and BOOTP Vendor
        Extensions.  RFC 2132, March 1997.

    [3] R. Atkinson.  IP Authentication Header.  RFC 1826, August 1995.

    [4] J. Bound and C. Perkins.  Dynamic Host Configuration Protocol
        for IPv6.  draft-ietf-dhc-dhcpv6-11.txt, May 1997.  (work in
        progress).

    [5] S. Bradner.  Key words for use in RFCs to Indicate Requirement
        Levels.  RFC 2119, March 1997.

    [6] M. W. Carney.  DHCP Option for IEEE 1003.1 POSIX Timezone
        Specifications.  draft-ietf-dhc-timezone-01.txt, January 1997.
        (work in progress).

    [7] B. Carpenter and Y. Rekhter.  Renumbering needs work.  RFC 1900,
        February 1996.

    [8] S. Deering and R. Hinden.  Internet Protocol, Version 6 (IPv6)
        Specification.  RFC 1883, December 1995.

    [9] Stan Hanks, Tony Li, Dino Farinacci, and Paul Traina.  Generic
        Routing Encapsulation (GRE).  RFC 1701, October 1994.

   [10] IEEE.  1003.1 POSIX Timezone Specification, 1988.

   [11] Editor J. Postel.  INTERNET OFFICIAL PROTOCOL STANDARDS.  STD 1,
        July 1997.





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   [12] H. Krawczyk, M. Bellare, and R. Cannetti.  HMAC: Keyed-Hashing
        for Message Authentication.  RFC 2104, February 1997.

   [13] Sun Microsystems.  System and Network Administration, March
        1992.

   [14] D. Mills.  Simple Network Time Protocol (SNTP) Version 4 for
        IPv4, IPv6 and OSI.  RFC 2030, October 1996.

   [15] David L. Mills.  Network Time Protocol (Version 3):
        Specification, Implementation and Analysis.  RFC 1305, March
        1992.

   [16] P. Mockapetris.  Domain Names - Concepts and Facilities.  STD
        13, November 1987.

   [17] Joyce K. Reynolds and Jon Postel.  Assigned Numbers.  STD 2,
        October 1994.

   [18] Joyce K. Reynolds and Jon Postel.  Assigned Numbers.  RFC 1700,
        October 1994.

   [19] Ronald L. Rivest.  The MD5 Message-Digest Algorithm.  RFC 1321,
        April 1992.

   [20] S. Thomson and T. Narten.  IPv6 stateless address
        autoconfiguration.  RFC 1971, August 1996.

   [21] J. Veizades, E. Guttman, C. Perkins, and S. Kaplan.  Service
        Location Protocol.  RFC 2165, July 1997.

   [22] P. Vixie, S. Thomson, Y. Rekhter, and J. Bound.  Dynamic Updates
        in the Domain Name System (DNS).  RFC 2136, April 1997.


















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Chair's Addresses

   The working group can be contacted via the current chair:

      Ralph Droms
      Computer Science Department
      323 Dana Engineering
      Bucknell University
      Lewisburg, PA 17837

      Phone:  (717) 524-1145
      EMail:  droms@bucknell.edu



Author's Address

   Questions about this memo can be directed to:

      Charles E. Perkins
      Technology Development Group
      Mail Stop MPK15-214
      Room 2682
      Sun Microsystems, Inc.
      901 San Antonio Road
      Palo Alto, California 94303
      USA

      Phone:  +1-415-786-6464
      Fax:  +1-415-786-6445
      email:  charles.perkins@Sun.COM




















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