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Internet Engineering Task Force                               C. Perkins
INTERNET DRAFT                             Sun Microsystems Laboratories
                                                                J. Bound
                                                   Compaq Computer Corp.
                                                        25 February 1999


    Extensions for the Dynamic Host Configuration Protocol for IPv6
                      draft-ietf-dhc-v6exts-11.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 and is in full conformance with
   all provisions of Section 10 of RFC2026.  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."

   The list of current Internet-Drafts can be accessed at:

      http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at:

      http://www.ietf.org/shadow.html.


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, which will be periodically updated as new
   extensions are defined.





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                                Contents


Status of This Memo                                                    i

Abstract                                                               i

 1. Introduction                                                       1

 2. DHCPv6 Extension Field Format                                      2

 3. IP Address Extension                                               3
     3.1. Client Considerations for the IP Address extension  . . .    7
           3.1.1. Address Lifetimes . . . . . . . . . . . . . . . .    7
           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  . . . . . . . . . . . . . . . .  10
           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  . . . . . .   13
           4.2.2. An Example  . . . . . . . . . . . . . . . . . . .   14
     4.3. Domain Name Server Extension  . . . . . . . . . . . . . .   14
     4.4. Domain Name . . . . . . . . . . . . . . . . . . . . . . .   15

 5. Application and Service Parameters                                15
     5.1. Service Location Protocol extensions  . . . . . . . . . .   15
           5.1.1. Typed Scope Lists . . . . . . . . . . . . . . . .   15
           5.1.2. Directory Agent Extension . . . . . . . . . . . .   17
           5.1.3. Service Scope Extension . . . . . . . . . . . . .   18
     5.2. Network Time Protocol Servers Extension . . . . . . . . .   19
     5.3. Network Information Service (NIS and NIS+) extensions . .   20
           5.3.1. NIS Domain Extension  . . . . . . . . . . . . . .   20
           5.3.2. NIS Servers Extension . . . . . . . . . . . . . .   20
           5.3.3. NIS+ Domain Extension . . . . . . . . . . . . . .   20
           5.3.4. NIS+ Servers Extension  . . . . . . . . . . . . .   21

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



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 7. DHCPv6 Extensions                                                 22
     7.1. Maximum DHCPv6 Message Size Extension . . . . . . . . . .   22
     7.2. DHCP Retransmission and Configuration Parameter Extension   22
     7.3. Platform Specific Information . . . . . . . . . . . . . .   23
     7.4. Platform Class Identifier . . . . . . . . . . . . . . . .   24
     7.5. Class Identifier  . . . . . . . . . . . . . . . . . . . .   25
     7.6. Reconfigure Multicast Address . . . . . . . . . . . . . .   26
     7.7. Renumber DHCPv6 Server Address  . . . . . . . . . . . . .   26
     7.8. DHCP Relay ICMP Error Message Format  . . . . . . . . . .   27
           7.8.1. ICMP Extension Client Considerations  . . . . . .   27
           7.8.2. ICMP Extension Relay Considerations . . . . . . .   27
     7.9. Client-Server Authentication Extension  . . . . . . . . .   28
    7.10. Client Key Selection Extension  . . . . . . . . . . . . .   29

 8. End Extension                                                     29

 9. Resource-Server Associations                                      30

10. Security Considerations                                           30
    10.1. Replay Protection . . . . . . . . . . . . . . . . . . . .   30
    10.2. Default Authentication Algorithm  . . . . . . . . . . . .   30

11. IANA Considerations                                               31

12. Acknowledgements                                                  32

13. Full Copyright Statement                                          32

Chair's Address                                                       36

Author's Addresses                                                    36


1. Introduction

   This document specifies extensions for use with the Dynamic Host
   Configuration Protocol for IP version 6, DHCPv6.  DHCPv6 message
   formats are described 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 overall format of information in the
   'extensions' field of DHCPv6 messages.  The extensions defined
   within this document specify a generalized way to distribute
   information useful to a wide class of machines, operating systems
   and configurations.  Sites with a DHCPv6 server that is shared among
   heterogeneous clients may choose to define other, site-specific
   formats for the use of the 'extensions' field.



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   Section 2 of this memo describes the formats of DHCPv6 extensions.
   Information on registering new extensions is contained in section 11.
   The other sections organize the format descriptions of various
   extensions according to their general type, as follows:

    -  IP Address extension

    -  General host configuration

    -  Application and Service Parameters

    -  TCP

    -  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 [27], 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.


2. DHCPv6 Extension Field Format

   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.  Every extension, except extension number
   65535, has a two octet unsigned integer Length field following the
   type field.  The value of the Length field does not include the
   four octets specifying the type and length.  For some extensions
   the Length field is always the same number, but it MUST still be
   specified.  In each case, unless otherwise specified, the Length
   field specifies the length of the extension data in octets.  There
   is no particular requirement for alignment of data fields within
   existing DHCPv6 extensions.  Any extensions defined subsequent to
   this document MUST contain a two-octet Length field even if the
   length is fixed or zero.

   Unrecognized extensions SHOULD be ignored by skipping over 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 that the maximum DHCP message size including extensions is 1280
   octets.




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   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.  Typically, the value of the Type field is shown directly in
   the format illustration, and for some fixed-length extensions the
   value of the Length field is also shown in the format illustration
   for the extension.

   All strings are encoded in UTF-8, which includes US-ASCII as a
   subset.


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 [28].

   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
   routing prefix of the link to which the client is currently attached.
   An IP Address Extension can contain at most one IP address.  To
   specify more than one IP address, multiple extensions are used.















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    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 = 1            |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    status     |C|L|Q|A|P|       reserved      |  prefix-size  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         (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.

      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 the
               server updates DNS with a new AAAA record, as specified
               by the client's FQDN.

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

      reserved MUST be zero.

      prefix-size
               If the client address is present (the 'C' bit is set), a
               nonzero prefix-size is the number of leftmost bits of the



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               client's IPv6 address which make up the routing prefix.
               Otherwise, if the 'C' bit is not set, prefix-size 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 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
       24   dynDNS Not Implemented

       25   Authoritative DNS Server could not be found
       33   The name server was unable to interpret the request
          due to a format error.

       34   dynDNS unavailable at this time (SERVFAIL)
       35   Some name that ought to exist, does not exist
          (NXDOMAIN)

       36   The name server does not support the specified Opcode
          (NOTIMP)

       37   The name server refuses to perform the specified
          operation for policy or security reasons (REFUSED)
       38   Some name that ought not to exist, does exist
          (YXDOMAIN)





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       39   Some RRset that ought not to exist, does exist
          (YXRRSET)

       40   Some RRset that ought to exist, does not exist
          (NXRRSET)
       41   The server is not authoritative for the zone named in
          the Zone Section (NOTAUTH)

       42   A name used in the Prerequisite or Update Section
          is not within the zone denoted by the Zone Section
          (NOTZONE)

   Status values 33 through 42 are described more fully within Dynamic
   Updates to DNS (RFC 2136 [28]).  Up-to-date values for the values
   of the status field are specified in the most recent "Assigned
   Numbers" [23].

   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 '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, indicating that the server was
   unable to honor the required extension parameters

   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 MAY be done even with IP addresses
   obtained by Stateless Address Autoconfiguration [26].  If the client
   wishes to have its FQDN associated with one of several existing IP
   addresses which it has received from the DHCP Server, the client MUST
   supply that IP address in the IP address extension along with the
   FQDN.

   By default, the client SHOULD update the AAAA record, and the server
   SHOULD update the PTR record.  The IP Address extension permit




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   clients and servers to use a different behavior than the default, and
   they MAY set the 'Q' and 'A' bits to suit their needs.


3.1. Client Considerations for the IP Address extension

3.1.1. Address Lifetimes

   An IP address returned to a client in a DHCP Reply message has a
   preferred and valid lifetime.  The valid lifetime represents the
   lease for addresses provided to the client, from the server.  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 [11] 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).  If the client does not make a new Request for
   an address before the valid lifetime expires, the server SHOULD
   assume the client does not want that address.  After it expires, the
   server MAY provide that address to another 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 prefix-size field to zero.  If nonzero, the IP address
       MUST be included, and the prefix-size MUST correspond to the
       appropriate routing prefix for that IP address.

    -  set the 'A' bit to request that the server update DNS with a new
       AAAA record, as specified by the client's FQDN.

    -  set the 'P' bit to request that the server update DNS with a new
       PTR record, as specified by the client's FQDN.

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




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

   A client may include multiple IP Address extensions in a single DHCP
   Request.  A client indicates that it cannot accept any configuration
   information other than that listed in the IP Address extension (e.g.,
   IP address) to the DHCP Request, by specifying the 'Q' (Required)
   bit.

   If the information in the IP extension is advisory, a server may send
   different parameters than requested in the DHCP Reply.  Otherwise,
   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.

   When a client requests an IP address, it MUST maintain a record
   (called a ``resource-server association'', and explained in
   section 9) 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.


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 [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, and 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) [26]; 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 a DHCP Release message, the client MUST provide at least one
   specific IP address in the extension.

   For each address extension:

    -  the client may include a name (which may be a host name or a
       FQDN).

    -  if the server originally updated DNS with one or more AAAA
       records for allocated IP addresses, the server MUST update DNS to
       delete those records, 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, made the DNS updates, it MUST
       perform the corresponding deletions before issuing the DHCP
       Release.


3.2. Server Considerations for the IP Address extension

   This section contains information specifying the handling of the IP
   Address extension by DHCP servers.


3.2.1. Use with the DHCP Advertise message

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

    -  the client's FQDN or host name

    -  the preferred lifetime

    -  the valid 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.








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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 link to which the client is attached.
   The link can be determined by the Agent address prefix in the DHCP
   Request message header, or, when there is no relay, by the link of
   the 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
   link when there is no server 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 Release
   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 following information:

    -  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 following information:

    -  the DNS name

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

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

   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 MAY attempt to update DNS if needed.



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   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.

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

   On a practical note, 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.  Of course, this only works when the site does
   not need global addresses.


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 = 2            |           Length = 4          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Time Offset                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   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

   Extension type 2, defined in section 4.1, specifies the Universal
   Coordinated Time (UTC) offset.  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 [15], as detailed in
   section 4.2.1.

    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 = 3             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    IEEE 1003.1 POSIX Timezone string (variable length) ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   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 Extension.  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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4.2.1. 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]]]

   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.




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      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:

      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

   Here, `5' is the Offset for Std, and `4' is the Offset for Dst.
   Start is 16, and End is 298.


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 = 6             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Domain Name System server addresses              |
   |                       (16 octets each)                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Domain Name Server extension specifies a list of Domain Name
   System [22] name servers available to the client.  Servers SHOULD be
   listed in order of preference.

   The minimum Length for this extension is 16 octets, and MUST always
   be a multiple of 16.





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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 = 10           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Domain Name (variable length)  ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The minimum Length for this extension is 1.  The domain name is a
   ASCII string, Length octets in size.  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.


5.1. Service Location Protocol extensions

   This subsection describes DHCP extensions useful for a client to
   begin operations using the Service Location Protocol (SLP) [27].


5.1.1. Typed Scope Lists

   In Service Location Protocol, multiple service types can be hosted on
   the same network node.  However, DHCP typically configures computers
   based on their IP address.  It is possible that different service
   types on the same computer would be administered from different
   scopes.  Thus, extensions 16 and 17 have additional syntax to allow
   this more detailed style of service configuration.

   In particular, the list of scopes contained in the extensions is
   syntactically separated into lists pertaining to each service type.

   Grammatically, a typed-scope-list in a DHCP Reply is structured as
   follows:

     typed-scope-list = one or more maybe-typed-scope-items,
                        separated by commas



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     maybe-typed-scope-item = typed-scope-item, or scope-list
     typed-scope-item = '(' service-type '=' scope-list ')'
     scope-list = one or more scope-items, comma-separated

   A typed-scope-list in a DHCP Request is structured as follows:

     typed-scope-list = one or more maybe-typed-scope-items,
                        separated by commas
     maybe-typed-scope-item = typed-scope-item, or
                                 maybe-empty-scope-list
     typed-scope-item = '(' service-type '=' maybe-empty-scope-list ')'
     maybe-empty-scope-list = zero or more scope-items, comma-separated

   A service type has the format defined in [12], and a scope-item has
   the format defined in [13] for "strval".  Basically, a scope-item is
   a character string that has alphanumeric characters not including
   control characters or `(',`)',`,', \',`!',`<',`=',`>', or `~' Service
   schemes are special cases of schemes as defined for general URLs [3].

   The typed-scope-list MAY contain both untyped-scope-lists and
   typed-scope-lists.  Each scope-item in each untyped-scope-list
   applies to every service type on the node.  The string containing the
   typed-scope-list is NOT null-terminated.  The typed-scope-list string
   must be UTF-8 character encoded.

   As an example, the scope-list ``A,B,C'' denotes scopes A, B and C
   for all service types on the client.  In a DHCP Request, this scope
   string would indicate that the client wishes a directory agent which
   supports ANY of these three scopes.  In a DHCP Reply, the scope
   indicates that the directory agent supports ALL of the three scopes.

   Suppose instead that service types "netman" and "proxystuff" are
   residing on a DHCP client.  Then, the typed-scope-list in a DHCP
   Reply could be,

        (netman=mgmt),(proxystuff=math-dept,labs)

   Assuming the DHCP client with two service types "netman" and
   "proxystuff" did not make any scope restriction, a corresponding
   typed-scope-list in a DHCP Request could be,

        (netman=),(proxystuff=)

   asking for scopes for those service types.








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5.1.2. Directory Agent Extension

   Entities using the Service Location Protocol (SLP) [27] need to find
   out the address of one or more Directory Agents in order to transact
   messages, and possibly the correct scope to be used in conjunction
   with the service attributes which are exchanged using the Service
   Location Protocol.

   The Directory Agent 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 = 16           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |D|F|M|T|        reserved       |           DA length           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               Directory Agent (variable length) ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        (if present) Typed-Scope-List (variable length) ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

      D        If the 'D' bit is set, the Directory Agent field and the
               DA Length fields are present.

      F        If the 'F' bit is set, the Directory Agent is indicated
               by including its variable length host name or Fully
               Qualified Domain Name (FQDN) instead of its IP address.

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

      T        If the 'T' bit is set, the Typed-Scope-List is present.

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

      DA Length
               The length (in octets) of the Directory Agent field.






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      Directory Agent
               The FQDN, host name, or IP address of the Directory
               Agent.

      Typed-Scope-List
               The string denoting the typed-scope-list (see
               Section 5.1.1).

   In order to simplify administration of the configuration of DAs for
   clients using SLP, the DA can be indicated by presenting its host
   name or FQDN 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
   typed-scope-list.  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 a nonempty typed-scope-list.  The length
   of the Typed-Scope-List is only indicated implicitly by the overall
   length of the extension.  The format of the Typed-Scope-List field is
   described in section 5.1.1.

   The `M' bit MUST NOT be set when the extension is used as part of a
   DHCP Request message.

   Extension 16 MUST include one or more scopes if a DA address is
   returned.  Using extension 16, it is not possible for different
   service types on the same node to be configured with different
   directory agents.  In other words, all service agents of the same
   service type on the same node will be configured with the same
   directory agent.


5.1.3. Service Scope Extension

   This extension indicates a scope that should be used by a Service
   Agent (SA) [27], when responding to Service Request messages as
   specified by the Service Location Protocol (SLP). This extension MAY
   be included multiple times in the same DHCP Request or DHCP Reply.








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    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 = 17           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Typed-Scope-List ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

      Typed-Scope-List
               see Section 5.1.1.

   The Typed-Scope-List is described in Section 5.1.1.  The DHCP
   client (i.e., user agent or service agent) which receives this
   extension will use the indicated scope for in all SLP requests and
   registrations.

   DHCP clients MAY use extension 17 to request scopes for one or more
   particular service types.  Note that more than one Service Scope
   extension may be present in a DHCP message.  The length of the
   typed-scope-list is only indicated implicitly by the overall length
   of the extension.


5.2. Network Time Protocol Servers Extension

   This extension specifies a list of IP addresses indicating NTP [20]
   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 = 18           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     NTP server addresses                      |
   |                       (16 octets each)                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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








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5.3. Network Information Service (NIS and NIS+) extensions

   This subsection describes DHCPv6 extensions useful for NIS and NIS+
   clients.


5.3.1. NIS Domain Extension

   This extension specifies the name of the client's NIS [19] domain.
   The domain is formatted as a character string consisting of
   characters from the US-ASCII character set.  The minimum Length for
   this extension 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 = 19           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              NIS Domain Name (variable length)  ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


5.3.2. NIS Servers Extension

   This extension specifies a list of IP addresses indicating NIS [19]
   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 = 20           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     NIS server addresses                      |
   |                       (16 octets each)                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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


5.3.3. NIS+ Domain Extension

   This extension specifies the name of the client's NIS+ [19]
   domain.  The domain is formatted as a character string consisting of
   characters from the US-ASCII character set.  The minimum Length for
   this extension is 1.





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    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 = 21           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              NIS+ Client Domain Name (variable length)  ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


5.3.4. NIS+ Servers Extension

   This extension specifies a list of IP addresses indicating NIS+ [19]
   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 = 22           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     NIS+ server addresses                     |
   |                       (16 octets each)                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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


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 = 32           |             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



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   keepalive messages on connections unless specifically requested by an
   application.

   The Length for this extension 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 32-bit integer.  A client may use
   the maximum DHCPv6 message size extension in DHCP Request messages,
   but MUST NOT use the extension in other DHCP messages (see [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 = 40           |           Length = 4          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   Max DHCPv6 Message Length                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Length for this extension is 4.  The minimum permissible value is
   1280 [11].


7.2. DHCP Retransmission and Configuration Parameter Extension

   This extension allows configuration of values for DHCP
   retransmission and configuration parameters, as specified
   for use when sending or receiving DHCPv6 messages [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 = 41           |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   DHCP Parameter Identifier                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      New Parameter Value                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Length for this extension is either 4 or 8.  If a client uses
   this extension as part of a DHCP Request message, the New Parameter



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   Value field does not have to be used as part of the extension.  The
   following table shows the current parameter names, their associated
   Parameter Identifier, and their default values.

    Parameter Name                  ParamID  Default Value
    =============================================================
    CLIENT_ADV_WAIT                  1       2000 milliseconds
    DEFAULT_SOLICIT_HOPCOUNT         2       4
    SERVER_MIN_ADV_DELAY             3       100 milliseconds
    SERVER_MAX_ADV_DELAY             4       1000 millisecond
    REQUEST_MSG_MIN_RETRANS          5       10 retransmissions
    REPLY_MSG_TIMEOUT                6       2000 milliseconds
    REPLY_MSG_RETRANS_INTERVAL       7       2000 milliseconds
    RECONF_MSG_TIMEOUT               8       12000 milliseconds
    RECONF_MSG_MIN_RETRANS           9       10 retransmissions
    RECONF_MSG_RETRANS_INTERVAL     10       12000 milliseconds
    RECONF_MMSG_MIN_RESP            11       2000 milliseconds
    RECONF_MMSG_MAX_RESP            12       10000 milliseconds
    MIN_SOLICIT_DELAY               13       1000 millisecond
    MAX_SOLICIT_DELAY               14       5000 milliseconds
    XID_TIMEOUT                     15       600000 milliseconds
    RECONF_MULTICAST_REQUEST_WAIT   16       120000 miliseconds


   All timing parameters are measured in milliseconds.  DHCP
   clients MUST be able to process this extension when part
   of a DHCP Reply message, and be able to reconfigure their
   values for DEFAULT_SOLICIT_HOPCOUNT, REQUEST_MSG_MIN_RETRANS,
   and REPLY_MSG_TIMEOUT, REPLY_MSG_RETRANS_INTERVAL, and
   RECONF_MULTICAST_REQUEST_WAIT. Servers MAY refuse client
   requests for configuration of the server's internal configuration
   variables.  Alternatively, a server MAY keep separate configuration
   variables for any requesting client that are different than for
   clients which do not make such requests.


7.3. Platform Specific Information

   A platform is defined as the combination of hardware and operating
   system (OS).

   This extension is used by clients and servers to exchange
   client-platform-specific information.  The information is an opaque
   collection of data, presumably interpreted by platform-specific code
   on the clients.  The definition of this information is platform
   specific.  Clients identify their platform through the use of the
   Platform Class identifier extension (see Section 7.4).  Clients which
   do not receive platform specific information SHOULD make an attempt




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   to operate without it, although they may do so (and announce that
   they are doing so) in a degraded mode.

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

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

    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 = 48           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Platform-specific extension information  ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The minimum Length for this extension is 4.

   When encapsulated platform-specific extensions are used, each one
   has the same format as for general DHCP extensions, as defined
   in section 2.  In other words, all platform-specific extensions
   are encoded in Type-Length-Value (TLV) format.  More than one
   platform-specific extension can, therefore, be included in the same
   DHCP "Platform Specific Information" extension.

   DHCP servers which support the configuration of Platform Specific
   Information extensions, and which have been configured with
   configuration information specific to some number of Platform Class
   Identifiers MUST select and return only those platform-specific
   extensions which match the Platform Class Identifier provided by the
   DHCP client.


7.4. Platform Class Identifier

   This extension is used by a DHCP client to identify the hardware type
   and operating system platform it is hosted on.  The extension value
   itself is an opaque value to a DHCP server, and is only used by the
   DHCP server to "lookup" Platform Specific Extensions associated with
   clients of a certain platform class.




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

   Note that unlike the User Class Identifier, the Platform Class
   Identifier does not need to be echoed back to the DHCP client because
   there can be one and only one Platform Class Identifier for a 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 = 49           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Platform Class Identifier ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

   The platform class identifier is a string of characters of Length
   octets.  The platform class identifier represents the hardware and
   Operating system class of which the client is a member.

   In order to prevent collisions in the Platform Class Identifier
   namespace, we recommend that platform vendors prefix their Platform
   Class Identifiers with their Stock symbol or some other globally
   recognized authority.  For example, Platform Class Identifiers for
   Sun Microsystems Inc platforms would be prefaced by "SUNW", the
   NASDAQ stock symbol for Sun.


7.5. 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 to the DHCP
   administrator).  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




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   corresponding to the given class 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 = 64           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Class Identifier ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The class identifier is a string of Length octets.  The class
   identifier represents the class identifier of which the client is a
   member.


7.6. 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 = 66           |           Length = 16         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Reconfigure Multicast Address                |
   |                          (16 octets)                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


7.7. 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
   to all of the server's clients instead of being unicast to each one
   individually.











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    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 = 67           |           Length = 16         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   New DHCPv6 Server Address                   |
   |                          (16 octets)                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


7.8. DHCP Relay ICMP Error Message Format

   A DHCP Relay ICMP Message extension is used to inform a client of an
   ICMP Error message received by the relay after forwarding a client
   Solicit or Request message.  A node which is not a DHCP Relay MUST
   NOT transmit this extension in any DHCP 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 = 68           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      ICMP Error Message                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Length of the DHCP Relay ICMP Message extension is the length of
   the ICMP error message received by the relay [9].


7.8.1. ICMP Extension Client Considerations

   When a client sends a Solicit or Request message it may often be
   forwarded by a relay.  When the relay forwards messages for a client
   the network may return an ICMP error [9] message to the relay.  The
   relay determines the client's link-local address within the UDP
   payload of the ICMP returned error message payload, and sends the
   client a DHCP Relay ICMP Error message as defined in section 7.8.2.

   The client MAY record these messages based on the ICMP type and
   reason codes provided in the ICMP Error payload [9], for future use
   or for system logging purposes.  How the client uses this information
   is implementation dependent.


7.8.2. ICMP Extension Relay Considerations

   If the relay receives an ICMP error message after forwarding a
   client's DHCP Solicit or Request message, it MUST inspect the



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   payload of the ICMP message [9], to determine the client's link-local
   address.  The relay MUST check that it is a link-local address; if
   not, the ICMP error message MUST be silently discarded.  Otherwise,
   the relay should forward the ICMP Error message to the client as
   specified in section 7.8.1, by using the client's link-local address
   from the ICMP error message as the IP destination address in the
   IP header sent to the client.  If the relay cannot determine the
   client's link-local address in the ICMP error message the packet MUST
   be silently discarded.


7.9. 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 = 84           |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Security Parameters Index (SPI)               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Replay Protection                      |
   |                           (8 octets)                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Authenticator (variable length) ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      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 [2] identifying a security
               context from among those available between the DHCPv6
               client and server.

      Replay Protection
               A 64-bit timestamp (in Network Time Protocol [21](NTP)
               format) (see section 10.1).

      Authenticator
               (variable length) (See Section 10.2.)

   This authentication extension remedies the inability of IPsec [17]
   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



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   either the client or server to authenticate the rest of the data in
   the DHCPv6 message.  The default authentication algorithm, which MUST
   be supported by all clients and servers, is defined in section 10.2.

   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., [16]).


7.10. 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 = 85           |           Length = 4          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Security Parameters Index (SPI)               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The SPI is a Security Parameters index [2] 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., [14]).


8. End Extension

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Type = 65535         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+








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9. Resource-Server Associations

   Some extensions may cause a client to receive allocated resources.
   When the client wishes to release such resources before the
   allocation has expired, the client will need to contact the server
   which allocated that resource.  Thus, the resource needs to be
   associated to the server that made the allocation.  This association
   is maintained in a data structure called a resource-server
   association for the appropriate extensions.

   The only extension currently defined which requires the maintenance
   of such a resource-server association is the IP Address extension,
   which is extension type 1 (see section 3).


10. Security Considerations

   A security protocol is urgently needed 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 7.9.  See also the
   Security Considerations in the companion specification [4].


10.1. Replay Protection

   A 64-bit timestamp, in Network Time Protocol [21](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.


10.2. Default Authentication Algorithm

   The default authentication algorithm is HMAC [18], using
   keyed-MD5 [24].  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.


11. IANA Considerations

   This document MAY be superseded by new documents for DHCPv6
   extensions, which will then include the entire current list of valid
   extensions.  This section details the method for specifying new
   extensions.

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

   The following steps MUST be followed by the author of any new DHCP
   extension, in order to obtain acceptance of the extension as a part
   of the DHCP Internet Standard:

    1. The author documents the new extension as an Internet Draft.

    2. The author submits the Internet Draft for review through the
       IETF standards process as defined in "Internet Official Protocol
       Standards" [16].  The new extension will be submitted for
       eventual acceptance as an Internet Standard.

    3. 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

    4. 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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    5. 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.


12. Acknowledgements

   The original form of this internet draft was copied directly from
   RFC1533 [1], written by Steve Alexander and Ralph Droms.  Thanks to
   Mike Carney for his many helpful comments, as well as contributing
   the design of the Platform Specific Information and Platform Class
   Identifier.  Thanks to Erik Guttman for his helpful suggestions
   for the Service Location extensions.  Thanks to Ralph Droms, Matt
   Crawford, Thomas Narten, and Erik Nordmark for their careful review
   as part of the Last Call process.


13. Full Copyright Statement

   Copyright (C) The Internet Society (1997).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph
   are included on all such copies and derivative works.  However,
   this document itself may not be modified in any way, such as by
   removing the copyright notice or references to the Internet Society
   or other Internet organizations, except as needed for the purpose
   of developing Internet standards in which case the procedures
   for copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.





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   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."














































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References

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

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

    [3] T. Berners-Lee, L. Masinter, and M. McCahill.  Uniform Resource
        Locators (URL).  RFC 1738, December 1994.

    [4] J. Bound and C. Perkins.  Dynamic Host Configuration Protocol
        for IPv6.  draft-ietf-dhc-dhcpv6-14.txt, February 1999.  (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] A. Conta and S. Deering.  Internet Control Message Protocol
        (ICMPv6) for the Internet Protocol Version 6 (IPv6).  RFC 1885,
        December 1995.

    [9] A. Conta and S. Deering.  RFC 2463:  Internet Control Message
        Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6)
        Specification, December 1998.  Obsoletes RFC1885 [8]. Status:
        DRAFT STANDARD.

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

   [11] S. Deering and R. Hinden.  RFC 2460:  Internet Protocol, Version
        6 (IPv6) specification, December 1998.  Obsoletes RFC1883 [10].
        Status:  DRAFT STANDARD.

   [12] E. Guttman, C. Perkins, and J. Kempf.  Service Templates and
        service:  Schemes.  draft-ietf-svrloc-service-scheme-05.txt,
        November 1997.  (work in progress).

   [13] E. Guttman, C. Perkins, J. Veizades, and M. Day.  Service
        Location Protocol version 2.  draft-ietf-svrloc-protocol-v2-04.txt,
        March 1998.  (work in progress).





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

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

   [16] Editor J. Postel.  INTERNET OFFICIAL PROTOCOL STANDARDS.  STD 1,
        May 1998.

   [17] Stephen Kent and Randall Atkinson.  IP Authentication Header.
        draft-ietf-ipsec-auth-header-07.txt, July 1998.  (work in
        progress).

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

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

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

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

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

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

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

   [25] S. Thomson and T. Narten.  IPv6 Stateless Address
        Autoconfiguration.  RFC 1971, August 1996.

   [26] S. Thomson and T. Narten.  RFC 2462:  IPv6 stateless address
        autoconfiguration, December 1998.  Obsoletes RFC1971 [25].
        Status:  DRAFT STANDARD.

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

   [28] 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 Addresses

   Questions about this memo can be directed to:

      Charles E. Perkins                Jim Bound
      Sun Microsystems Laboratories     Compaq Computer Corporation
      Mail Stop MPK15-214, Room 2682    ZKO3-3/U14
      15 Network Circle                 110 Spitbrook Road
      Menlo Park, CA 94025              Nashua, NH 03062
      USA                               USA

      Phone:  +1 650 786-6464           Phone:  +1-603-884-0400
      EMail:  cperkins@eng.sun.com      EMail:  bound@zk3.dec.com
      Fax:  +1 650 786-6445
      web:  http://www.svrloc.org/~charliep






















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