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Versions: 00 01 02                                                      
MIF Working Group                                               T. Reddy
Internet-Draft                                                  P. Patil
Intended status: Standards Track                                 D. Wing
Expires: April 18, 2013                                            Cisco
                                                        October 15, 2012


                Relay-Supplied DHCPv6 Precedence Options
                draft-reddy-mif-dhcpv6-precedence-ops-02

Abstract

   Network configuration of hosts is currently relatively static with
   little consideration of dynamic network characteristics.  The network
   infrastructure is aware of dynamic network characteristics.  This
   specification extends DHCPv6 so that the DHCPv6 relay agent can
   influence a host's configuration.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on April 18, 2013.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as



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   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Usage Scenarios  . . . . . . . . . . . . . . . . . . . . . . .  3
     3.1.  IPv6 Multihoming . . . . . . . . . . . . . . . . . . . . .  3
     3.2.  Disabling IPv6 Temporary Addresses . . . . . . . . . . . .  4
       3.2.1.  Avoiding Excessive IP-Based Authentication . . . . . .  4
       3.2.2.  Reducing Management Impact . . . . . . . . . . . . . .  5
   4.  Options  . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     4.1.  Address Selection option . . . . . . . . . . . . . . . . .  6
     4.2.  Relay-Supplied Prefix Option . . . . . . . . . . . . . . .  7
   5.  Relay Agent Behaviour  . . . . . . . . . . . . . . . . . . . .  8
   6.  DHCPv6 Server Behaviour  . . . . . . . . . . . . . . . . . . .  8
     6.1.  Address Selection option . . . . . . . . . . . . . . . . .  8
     6.2.  Relay-Supplied Prefix Option . . . . . . . . . . . . . . .  9
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   9.  Change History . . . . . . . . . . . . . . . . . . . . . . . .  9
     9.1.  Changes from draft-reddy-mif-dhcpv6-precedence-ops-00
           to -01 . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     9.2.  Changes from draft-reddy-mif-dhcpv6-precedence-ops-01
           to -02 . . . . . . . . . . . . . . . . . . . . . . . . . . 10
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 10
     10.2. Informative References . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11





















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1.  Introduction

   DHCPv6 allows relatively static information to be configured in
   hosts, which is somewhat limiting.  On a dynamic network, the DHCPv6
   relay agent can observe characteristics of a network -- such as IPv6
   multihoming which might be temporarily unavailable or need load
   balancing of traffic towards each upstream ISPs.  By including
   additional information in relayed DHCPv6 messages, the DHCPv6 relay
   agent can influence the DHCPv6 server to provide answers that are
   better suited to the host's configuration on the network.

   In this document we propose new DHCPv6 options to be added by the
   DHCPv6 relay agent when it generates a Relay-Forwarded message.
   [RFC6724] defines default address selection mechanisms for IPv6 that
   allow nodes to select appropriate address when faced with multiple
   source and/or destination addresses to choose between.  An initial
   desire is to influence the DHCPv6 server's responses that modify the
   host's address policy table [I-D.ietf-6man-addr-select-opt] based on
   observed network characteristics.


2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].


3.  Usage Scenarios

   The DHCPv6 extension described in this document is useful with IPv6
   multihoming and with IP address-based authentication.

3.1.  IPv6 Multihoming

   o  In Proxy Mobile IPv6 [RFC5213] where Mobile Node is assigned
      prefixes from both local access network and home network.  This
      will allow selected traffic to go through the Mobile Packet Core
      and the rest through the Local access Network.  When DHCPv6 Relay
      Agent is co-located with the mobile access gateway, the proposal
      is for the relay agent to influence the DHCPv6 Server in the home
      network by adding the Address Selection option.  The relay agent
      can add an Address Selection option to the DHCPv6 request
      suggesting the local access network address selection policy table
      overiding the default address selection parameters and policy
      table.  The DHCPv6 server in the home network will merge the
      policy received in Address Selection option with it's own policy
      table as explained in section 4.3 of



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      [I-D.ietf-6man-addr-select-opt].  This updated policy table will
      be provided to the DHCPv6 client (MN) in Address Selection option
      (OPTION_ADDRSEL_TABLE).  When the DHCPv6 Server is co-located with
      the mobile access gateway, the DHCPv6 Server in the local access
      network will receive the policy table from the DHCPv6 server in
      the home network using DHCPv6 INFORMATION-REQUEST.  The DHCPv6
      server in local access network will merge the received policy
      table with it's local policy table.  The following figure depicts
      this scenario.
                   _----_
                 _(      )_
                ( Internet )
                 (_      _)
                   '----'
                     |
                     :
                     :
                     |
          .........................................................
                     |                              |
          +--------+ |                   +---------------------+
          |  Local |-|                   | Operator Value      |
          |Services| |                   | Added Services      |
          +--------+ |                   |                     |
                     |                   +---------------------+
                     |                              |
                     |            _----_            |
                  +-----+       _(      )_       +-----+
          [MN]----| MAG |======(    IP    )======| LMA |-- Internet
                  +-----+       (_      _)       +-----+
                                  '----'
                                     .
                                     .
                                     .
              [Access Network]       .        [Home Network]
          ..........................................................

       MN - Mobile Node

                         Figure 1: Proxy Mobile IPv6

3.2.  Disabling IPv6 Temporary Addresses

3.2.1.  Avoiding Excessive IP-Based Authentication

   Some managed networks authenticate hosts with an authentication
   supplicant or for hosts lacking the supplicant perform address-based
   authentication.  When Address-based authentication is used, re-



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   authentication occurs for each address obtained by the host, which
   can create a lot of authentication transactions.  To reduce this
   chatter, it can be useful to disable IPv6 Privacy Addresses [RFC4941]
   on those hosts using address-based authentication.  In a managed
   network, this option will ensure that temporary addresses are
   disabled for hosts without authentication supplicant.  This way
   managed networks can conditionally disable temporary addresses for
   only a set of hosts.

   The relay agent may be configured with the external prefixes that
   will be assigned to the host.  In that case, the relay agent would
   use the Address Selection option.  In the case where the relay agent
   is unaware of the external prefixes that will be assigned to the
   host, the relay agent uses the Relative Precedence option.  Details
   for processing those options are described later in the document.

   Whenever either of those options is used, a DHCPv6 server that
   understands those options will ignore the IA_TA options in the DHCPv6
   request, effectively disabling the use of temporary addresses for
   that host.

3.2.2.  Reducing Management Impact

   In addition, there are known issues in managing privacy extensions in
   certain scenarios.  These are described in managing privacy
   extensions [I-D.gont-6man-managing-privacy-extensions].  In such
   scenarios, conditionally disabling temporary addresses allows
   administrators to better manage deployments.


4.  Options

   To realize the functions described above, this document defines new
   DHCPv6 option Relay-Supplied Prefix and updates the Address Selection
   option defined in [I-D.ietf-6man-addr-select-opt].  These DHCPv6
   options are added by the DHCPv6 relay agent when it relays a DHCPv6
   message, and both MAY appear together in the same DHCPv6 message.














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      DHCPv6 Client        DHCPv6 Relay Agent           DHCPv6 Server
            |                    |                              |
            |------------------->|                              |
            |  DHCPv6 REQUEST    |                              |
            |                    |                              |
            |      (adds Relay-Supplied Prefix and/or           |
            |   Address Selection option to the request)        |
            |                    |                              |
            |                    |----------------------------->|
            |                    | DHCPv6 REQUEST with          |
            |                    | Relay-Supplied Prefix and/or |
            |                    | Address Selection Options    |
            |                    |                              |
            |                    |<-----------------------------|
            |                    | DHCPv6 REPLY                 |
            |<-------------------|                              |
            |  DHCPv6 REPLY      |                              |

             Figure 2: Message Flow, Relay Agent adding Option

   Relay-Supplied Prefix option carries host and network information
   observed by the DHCPv6 relay agent such as host does not support
   802.1x supplicant and will be subjected to web-authentication.  The
   Address Selection option allows prioritizing among a list of prefixes
   the DHCPv6 relay agent expects the DHCPv6 server to provide to the
   host.

4.1.  Address Selection option

   The layout of the Address Selection option is below:

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  OPTION_ADDRSEL_TABLE         |          option-len           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Reserved|N|A|P|                                               |
     +-+-+-+-+-+-+-+-+      POLICY TABLE OPTIONS                     |
     |                       (variable  length)                      |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 3: Option Type 1 message format

   The fields are described below:







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   option-code :  OPTION_ADDRSEL_TABLE defined in
      [I-D.ietf-6man-addr-select-opt]

   option-len:  Option Length

   Reserved:  Must be 0 and ignored by the server.

   N: A value of 1 indicates that the relay agent wants the DHCPv6
      server to ignore any IA_TA options in the DHCPv6 request, as if
      the IA_TA options were not present.  This effectively disables
      privacy extensions [RFC4941].  A value of 0 indicates the IA_TA
      options, if present in the DHCPv6 request, are processed normally
      by the DHCPv6 server.  This value has no impact on destination
      prefixes.

   A: This flag MUST be set to 0 and ignored by the DHCPv6 server

   P: This flag MUST be set to 0 and ignored by the DHCPv6 server.

   Prefix Table Options:  Zero or more Address Selection Policy Table
      options defined in [I-D.ietf-6man-addr-select-opt].

4.2.  Relay-Supplied Prefix Option

   The Relay-Supplied Prefix option is defined below:

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  OPTION_RS_PREFIX    |          option-len                    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Policy flag   |         Reserved                              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 4: Option Type 2 message format

   option-len:  Length of the option.

   Policy flag:   8-bit unsigned integer.

   Reserved:  Must be 0 and ignored by the server.

   The Policy Flag is defined below, and the actions taken by the DHCPv6
   server based on this flag are described in Section 6.







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   +------+------------------------------------------------------------+
   |Value | Name               | Description                           |
   +------+------------------------------------------------------------+
   | 0x01 | IPV6_DIS_TEMP_ADDR | Disable IPv6 Temporary Address        |
   +------+------------------------------------------------------------+

                       Figure 5: Policy flag Values


5.  Relay Agent Behaviour

   DHCPv6 relay agents that implement this specification MUST be
   configurable for sending the Address Selection option and the Relay-
   Supplied Prefix option.  Relay agents SHOULD have separate
   configuration for each option to determine if it is to be added to
   DHCPv6 request.  A relay agent will include these options in the
   option payload of a Request message.  DHCPv6 relay agent should set
   Address Selection option when there is a need to change the label/
   precedence value for prefixes in scenario's discussed in Section 3.1
   and/or disable IPv6 temporary addresses for the host.

      Discussion: To reduce end-user configuration of the DHCPv6 relay
      agent, the DHCPv6 relay agent can use the mechanism specified in
      [RFC3633] to automatically learn the IPv6 prefixes that will be
      delegated to DHCPv6 clients.  DHCPv6 relay agent in future can use
      leasequery-like capability discussed in section 3.2 of RFC
      [RFC5007] to learn the prefix information from DHCPv6 server.

   DHCPv6 relay agent should set Relay-Supplied Prefix option when it
   receives DHCPv6 request from a host with specific characteristics
   like authenticated using address based mechanism.  Relative
   Precedence option is used when the relay agent is unaware of the
   external prefixes to be assigned to the host.


6.  DHCPv6 Server Behaviour

   Upon receiving a DHCPv6 request containing the Address Selection
   option or the Relay-Supplied Prefix Option, the DHCPv6 server
   processing is described below:

6.1.  Address Selection option

   Address Selection option - The DHCPv6 server should send a reply to
   the host with the prefixes received from DHCPv6 relay agent along
   with Precedence.  The DHCPv6 server will merge the policy received in
   Address Selection option with it's own policy table as explained in
   section 4.3 of [I-D.ietf-6man-addr-select-opt].



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   If the option has "N" bit set to 1, the server SHOULD ignore the
   IA_TA options in the DHCPv6 request, effectively disabling the use of
   temporary addresses for that prefix.  The DHCPv6 server will ignore
   the "N" bit for destination prefixes.

   Note : If DHCPv6 servers receives both options with conflicting flags
   IPV6_DIS_TEMP_ADDR and "N" bit then it SHOULD treat it as mis-
   configuration on the relay agent and discard these options.

6.2.  Relay-Supplied Prefix Option

   The Relay-Supplied Prefix Option contains flags that defines the
   characteristics of the host.

   1.  IPV6_DIS_TEMP_ADDR - This flag indicates that Temporary IPv6
       address allocation is to be disabled for the host.  The DHCPv6
       server should ignore any IA_TA options in the DHCPv6 request.


7.  Security Considerations

   Relay-Supplied Prefix is exchanged only between the DHCPv6 relay
   agent and DHCPv6 server and Address Selection option can originate
   either from the server or the relay agent, section 21.1 of [RFC3315]
   provides details on securing DHCPv6 messages sent between servers and
   relay agents.  And, section 23 of [RFC3315] provides general DHCPv6
   security considerations.

   It is possible for a DHCPv6 client to include the Relay-Supplied
   Prefix option or the Address Selection options, which would be
   received by a DHCPv6 server.  This would cause the DHCPv6 client to
   receive a different DHCPv6 response than it would have otherwise
   received. .


8.  IANA Considerations

   IANA is requested to assign option code to OPTION_RS_PREFIX from the
   option-code space as defined in section "DHCPv6 Options" of
   [RFC3315].


9.  Change History

   [Note to RFC Editor: Please remove this section prior to
   publication.]





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9.1.  Changes from draft-reddy-mif-dhcpv6-precedence-ops-00 to -01

   o  Added Proxy Mobile IPv6 with traffic offload use-case in Section
      3.1.

   o  Updated Section 3.2.1 to highlight the ability to disable
      temporary addresses selectively.

9.2.  Changes from draft-reddy-mif-dhcpv6-precedence-ops-01 to -02

   o  Updated usecase in section 3.1

   o  Changed Absolute Precedence Option


10.  References

10.1.  Normative References

   [I-D.gont-6man-managing-privacy-extensions]
              Gont, F. and R. Broersma, "Managing the Use of Privacy
              Extensions for Stateless Address Autoconfiguration in
              IPv6", draft-gont-6man-managing-privacy-extensions-01
              (work in progress), March 2011.

   [I-D.ietf-6man-addr-select-opt]
              Matsumoto, A., Fujisaki, T., and T. Chown, "Distributing
              Address Selection Policy using DHCPv6",
              draft-ietf-6man-addr-select-opt-06 (work in progress),
              September 2012.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
              and M. Carney, "Dynamic Host Configuration Protocol for
              IPv6 (DHCPv6)", RFC 3315, July 2003.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, February 2006.

   [RFC4941]  Narten, T., Draves, R., and S. Krishnan, "Privacy
              Extensions for Stateless Address Autoconfiguration in
              IPv6", RFC 4941, September 2007.

   [RFC5007]  Brzozowski, J., Kinnear, K., Volz, B., and S. Zeng,
              "DHCPv6 Leasequery", RFC 5007, September 2007.




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   [RFC5213]  Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,
              and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008.

   [RFC6724]  Thaler, D., Draves, R., Matsumoto, A., and T. Chown,
              "Default Address Selection for Internet Protocol Version 6
              (IPv6)", RFC 6724, September 2012.

10.2.  Informative References

   [RFC3633]  Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
              Host Configuration Protocol (DHCP) version 6", RFC 3633,
              December 2003.


Authors' Addresses

   Tirumaleswar Reddy
   Cisco Systems, Inc.
   Cessna Business Park, Varthur Hobli
   Sarjapur Marathalli Outer Ring Road
   Bangalore, Karnataka  560103
   India

   Email: tireddy@cisco.com


   Prashanth Patil
   Cisco Systems, Inc.
   Cessna Business Park, Varthur Hobli
   Sarjapur Marthalli Outer Ring Road
   Bangalore, Karnataka  560103
   India

   Email: praspati@cisco.com


   Dan Wing
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, California  95134
   USA

   Email: dwing@cisco.com








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