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Versions: 00

IPv6 Operations Working Group                               A. Matsumoto
Internet-Draft                                               T. Fujisaki
Intended status: Informational                                       NTT
Expires: November 2, 2007                                      R. Hiromi
                                                             K. Kanayama
                                                           Intec Netcore
                                                                May 2007


           Solution approaches for address-selection problems
               draft-arifumi-v6ops-addr-select-sol-00.txt

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Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   In response to address selection problem statement and requirement
   documents, this document describes approaches to solutions and
   evaluates proposed solution mechanisms in line with requirements.  It
   also examines the applicability of each solution mechanism from the
   viewpoint of practical application.



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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Solution Design  . . . . . . . . . . . . . . . . . . . . . . .  3
     2.1.  Proactive approaches . . . . . . . . . . . . . . . . . . .  3
     2.2.  Reactive approaches  . . . . . . . . . . . . . . . . . . .  4
   3.  Solution approaches  . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Obtain all information prior to communication (Most
           Proactive) . . . . . . . . . . . . . . . . . . . . . . . .  4
       3.1.1.  Overview . . . . . . . . . . . . . . . . . . . . . . .  4
       3.1.2.  Requirements correspondence analysis . . . . . . . . .  5
       3.1.3.  Other issues . . . . . . . . . . . . . . . . . . . . .  6
     3.2.  Routing system assistance for address selection
           (Proactive)  . . . . . . . . . . . . . . . . . . . . . . .  6
       3.2.1.  Overview . . . . . . . . . . . . . . . . . . . . . . .  6
       3.2.2.  Requirements correspondence analysis . . . . . . . . .  6
       3.2.3.  Other issues . . . . . . . . . . . . . . . . . . . . .  7
     3.3.  Trial-and-error approach (Reactive)  . . . . . . . . . . .  7
       3.3.1.  Overview . . . . . . . . . . . . . . . . . . . . . . .  7
       3.3.2.  Requirement correspondence analysis  . . . . . . . . .  8
       3.3.3.  Other issues . . . . . . . . . . . . . . . . . . . . .  9
     3.4.  All-by-oneself approach (Most Reactive)  . . . . . . . . .  9
       3.4.1.  Overview . . . . . . . . . . . . . . . . . . . . . . .  9
       3.4.2.  Requirement correspondence analysis  . . . . . . . . .  9
       3.4.3.  Other issues . . . . . . . . . . . . . . . . . . . . . 10
   4.  Applicability Comparison . . . . . . . . . . . . . . . . . . . 11
     4.1.  Dynamic-static and managed-unmanaged . . . . . . . . . . . 11
     4.2.  Deployment Difficulty  . . . . . . . . . . . . . . . . . . 12
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
   7.  Conclusions  . . . . . . . . . . . . . . . . . . . . . . . . . 13
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 13
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
   Intellectual Property and Copyright Statements . . . . . . . . . . 16















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1.  Introduction

   One physical network can have multiple logical networks.  In that
   case, an end-host has multiple IP addresses. (e.g, in the IPv4-IPv6
   dual-stack environment, in a site that uses both ULA [RFC4193] and
   global scope addresses or in a site connected to multiple upstream
   IPv6 networks.)  For such a host, RFC 3484 [RFC3484] defines default
   address-selection rules for the source and destination addresses.

   Today, the RFC 3484 mechanism is widely implemented in major OSs.
   However, many people, including us, have found that in many sites the
   default address-selection rules are not appropriate for the network
   structure.  PS [I-D.ietf-v6ops-addr-select-ps] lists problematic
   cases that resulted from incorrect address selection.

   Though RFC 3484 made the address-selection behavior of a host
   configurable, typical users cannot make use of that because of the
   complexity of the mechanism and their lack of knowledge about their
   network topologies.  Therefore, an address-selection
   autoconfiguration mechanism is necessary, especially for the
   unmanaged hosts of typical users.

   REQ [I-D.ietf-v6ops-addr-select-req] document enumerates requirements
   for address-selection mechanisms that enable hosts to perform
   appropriate address selection automatically.

   In the IETF mailing lists and in the internet-draft archives, some
   mechanisms for solving address-selection problems have already been
   proposed.  This document describes possible design approaches for
   solving address selection problems.  After that, we try to put
   together an overview as well as an analysis of how well the method
   corresponds with the requirements.


2.  Solution Design

   There are two types of approaches that can control the behavior of
   hosts in terms of the selection of destination address and source
   address.  The first type is proactive, where the host is given the
   necessary information to decide the destination and source addresses
   before the beginning of transmission.  The other type is reactive,
   where the host decides appropriate destination address and source
   addresses through trial and error.

2.1.  Proactive approaches

   There can be two types of proactive approaches.  One gives hosts all
   the information for selecting destination and address and source



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   addresses beforehand.  Under some circumstances, a lot of information
   could be stored in hosts.

   The other type informs hosts about which prefixes should be used in
   the source address for the different destinations every time before
   starting each connection.

2.2.  Reactive approaches

   In these approaches, the host does not have initial information for
   address selection.  It will try using different pairs of destination
   and source addresses until the connection is established.  When an
   outage occurs, the host must detect it and try again with a new pair
   of destination address and source address.  Some reactive solutions
   may use some kind of control message that enables the gateway to
   indicate the outage.


3.  Solution approaches

   This section describes the evaluation of the four approaches to
   finding solutions.  The evaluation value has a 3-point scale for each
   of 8 requirements in the requirement document.  The meaning of the
   points is as follows.

           1 : bad
           2 : fair
           3 : good

   About "Effectiveness", the score is 1 if the approach solves no
   problematic cases described in the problem statement document, 2 if
   it can handle at least one, and 3 if it solves every case.

3.1.  Obtain all information prior to communication (Most Proactive)

3.1.1.  Overview

   In this approach, a host obtains everything needed to select
   addresses at once prior to communication.  A host receives all policy
   information from a server beforehand.  It then sets up communication
   whenever it wants to.  DHCPv6 and RA fall into this category as known
   protocols.  There is a reference document
   [I-D.fujisaki-dhc-addr-select-opt] in which DHCPv6 is used for this
   purpose.

   This approach can take advantage of the RFC 3484 Policy Table, which
   is already widely deployed.  By distributing policies for the Policy
   Table, you can auto-configure a host's address selection policy.



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3.1.2.  Requirements correspondence analysis

   1.  Effectiveness: 3
      It can support all cases by using the policy table.

   2.  Timing: 3
      All information for communication is in a host in advance.
      Communication starts at once when it is necessary and the
      communication process refers to local policy information, so it
      exhibits good usability.  Moreover, this leads to fewer overheads
      than per-connection mechanisms.

   3.  Dynamic update: 3
      Though it depends on what protocol is used to distribute the
      policies, some mechanisms support information updates from the
      server.  Moreover, it is difficult to support dynamic network
      changes and real-time updates in some specific protocols.

   4.  Node-specific behavior: 3
      For distribution to individual hosts in the same segment, DHCPv6
      can be used.

   5.  Application-specific behavior: 2
      The policy table itself doesn't support application-specific
      address selection.  It can be done using the address selection
      API.  [I-D.chakrabarti-ipv6-addrselect-api]

   6.  Multiple interfaces: 2
      If all interfaces belong to the same administration domain, it is
      possible for the address-selection information to be controlled by
      administrators of that domain.  However, if not, routing
      information and address selection policies are not always
      equivalent between domains, and it is not possible to handle them.

   7.  Central control: 3
      It can support central control.  A site administrator or a service
      provider can determine users' policy tables.

   8.  Route selection: 2
      Current solutions, such as DHCPv6 and RA, do not have a mechanism
      for cooperation with routing protocols.  This could be done with
      other techniques such as "source address based routing" or
      "Default Router Preferences and More-Specific Routes" RFC4191.
      [RFC4191]







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3.1.3.  Other issues
   -  The traffic volume will be equal to the number of policies.

   -  Hosts and servers need to support this function.

3.2.  Routing system assistance for address selection (Proactive)

3.2.1.  Overview

   Fred Baker proposed this approach.  A host asks the DMZ routers or
   the local router which is the best pair of source and destination
   addresses when the host has a set of addresses A and the destination
   host has a set of addresses B. Then, the host uses the policy
   provided by the server/routing system as a guide in applying the
   response.  He also proposed a mechanism that utilizes the ICMP error
   message to change the source address of the existing session.  This
   point resembles Section 3.3 3484update mechanism, so the following
   evaluation is based on only the first part of his proposal.

3.2.2.  Requirements correspondence analysis

   1.  Effectiveness: 3
      A routing system knows about information about paths toward the
      destination and information about which of their prefixes should
      be used.  Therefore, it is possible to select an appropriate pair
      of source and destination addresses.

   2.  Timing: 3
      A routing system always has up-to-date routing information, so it
      will be possible to provide suitable information whenever requests
      come.  However, the amount of information that the system must
      handle is huge, so there will be cases where it takes time to
      answer the request because appropriate information must be
      retrieved from a huge database.
      If any server or routing trouble occurs, the requester cannot get
      the answer, and address selection will fail.  This point is the
      same in all systems that depend on other servers.

   3.  Dynamic update: 3
      A routing system always has up-to-date routing information, and it
      will be possible to provide suitable information whenever requests
      come.

   4.  Node-pecific behavior: 3







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      Node-specific information can be provided if a server recognizes
      individual nodes.

   5.  Application-specific behavior: 2
      A routing system does not care about applications.  Using address
      selection API allows nodes to behave in an application-specific
      way.

   6.  Multiple Interfaces: 2
      If all interfaces belong to the same administration domain, it is
      possible for the address-selection information to be controlled by
      administrators of that domain.  However, if not, routing
      information and address selection policies are not always
      equivalent between domains, and it is not possible to handle them.

   7.  Central Control: 3
      It is possible to provide address selection information from one
      source.  However, because routing information changes dynamically,
      it is difficult to control it in the way that administrators want.

   8.  Route Selection: 3
      It is possible to give next-hop selection advice to a host.  As
      routers have routing information, it would seem to be easier for
      routers to implement this function.

3.2.3.  Other issues
   -  A host must consult the routing system every time it starts a
      connection if the host does not have address selection information
      for the destination host or if the information lifetime has
      expired.  This could be a possible scalability problem.

   -  The existing host/router OS implementation must be changed a lot.
      In the existing TCP/IP protocol stack implementation, destination
      address selection is mainly the role of the application and not
      that of the kernel unlike source address selection.  Therefore,
      implementing this model without affecting applications is not so
      easy.

3.3.  Trial-and-error approach (Reactive)

3.3.1.  Overview

   M. Bagnulo proposed a new address selection method in his draft.
   When the host notices that a network failure has occurred or packets
   have been dropped somewhere in the network by, for example, an
   ingress filter, the host changes the source address of the connection
   to another source address.




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   Hosts may use some kinds of error messages, e.g, ICMP error messages,
   from a network to detect that sent packets did not reach the
   destination quickly.

   The host stores a cache of address selection information so that the
   host can select an appropriate source address for new connections.

   For source address selection by the application that initiated a
   communication, this method provides an ordered list of source
   addresses for the destination address to the application.

3.3.2.  Requirement correspondence analysis

   1.  Effectiveness: 2
      This solution is not effective for the problem about IPv4 or IPv6
      prioritization described in the problem statement document.

   2.  Timing: 2
      Hosts should try to use all the available source addresses to the
      maximum to find an appropriate source address.  If the host tries
      the next source address after the previous trial using another
      source address has failed, it may take a long time because this
      trial-and-error process lasts until the connection succeeds.  If
      the host does not use an error message from a network to detect a
      connection error, it takes longer to wait for a time-out.

   3.  Dynamic update: 3
      If hosts detect a connection failure using some reliable
      mechanism, such like TCP or ICMP error messages, a connection
      failure caused by some changes in the network will be detected
      immediately by the hosts.

   4.  Node-specific behavior: 2
      This solution does not have a function for node-specific behavior.
      However, it is not impossible to implement by setting a packet
      filter for each node at the gateways through which the packets
      from nodes pass.

   5.  Application-specific behavior: 2
      This solution does not have a function for application-specific
      behavior.  However, the mechanism of this approach does not
      exclude address selection by each application.

   6.  Multiple interfaces: 3







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      If the protocol-stack or an application supports interface
      selection and it tries to establish a connection by changing
      addresses and also interfaces, it can find a working combination
      of addresses and interface.

   7.  Central control: 2
      The only way that a central administrator has to control the node
      behavior is switching a filter on/off on the network.  Therefore,
      advanced control such as traffic engineering and QoS is almost
      impossible.

   8.  Route Selection: 2
      This solution does not refer to next-hop selection for the
      transmission of a packet.  So, it should be used with some routing
      function such as RFC 4191 on the nodes.

3.3.3.  Other issues
   -  A host must learn address selection information for each
      destination host.  Therefore, the number of cache entries could be
      very large.

   -  The existing host/router OS implementation must be changed a lot.
      In particular, changing the source address of the existing
      connection is not so easy and has a big impact on the existing
      TCP/IP protocol stack implementation.

3.4.  All-by-oneself approach (Most Reactive)

3.4.1.  Overview

   shim6 was designed for site-multihoming.  This mechanism introduces a
   new address selection method for session initiation and session
   survivability; it is documented in two drafts:
   [I-D.ietf-shim6-locator-pair-selection] and
   [I-D.ietf-shim6-failure-detection].

   The shim6 host detects connection failures and changes the
   destination and source addresses during the session.

   In this document, we focus on address selection issues in the
   connection initiation phase of shim6 and not on any other functions,
   such as session survivability.

3.4.2.  Requirement correspondence analysis

   1.  Effectiveness: 2





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      This solution is not effective for the problem about IPv4 or IPv6
      prioritization described in the problem statement document.

   2.  Timing: 2
      Hosts should try to use all the available source addresses to the
      maximum to find an appropriate source address.  If the host tries
      the next source address after the previous trial using another
      source address has failed, it may take a long time because this
      trial-and-error process lasts until the connection succeeds.  If
      the host does not use error messages from a network to detect a
      connection error, it takes longer to wait for a time-out.

   3.  Dynamic update: 3
      It can reflect dynamically changing network, as far as it always
      tries all possible addresses and next-hops.

   4.  Node-specific behavior: 2
      This solution does not have a function for node-specific behavior.
      However, it is not impossible to implement by setting a packet
      filter for each node on the gateways through which the packets
      from nodes pass.

   5.  Application-specific behavior: 2
      The use of shim6 API [I-D.ietf-shim6-multihome-shim-api] allows
      applications to override address selection behavior.

   6.  Multiple interfaces: 3
      If the protocol-stack supports interface selection and it tries to
      establish a connection by changing addresses and also interfaces,
      it can find a working combination of addresses and interface.

   7.  Central control: 2
      The only way that a central administrator has to control the node
      behavior is switching a filter on/off on the network.  Therefore,
      advanced control such as traffic engineering and QoS is almost
      impossible.

   8.  Route Selection: 2
      This solution does not refer to next-hop selection for the
      transmission of a packet.  Therefore, it should be used with some
      routing function such as RFC 4191 on the nodes.

3.4.3.  Other issues
   -  The shim6 host performs address selection that reflects network
      failures that have occurred between the source and destination
      host.





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   -  End hosts themselves can avoid network failure.  There is no need
      to modify or reconfigure routers in the path.

   -  A host must learn address selection information for each
      destination host.  Therefore, the number of cache entries can be
      very large.

   -  The existing host OS implementation must be changed significantly.


4.  Applicability Comparison

   In the previous section, every approach scored "fair" or better for
   every requirement.  This means that every approach can meet the
   demands of address selection.  However, if you actually want to
   choose one mechanism to solve your address selection problem, it is
   important to figure out which approach is best suited to your
   situation.  This section tries to evaluate the applicability of each
   approach from several aspects.

4.1.  Dynamic-static and managed-unmanaged

   First, we use two axes to evaluate the applicability of the four
   approaches.  One axis shows whether or not the network structure
   changes dynamically and the other axis shows whether the site is
   managed or unmanaged.  In a managed network, by our definition, a
   network administrator manages his or her network, routers, and hosts.
   For example, an enterprise network is managed, whereas a home network
   and a SOHO network are unmanaged.

                 static                               dynamic
                 <-------------------------------------------->
      unmanaged ^ +----------+   +---------------------------+
                | |          | +-+--------------+      shim6 |
                | |          | | |              |            |
                | |       +--+-+-+------------+ |            |
                | |       |  | | |            | |            |
                | |       |  | | |            | |            |
                | |       |  | | +------------+-+------------+
                | |       |  | |    3484update| |
                | |       +--+-+--------------+ |
                | |          | |                |
                | |          | |                |
                | |  Policy  | |   RouterAssist |
                | |   Dist   | |                |
                | |          | |                |
                | +----------+ +----------------+



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        managed v


   PolicyDist:
   -  In a dynamic site, the policy table must be updated accordingly
      and traffic for policy table distribution increases.

   3484update:
   -  This is a slightly manageable than shim6 in that 3484update does
      not change the paths of established connections dynamically.

   -  In a very dynamic site, the use of an address selection
      information cache does not have a good effect.  This results in
      connection failure and may degrade usability badly.

   -  Even in a very static site, a host may try inappropriate addresses
      or next-hops and experience connection failures.

   RouterAssist:
   -  A host must send at least as many queries as the number
      destination hosts.  Therefore, in a static site, this method is
      not optimal.

   -  In a very dynamic site, address selection information cache is no
      help.  If the cache function is not used, then connection failures
      do not occur.

   shim6:
   -  In a static site, shim6 is not desirable because of its connection
      sequence overhead and timeout-wait for path exploration.

   -  In a managed site, shim6 is not easy to manage in terms of node-
      specific address selection control and central control.

4.2.  Deployment Difficulty


       less                                      more
       <------------------------------------------->
           policy-dist   3484update   shim6   Fred


   PolicyDist:
   -  What must be implemented is a distribution mechanism.  The
      existing protocols, such as RA and DHCP, can be used for this
      purpose.

   3484update:



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   -  The protocol stack or applications on a host must be modified.
      Routers in a site must be configured to return error messages to
      the sender of inappropriately addressed packets.

   RouterAssist:
   -  The protocol stack and applications on a host must be modified.
      Furthermore, routers must be modified.

   shim6:
   -  The protocol stack must be modified.  For this address selection
      purpose, corresponding nodes need not support shim6.  Basically,
      there is no need to change the router implementation or
      configuration.


5.  Security Considerations

   Incorrect address selection can lead to serious security problems,
   such as session hijacking.  However, we should note that address-
   selection is ultimately decided by nodes and their users.  There are
   no means to enforce a specific address-selection behavior upon every
   end-host from outside the host.  Therefore, a network administrator
   must take countermeasures against unexpected address selection.


6.  IANA Considerations

   This document has no actions for IANA.


7.  Conclusions

   In this document, we examined solutions to address selection problems
   in the IPv6 multi-prefix environment.  Although almost all solutions
   examined in this document could be applied to any environment and
   situation, a solution with a mechanism that is suitable for the
   situation should be selected.


8.  References

8.1.  Normative References

   [I-D.ietf-v6ops-addr-select-ps]
              Matsumoto, A., "Problem Statement of Default Address
              Selection in Multi-prefix Environment:  Operational Issues
              of RFC3484 Default Rules",
              draft-ietf-v6ops-addr-select-ps-01 (work in progress),



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              April 2007.

   [I-D.ietf-v6ops-addr-select-req]
              Matsumoto, A., "Requirements for address selection
              mechanisms", draft-ietf-v6ops-addr-select-req-02 (work in
              progress), May 2007.

   [RFC3484]  Draves, R., "Default Address Selection for Internet
              Protocol version 6 (IPv6)", RFC 3484, February 2003.

8.2.  Informative References

   [I-D.chakrabarti-ipv6-addrselect-api]
              Nordmark, E., "IPv6 Socket API for Address Selection",
              draft-chakrabarti-ipv6-addrselect-api-06 (work in
              progress), May 2007.

   [I-D.fujisaki-dhc-addr-select-opt]
              Fujisaki, T., "Distributing Default Address Selection
              Policy using DHCPv6",
              draft-fujisaki-dhc-addr-select-opt-03 (work in progress),
              January 2007.

   [I-D.ietf-shim6-failure-detection]
              Arkko, J. and I. Beijnum, "Failure Detection and Locator
              Pair Exploration Protocol for IPv6  Multihoming",
              draft-ietf-shim6-failure-detection-07 (work in progress),
              December 2006.

   [I-D.ietf-shim6-locator-pair-selection]
              Bagnulo, M., "Default Locator-pair selection algorithm for
              the SHIM6 protocol",
              draft-ietf-shim6-locator-pair-selection-01 (work in
              progress), October 2006.

   [I-D.ietf-shim6-multihome-shim-api]
              Komu, M., "Socket Application Program Interface (API) for
              Multihoming Shim", draft-ietf-shim6-multihome-shim-api-02
              (work in progress), March 2007.

   [RFC4191]  Draves, R. and D. Thaler, "Default Router Preferences and
              More-Specific Routes", RFC 4191, November 2005.

   [RFC4193]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
              Addresses", RFC 4193, October 2005.






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Authors' Addresses

   Arifumi Matsumoto
   NTT PF Lab
   Midori-Cho 3-9-11
   Musashino-shi, Tokyo  180-8585
   Japan

   Phone: +81 422 59 3334
   Email: arifumi@nttv6.net


   Tomohiro Fujisaki
   NTT PF Lab
   Midori-Cho 3-9-11
   Musashino-shi, Tokyo  180-8585
   Japan

   Phone: +81 422 59 7351
   Email: fujisaki@syce.net


   Ruri Hiromi
   Intec Netcore, Inc.
   Shinsuna 1-3-3
   Koto-ku, Tokyo  136-0075
   Japan

   Phone: +81 3 5665 5069
   Email: hiromi@inetcore.com


   Ken-ichi Kanayama
   Intec Netcore, Inc.
   Shinsuna 1-3-3
   Koto-ku, Tokyo  136-0075
   Japan

   Phone: +81 3 5665 5069
   Email: kanayama@inetcore.com











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Internet-Draft         Address-Selection Solutions              May 2007


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