[Search] [txt|pdf|bibtex] [Tracker] [Email] [Nits]

Versions: 00                                                            
Network Working Group                                            M. Komu
Internet-Draft                                                      HIIT
Expires: August 5, 2006                                       M. Bagnulo
                                                                    UC3M
                                                               K. Slavov
                                                        S. Sugimoto, Ed.
                                                                Ericsson
                                                           February 2006


    Socket Application Program Interface (API) for Multihoming Shim
                  draft-sugimoto-multihome-shim-api-00

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   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.

   This Internet-Draft will expire on August 5, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This document specifies a socket API for the multihoming shim layer.
   The API aims to enable interactions between the applications and the
   multihoming shim layer for advanced locator management and also for
   accessing to information about failure detection and path



Komu, et al.             Expires August 5, 2006                 [Page 1]


Internet-Draft            Multihoming Shim API             February 2006


   exploration.

   This document is based on an assumption that a multhomed host is
   equipped with a 'shim' layer which essentially maintains mappings
   between identifiers and locators at the IP layer.  SHIM6 and HIP are
   examples of this shim layer.  Hence, the API can be commonly used by
   SHIM6 and HIP.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Target . . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   4.  System Overview  . . . . . . . . . . . . . . . . . . . . . . .  6
   5.  Requirements . . . . . . . . . . . . . . . . . . . . . . . . .  7
   6.  Socket Options for Multihomed Shim Layer . . . . . . . . . . .  9
     6.1.  SHIM_ASSOCIATED  . . . . . . . . . . . . . . . . . . . . . 12
     6.2.  SHIM_DONTSHIM  . . . . . . . . . . . . . . . . . . . . . . 12
     6.3.  SHIM_HOT_STANDBY . . . . . . . . . . . . . . . . . . . . . 13
     6.4.  SHIM_PATHEXPLORE . . . . . . . . . . . . . . . . . . . . . 13
     6.5.  SHIM_LOC_LOCAL_PREF  . . . . . . . . . . . . . . . . . . . 13
     6.6.  SHIM_LOC_PEER_PREF . . . . . . . . . . . . . . . . . . . . 14
     6.7.  SHIM_LOC_LOCAL_RECV  . . . . . . . . . . . . . . . . . . . 14
     6.8.  SHIM_LOC_PEER_RECV . . . . . . . . . . . . . . . . . . . . 15
     6.9.  SHIM_LOCLIST_LOCAL . . . . . . . . . . . . . . . . . . . . 15
     6.10. SHIM_LOCLIST_PEER  . . . . . . . . . . . . . . . . . . . . 15
     6.11. SHIM_APP_TIMEOUT . . . . . . . . . . . . . . . . . . . . . 16
     6.12. SHIM_FEEDBACK_POSITIVE . . . . . . . . . . . . . . . . . . 16
     6.13. SHIM_FEEDBACK_NEGATIVE . . . . . . . . . . . . . . . . . . 16
     6.14. SHIM_DEFERRED_CONTEXT_SETUP  . . . . . . . . . . . . . . . 17
     6.15. SHIM_IF_RECV . . . . . . . . . . . . . . . . . . . . . . . 17
     6.16. SHIM_IF_SEND . . . . . . . . . . . . . . . . . . . . . . . 17
     6.17. Error Handling . . . . . . . . . . . . . . . . . . . . . . 17
   7.  Access to Locator Information  . . . . . . . . . . . . . . . . 18
     7.1.  Get Locator Information from Incoming Packet . . . . . . . 19
     7.2.  Specify Locator Information for Outgoing Packet  . . . . . 20
   8.  Data Structures  . . . . . . . . . . . . . . . . . . . . . . . 20
     8.1.  Placeholder for Locator Information  . . . . . . . . . . . 20
       8.1.1.  addrinfo structure . . . . . . . . . . . . . . . . . . 20
       8.1.2.  sockaddr_storage structure . . . . . . . . . . . . . . 21
   9.  Implications for Existing Socket API Extensions  . . . . . . . 22
   10. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 23
     10.1. Issues with a Context Shared by Applications . . . . . . . 23
     10.2. Issues with Shim Unaware Application . . . . . . . . . . . 24
       10.2.1. Initial Contact with Multiple Locator Pairs  . . . . . 24
       10.2.2. Naming at Socket Layer . . . . . . . . . . . . . . . . 25
     10.3. Additional Requirements from Application . . . . . . . . . 25



Komu, et al.             Expires August 5, 2006                 [Page 2]


Internet-Draft            Multihoming Shim API             February 2006


     10.4. Issues of Header Conversion among Different Address
           Family . . . . . . . . . . . . . . . . . . . . . . . . . . 26
     10.5. Handling of Unknown Locator Provided by Application  . . . 26
   11. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 26
   12. Security Considerations  . . . . . . . . . . . . . . . . . . . 26
   13. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 27
   14. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 27
   15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 27
     15.1. Normative References . . . . . . . . . . . . . . . . . . . 27
     15.2. Informative References . . . . . . . . . . . . . . . . . . 28
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29
   Intellectual Property and Copyright Statements . . . . . . . . . . 30







































Komu, et al.             Expires August 5, 2006                 [Page 3]


Internet-Draft            Multihoming Shim API             February 2006


1.  Introduction

   This document specifies a socket API for the multihoming shim layer.
   The API aims to enable interactions between application and the
   multihoming shim layer for advanced locator management and for
   accessing to information about failure detection and path
   exploration.

   This document is based on an assumption that a multhomed host is
   equipped with a 'shim' layer which essentially maintains mapping
   between identifiers and locators at the IP layer.  SHIM6 and HIP are
   examples of the shim.  Hence, the API can be commonly used by SHIM6
   and HIP.

   We suggest that the ID/Locator adaptation is done only once inside
   the network stack.  In other words, if there exist multiple shim
   sublayers at the IP layer, any one of them should be exclusively
   applied for a given flow.

   We try to make this document be in line with Posix standard [POSIX]
   as much as possible.  And the API defines how to use ancillary data
   (aka cmsg) to access locator information with recvmsg() and/or
   sendmsg() I/O calls.  Definition of API is presented in C language
   and data types follow Posix format: intN_t means a singed integer of
   exactly N bits (e.g. int16_t) and uintN_t means an unsigned integer
   of exactly N bits (e.g. uint32_t).


2.  Target

   The primary target reader of this document is application programmers
   who develop application software which may run on top of a multihomed
   environment.  In particular, the API should be beneficial for
   application development of the software which takes advantage of
   multihomed environment aiming to achieve better failover.

   Secondly, this document should be of interest for the developers of a
   given protocol stack for the shim layer (e.g.  SHIM6 and HIP).  This
   is because this document specifies what kinds of information exchange
   should be possible between the applications and the shim layer.


3.  Terminology

   This document does not intend to give new definitions for technical
   terms that are relevant to multihomed environments but tries to
   inherit definitions provided in the existing documents as listed
   below:



Komu, et al.             Expires August 5, 2006                 [Page 4]


Internet-Draft            Multihoming Shim API             February 2006


   o  SHIM6 Protocol Specification[I-D.ietf-shim6-proto]
   o  HIP Architecture[I-D.ietf-hip-arch]
   o  Reachability Protocol (REAP)[I-D.ietf-shim6-failure-detection]

   For clarification, we provide definition for the terms that are
   frequently used in this document:

   o  Endpoint Identifier (EID) - An identifier used by the application
      to specify an endpoint of the communication.  As addressed in
      [I-D.ietf-shim6-app-refer], application may handle and EID in
      various ways in different types of communication models such as
      long-lived connections, callbacks, and referrals.
      *  In case of SHIM6, the EID is called ULID.  The ULID is chosen
         from one of the locators available on the host.
      *  In case of HIP, the EID is essentially a public key of the
         host.  In order to preserve backward compatibility with legacy
         applications, a hash of public key called Host Identity Tag
         (HIT) is used by the applications as a handle for the EID.
   o  Locator - An IP address actually used to deliver IP packets.
      Locators should be present in the source and destination fields of
      the IP header of a packet that appears on wire.  Normally, a
      locator is assigned to the network interface of the host.  And the
      IP packet destined to a given locator is delivered to the
      correspondent network interface by the routing system.
   o  Shim - A conceptual (sub-)layer inside the IP Layer which
      maintains mappings of EIDs and locators.  An EID can be associated
      with more than one locator at a time when the host is multihomed.
      It should be noted that the term 'shim' does not refer to a
      specific protocol but refers to the generic concept of a layer
      that enables the mapping between identifiers and locators.  SHIM6
      and HIP are examples of the shim.
   o  Context - A state information shared by the peers, which
      essentially stores a binding between the EIDs and associated
      locators.  The context is maintained at the shim layer of the
      host.
   o  List of Locators - A list of locators associated with an EID.
      There are two lists of locators stored in a given context, one is
      associated with the local EID and the other is associated with the
      remote EID.  As defined in [I-D.ietf-shim6-proto], the list of
      locators associated with an EID 'A' can be denoted as Ls(A).
   o  Preferred Locator - The (source/destination) locator currently
      used to send packets.  As defined in [I-D.ietf-shim6-proto], the
      preferred locator of a host which EID is 'A' can be denoted as
      Lp(A).
   o  Reachability Detection - A procedure to detect reachability
      between a given locator pair.





Komu, et al.             Expires August 5, 2006                 [Page 5]


Internet-Draft            Multihoming Shim API             February 2006


   o  Path - A sequence of routers that an IP packet goes through to
      reach the destination.
   o  Path Exploration - A procedure to explore available paths for a
      given set of locator pairs.
   o  Outage - An incident meaning that the reachability among a given
      locator pair is lost.  The outage could be caused by any kind of
      problems inside the routing infrastructure and/or problems of the
      network interfaces of the end hosts.
   o  Working Address Pair - An address pair is said to be working if
      the packet containing the first address from the pair as source
      address and the second address from the pair as destination
      address can safely travel from the source to the destination.  If
      the reachability is confirmed in both directions, the address
      pairs is said to be bi-directional.  Otherwise, it's
      unidirectional.
   o  REAP - A protocol for detecting failure and exploring reachability
      in a multihomed environment.  REAP is defined in[I-D.ietf-shim6-
      failure-detection].
   o  Endpoint Descriptor (ED) - The representation of endpoints is
      hidden from the applications.  ED is a "handle" or "pointer" to
      the actual EID.


4.  System Overview


                        +------------------------+
                        |       Application      |
                        +------------------------+
                           ^                 ^
              ~~~~~~~~~~~~~|~Socket Interface|~~~~~~~~~~~~~~
                           |                 v
               +-----------|------------------------------+
               |           |  Transport Layer             |
               +-----------|------------------------------+
                     ^     |
       +-------------|-----|-------------------------------------+
       |             v     v                                     |
       |   +-----------------------------+       +----------+    |  IP
       |   |            Shim             |<----->|   REAP   |    | Layer
       |   +-----------------------------+       +----------+    |
       |                       ^                      ^          |
       +-----------------------|----------------------|----------+
                               v                      v
               +------------------------------------------+
               |                Link Layer                |
               +------------------------------------------+




Komu, et al.             Expires August 5, 2006                 [Page 6]


Internet-Draft            Multihoming Shim API             February 2006


   Figure 1: System overview

   Figure 1 illustrates the system overview.  The application can use
   the socket API to interact with the shim layer and the transport
   layer for better control of locator management, failure detection and
   path exploration.

   Inside the IP layer, there is the shim which closely interacts with
   REAP component.  There could be interactions between the shim and the
   transport layer, however they are outside of scope of this document.
   The scope of this document is an interface from the application to
   the shim layer, which is enabled via the socket interface.


5.  Requirements

   The list of requirements from the application perspective is the
   following.  These requirements are mainly identified during the
   discussions on SHIM6 WG mailing list.  Some requirements are derived
   from Reachability Protocol document[I-D.ietf-shim6-failure-
   detection].

   o  Locator management.  The shim layer selects a pair of locators for
      sending IP packets within a given context.  The selection is made
      by taking miscellaneous conditions into account such as
      reachability of the path, application's preference, and
      characteristics of path.  From the application's perspective:
      *  It should be possible to obtain the lists of locators of a
         given context: Ls(local) and Ls(remote).
      *  It should be possible to obtain the preferred locators of a
         given context: Lp(local) and Lp(remote).
   o  Notification from the application to the shim layer about the
      status of the communication.  Note that the notification is made
      in an event based manner.  There are mainly two aspects of the
      feedback that application or upper layer protocol may provide for
      the shim layer, positive and negative feedbacks [NOTE: These
      feedbacks are addressed in section 4.3 and section 5.2 of REAP
      specification]:
      *  Positive feedback could be given by the application or upper
         layer protocol (e.g.  TCP) to the shim layer informing that the
         communication is going well.
      *  Negative feedback could be given by the application or upper
         layer protocol (e.g.  TCP) to the shim layer informing that the
         communication status is not satisfactory.  TCP could detect a
         problem when it does not receives expected ACK from the peer.
         ICMP error messages delivered to the upper layer protocol could
         be a clue for application to detect potential problems.  REAP
         module may be triggered by these negative feedbacks and invoke



Komu, et al.             Expires August 5, 2006                 [Page 7]


Internet-Draft            Multihoming Shim API             February 2006


         procedure of path exploration.
   o  Feedback from application to shim layer.  The application should
      be able to inform the shim layer about the timeout values for
      detecting failures, for sending keepalives, for starting the
      exploration procedure.  In particular, the application should be
      able to suppress the keepalives.
   o  Hot-standby.  The application may request the shim layer for hot-
      standby capabilities.  In this case, alternative paths are known
      to be working before a failure is detected.  Hence it is possible
      for the host to immediately replace the current locator pair with
      the alternative locator pair.  Hot-standby may allow applications
      to achieve better failover.
   o  Eagerness of locator exploration.  The application should be able
      to inform the shim layer how aggressive it wants REAP mechanism to
      perform path exploration (e.g. specifying the number of concurrent
      attempts of discovering working locator pair) when an outage
      occurs on the path between the currently selected locator pair.
   o  Providing locator information to application.  The application
      should be able to obtain information about the locator pair which
      was actually used to send or receive the packet.
      *  For inbound traffic, the application may be interested in the
         locator pair which was actually used to receive the packet.
      *  For outbound traffic, the application may be interested in the
         locator pair which was actually used to transmit the packet.
      In this way, the application may have additional control on the
      locator management.  For example, the application can verify if
      its preference of locator is actually applied to the flow or not.
   o  The application should be able to specify if it wants to defer the
      context setup or if it wants context establishment to be started
      immediately in case there is no available context.  With deferred
      context setup, there should be no additional delay imposed by
      context establishment in initiation of communication.
   o  Turn on/off shim.  The application should be able to request to
      turn on/off the multihoming support by the shim layer:
      *  Apply shim.  The application should be able to explicitly
         request the shim layer to apply multihoming support.
      *  Don't apply shim.  The application should be able to request
         the shim layer not to apply the multihoming support but to
         apply normal IP processing at the IP layer.
   o  The application should be able to know if the communication is now
      served by the shim layer or not.
   o  The application should be able to access locator information
      regardless of its address family.  In other words, no matter the
      target locator is IPv4 or IPv6, the application should be able to
      use common interface to access the locator information.






Komu, et al.             Expires August 5, 2006                 [Page 8]


Internet-Draft            Multihoming Shim API             February 2006


6.  Socket Options for Multihomed Shim Layer

   In this section, the socket options for the interface between the
   application and the multihomed shim layer are defined.  These options
   can be used either by getsockopt() and/or setsockopt() system calls
   for an opened socket.  Table 1 provides a list of the socket options.
   Note that all socket options are defined at level SOL_SHIM.

   The first column of the table gives the name of the option.  The
   second and third columns indicates whether if the option is for
   getsockopt() and/or setsockopt(), respectively.  The fourth column
   provides a brief description of the socket option.  The fifth column
   shows the data structure specified with the socket option, which can
   store an argument for setsockopt() and result for getsockopt().  By
   default, the data structure is an integer.

   +-----------------------------+-----+-----+-----------------+-------+
   | optname                     | get | set | description     | dtype |
   +-----------------------------+-----+-----+-----------------+-------+
   | SHIM_ASSOCIATED             | o   |     | Check if the    | int   |
   |                             |     |     | socket is       |       |
   |                             |     |     | associated with |       |
   |                             |     |     | any shim        |       |
   |                             |     |     | context or not. |       |
   | SHIM_DONTSHIM               | o   | o   | Request the     | int   |
   |                             |     |     | shim layer not  |       |
   |                             |     |     | to apply any    |       |
   |                             |     |     | multihoming     |       |
   |                             |     |     | support for the |       |
   |                             |     |     | communication.  |       |
   | SHIM_HOT_STANDBY            |     | o   | Request the     | int   |
   |                             |     |     | shim layer to   |       |
   |                             |     |     | prepare a       |       |
   |                             |     |     | hot-standby     |       |
   |                             |     |     | connection (in  |       |
   |                             |     |     | addition to the |       |
   |                             |     |     | current path).  |       |
   | SHIM_LOC_LOCAL_PREF         | o   | o   | Get or set the  | *1    |
   |                             |     |     | preferred       |       |
   |                             |     |     | locator on the  |       |
   |                             |     |     | local side for  |       |
   |                             |     |     | the context     |       |
   |                             |     |     | associated with |       |
   |                             |     |     | the socket.     |       |







Komu, et al.             Expires August 5, 2006                 [Page 9]


Internet-Draft            Multihoming Shim API             February 2006


   | SHIM_LOC_PEER_PREF          | o   | o   | Get or set the  | *1    |
   |                             |     |     | preferred       |       |
   |                             |     |     | locator on the  |       |
   |                             |     |     | remote side for |       |
   |                             |     |     | the context     |       |
   |                             |     |     | associated with |       |
   |                             |     |     | the socket.     |       |
   | SHIM_LOC_LOCAL_RECV         |     | o   | Request for the | int   |
   |                             |     |     | destination     |       |
   |                             |     |     | locator of the  |       |
   |                             |     |     | received IP     |       |
   |                             |     |     | packet.         |       |
   | SHIM_LOC_PEER_RECV          |     | o   | Request for the | int   |
   |                             |     |     | source locator  |       |
   |                             |     |     | of the received |       |
   |                             |     |     | IP packet.      |       |
   | SHIM_LOCLIST_LOCAL          | o   | o   | Get or set a    | *1    |
   |                             |     |     | list of         |       |
   |                             |     |     | locators        |       |
   |                             |     |     | associated with |       |
   |                             |     |     | the local EID.  |       |
   | SHIM_LOCLIST_PEER           | o   | o   | Get or set a    | *1    |
   |                             |     |     | list of         |       |
   |                             |     |     | locators        |       |
   |                             |     |     | associated with |       |
   |                             |     |     | the peer's EID. |       |
   | SHIM_APP_TIMEOUT            |     | o   | Inform the shim | int   |
   |                             |     |     | layer about a   |       |
   |                             |     |     | timeout value   |       |
   |                             |     |     | for detecting   |       |
   |                             |     |     | failure.        |       |
   | SHIM_FEEDBACK_POSITIVE      |     | o   | Provide a       | int   |
   |                             |     |     | positive        |       |
   |                             |     |     | feedback to the |       |
   |                             |     |     | shim layer.     |       |
   | SHIM_FEEDBACK_NEGATIVE      |     | o   | Provide a       | *2    |
   |                             |     |     | negative        |       |
   |                             |     |     | feedback to the |       |
   |                             |     |     | shim layer.     |       |
   | SHIM_PATHEXPLORE            |     | o   | Specify how     | *3    |
   |                             |     |     | path            |       |
   |                             |     |     | exploration     |       |
   |                             |     |     | should be       |       |
   |                             |     |     | performed in    |       |
   |                             |     |     | case of         |       |
   |                             |     |     | failure.        |       |





Komu, et al.             Expires August 5, 2006                [Page 10]


Internet-Draft            Multihoming Shim API             February 2006


   | SHIM_CONTEXT_DEFERRED_SETUP |     | o   | Specify if the  | int   |
   |                             |     |     | context setup   |       |
   |                             |     |     | can be deferred |       |
   |                             |     |     | or not.         |       |
   | SHIM_IF_RECV                |     | o   | Request for a   | int   |
   |                             |     |     | receiving       |       |
   |                             |     |     | interface.      |       |
   | SHIM_IF_SEND                |     | o   | Request for an  | int   |
   |                             |     |     | outgoing        |       |
   |                             |     |     | interface.      |       |
   +-----------------------------+-----+-----+-----------------+-------+

        Table 1: Shim specific socket options for getsockopt() and
                               setsockopt()

   *1: Pointer to the buffer which stores arrays of locator information.
   The buffer is actually the chained list of addrinfo structure.

   *2: TBD.

   *3: TBD.

   Figure 2 illustrates how the shim specific socket options fit into
   the system model of socket API.  In the figure, it can be seen that
   the shim layer and the additional protocol components (IPv4 and IPv6)
   below the shim layer are new to the system model.  As previously
   mentioned, all the shim specific socket options are defined at
   SOL_SHIM level.  This design choice brings the following advantages:

   1.  It is assured that the existing socket API continue to work at
       the layer above the shim layer.  That is, those legacy API deal
       with 'identifier' aspect of the IP addresses.
   2.  With newly defined socket options for the shim layer, the
       application obtains additional control on locator management.
   3.  The shim specific socket options are not specific to any address
       family (IPPROTO_IP or IPPROTO_IPV6) nor any transport protocol
       (SOCK_STREAM or SOCK_DGRAM or SOCK_RAW).














Komu, et al.             Expires August 5, 2006                [Page 11]


Internet-Draft            Multihoming Shim API             February 2006


                            s1 s2      s3 s4
                             |  |       |  |
            +----------------|--|-------|--|----------------+
            |             +-------+   +-------+             |
            | IPPROTO_TCP |  TCP  |   |  UDP  |             |
            |             +-------+   +-------+             |
            |                |   \     /   |                |
            |                |    -----    |                |
            |                |   /     \   |                |
            |              +------+   +------+              |
            |   IPPROTO_IP | IPv4 |   | IPv6 | IPPROTO_IPV6 |
            |              +------+   +------+              |
            |                  \         /             SOL_SOCKET
            |          +--------\-------/--------+          |
            | SOL_SHIM |          shim           |          |
            |          +--------/-------\--------+          |
            |                  /         \                  |
            |              +------+   +------+              |
            |              | IPv4 |   | IPv6 |              |
            |              +------+   +------+              |
            |                  |          |                 |
            +------------------|----------|-----------------+
                               |          |
                             IPv4       IPv6
                           Datagram   Datagram


   Figure 2: System model of socket API with shim layer

6.1.  SHIM_ASSOCIATED

   This option can be specified by getsockopt() to check if the socket
   is associated with a shim context or not.  Thus, the option is read-
   only and the result (0 or 1) is set in optval.  A returned value 1
   means that the socket is associated with a given shim context at the
   shim layer, while a return value 0 indicates that there is no context
   associated with the socket.

   This option is particularly meaningful in a case where locator
   information of the received IP packet is not enough for identifying
   if the ID/Locator adaptation is performed or not.  Note that the EID
   pair and locator pair maybe identical in some case.

   ISSUE: Should we limit this option only for 'connected' socket ?

6.2.  SHIM_DONTSHIM

   This option can be specified either by getsockopt() or setsockopt().



Komu, et al.             Expires August 5, 2006                [Page 12]


Internet-Draft            Multihoming Shim API             February 2006


   The application can specify the option by setsockopt() taking the
   argument optval with value 1 to request the shim layer not to apply
   any multihoming support for the communication.  The application can
   also obtain the current setting by specifying the the socket option
   in getsockopt().  The result should be binary (0 or 1).

   By default, the value is set to 0, meaning that the shim layer will
   try to apply ID/Locator adaptation for the communication over a given
   socket.

   Once the socket option is specified by setsockopt(), it remains
   effective until it is deactivated (sticky option).

6.3.  SHIM_HOT_STANDBY

   This option can be specified by setsockopt().

   By setting 1 in the optval for the setsockopt(), the application can
   request the shim layer to use a hot-standby connection.  The hot-
   standby connection is another working locator pair than the current
   locator pair.

   By default, the value is set to 0, meaning that hot-standby
   connection is disabled.

   Once the socket option is specified by setsockopt(), it remains
   effective until it is deactivated (sticky option).

6.4.  SHIM_PATHEXPLORE

   This option can be specified either by setsockopt() or getsockopt().
   The value specified by the option indicates how aggressive the
   application wants path exploration to be performed in case of
   failure.  Therefore, this option is effective only when there is
   associated shim context for the socket.

   The information to be provided by this socket option should contain:
   suggested number of attempts for path exploration, frequency of the
   path exploration, and so on.  Need further discussions.

   The data type for the argument optval is TBD.

   Once the socket option is specified by setsockopt(), it remains
   effective until it is deactivated (sticky option).

6.5.  SHIM_LOC_LOCAL_PREF

   This option can be specified either by setsockopt() or getsockopt().



Komu, et al.             Expires August 5, 2006                [Page 13]


Internet-Draft            Multihoming Shim API             February 2006


   When specified by setsockopt(), the preferred locator on local side
   is explicitly given to the shim layer.  The shim layer shall
   accordingly update the preferred locator of the context associated
   with the socket.

   When specified by getsockopt(), the preferred locator on local side
   is returned by the shim layer.

   An error ENOSHIMCONTEXT will be returned when there is no context
   associated with the socket.

   Once the socket option is specified by setsockopt(), it remains
   effective until it is deactivated (sticky option).

6.6.  SHIM_LOC_PEER_PREF

   This option can be specified either by setsockopt() or getsockopt().

   When specified by setsockopt(), the preferred locator on remote side
   is explicitly given to the shim layer.  The shim layer shall
   accordingly update the preferred locator of the context associated
   with the socket.

   When specified by getsockopt(), the preferred locator on remote side
   is returned by the shim layer.

   An error ENOSHIMCONTEXT will be returned when there is no context
   associated with the socket.

   An error EINVALIDLOCATOR will be returned when the validation of the
   specified locator failed.

   Once the socket option is specified by setsockopt(), it remains
   effective until it is deactivated (sticky option).

6.7.  SHIM_LOC_LOCAL_RECV

   This option can be specified by setsockopt().

   When specified by setsockopt(), the shim layer stores the destination
   locator of the received IP packet in an ancillary data object which
   can be accessed by recvmsg().  The argument optval value should be
   set to 1.

   An error ENOSHIMCONTEXT will be returned when there is no context
   associated with the socket.

   Once the socket option is specified by setsockopt(), it remains



Komu, et al.             Expires August 5, 2006                [Page 14]


Internet-Draft            Multihoming Shim API             February 2006


   effective until it is deactivated (sticky option).

6.8.  SHIM_LOC_PEER_RECV

   This option can be specified by setsockopt().

   When specified by setsockopt(), the shim layer stores the source
   locator of the received IP packet in an ancillary data object which
   can be accessed by recvmsg().  The argument optval value should be
   set to 1.

   An error ENOSHIMCONTEXT will be returned when there is no context
   associated with the socket.

   Once the socket option is specified by setsockopt(), it remains
   effective until it is deactivated (sticky option).

6.9.  SHIM_LOCLIST_LOCAL

   This option can be specified either by getsockopt() or setsockopt().

   When specified by setsockopt(), the application provides a list of
   locators which is associated with the local EID to the shim layer.
   Accordingly, the shim layer shall update the list of locators
   Ls(local).  The argument optval should contain a pointer to the
   buffer in which a list of locators are stored.  See Section 8 for
   detail.

   When specified by getsockopt(), the application obtains a list of
   locators which is associated with the local EID.

   An error ENOSHIMCONTEXT will be returned when there is no context
   associated with the socket.

   Once the socket option is specified by setsockopt(), it remains
   effective until it is deactivated (sticky option).

6.10.  SHIM_LOCLIST_PEER

   This option can be specified either by getsockopt() or setsockopt().

   When specified by setsockopt(), the application provides a list of
   locators which is associated with the remote EID to the shim layer.
   Accordingly, the shim layer shall update the list of locators
   Ls(remote).  The argument optval should contain a pointer to the
   buffer in which a list of locators are stored.  See Section
   Section 8.1for detail.




Komu, et al.             Expires August 5, 2006                [Page 15]


Internet-Draft            Multihoming Shim API             February 2006


   When specified by getsockopt(), the application obtains a list of
   locators which is associated with the remote EID.

   An error ENOSHIMCONTEXT will be returned when there is no context
   associated with the socket.

   Once the socket option is specified by setsockopt(), it remains
   effective until it is deactivated (sticky option).

6.11.  SHIM_APP_TIMEOUT

   This option can be specified by setsockopt().

   The application can inform the shim layer about the timeout value for
   detecting failure.  The argument optval should contain the timeout
   value in seconds.  Accordingly, the shim layer shall update the
   strategy for reachability test.  Especially, this is efficient in a
   case where the informed timeout value is shorter than the interval of
   keepalive.  In such case, keepalives to be performed by REAP may be
   suppressed.

   An error ENOSHIMCONTEXT will be returned when there is no context
   associated with the socket.

   Once the socket option is specified by setsockopt(), it remains
   effective until it is deactivated (sticky option).

6.12.  SHIM_FEEDBACK_POSITIVE

   This option can be specified by setsockopt().

   The application can simply inform the shim layer that its
   communication is going well.  The argument optval should be set to 1.

   An error ENOSHIMCONTEXT will be returned when there is no context
   associated with the socket.

6.13.  SHIM_FEEDBACK_NEGATIVE

   This option can be specified by setsockopt().

   The application can inform the shim layer that its communication is
   not going well.  The argument optval should be TBD.

   An error ENOSHIMCONTEXT will be returned when there is no context
   associated with the socket.





Komu, et al.             Expires August 5, 2006                [Page 16]


Internet-Draft            Multihoming Shim API             February 2006


6.14.  SHIM_DEFERRED_CONTEXT_SETUP

   This option can be specified by setsockopt().

   When specified by the setsockopt(), optval should be set to 1 if the
   context setup can be deferred.  Otherwise, the context setup is
   invoked immediately when there is no shim context setup for the flow.
   By default, the value is set to 1.

   It should be noted that in some case, deferred context setup is not
   possible; given EID is non-routable address and there is no way to
   transmit any IP packet unless there is a context providing the
   locators.  In such case, context establishment should be made prior
   to communication.

6.15.  SHIM_IF_RECV

   This option can be specified by setsockopt().

   The application can request the shim layer to provide information
   about interface from which the packet was received.  Once the socket
   option is successfully set, the interface information can be obtained
   by recvmsg() from the ancillary data.  The argument optval should be
   set to 1.

   An error ENOSHIMCONTEXT will be returned when there is no context
   associated with the socket.

   Once the socket option is specified by setsockopt(), it remains
   effective until it is deactivated (sticky option).

6.16.  SHIM_IF_SEND

   This option can be specified by setsockopt().

   The application can specify outgoing interface of the outbound
   traffic over the socket.  Application should specify the requested
   interface identifier in the argument optval.  Alternatively, this
   option can also be specified in ancillary data in along with
   sendmsg() call.

   Once the socket option is specified by setsockopt(), it remains
   effective until it is deactivated (sticky option).

6.17.  Error Handling

   If successful, getsockopt() and setsockopt() return 0; otherwise, the
   functions return -1 and set errno to indicate error.



Komu, et al.             Expires August 5, 2006                [Page 17]


Internet-Draft            Multihoming Shim API             February 2006


   Following are errno codes newly defined for some shim specific socket
   options indicating that the getsockopt() or setsockopt() finished
   incompletely:

   ENOSHIIMCONTEXT
      There is no shim context associated with the socket.
   EINVALIDLOCATOR
      This indicates that at least one of the necessary validations
      inside the shim layer for the specified locator has failed.  In
      case of SHIM6, there are two kinds of verifications required prior
      sending an IP packet to the peer's new address; one is return
      routability (check if the peer is actually willing to receive data
      with the specified locator) and the other is verifications based
      on given crypto identifier mechanisms[RFC3972], [I-D.ietf-shim6-
      hba].


7.  Access to Locator Information

   In this section, the way how to access locator information with some
   I/O calls is presented.  As defined in Posix, sendmsg() and recvmsg()
   take msghdr structure as its argument and they can additionally
   handle control information in along with data.  Figure 3 shows the
   msghdr structure which is defined in <sys/socket.h>. msg_control
   member holds a pointer to the buffer where the shim specific
   ancillary data objects are stored.

        struct msghdr {
                caddr_t msg_name;       /* optional address */
                u_int   msg_namelen;    /* size of address */
                struct  iovec *msg_iov; /* scatter/gather array */
                u_int   msg_iovlen;     /* # elements in msg_iov */
                caddr_t msg_control;    /* ancillary data, see below */
                u_int   msg_controllen; /* ancillary data buffer len */
                int     msg_flags;      /* flags on received message */
        };

   Figure 3: msghdr structure

   ISSUE: Should we introduce a new flag for msg_flags (e.g.
   MSG_SHIMMED) ?  Following the practice, it seems reasonable to do so,
   but not sure how much it is useful.

   The buffer pointed from the msg_control member of the msghdr
   structure should contain a single locator and it should be possible
   to process them with the existing macros defined in Posix and
   [RFC3542].  Each cmsghdr{} should be followed by a data which stores
   a single locator.



Komu, et al.             Expires August 5, 2006                [Page 18]


Internet-Draft            Multihoming Shim API             February 2006


   In case of non-connected socket, msg_name member stores the socket
   address of the peer which should be considered as an identifier
   rather than a locator.  The locator of the peer node should be
   retrieved by SHIM_LOC_PEER_RECV as specified below.

   Table 2 is a list of the shim specific ancillary data which can be
   used for recvmsg() or sendmsg().  In any case, SOL_SHIM must be set
   as cmsg_level.

       +---------------------+-----------+-----------+-------------+
       | cmsg_type           | sendmsg() | recvmsg() | cmsg_data[] |
       +---------------------+-----------+-----------+-------------+
       | SHIM_LOC_LOCAL_RECV |           | o         | *1          |
       | SHIM_LOC_PEER_RECV  |           | o         | *1          |
       | SHIM_LOC_LOCAL_SEND | o         |           | *1          |
       | SHIM_LOC_PEER_SEND  | o         |           | *1          |
       | SHIM_IF_RECV        |           | o         | int         |
       | SHIM_IF_SEND        | o         |           | int         |
       +---------------------+-----------+-----------+-------------+

                   Table 2: Shim specific ancillary data

   *1: cmsg_data[] should include padding (if necessary) and a single
   sockaddr_storage{} a protocol independent placeholder for socket
   addresses.

   ISSUE: Is the design choice (to use sockaddr_storage{}) reasonable ?

   It should be noted that the above ancillary data can only be handled
   in UDP and raw sockets, not in TCP sockets.  As explained in
   [RFC3542], there is no one-to-one mapping of send/receive operations
   and the TCP segments being transmitted/received.  In case of TCP,
   application may use setsockopt() or getsockopt() to access or specify
   some of locator information provided by the shim layer.

7.1.  Get Locator Information from Incoming Packet

   Application can get locator information from the received IP packet
   by specifying the shim specific socket options for the socket.  When
   SHIM_LOC_LOCAL_RECV and/or SHIM_LOC_PEER_RECV socket options are set,
   the application can retrieve local and/or remote locator from the
   ancillary data.

   In addition, the application can get the receiving interface from the
   ancillary data marked with SHIM_IF_RECV.  The ancillary data should
   contain an interface identifier of the physical interface which was
   actually used to receive the packet.




Komu, et al.             Expires August 5, 2006                [Page 19]


Internet-Draft            Multihoming Shim API             February 2006


7.2.  Specify Locator Information for Outgoing Packet

   Application can specify the locators to be used for transmitting an
   IP packet by sendmsg().  When ancillary data of cmsg_type
   SHIM_LOC_LOCAL_SEND and/or SHIM_LOC_PEER_SEND are specified, the
   application can explicitly specify source and/or destination locators
   to be used for the communication over the socket.

   In addition, the application can specify the outgoing interface by
   SHIM_IF_SEND ancillary data.  The ancillary data should contain an
   interface identifier of the physical interface over which the
   application expect the packet to be transmitted.

   Note that the effect is limited to the datagram transmitted by the
   sendmsg().  If the specified locator pair seem to be valid, the shim
   layer overrides the locator of the IP packet as requested.

   An error EINVALIDLOCATOR will be returned when validation of the
   specified locator failed.

   ISSUE: Is there any other type of error that we should specifically
   handle ?


8.  Data Structures

   Some of the socket options defined in this document requires specific
   data structures for exchanging information.  Those data structures
   are illustrated in this section.

8.1.  Placeholder for Locator Information

   Some of the socket options defined in this document handle locator
   information.  Locator information could be a single locator or an
   array of locators.  An important requirement is that the locator
   information should be handled in a protocol independent manner.  In
   other words, an interface to the locator information should not be
   dependent to any address family.

8.1.1.  addrinfo structure

   addrinfo structure in along with getaddrinfo() function are defined
   in Posix, which is useful for programming applications in protocol
   independent manner.  As mentioned earlier, protocol independency is
   required for the locator management at the shim layer, thus we
   propose to use addrinfo structure as a placeholder for locators.

   A chain of addrinfo structures can be used to represent a list of



Komu, et al.             Expires August 5, 2006                [Page 20]


Internet-Draft            Multihoming Shim API             February 2006


   locators.  Note that addrinfo structure itself does not contain the
   locator data but it holds a pointer to sockaddr structure where the
   actual data of a given locator is stored.  Figure 4 illustrates the
   addrinfo structure defined in <netdb.h>.

       struct addrinfo {
               int ai_flags;           /* input flags */
               int ai_family;          /* protocol family for socket */
               int ai_socktype;        /* socket type */
               int ai_protocol;        /* protocol for socket */
               socklen_t ai_addrlen;   /* length of socket-address */
               struct sockaddr *ai_addr; /* socket-address for socket */
               char *ai_canonname;     /* canonical name for
                                          service location */
               struct addrinfo *ai_next; /* pointer to next in list */
       };

   Figure 4: addrinfo structure

8.1.2.  sockaddr_storage structure

   [RFC3493] specifies a protocol independent placeholder for socket
   address, called sockaddr_storage structure as shown in Figure 5.  By
   definition, the structure can store socket address of any protocol
   (IPv4 or IPv6) and is simply suitable for a placeholder for the
   locator information.  In this document, we suggest to use
   sockaddr_storage structure to store the locator information to be
   specified in the ancillary data.  In those cases, the locator
   information is a single locator.






















Komu, et al.             Expires August 5, 2006                [Page 21]


Internet-Draft            Multihoming Shim API             February 2006


   /*
    * Desired design of maximum size and alignment
    */
   #define _SS_MAXSIZE    128  /* Implementation specific max size */
   #define _SS_ALIGNSIZE  (sizeof (int64_t))
                      /* Implementation specific desired alignment */
   /*
    * Definitions used for sockaddr_storage structure paddings design.
    */
   #define _SS_PAD1SIZE   (_SS_ALIGNSIZE - sizeof (sa_family_t))
   #define _SS_PAD2SIZE   (_SS_MAXSIZE - (sizeof (sa_family_t) +
                                 _SS_PAD1SIZE + _SS_ALIGNSIZE))

       struct sockaddr_storage {
           sa_family_t  ss_family;    /* address family */
           /* Following fields are implementation specific */
           char      __ss_pad1[_SS_PAD1SIZE];
           int64_t   __ss_align;
           char      __ss_pad2[_SS_PAD2SIZE];
       };

   Figure 5: sockaddr_storage structure


9.  Implications for Existing Socket API Extensions

   As the socket options proposed in this document allow the application
   to specify the locators for transmitting IP packet, there may be
   conflict with some of the existing socket API.  As stated in
   Section 6, a basic assumption is that the legacy API should continue
   to work above the shim layer.

   In IPv4, application can obtain the destination IP address of the
   received IP packet (IP_RECVDSTADDR) as well as the receiving
   interface (IP_RECVIF).  If the shim layer performs ID/Locator
   adaptation for the received packet, the destination EID should be
   stored in the ancillary data (IP_RECVDSTADDR).  Accordingly, the
   receiving interface should be aligned with the destination EID of the
   packet.  That is, the shim layer should set appropriate interface to
   which the destination EID is assigned in the ancillary data object.
   However, from the application perspective, knowing the receiving
   interface which is associated with the destination EID may not be
   useful, especially in the case where application is particularly
   interested in the characteristics of the receiving interface.  Hence,
   we suggest application programmer to use SHIM_IF_RECV instead of
   IP_RECVIF in such case.

   In IPv6, [RFC3542] defines that IPV6_PKTINFO can be used to specify



Komu, et al.             Expires August 5, 2006                [Page 22]


Internet-Draft            Multihoming Shim API             February 2006


   source IPv6 address and the outgoing interface for outgoing packets,
   and retrieve destination IPv6 address and receiving interface for
   incoming packets.  This information is stored in ancillary data being
   IPV6_PKTINFO specified as cmsg_type.  Now, similar to the case of
   IPv4, the shim layer may affect the behavior of socket API which
   deals with IPV6_PKFINFO.  We again would like note that existing
   socket API should continue to work above the shim layer, that is, the
   IP addresses handled in IPV6_PKTINFO should be EIDs, not the
   locators.  Hence we recommend application programmers to use shim
   specific socket options (SHIM_IF_RECV or SHIM_IF_SEND) if the
   interest in the communicating interface comes from lower level (e.g.
   characteristics of physical interface).  For the same reason, in
   order to handle locator information, we suggest to use shim specific
   socket options defined in Section 7.

   In summary, a care should be taken in potential conflict with
   existing socket API which treats the IP address as a locator rather
   than identifier.  Basic assumption is that the existing socket API
   works above the shim layer.


10.  Discussion

   In this section, open discussion issues are noted.

10.1.  Issues with a Context Shared by Applications

   A context is by definition, system-wide.  This means that a context
   could be shared by applications whose communications are using the
   same EID pair.

   When a context is shared by applications, there may be some problems
   when the shim layer needs to handle feedbacks from the multiple
   applications.  As mentioned in Section X, an application may provide
   the shim layer feedback about timeout values from its own settings.
   This implies that there is potentially a race condition at the shim
   layer.

   First of all, the socket options must be used with a proper
   privilege.  Feedback from the application which is run under a root
   privilege must always override the feedback provided by application
   which is run under normal user privilege.

   For other cases, one could rely on a kind of heuristics of the
   configuration.  For instance, prioritizing feedback with higher
   demand (e.g. timeout value 300 seconds are more demanding then
   timeout value 600 seconds) may make sense in some cases.  However, it
   is still an open issue what kind of timer value could be handled in



Komu, et al.             Expires August 5, 2006                [Page 23]


Internet-Draft            Multihoming Shim API             February 2006


   this way.

   Further discussions are needed how the shim layer can accommodate
   feedbacks from multiple applications within a same context.

10.2.  Issues with Shim Unaware Application

   In multihomed environment where either or both of the peers have
   multiple locators, there are some issues with shim unaware
   application which uses legacy socket API.

10.2.1.  Initial Contact with Multiple Locator Pairs

   In a connection oriented communication, the connect() system call is
   used to make the initial contact to the peer, which typically
   requires IP address and port number to specify the endpoint.  Hence,
   name-to-address resolution should be performed prior to connect().
   The application needs to resolve the FQDN of the peer to an IP
   address by any available name-to-address conversion method.

   In typical case, the application receives information from the
   resolver.  If the application ends up with receiving multiple IP
   addresses to reach the peer, it should iterate through each
   destination address one-by-one.  It should be noted that the host may
   also have multiple source addresses.

   The different resulting address pairs may have different reachability
   status so, in order to find a working address pair, it may be
   required to explore all the available address pairs (as opposed to
   explore all available destination addresses).

   In normal case, the application issues a connect() by specifying the
   resolved IP address of the peer.  If the connect() fails, it iterates
   through the available IP addresses one by one sequentially until
   working pair is found.  Another approach is to initiate concurrent
   connect() with every locator of the peer. connect() can also be
   called in a sequence which would probably require more time to find
   the working pair.

   There is a case where involvement of the shim layer is expected for
   handling initial contact.  In such case, behavior of the shim layer
   will depend on presence of the required context.  This case occurs
   when there exists a context for the EID specified in connect(), the
   initial contact can be made in accordance with the context
   information.  Otherwise, the shim layer should invoke context
   establishment with the peer EID specified in the argument for
   connect().




Komu, et al.             Expires August 5, 2006                [Page 24]


Internet-Draft            Multihoming Shim API             February 2006


   Additional efforts would be required in a case where the peer cannot
   be reachable through the EID (for example, EID is non-routable or
   non-IP reachable) but it can be reached through alternative locator.
   In particular, the shim layer should somehow discover the alternate
   locator for the EID to establish context.  [I-D.nordmark-shim6-esd]
   addresses the possible approach to perform reverse DNS lookup from
   EID to FQDN, then perform forward lookup again to find the full-set
   of locators and EID.

   In HIP, resolving HITs to IP addresses using DNS is not feasible
   because HITs do not contain any hierarchical information.  To
   mitigate this problem, there are a few alternatives.  Firstly,
   resolver library on end-host can be modified to provide HIT-to-IP
   mappings for HIP software module.  Secondly, a distributed hash table
   (DHT) service can be used for storing and looking up the mappings
   because it supports non-hierarchical identifiers, such as HITs
   [I-D.ietf-hip-arch].  Thirdly, it is possible to use IP addresses in
   legacy applications as described in [I-D.henderson-hip-applications].

10.2.2.  Naming at Socket Layer

   getsockname() and getpeername() system calls are used to obtain the
   'name' of endpoint which is actually a pair of IP address and port
   number assigned to a given socket. getsockname() is used when an
   application wants to obtain the local IP address and port number
   assigned for a given socket instance. getpeername() is used when an
   application wants to obtain the remote IP address and port number.

   The above is based on a traditional system model of the socket API
   where an IP address is expected to play both the role of identifier
   and the role of locator.

   In a system model where a shim layer exists inside the IP layer, both
   getsockname() and getpeername() deal with identifiers, namely EIDs.
   In this sense, the shim layer serves to (1) hide locators and (2)
   provide access to the identifier for the application over the legacy
   socket APIs.

10.3.  Additional Requirements from Application

   At the moment, it is not certain if following requirements are common
   in all the multihomed environments (SHIM6 and HIP).  These are mainly
   identified during discussions made on SHIM6 WG mailing list.
   o  The application should be able to set preferences for the
      locators, local and remote one and also to the preferences of the
      local locators that will be passed to the peer.





Komu, et al.             Expires August 5, 2006                [Page 25]


Internet-Draft            Multihoming Shim API             February 2006


10.4.  Issues of Header Conversion among Different Address Family

   The shim layer performs ID/Locator adaptation.  Therefore, in some
   case, the whole IP header can be replaced with new IP header of a
   different address family (e.g. conversion from IPv4 to IPv6 or vice
   versa).  Hence, there is an issue how to make the conversion with
   minimum impact.  Note that this issue is common in other protocol
   conversion such as SIIT[RFC2765].

   As addressed in SIIT specification, some of the features (IPv6
   routing headers, hop-by-hop extension headers, or destination
   headers) from IPv6 are not convertible to IPv4.  In addition, notion
   of source routing is not exactly the same in IPv4 and IPv6.  Hence,
   there is certain limitation in protocol conversion between IPv4 and
   IPv6.

   The question is how should the shim layer behave when it is face with
   limitation problem of protocol conversion.  Should we introduce new
   error something like ENOSUITABLELOCATOR ?

10.5.  Handling of Unknown Locator Provided by Application

   There might be a case where application provides the shim layer new
   locator with the SHIM_LOC_*_PREF socket options or SHIM_LOC_*_SEND
   ancillary data.  Then there is a question how should the shim layer
   treat the new locator informed by the application.

   In principle, locator information are exchanged by the shim protocol.
   However, there might be a case where application acquires information
   about the locator and prefers to use it for its communication.


11.  IANA Considerations

   This document contains no IANA consideration.


12.  Security Considerations

   This document does not specify any security mechanism for the shim
   layer.  Fundamentally, the shim layer has a potential to impose
   security threats, as it changes the source and/or destination IP
   addresses of the IP packet being sent or received.  Therefore, the
   basic assumption is that the security mechanism defined in each
   protocol of the shim layer is strictly applied.






Komu, et al.             Expires August 5, 2006                [Page 26]


Internet-Draft            Multihoming Shim API             February 2006


13.  Conclusion

   In this document, the Application Program Interface (API) for
   multihomed shim layer is specified.  The socket API allows
   applications to have additional control on the locator management and
   interface to the REAP mechanism inside the shim layer.  The socket
   API is expected to be useful for the application that takes full
   advantage of multihomed environment.  From architectural perspective,
   the socket API aims to enhance software development environment in
   terms of support for separation of identifier and locator.  That is,
   with new API, application can handle identifier and locator
   separately still being allowed to use legacy socket API.

   Shim specific socket options can be used by getsockopt() and/or
   setcokopt() system calls, which allows applications to get
   information about locator management.  Additionally, applications can
   specify locator information for outgoing packet and get locator
   information from incoming packet by using ancillary data.


14.  Acknowledgments

   Jari Arkko participated in the discussion that lead to the first
   version of this document.


15.  References

15.1.  Normative References

   [I-D.henderson-hip-applications]
              Henderson, T. and P. Nikander, "Using HIP with Legacy
              Applications", draft-henderson-hip-applications-03 (work
              in progress), May 2006.

   [I-D.ietf-hip-arch]
              Moskowitz, R. and P. Nikander, "Host Identity Protocol
              Architecture", draft-ietf-hip-arch-03 (work in progress),
              August 2005.

   [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-03 (work in progress),
              December 2005.

   [I-D.ietf-shim6-proto]
              Bagnulo, M. and E. Nordmark, "Level 3 multihoming shim



Komu, et al.             Expires August 5, 2006                [Page 27]


Internet-Draft            Multihoming Shim API             February 2006


              protocol", draft-ietf-shim6-proto-03 (work in progress),
              December 2005.

   [POSIX]    "IEEE Std. 1003.1-2001 Standard for Information Technology
              -- Portable Operating System Interface (POSIX). Open group
              Technical Standard: Base Specifications, Issue 6,
              http://www.opengroup.org/austin", December 2001.

   [RFC3493]  Gilligan, R., Thomson, S., Bound, J., McCann, J., and W.
              Stevens, "Basic Socket Interface Extensions for IPv6",
              RFC 3493, February 2003.

   [RFC3542]  Stevens, W., Thomas, M., Nordmark, E., and T. Jinmei,
              "Advanced Sockets Application Program Interface (API) for
              IPv6", RFC 3542, May 2003.

15.2.  Informative References

   [I-D.ietf-shim6-app-refer]
              Nordmark, E., "Shim6 Application Referral Issues",
              draft-ietf-shim6-app-refer-00 (work in progress),
              July 2005.

   [I-D.ietf-shim6-hba]
              Bagnulo, M., "Hash Based Addresses (HBA)",
              draft-ietf-shim6-hba-01 (work in progress), October 2005.

   [I-D.nordmark-shim6-esd]
              Nordmark, E., "Extended Shim6 Design for ID/loc split and
              Traffic Engineering", draft-nordmark-shim6-esd-00 (work in
              progress), February 2006.

   [RFC2765]  Nordmark, E., "Stateless IP/ICMP Translation Algorithm
              (SIIT)", RFC 2765, February 2000.

   [RFC3972]  Aura, T., "Cryptographically Generated Addresses (CGA)",
              RFC 3972, March 2005.














Komu, et al.             Expires August 5, 2006                [Page 28]


Internet-Draft            Multihoming Shim API             February 2006


Authors' Addresses

   Miika Komu
   Helsinki Institue for Information Technology
   Tammasaarenkatu 3
   Helsinki
   Finland

   Phone: +358503841531
   Fax:   +35896949768
   Email: miika@iki.fi
   URI:   http://www.hiit.fi/


   Marcelo Bagnulo
   Universidad Carlos III de Madrid
   Av. Universidad 30
   Leganes  28911
   SPAIN

   Phone: +34 91 6248837
   Email: marcelo@it.uc3m.es
   URI:   http://it.uc3m.es/marcelo


   Kristian Slavov
   Ericsson Research Nomadiclab
   Hirsalantie 11
   Jorvas  FI-02420
   Finland

   Phone: +358 9 299 3286
   Email: kristian.slavov@ericsson.com


   Shinta Sugimoto (editor)
   Nippon Ericsson K.K.
   Koraku Mori Building
   1-4-14, Koraku, Bunkyo-ku
   Tokyo  112-0004
   Japan

   Phone: +81 3 3830 2241
   Email: shinta.sugimoto@ericsson.com







Komu, et al.             Expires August 5, 2006                [Page 29]


Internet-Draft            Multihoming Shim API             February 2006


Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.


Disclaimer of Validity

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
   ENGINEERING TASK FORCE DISCLAIM 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.


Copyright Statement

   Copyright (C) The Internet Society (2006).  This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.


Acknowledgment

   Funding for the RFC Editor function is currently provided by the
   Internet Society.




Komu, et al.             Expires August 5, 2006                [Page 30]