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Internet Engineering Task Force                                    M. Xu
Internet-Draft                                                   Z. Ming
Intended status: Experimental                        Tsinghua University
Expires: March 21, 2011                                       J. Ubillos
                                           Swedish Institute of Computer
                                                                 C. Vogt
                                                      September 17, 2010

                       Name Based Sockets - Shim6


   This document describes and defines shim6 as a mobility solution for
   name-based sockets.  Using names rather than pseudo IP addresses,
   shim6 can handle a more diverse set of mobility scenarios.  These
   changes allow a shim6 session to persist even through cases where one
   node has no working locators to its correspondent node.  If the name
   is also a resolvable fully qualified domain name, the connection can
   be kept alive even if neither node have a working locator to the
   corresponding node.  As can be the case if both nodes are mobile

Status of This Memo

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

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

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

   This Internet-Draft will expire on March 21, 2011.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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

Table of Contents

   1.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
     3.1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . 3
   4.  Mobility support  . . . . . . . . . . . . . . . . . . . . . . . 4
     4.1.  Shim6 . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
       4.1.1.  Brief overview of changes . . . . . . . . . . . . . . . 4
       4.1.2.  Identity change . . . . . . . . . . . . . . . . . . . . 5
       4.1.3.  The hand-shake with name exchange . . . . . . . . . . . 5
       4.1.4.  Triggers of shim6 . . . . . . . . . . . . . . . . . . . 6
       4.1.5.  Establishing Shim6 context  . . . . . . . . . . . . . . 6
       4.1.6.  Problems for Shim6 to support mobility  . . . . . . . . 6
       4.1.7.  Changes to REAP . . . . . . . . . . . . . . . . . . . . 8
       4.1.8.  Changes to STATE Machine  . . . . . . . . . . . . . . . 8
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 9
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 9
   7.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . 9
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 9
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 9
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 9
     8.3.  URL References  . . . . . . . . . . . . . . . . . . . . . . 9

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1.  Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Terminology

   Locator - An IP address (v4 or v6) on which a host can be reached.

   Multi-home - A host which is reachable through multiple locators (on
   one interface or more)

   Name - A character string (max 255 chars long) on which an endpoint
   can be identified.  A name maps to zero or more locators.

3.  Overview

3.1.  Introduction

   Mobility can be treated as a special case of multihoming.  Shim6
   provides a promising way to implement multihoming for upper layer
   protocols, thus it is reasonable to use Shim6 to provide NBS with
   mobility functionality.

   The traditional Shim6 defined in RFC5533 [RFC5533] does not aim to
   solve mobility problem, so changes need to be made to the existing
   Shim6 protocol.  One of the reasons for not supporting mobility is
   that Shim6 uses a specific IP address as the identifier of the upper
   lay protocol.  To avoid confusion, communication must be stopped when
   this IP address becomes unavailable.  With the presence of name based
   socket, Shim6 can use the name as the upper layer identifier rather
   than IP.  In such a way, Shim6 will not encounter the problem that
   connection must be terminated when the locator used as ULID becomes

   To allow connections to survive during movement, Shim6 context should
   be preserved for a certain period of time when there are no available
   locator to use.  When both nodes move simultaneously, Shim6 path
   exploration may fail due to lost update messages.  To keep the
   connection from being terminated in this case, DNS is involved to
   provide address information.

   Technical details will be covered in this document.

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4.  Mobility support

4.1.  Shim6

   "...  The Shim6 protocol, a layer 3 shim for providing locator
   agility below the transport protocols, so that multihoming can be
   provided for IPv6 with failover and load-sharing properties, without
   assuming that a multihomed site will have a provider-independent IPv6
   address prefix announced in the global IPv6 routing table.  The hosts
   in a site that has multiple provider- allocated IPv6 address prefixes
   will use the Shim6 protocol specified in this document to set up
   state with peer hosts so that the state can later be used to failover
   to a different locator pair, should the original one stop working. "
   RFC5533 [RFC5533]

4.1.1.  Brief overview of changes

   To the upper layers, shim6 provides a stable IP address-like
   identifier (ULID) to identify the remote host and make the IP
   addresses (locators) transparent to the application.  This way of
   providing a pseudo-address (ULID) does however invite confusion.  The
   ULID selected by Shim6 is actually the IP address which is available
   for the application when the connection is being established.  This
   address (ULID) may become invalid during the connection (RFC5533
   Section 1.5 [RFC5533]).  ULID invalidation is beyond the control of
   the individual hosts, it is controlled by the network.  This might
   cause confusion if the applications continues to use the ULIDs which
   are no longer valid.  Shim6s solution to this problem to terminate
   the communication immediately when ever any ULID becomes invalid.
   This is definitely inappropriate in a mobile scenario as connections
   are expected to be preserved during the mobile period.  Moving
   between two distinct networks, changing your complete locator set is
   the common scenario (e.g. entirely switching from one WiFi-provider
   to another.)

   Name Based Sockets suggest using the name of a host as the
   identifier.  This solves the above problems, as a name is valid for
   as long as a host wishes it to be.  Also, as Name Based Sockets
   provide a new explicit interface (names rather than 'pseudo IP
   addresses'), applications that use it will be aware of the available
   features, and may make correct assessments of the underlying IP stack
   and its enhancements.

   This document describes a set of changes and improvements to shim6
   that are to be incorporated with the Name Based Sockets.

   Briefly, the changes are:

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   o  Name is used as ULID rather than an IP (Section 4.1.2).

   o  Node inter-reachability resilience, for when both nodes are
      simultaneously mobile using DNS (Section

4.1.2.  Identity change

   Shim6 selects a locator (IP) in the initial contact with the remote
   peer and uses this locator as an upper-layer identifier (ULID).  To
   support NBS, we use name (or some structure related to name) as ULID
   instead of IP addresses.

   Because the end point identifier is no longer a locator but rather a
   name, the initial name exchange is performed by NBS and Shim6 uses
   this name to construct the ULID.

   Shim6 requires that any communication using a ULID MUST be terminated
   when the ULID becomes invalid.  Using names as ULIDs instead of IP
   address is more in line with the transport semantic.  Having names as
   ULIDs means that the session may still exist even if both
   communicating hosts locator lists are empty at a given point of time.
   This is particularly important when one or both peer(s) are moving.

   Note that replacing a ULID with a name does not necessarily mean
   representing the ULID as a string or a string-like structure
   internally.  In order to lower the complexity, one should make the
   least possible modification to both the Shim6 protocol (where ULID is
   a 128-bit IPv6 address) and its definition implementation, we propose
   to internally represent the name as a 128-bit MD5-hash and use this
   MD5-hash as the corresponding ULID.

4.1.3.  The hand-shake with name exchange

   As is described in RFC5533 [RFC5533], Shim6 does not need to react
   immediately when connections start up.  The initial name exchange is
   performed by NBS and it requires no help from Shim6.  The name
   exchanged by NBS will be further used as ULID by Shim6.  At some time
   during the communication, some heuristic may determine that it is
   appropriate to use shim6 to support mobility/multi-homing, so the
   communicating hosts initiate a 4-way, context-establishment exchange.
   As a result, both hosts get a locator list of each other.

   As an extension to Shim6, we do not change the operation sequence of
   the 4-way exchange, namely the order of I1, R1, I2, R2 will not be
   changed.  What is changed is that the IP-based ULID is replaced by a
   name-based ULID and the hand shake no longer requires ULID
   negotiation because it has already been done by NBS.

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4.1.4.  Triggers of shim6

   It is not necessarily worth paying the overhead of setting up a shim
   context when e.g. only a small number of packets are exchanged
   between two hosts.  As a result, Shim6 functionality will not be
   started immediately as a new communication is initiated.

   NBS uses some heuristic for determining when to perform a deferred
   context establishment.  This heuristic might be that more than 50
   packets have been sent or received, or that a timer expires while
   active packet exchange was in place RFC 5533 [RFC5533].  Exactly how
   the heuristic is designed is beyond the scope of this document.

4.1.5.  Establishing Shim6 context

   At a certain time during the connection, some heuristic on host A or
   B (or both) determine that it is appropriate to pay the Shim6
   overhead to improve host-to-host communication.  This makes the Shim6
   initiate the 4-way, context-establishment exchange (defined in RFC

   As a result, both A and B get a list of each others locators.  In
   name-based Shim6, the ULID is represented as a MD5-hash of name
   rather than IP.

4.1.6.  Problems for Shim6 to support mobility

   When only one host moves to a new network, a REAP Update is triggered
   to prevent connection from being terminated.  Under normal
   circumstances, connection will be smoothly preserved during the REAP
   Update process.

   However, REAP itself is not sufficient to support full mobility
   functionality, as when both hosts move simultaneously, neither of
   them will receive the update message, which will lead to a connection
   loss.  To deal with this problem, DNS should be involved to provide
   address information.  DNS querying

   An effective solution for the mobility problem is to have a
   "stationary infrastructure" to provide address information for all
   mobile devices.  We propose to use DNS as the stationary
   infrastructure as it associates addresses with names and has enough
   capability.  How DNS incorporates with name-based Shim6 is described
   in the following part.

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Internet-Draft                 NBS: Shim6                 September 2010  One peer moves

   In the case that only one host moves, the moving host starts a REAP
   Update process to re-establish Shim6 context with the correspondent
   host.  At the same time, DNS should be updated by the moving host.
   This procedure is the normal REAP [RFC5534] procedure with the added
   update to DNS.

   The following sequence illustrates the details:

   1.  Two hosts, A and B are communicating using NBS and Shim6.

   2.  At certain moment, A moves to a new network and changes its IP
       address (locator).

   3.  A updates the authoritative DNS with its new IP address.  In
       parallel, A starts the REAP Update process by sending B an Update
       Request and the REAP Update process is invoked.

   4.  New operational locator pair is found by REAP Update process.

   5.  Handover process is completed and connection is preserved during
       the process.  Both peers move

   When both hosts moves simultaneously, neither host will receive the
   REAP Update Request, thus REAP will fail in finding the new
   operational locator pair.  Under such circumstances, both hosts need
   to query DNS for the correspondent hosts addresses.  When new address
   is retrieved, both hosts initiate REAP Update process as specified in
   RFC5534 [RFC5534].

   The following sequence illustrates the details:

   1.  Two hosts, A and B are communicating using NBS and Shim6.

   2.  At certain moment, both A and B move simultaneously and both
       hosts change their respective IP addresses.

   3.  Both hosts update DNS with their new addresses and send REAP
       Update Request to their correspondent peer.

   4.  Due to concurrent move, Update Requests are lost for both

   5.  Both hosts experience an Update Timeout and query DNS for
       correspondent hosts' locators using their names.

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   6.  New addresses are returned by the respective DNS queries and REAP
       Update is now able to operate.  A and B re-invoke a REAP Update
       process using the new addresses.

   7.  New operational locator pair is found by REAP Update process.

   8.  Handover process is completed and connection is preserved during
       the handover process.

4.1.7.  Changes to REAP

   We extend REAP by adding DNS Querying into its Path Exploration.  For
   the sake of backwards compatibility, DNS can be implemented as a
   separate module and has no impact on the other part of REAP which is
   specified in RFC 5534.  The DNS functionality can be turned off for
   stationary hosts and be turned on for mobile devices.

   In the mobile scenario, DNS Query and REAP Path Exploration may work
   together to provide stronger reliability.  DNS query might be lost
   due to link failure or timeout due to high network delay.  Under such
   circumstances, REAP Path Exploration will be triggered because of a
   SEND TIMEOUT and tries to find an available path.  This is meaningful
   when a host has multiple available interfaces (for instance Wi-Fi and
   3G) and the address change for one interface does not lead to the
   change for others.

4.1.8.  Changes to STATE Machine

   In order to implement mobility, we propose to add a new state ?C
   NO_LOC into the shim6 state machine.  With this state, Shim6 does not
   directly transmit to a dead state when there is no available address,
   but transmits to NO_LOC state to wait for a new locator.  There is a
   minor difference between the Exploring state and the InBoundOK state.
   For simplicity, in this draft we use the Exploring state to represent
   both Exploring state and InBoundOK state.

   Upon realizing that there is no available address to use, Shim6 sets
   the state to NO_LOC, starts a time and wait for an available address.
   If the host successfully attaches to a new network, Shim6 performs
   the following operations:

   1.  Update the context.

   2.  Send Update Request to the remote peer.

   3.  Transitions into the Exploring state.

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   4.  Stops the timer.

   If the timer expires, Shim6 removes the context.

   Upon entering the Exploring state, Shim6 waits for the Update ACK
   from the peer.  If the update ACK is received, Shim6 can perform the
   normal operation as defined by RFC 5533 and RFC 5534 to continue the
   connection.  Otherwise, Shim6 infers that the peer may also move and
   asks the DNS for the peers locator, insert the locator into the
   locator list of the peer (if not already present in the list) and
   starts the Reap Path Exploration process.  As the DNS stores the
   latest address of the peer, we believe this locator is most likely to
   be available, thus in the Reap Path Exploration process, we first try
   the locator returned by DNS and then other locators (if any).

5.  Security Considerations

6.  IANA Considerations

7.  Contributors

8.  References

8.1.  Normative References

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

8.2.  Informative References

   [RFC5533]  Nordmark, E. and M. Bagnulo, "Shim6: Level 3 Multihoming
              Shim Protocol for IPv6", RFC 5533, June 2009.

   [RFC5534]  Arkko, J. and I. van Beijnum, "Failure Detection and
              Locator Pair Exploration Protocol for IPv6 Multihoming",
              RFC 5534, June 2009.

8.3.  URL References

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Authors' Addresses

   Mingwei Xu
   Tsinghua University
   FIT Building  4-104, Tsinghua  University

   EMail: xmw@cernet.edu.cn

   Zhongxing Ming
   Tsinghua University
   FIT Building  4-104, Tsinghua  University

   EMail: mingzx@126.com

   Javier Ubillos
   Swedish Institute of Computer Science
   Kistagangen 16

   Phone: +46767647588
   EMail: jav@sics.se

   Christian Vogt
   200 Holger Way
   San Jose, CA  95134-1300

   EMail: christian.vogt@ericsson.com

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