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INFORMATIONAL

Internet Engineering Task Force (IETF)                          A. Yegin
Request for Comments: 8653                                      Actility
Category: Informational                                         D. Moses
ISSN: 2070-1721                                                    Intel
                                                                 S. Jeon
                                                 Sungkyunkwan University
                                                            October 2019


                     On-Demand Mobility Management

Abstract

   Applications differ with respect to whether they need session
   continuity and/or IP address reachability.  The network providing the
   same type of service to any mobile host and any application running
   on the host yields inefficiencies, as described in RFC 7333.  This
   document defines a new concept of enabling applications to influence
   the network's mobility services (session continuity and/or IP address
   reachability) on a per-socket basis, and suggests extensions to the
   networking stack's API to accommodate this concept.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are candidates for any level of Internet
   Standard; see Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8653.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://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.  Introduction
   2.  Notational Conventions
   3.  Solution
     3.1.  High-Level Description
     3.2.  Types of IP Addresses
     3.3.  Granularity of Selection
     3.4.  On-Demand Nature
   4.  Backwards Compatibility Considerations
     4.1.  Applications
     4.2.  IP Stack in the Mobile Host
     4.3.  Network Infrastructure
     4.4.  Merging this work with RFC 5014
   5.  Security Considerations
   6.  IANA Considerations
   7.  References
     7.1.  Normative References
     7.2.  Informative References
   Appendix A.  Conveying the Desired Address Type
   Acknowledgements
   Contributors
   Authors' Addresses

1.  Introduction

   In the context of Mobile IP [RFC5563] [RFC6275] [RFC5213] [RFC5944],
   the following two attributes are defined for IP service provided to
   mobile hosts:

   Session Continuity
      The ability to maintain an ongoing transport interaction by
      keeping the same local endpoint IP address throughout the lifetime
      of the IP socket despite the mobile host changing its point of
      attachment within the IP network topology.  The IP address of the
      host may change after closing the IP socket and before opening a
      new one, but that does not jeopardize the ability of applications
      using these IP sockets to work flawlessly.  Session continuity is
      essential for mobile hosts to maintain ongoing flows without any
      interruption.

   IP Address Reachability
      The ability to maintain the same IP address for an extended period
      of time.  The IP address stays the same across independent
      sessions, even in the absence of any session.  The IP address may
      be published in a long-term registry (e.g., DNS) and is made
      available for serving incoming (e.g., TCP) connections.  IP
      address reachability is essential for mobile hosts to use
      specific/published IP addresses.

   Mobile IP is designed to provide both session continuity and IP
   address reachability to mobile hosts.  Architectures using these
   protocols (e.g., 3GPP, 3GPP2, WiMAX) ensure that any mobile host
   attached to a compliant network can enjoy these benefits.  Any
   application running on these mobile hosts is subjected to the same
   treatment with respect to session continuity and IP address
   reachability.

   Achieving session continuity and IP address reachability with Mobile
   IP incurs some cost.  Mobile IP forces the mobile host's IP traffic
   to traverse a centrally located router (Home Agent, HA), which incurs
   additional transmission latency and use of additional network
   resources, adds to the network's operating and capital expenditures,
   and decreases the reliability of the network due to the introduction
   of a single point of failure [RFC7333].  Therefore, session
   continuity and IP address reachability SHOULD be provided only when
   necessary.

   In reality, not every application may need these benefits.  IP
   address reachability is required for applications running as servers
   (e.g., a web server running on the mobile host), but a typical client
   application (e.g., web browser) does not necessarily require IP
   address reachability.  Similarly, session continuity is not required
   for all types of applications either.  Applications performing brief
   communication (e.g., text messaging) can survive without having
   session continuity support.

   Furthermore, when an application needs session continuity, it may be
   able to satisfy that need by using a solution above the IP layer,
   such as Multipath TCP [RFC6824], SIP mobility [RFC3261], or an
   application-layer mobility solution.  These higher-layer solutions
   are not subject to the same issues that arise with the use of Mobile
   IP since they can use the most direct data path between the
   endpoints.  But, if Mobile IP is being applied to the mobile host,
   the higher-layer protocols are rendered useless because their
   operation is inhibited by Mobile IP.  Since Mobile IP ensures that
   the IP address of the mobile host remains fixed (despite the location
   and movement of the mobile host), the higher-layer protocols never
   detect the IP-layer change and never engage in mobility management.

   This document proposes a solution for applications running on mobile
   hosts to indicate when establishing the network connection ('on
   demand') whether they need session continuity or IP address
   reachability.  The network protocol stack on the mobile host, in
   conjunction with the network infrastructure, provides the required
   type of service.  It is for the benefit of both the users and the
   network operators not to engage an extra level of service unless it
   is absolutely necessary.  It is expected that applications and
   networks compliant with this specification will utilize this solution
   to use network resources more efficiently.

2.  Notational Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Solution

3.1.  High-Level Description

   Enabling applications to indicate their mobility service requirements
   (e.g., session continuity and/or IP address reachability) comprises
   the following steps:

   1.  The application indicates to the network stack (local to the
       mobile host) the desired mobility service.

   2.  The network stack assigns a source IP address based on an IP
       prefix with the desired services that was previously provided by
       the network.  If such an IP prefix is not available, the network
       stack performs the additional steps below.

   3.  The network stack sends a request to the network for a new source
       IP prefix that is associated with the desired mobility service.

   4.  The network responds with the suitable allocated source IP prefix
       (or responds with a failure indication).

   5.  If the suitable source IP prefix was allocated, the network stack
       constructs a source IP address and provides it to the
       application.

   This document specifies the new address types associated with
   mobility services and details the interaction between the
   applications and the network stack steps.  It uses the socket
   interface as an example for an API between applications and the
   network stack.  Other steps are outside the scope of this document.

3.2.  Types of IP Addresses

   Four types of IP addresses are defined with respect to mobility
   management:

   Fixed IP address
      A Fixed IP address is an address guaranteed to be valid for a very
      long time, regardless of whether it is being used in any packet
      to/from the mobile host, or whether or not the mobile host is
      connected to the network, or whether it moves from one point of
      attachment to another (with a different IP prefix) while it is
      connected.

      Fixed IP addresses are required by applications that need both
      session continuity and IP address reachability.

   Session-Lasting IP address
      A Session-Lasting IP address is an address guaranteed to be valid
      for the lifetime of the socket(s) for which it was requested.  It
      is guaranteed to be valid even after the mobile host has moved
      from one point of attachment to another (with a different IP
      prefix).

      Session-Lasting IP addresses are required by applications that
      need session continuity but do not need IP address reachability.

   Nonpersistent IP address
      This type of IP address is not guaranteed to exist after a mobile
      host moves from one point of attachment to another; therefore, no
      session continuity nor IP address reachability are provided.  The
      IP address is created from an IP prefix that is obtained from the
      serving IP gateway and is not maintained across gateway changes.
      In other words, the IP prefix may be released and replaced by a
      new one when the IP gateway changes due to the movement of the
      mobile host forcing the creation of a new source IP address with
      the updated allocated IP prefix.

   Graceful-Replacement IP address
      In some cases, the network cannot guarantee the validity of the
      provided IP prefix throughout the duration of the opened socket,
      but can provide a limited graceful period of time in which both
      the original IP prefix and a new one are valid.  This enables the
      application some flexibility in the transition from the existing
      source IP address to the new one.

      This gracefulness is still better than the nonpersistence type of
      address for applications that can handle a change in their source
      IP address but require that extra flexibility.

   Applications running as servers at a published IP address require a
   Fixed IP address.  Long-standing applications (e.g., an SSH session)
   may also require this type of address.  Enterprise applications that
   connect to an enterprise network via virtual LAN require a Fixed IP
   address.

   Applications with short-lived transient sessions (e.g., web browsers)
   can use Session-Lasting IP addresses.

   Applications with very short sessions, such as DNS clients and
   instant messengers, can use Nonpersistent IP addresses.  Even though
   they could very well use Fixed or Session-Lasting IP addresses, the
   transmission latency would be minimized when a Nonpersistent IP
   address is used.

   Applications that can tolerate a short interruption in connectivity
   can use the Graceful-Replacement IP addresses, for example, a
   streaming client that has buffering capabilities.

3.3.  Granularity of Selection

   IP address type selection is made on a per-socket granularity.
   Different parts of the same application may have different needs.
   For example, the control plane of an application may require a Fixed
   IP address in order to stay reachable, whereas the data plane of the
   same application may be satisfied with a Session-Lasting IP address.

3.4.  On-Demand Nature

   At any point in time, a mobile host may have a combination of IP
   addresses configured.  Zero or more Fixed, zero or more Session-
   Lasting, zero or more Nonpersistent, and zero or more Graceful-
   Replacement IP addresses may be configured by the IP stack of the
   host.  The combination may be a result of the host policy,
   application demand, or a mix of the two.

   When an application requires a specific type of IP address, and such
   an address is not already configured on the host, the IP stack SHALL
   attempt to configure one.  For example, a host may not always have a
   Session-Lasting IP address available.  When an application requests
   one, the IP stack SHALL make an attempt to configure one by issuing a
   request to the network.  If the operation fails, the IP stack SHALL
   fail the associated socket request and return an error.  If
   successful, a Session-Lasting IP address is configured on the mobile
   host.  If another socket requests a Session-Lasting IP address at a
   later time, the same IP address may be served to that socket as well.
   When the last socket using the same configured IP address is closed,
   the IP address may be released, or it may be kept for applications
   requiring a Session-Lasting IP address that may be launched in the
   future.

   In some cases, it might be preferable for the mobile host to request
   a new Session-Lasting IP address for a new opening of an IP socket
   (even though one was already assigned to the mobile host by the
   network and might be in use in a different, already active IP
   socket).  It is outside the scope of this specification to define
   criteria for choosing to use available addresses or choosing to
   request new ones.  It supports both alternatives (and any
   combination).

   It is outside the scope of this specification to define how the host
   requests a specific type of prefix and how the network indicates the
   type of prefix in its advertisement or in its reply to a request.

   The following are matters of policy, which may be dictated by the
   host itself, the network operator, or the system architecture
   standard:

   *  The initial set of IP addresses configured on the host at boot
      time

   *  Permission to grant various types of IP addresses to a requesting
      application

   *  Determination of a default address type when an application does
      not explicitly indicate whether it supports the required API or is
      a legacy application

4.  Backwards Compatibility Considerations

   Backwards compatibility support is REQUIRED by the following three
   types of entities:

   *  The applications on the mobile host

   *  The IP stack in the mobile host

   *  The network infrastructure

4.1.  Applications

   Legacy applications that do not support the On-Demand functionality
   will use the legacy API and will not be able to take advantage of the
   On-Demand Mobility feature.

   Applications using the new On-Demand functionality should be aware
   that they may be executed in legacy environments that do not support
   it.  Such environments may include a legacy IP stack on the mobile
   host, legacy network infrastructure, or both.  In either case, the
   API will return an error code, and the invoking application may just
   give up and use legacy calls.

4.2.  IP Stack in the Mobile Host

   New IP stacks (that implement On-Demand functionality) MUST continue
   to support all legacy operations.  If an application does not use On-
   Demand functionality, the IP stack MUST respond in a legacy manner.

   If the network infrastructure supports On-Demand functionality, the
   IP stack SHOULD follow the application request: If the application
   requests a specific address type, the stack SHOULD forward this
   request to the network.  If the application does not request an
   address type, the IP stack MUST NOT request an address type.
   Instead, the network will choose the type of allocated IP prefix.
   How the network selects the type of allocated IP prefix is outside
   the scope of this document.  If an IP prefix was already allocated to
   the host, the IP stack uses it and may not request a new one from the
   network.

4.3.  Network Infrastructure

   The network infrastructure may or may not support the On-Demand
   functionality.  How the IP stack on the host and the network
   infrastructure behave in case of a compatibility issue is outside the
   scope of this API specification.

4.4.  Merging this work with RFC 5014

   [RFC5014] defines new flags that may be used with setsockopt() to
   influence source IP address selection for a socket.  The list of
   flags include the following: source home address, care-of address,
   temporary address, public address CGA (Cryptographically Created
   Address), and non-CGA.  When applications require session continuity
   service, they SHOULD NOT set the flags specified in [RFC5014].

   However, if an application erroneously performs a combination of (1)
   using setsockopt() to set a specific option (using one of the flags
   specified in [RFC5014]) and (2) selecting a source IP address type,
   the IP stack will fulfill the request specified by (2) and ignore the
   flags set by (1).

5.  Security Considerations

   The different service types (session continuity types and address
   reachability) associated with the allocated IP address types may be
   associated with different costs: the cost to the operator for
   enabling a type of service, and the cost to applications using a
   selected service.  A malicious application may use these to
   indirectly generate extra billing of a mobile subscriber, and/or
   impose costly services on the mobile operator.  When expensive
   services are limited, malicious applications may exhaust them,
   preventing other applications on the same mobile host from being able
   to use them.

   Mobile hosts that enable such service options should provide
   capabilities for ensuring that only authorized applications can use
   the expensive (or limited) service types.

   The ability to select service types requires the exchange of the
   association of source IP prefixes and their corresponding service
   types, between the mobile host and mobile network.  Exposing these
   associations may provide information to passive attackers even if the
   traffic that is used with these addresses is encrypted.

   To avoid profiling an application according to the type of IP
   address, it is expected that prefixes provided by the mobile operator
   are associated with various types of addresses over time.  As a
   result, the type of address cannot be associated with the prefix,
   making application profiling based on the type of address more
   difficult.

   The application or the OS should ensure that IP addresses regularly
   change to limit IP tracking by a passive observer.  The application
   should regularly set the On-Demand flag.  The application should be
   able to ensure that Session-Lasting IP addresses are regularly
   changed by setting a lifetime, for example, handled by the
   application.  In addition, the application should consider the use of
   Graceful-Replacement IP addresses.

   Similarly, the OS may also associate IP addresses with a lifetime.
   Upon receiving a request for a given type of IP address, after some
   time, the OS should request a new address to the network even if it
   already has one IP address available with the requested type.  This
   includes any type of IP address.  IP addresses of type Graceful-
   Replacement or nonpersistent should be regularly renewed by the OS.

   The lifetime of an IP address may be expressed in number of seconds
   or in number of bytes sent through this IP address.

6.  IANA Considerations

   This document has no IANA actions.

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC5014]  Nordmark, E., Chakrabarti, S., and J. Laganier, "IPv6
              Socket API for Source Address Selection", RFC 5014,
              DOI 10.17487/RFC5014, September 2007,
              <https://www.rfc-editor.org/info/rfc5014>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

7.2.  Informative References

   [API-EXT]  Jeon, S., Figueiredo, S., Kim, Y., and J. Kaippallimalil,
              "Use Cases and API Extension for Source IP Address
              Selection", Work in Progress, Internet-Draft, draft-
              sijeon-dmm-use-cases-api-source-07, 10 September 2017,
              <https://tools.ietf.org/html/draft-sijeon-dmm-use-cases-
              api-source-07>.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              DOI 10.17487/RFC3261, June 2002,
              <https://www.rfc-editor.org/info/rfc3261>.

   [RFC5213]  Gundavelli, S., Ed., Leung, K., Devarapalli, V.,
              Chowdhury, K., and B. Patil, "Proxy Mobile IPv6",
              RFC 5213, DOI 10.17487/RFC5213, August 2008,
              <https://www.rfc-editor.org/info/rfc5213>.

   [RFC5563]  Leung, K., Dommety, G., Yegani, P., and K. Chowdhury,
              "WiMAX Forum / 3GPP2 Proxy Mobile IPv4", RFC 5563,
              DOI 10.17487/RFC5563, February 2010,
              <https://www.rfc-editor.org/info/rfc5563>.

   [RFC5944]  Perkins, C., Ed., "IP Mobility Support for IPv4, Revised",
              RFC 5944, DOI 10.17487/RFC5944, November 2010,
              <https://www.rfc-editor.org/info/rfc5944>.

   [RFC6275]  Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility
              Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July
              2011, <https://www.rfc-editor.org/info/rfc6275>.

   [RFC6824]  Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
              "TCP Extensions for Multipath Operation with Multiple
              Addresses", RFC 6824, DOI 10.17487/RFC6824, January 2013,
              <https://www.rfc-editor.org/info/rfc6824>.

   [RFC7333]  Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J.
              Korhonen, "Requirements for Distributed Mobility
              Management", RFC 7333, DOI 10.17487/RFC7333, August 2014,
              <https://www.rfc-editor.org/info/rfc7333>.

Appendix A.  Conveying the Desired Address Type

   The following are some suggestions of possible extensions to the
   socket API for enabling applications to convey their session
   continuity and address reachability requirements.

   [RFC5014] introduced the ability of applications to influence the
   source address selection with the IPV6_ADDR_PREFERENCE option at the
   IPPROTO_IPV6 level.  This option is used with setsockopt() and
   getsockopt() calls to set/get address selection preferences.

   One alternative is to extend the definition of the
   IPV6_ADDR_REFERENCE option with flags that express the invoker's
   desire.  An "OnDemand" field could contain one of the following
   values: FIXED_IP_ADDRESS, SESSION_LASTING_IP_ADDRESS,
   NON_PERSISTENT_IP_ADDRESS, or GRACEFUL_REPLACEMENT_IP_ADDRESS.

   Another alternative is to define a new socket function used by the
   invoker to convey its desire.  This enables the implementation of two
   behaviors of socket functions: the existing setsockopt() is a
   function that returns after executing, and the new setsc() (Set
   Service Continuity) is a function that may initiate a request for the
   desired service, and wait until the network responds with the
   allocated resources, before returning to the invoker.

   After obtaining an IP address with the desired behavior, the
   application can call the bind() socket function to associate that
   received IP address with the socket.

Acknowledgements

   We would like to thank Wu-chi Feng, Alexandru Petrescu, Jouni
   Korhonen, Sri Gundavelli, Dave Dolson, Lorenzo Colitti, and Daniel
   Migault for their valuable comments and suggestions on this work.

Contributors

   This document was merged with "Use Cases and API Extension for Source
   IP Address Selection" [API-EXT].  We would like to acknowledge the
   contribution of the following people to that document as well:

   Sergio Figueiredo
   Altran Research
   France
   Email: sergio.figueiredo@altran.com

   Younghan Kim
   Soongsil University
   Republic of Korea
   Email: younghak@ssu.ac.kr

   John Kaippallimalil
   Huawei
   United States of America
   Email: john.kaippallimalil@huawei.com

Authors' Addresses

   Alper Yegin
   Actility
   Istanbul/
   Turkey

   Email: alper.yegin@actility.com


   Danny Moses
   Intel Corporation
   Petah Tikva
   Israel

   Email: danny.moses@intel.com


   Seil Jeon
   Republic of Korea
   Suwon
   Sungkyunkwan University

   Email: seiljeon.ietf@gmail.com


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