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.
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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
