On-Demand Mobility ManagementActilityIstanbulTurkeyalper.yegin@actility.comIntel CorporationPetah TikvaIsraeldanny.moses@intel.comSungkyunkwan UniversitySuwonRepublic of Koreaseiljeon.ietf@gmail.comDMM Working GroupApplications 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
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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.
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Table of Contents
. Introduction
. Notational Conventions
. Solution
. High-Level Description
. Types of IP Addresses
. Granularity of Selection
. On-Demand Nature
. Backwards Compatibility Considerations
. Applications
. IP Stack in the Mobile Host
. Network Infrastructure
. Merging this work with RFC 5014
. Security Considerations
. IANA Considerations
. References
. Normative References
. Informative References
. Conveying the Desired Address Type
Acknowledgements
Contributors
Authors' Addresses
IntroductionIn the context of Mobile IP ,
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 . 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 , SIP mobility , 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.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 when, and only when, they appear in all capitals, as
shown here.
SolutionHigh-Level Description Enabling applications to indicate their mobility service requirements
(e.g., session continuity and/or IP address reachability) comprises the
following steps:
The application indicates to the network stack (local to the
mobile host) the desired mobility service.
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.
The network stack sends a request to the network for a new source
IP prefix that is associated with the desired mobility service.
The network responds with the suitable allocated source IP prefix
(or responds with a failure indication).
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.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.Granularity of SelectionIP 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.On-Demand NatureAt 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
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
ApplicationsLegacy 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. IP Stack in the Mobile HostNew 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.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. Merging this work with RFC 5014 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 .However, if an application erroneously performs a combination of (1) using
setsockopt() to set a specific option (using one of the flags specified in
) 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).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. IANA ConsiderationsThis document has no IANA actions.ReferencesNormative ReferencesKey words for use in RFCs to Indicate Requirement LevelsIn many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.IPv6 Socket API for Source Address SelectionThe IPv6 default address selection document (RFC 3484) describes the rules for selecting source and destination IPv6 addresses, and indicates that applications should be able to reverse the sense of some of the address selection rules through some unspecified API. However, no such socket API exists in the basic (RFC 3493) or advanced (RFC 3542) IPv6 socket API documents. This document fills that gap partially by specifying new socket-level options for source address selection and flags for the getaddrinfo() API to specify address selection based on the source address preference in accordance with the socket-level options that modify the default source address selection algorithm. The socket API described in this document will be particularly useful for IPv6 applications that want to choose between temporary and public addresses, and for Mobile IPv6 aware applications that want to use the care-of address for communication. It also specifies socket options and flags for selecting Cryptographically Generated Address (CGA) or non-CGA source addresses. This memo provides information for the Internet community.Ambiguity of Uppercase vs Lowercase in RFC 2119 Key WordsRFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.Informative ReferencesUse Cases and API Extension for Source IP Address SelectionThis draft specifies and analyzes the expected cases regarding the selection of a proper source IP address and address type by an application in a distributed mobility management (DMM) network. It also proposes a new Socket API to address further selection issues with three source IP address types defined in the on-demand mobility API draft.Work in ProgressSIP: Session Initiation ProtocolThis document describes Session Initiation Protocol (SIP), an application-layer control (signaling) protocol for creating, modifying, and terminating sessions with one or more participants. These sessions include Internet telephone calls, multimedia distribution, and multimedia conferences. [STANDARDS-TRACK]Proxy Mobile IPv6Network-based mobility management enables IP mobility for a host without requiring its participation in any mobility-related signaling. The network is responsible for managing IP mobility on behalf of the host. The mobility entities in the network are responsible for tracking the movements of the host and initiating the required mobility signaling on its behalf. This specification describes a network-based mobility management protocol and is referred to as Proxy Mobile IPv6. [STANDARDS-TRACK]WiMAX Forum / 3GPP2 Proxy Mobile IPv4Mobile IPv4 is a standard mobility protocol that enables an IPv4 device to move among networks while maintaining its IP address. The mobile device has the Mobile IPv4 client function to signal its location to the routing anchor, known as the Home Agent. However, there are many IPv4 devices without such capability due to various reasons. This document describes Proxy Mobile IPv4 (PMIPv4), a scheme based on having the Mobile IPv4 client function in a network entity to provide mobility support for an unaltered and mobility-unaware IPv4 device. This document also describes a particular application of PMIPv4 as specified in the WiMAX Forum and another application that is to be adopted in 3GPP2. This document is not an Internet Standards Track specification; it is published for informational purposes.IP Mobility Support for IPv4, RevisedThis document specifies protocol enhancements that allow transparent routing of IP datagrams to mobile nodes in the Internet. Each mobile node is always identified by its home address, regardless of its current point of attachment to the Internet. While situated away from its home, a mobile node is also associated with a care-of address, which provides information about its current point of attachment to the Internet. The protocol provides for registering the care-of address with a home agent. The home agent sends datagrams destined for the mobile node through a tunnel to the care-of address. After arriving at the end of the tunnel, each datagram is then delivered to the mobile node. [STANDARDS-TRACK]Mobility Support in IPv6This document specifies Mobile IPv6, a protocol that allows nodes to remain reachable while moving around in the IPv6 Internet. Each mobile node is always identified by its home address, regardless of its current point of attachment to the Internet. While situated away from its home, a mobile node is also associated with a care-of address, which provides information about the mobile node's current location. IPv6 packets addressed to a mobile node's home address are transparently routed to its care-of address. The protocol enables IPv6 nodes to cache the binding of a mobile node's home address with its care-of address, and to then send any packets destined for the mobile node directly to it at this care-of address. To support this operation, Mobile IPv6 defines a new IPv6 protocol and a new destination option. All IPv6 nodes, whether mobile or stationary, can communicate with mobile nodes. This document obsoletes RFC 3775. [STANDARDS-TRACK]TCP Extensions for Multipath Operation with Multiple AddressesTCP/IP communication is currently restricted to a single path per connection, yet multiple paths often exist between peers. The simultaneous use of these multiple paths for a TCP/IP session would improve resource usage within the network and, thus, improve user experience through higher throughput and improved resilience to network failure.Multipath TCP provides the ability to simultaneously use multiple paths between peers. This document presents a set of extensions to traditional TCP to support multipath operation. The protocol offers the same type of service to applications as TCP (i.e., reliable bytestream), and it provides the components necessary to establish and use multiple TCP flows across potentially disjoint paths. This document defines an Experimental Protocol for the Internet community.Requirements for Distributed Mobility ManagementThis document defines the requirements for Distributed Mobility Management (DMM) at the network layer. The hierarchical structure in traditional wireless networks has led primarily to centrally deployed mobility anchors. As some wireless networks are evolving away from the hierarchical structure, it can be useful to have a distributed model for mobility management in which traffic does not need to traverse centrally deployed mobility anchors far from the optimal route. The motivation and the problems addressed by each requirement are also described.Conveying the Desired Address TypeThe following are some suggestions of possible extensions to the socket API
for enabling applications to convey their session continuity and address
reachability requirements. 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.AcknowledgementsWe 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.ContributorsThis document was merged with "Use Cases and API Extension for Source IP Address
Selection" .
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' AddressesActilityIstanbulTurkeyalper.yegin@actility.comIntel CorporationPetah TikvaIsraeldanny.moses@intel.comSungkyunkwan UniversitySuwonRepublic of Koreaseiljeon.ietf@gmail.com