RFC 8653: On-Demand Mobility Management

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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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

4. Backwards Compatibility Considerations

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

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.¶

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