NEMO Working Group Thierry Ernst, Editor
Internet-Draft WIDE and INRIA
May, 2003
"Network Mobility Support Goals and Requirements"
<draft-ietf-nemo-requirements-01.txt>
Status of This Memo
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Abstract
Network mobility arises when a router connecting an entire network to
the Internet dynamically changes its point of attachment to the
Internet therefrom causing the reachability of the entire network to
be changed in the topology. Such kind of network is referred to as a
mobile network. Without appropriate mechanisms, sessions established
between nodes in the mobile network and the global Internet cannot be
maintained while the mobile router changes its point of attachment.
The required support mechanisms will be provided in two phases. The
first phase, referred to as NEMO Basic Support is to provide session
continuity while the necessary optimizations mechanims referred to as
NEMO Extended Support might be provided later. This document outlines
the goals expected from network mobility support and defines the
requirements that must be met by NEMO Basic Support solutions.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 03
2. Terminology. . . . . . . . . . . . . . . . . . . . . . . . . 04
3. NEMO Working Group Goals and Methodology . . . . . . . . . . 04
4. NEMO Support Design Goals . . . . . . . . . . . . . . . . . 05
5. NEMO Basic Support One-liner Requirements . . . . . . . . . 09
6. Changes From Previous Version . . . . . . . . . . . . . . . 11
A. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . 11
B. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
C. Editors' Addresses . . . . . . . . . . . . . . . . . . . . . 12
D. Full Copyright Statement . . . . . . . . . . . . . . . . . . 13
Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
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1. Introduction
Network mobility support is concerned with managing the mobility of
an entire network, viewed as a single unit, which changes its point
of attachment to the Internet and thus its reachability in the
Internet topology. Such kind of network is referred to as a mobile
network and includes one or more mobile routers (MRs) which connect
it to the global Internet. Nodes behind the MR(s) (MNNs) are both
fixed (LFNs) and mobile (VMNs or LMNs). In most cases, the internal
structure of the mobile network will in effect be relatively stable
(no dynamic change of the topology), but this is not a general
assumption.
Cases of mobile networks include for instance:
- networks attached to people (Personal Area Networks or PANs): a
cell-phone with one cellular interface and one Bluetooth interface
together with a Bluetooth-enabled PDA constitute a very simple
instance of a mobile network. The cell-phone is the mobile router
while the PDA is used for web browsing or runs a personal web
server.
- networks of sensors and computers deployed in vehicles: vehicles
are more and more embedded with a number of processing units for
safety and ease of driving reasons, as advocated by ITS
(Intelligent Transportation Systems) applications.
- access networks deployed in public transportation (buses,
trains, taxis, aircrafts): they provide Internet access to IP
devices carried by passengers (laptop, camera, mobile phone: host
mobility within network mobility or PANs: network mobility within
network mobility, i.e. nested mobility).
- ad-hoc networks connected to the Internet via a MR: for instance
students in a train that both need to set up an ad-hoc network
among themselves and to get Internet connectivity through the MR
connecting the train to the Internet.
Mobility of networks does not cause MNNs to change their own physical
point of attachment, however they happen to change their topological
location with respect to the global Internet. If network mobility is
not explicitly supported by some mechanisms, the mobility of the MR
results into MNNs losing Internet access and breaking ongoing
sessions entertained between arbitrary correspondent node (CNs) in
the global Internet and those MNNs located within the mobile network.
In addition, the communication path between MNNs and arbitrary
correspondent nodes (CN) becomes sub-optimal, whereas multiple levels
of mobility will cause extremely sub-optimal routing.
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The mechanisms required for handling such mobility issues are
currently lacking within the IETF standards. Traditional work
conducted on mobility support (particularly in the Mobile IP working
group) is to provide continuous Internet connectivity and optimal
routing to mobile hosts only (host mobility support) and are unable
to support network mobility. The NEMO working group has therefore
been set up to deal with issues specific to network mobility. The
purpose of this document is thus to detail the methodology that will
be followed by the NEMO working group, its goals, and to define
requirements for network mobility support.
This document is structured as follows: in section 3, we define the
goals and methodology of the NEMO working group and we emphasize the
stepwise approach the working group has decided to follow. A number
of desirable design goals are listed in section 4. Those design goals
serve as guidelines to edict the requirements for basic network
mobility support.
2. Terminology
Mobility-related terms used in this document are defined in
[MOBILITY-TERMS] whereas terms pertaining to network mobility
specifically are defined in [NEMO-TERMS].
3. NEMO Working Group Goals and Methodology
The primary goal of the NEMO work is to specify a solution which
allows mobile network nodes (MNNs) to remain connected to the
Internet and continuously reachable at all times while the mobile
network they are attached to changes its point of attachment.
Secondary goals of the work is to investigate the effects of network
mobility on various aspects of internet communication such as routing
protocol changes, implications of realtime traffic and fast
handovers, optimizations. These should all support the primary goal
of reachability for mobile network nodes. Security is an important
consideration too, and efforts should be made to use existing
solutions if they are appropriate. Although a well-designed solution
may include security inherent in other protocols, mobile networks
also introduce new challenges.
For doing so, the NEMO working group has decided to take a stepwise
approach by standardizing a basic solution to preserve session
continuity (NEMO Basic Support), and at the same time study the
possible approaches and issues with providing more optimal routing
with potentially nested mobile networks (NEMO Extended Support).
However, the working group is not chartered to actually standardize a
solution to such route optimization at this point in time.
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For NEMO Basic Support, the working group will assume that none of
the nodes behind the MR will be aware of the network's mobility, thus
the network's movement needs to be completely transparent to the
nodes inside the mobile network. This assumption will be made to
accommodate nodes inside the network that are not generally aware of
mobility.
The efforts of the Mobile IP working group have resulted in the
Mobile IPv4 and Mobile IPv6 protocols, which have already solved the
issue of host mobility support. Since challenges to enabling mobile
networks are vastly reduced by this work, basic network mobility
support will adopt the methods for host mobility support used in
Mobile IP, and extend them in the simplest way possible to achieve
its goals. The basic support solution is for each MR to have a Home
Agent, and use bidirectional tunneling between the MR and HA to
preserve session continuity while the MR moves. The MR will acquire a
Care-of-address from its attachment point much like what is done for
mobile nodes (MN) using Mobile IP. This approach allows nested mobile
networks, since each MR will appear to its attachment point as a
single node.
4. NEMO Suppport Design Goals
This section details the fundamental design goals the solutions will
tend to achieve. Those design goals will serve to edict and
understand the requirements defined for forthcoming solutions. Actual
requirements for NEMO Basic Support are in the next section, whereas
NEMO Extended Support has not yet been considered.
- Migration Transparency: a permanent connectivity to the Internet
has to be provided to all MNNs while continuous sessions are
expected to be maintained as the mobile router changes its point
of attachment. For doing so, MNNs are expected to be reachable via
their permanent IP addresses.
- Performance Transparency and Seamless Mobility: NEMO support is
expected to be provided with limited signaling overhead and to
minimize the impact of handover over applications, in terms of
packet loss or delay. However, although variable delays of
transmission and losses between MNNs and their respective CNs
could be perceived as the network is displaced, it would not be
considered a lack of performance transparency.
- Network Mobility Support Transparency: MNNs behind the MR(s)
don't change their own physical point of attachment as a result of
the mobile network's displacement in the Internet topology.
Consequently, NEMO support is expected to be performed by the sole
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MR(s) and specific support functions on any other node than the
MR(s) would better be avoided.
- Operational Transparency: NEMO support is to be implemented at
the IP layer level. It is expected to be transparent to upper
layers so that any upper layer protocol can run unchanged on top
of an IP layer extended with NEMO support.
- Arbitrary Configurations: The formation of a mobile network can
exist in various levels of complexity. In the simplest case, a
mobile network contains just a mobile router and a host. In the
most complicated case, a mobile network is multi-homed and is
itself a multi-level aggregation of mobile networks with
collectively thousands of mobile routers and hosts. While the list
of potential configurations of mobile networks cannot be limited,
at least the following configurations are desirable:
o mobile networks of any size, ranging from a sole subnet with
a few IP devices to a collection of subnets with a large
number of IP devices,
o nodes that change their point of attachment within the mobile
network,
o foreign mobile nodes that attach to the mobile network,
o multi-homed mobile network either when a single MR has
multiple attachments to the internet, or when the mobile
network is attached to the Internet by means of multiple
MRs (see definition in [NEMO-TERMS]),
o nested mobile networks (mobile networks attaching to other
mobile networks, see definition in [NEMO-TERMS]. Although the
complexity requirements of those nested networks is not
clear, it is desirable to support arbitrary levels of
recursive networks, and only in the case where this is
impractical and protocol concerns preclude this support
should the solution impose restrictions on nesting
(e.g. path MTU),
o distinct mobility frequencies,
o distinct access medium.
In order to keep complexity minimal, transit networks are excluded
from this list. A transit network is one in which data would be
forwarded between two endpoints outside of the network, so that
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the network itself simply serves as a transitional conduit for
packet forwarding. A stub network (leaf network), on the other
hand, does not serve as a data forwarding path. Data on a stub
network is either sent by or addressed to a node located within
that network.
- Local Mobility and Global Mobility: mobile networks and mobile
nodes owned by administratively different entities are expected to
be displaced within a domain boundary or between domain
boundaries. Multihoming, vertical and horizontal handoffs, and
access control mechanisms are desirable to achieve this goal. Such
mobility type is not expected to be limited for any consideration
other than administrative and security policies.
- Scalability: NEMO support signaling and processing is expected
to scale to a potentially large number of mobile networks
irrespective of their configuration, mobility frequency, size and
number of CNs.
- Backward Compatibility: NEMO support will have to co-exist with
existing IPv6 standards without interfering with them. Standards
defined in other IETF working groups have to be reused as much as
possible and extended only if deemed necessary. For instance, the
following mechanisms defined by other working groups are expected
to function without modidications:
o Address allocation and configuration mechanisms
o Host mobility support: mobile nodes and correspondent nodes,
either located within or outside the mobile network are
expected to keep operating protocols defined by the Mobile IP
working group. This include mechanisms for host mobility
support (Mobile IPv6) and seamless mobility (FMIPv6).
o Multicast support entertained by MNNs are expected to be
maintained while the mobile router changes its point of
attachment.
o Access control protocols and mechanisms used by visiting
mobile hosts and routers to be authenticated and authorized
to gain access to the Internet via the mobile network
infrastructure (MRs).
o Security protocols and mechanisms
o Mechanisms performed by routers deployed both in the visited
networks and in mobile networks (routing protocols, Neighbor
Discovery, ICMP, Router Renumbering, ...).
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- Secure Signaling: NEMO support will have to comply with usual
IETF security policies and recommendations and is expected to have
its specific security issues fully addressed. In practice, all
NEMO support control messages transmitted in the network will have
to ensure an acceptable level of security to prevent intruders to
usurp identities and forge data. Specifically, the following
issues have to be considered:
o Authentication of the sender to prevent identity usurpation.
o Authorization, to make sure the sender is granted permission
to perform the operation as indicated in the control message.
o Confidentiality of the data contained in the control message.
- Location Privacy: means to hide the actual location of MNNS to
third parties other than the HA are desired. In which extend this
has to be enforced is not clear since it is always possible to
determine the topological location by analysing IPv6 headers. It
would thus require some kind of encryption of the IPv6 header to
prevent third parties to monitor IPv6 addresses between the MR and
the HA. On the other hand, it is at the very least desirable to
provide means for MNNs to hide their real topological location to
their CNs.
- IPv4 and NAT traversal: IPv4 clouds and NAT are likely to co-
exist with IPv6 for a long time, so it is desirable to ensure
mechanisms developped for NEMO will be able to traverse such
clouds.
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5. NEMO Basic Support One-liner Requirements
The NEMO WG will specify a unified and unique solution for "Basic
Network Mobility Support". The solution will allow all nodes in the
mobile network to be reachable via permanent IP addresses, as well as
maintain ongoing sessions as the MR changes its point of attachment
to the Internet topology. This will be done by maintaining a
bidirectional tunnel between a MR and its Home Agent. The Working
Group will investigate reusing the existing Mobile IPv6 mechanisms
for the tunnel management, or extend it if deemed necessary.
The following requirements are placed on the NEMO Basic Support
solution, hereafter referred to as "the solution":
R01: The solution MUST be implemented at the IP layer level.
R02: The solution MUST set up a bi-directional tunnel between a
MR and its Home Agent.
R03: All traffic exchanged between a MNN and a CN in the global
Internet MUST transit through the bidirectional tunnel.
R04: MNNs MUST be reachable at a permanent IP address and name.
R05: The solution MUST maintain continuous sessions (both unicast
and multicast) between MNNs and arbitrary CNs after IP
handover of (one of) the MR.
R06: The solution MUST not require modifications to any node other
than MRs and HAs.
R07: The solution MUST support fixed nodes, mobile hosts and mobile
routers in the mobile network.
R08: The solution MUST allow MIPv6-enabled MNNs to use a mobile
network link as either a home link or a foreign link.
R09: The solution MUST not prevent the proper operation of Mobile
IPv6 (i.e. the solution MUST allow MIPv6-enabled MNNs to operate
either the CN, HA, or MN operations defined in [MIPv6])
[SHOULD BE MOVED UNDER R17]
R10: The solution MUST treat all the potential configurations the
same way (whatever the number of subnets, MNNs, nested levels
of MRs, egress interfaces, ...)
R11: The solution MUST support at least 2 levels of nested mobile
networks, while, in principle, arbitrary levels of recursive
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mobile networks SHOULD be supported.
R12: The solution MUST function for multihomed MR and multihomed
mobile networks as defined in [NEMO-TERMS]). Particularly:
R12.1: The solution MUST function for multi-MR mobile networks
R12.2: The solution MUST function for multi-egress
interfaces
R12.3: The solution MUST function for MR with multiple global
addresses on an egress interface.
[I PROPOSE TO REMOVE R12.1, 2 and 3 BECAUSE THIS IS
CONTAINED IN THE DEFINITION IN [NEMO-TERMS]].
R13: NEMO Support signaling over the bidirectional MUST be minimized
[NEW REQUIREMENT PROPOSED BY EDITOR]
R14: Signaling messages between the HA and the MR MUST be secured:
R14.1: The receiver MUST be able to authenticate the sender
R14.2: The function performed by the sender MUST be authorized
for the content carried
R14.3: Anti-replay MUST be provided
R14.4: The signaling messages SHOULD be encrypted [ACCORDING TO
DISCUSSION AT IETF56, SHALL BE REMOVED or SOFTENED TO
"MAY" (?)]
R15: The solution MUST ensure transparent continuation of routing and
management operations over the bi-directional tunnel when the MR
is away from home. (this includes e.g. routing protocols, router
renumbering, DHCPv6, etc)
R16: The solution MUST not impact on the routing fabric neither on
the Internet addressing architecture. [ACCORDING TO IETF56
minutes, SHOULD BE REMOVED]
R17: The solution MUST ensure backward compatibility with other
standards defined by the IETF [SPECIFIC PROTOCOLS SHOULD BE
EXPLICITLY LISTED: MLD, ... etc. PLEASE CONTRIBUTE THE NAMES OF
PROTOCOLS TO BE INCLUDED ON THE MAILING LIST. MAYBE MIPV6 COULD
BE INCLUDED HERE INSTEAD OF R09.] Particularly:
R18: The solution SHOULD preserve sessions established through
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another egress interface when one fails [PROPOSED BY EDITOR OF
THIS DOCUMENT AT THE IETF56 MEETING. TO BE DISCUSSED ON THE
MAILING LIST]
6. Changes since last version
- title of documents: included the word "goals"
- entire document: some rewording
- section 4: changed title of section to "NEMO Design Goals".
- section 4: removed "MUST" and "MAY"
- section 4: more text about location privacy
- section 4: changed "Administration" paragraph to "Local and
Global Mobility". Text enhanced.
- section 5:
R02: replace "between MR and MR's HA" with "a MR and its HA"
R11: specified at least 2 levels
R12: replaced "support" with "function" and add "multihomed MR"
R13.x renumbered to R12.x since part of R12 (editing mistake)
R13 and R18: new requirements proposed by editor
and minor changes in the formulation of other Requirements
A. Acknowledgments
The material presented in this document takes most of its text from
discussions and previous documents submitted to the NEMO working
group. This includes initial contributions from Motorola, INRIA,
Ericsson and Nokia. We are particularly grateful to Hesham Soliman
(Ericsson) and the IETF ADs (Erik Nordmark and Thomas Narten) who
highly helped to set up the NEMO working group. We are also grateful
to all the following people whose comments highly contributed to the
present document: TJ Kniveton (Nokia), Alexandru Petrescu (Motorola),
Christophe Janneteau (Motorola), Pascal Thubert (CISCO), Hong-Yon
Lach (Motorola), Mattias Petterson (Ericsson) and all the others
people who have expressed their opinions on the NEMO (formely MONET)
mailing list. Thierry Ernst wish to personally grant support to its
previous employers, INRIA, and Motorola for their support and
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direction in bringing this topic up to the IETF, particularly Claude
Castelluccia (INRIA) and Hong-Yon Lach (Motorola).
B. References
[IPv6-NODE] John Loughney
"IPv6 Node Requirements"
draft-ietf-ipv6-node-requirements.txt
Work in progress.
[MobileIPv4] Charles Perkins
"IP Mobility Support"
RFC 2002, IETF, October 1996.
[MobileIPv6] David B. Johnson and C. Perkins.
"Mobility Support in IPv6"
draft-ietf-mobileip-ipv6.txt,
Work in progress.
[MOBILITY-TERMS] J. Manner
"Mobility Related Terminology
<draft-ietf-seamoby-mobility-terminology.txt>
Work in progress.
[NEMO-TERMS] Thierry Ernst and Hong-Yon Lach
"Terminology for Network Mobility Support",
draft-ietf-nemo-terminology.txt
Work in progress.
[RFC1122] R. Braden (editor).
"Requirements for Internet Hosts - Communication
Layers". IETF RFC 1122, October 1989.
[RFC2119] S. Bradner
"Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, IETF, March 1997.
[RFC2460] S. Deering and R. Hinden.
"Internet Protocol Version 6 (IPv6) Specification"
IETF RFC 2460, December 1998.
C. Editors's Addresses
Questions about this document can be directed to the NEMO working
group chairs:
Thierry Ernst,
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Keio University.
5322 Endo, Fujisawa-shi,
Kanagawa 252-8520, Japan.
Phone : +81-466-49-1100
Fax : +81-466-49-1395
Email : ernst@sfc.wide.ad.jp
T. J. Kniveton
Communications Systems Lab
Nokia Research Center
313 Fairchild Drive
Mountain View, California 94043, USA
Phone : +1 650 625-2025
Fax : +1 650 625-2502
EMail : Timothy.Kniveton@Nokia.com
D. Full Copyright Statement
Copyright (C) The Internet Society (2002). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published and
distributed, in whole or in part, without restriction of any kind,
provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of developing
Internet standards in which case the procedures for copyrights defined
in the Internet Standards process must be followed, or as required to
translate it into languages other than English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
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TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT
NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN
WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Funding for the RFC editor function is currently provided by the
Internet Society.
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