MANET Autoconfiguration (Autoconf) E. Baccelli (Ed.)
Internet-Draft INRIA
Expires: October 5, 2007 K. Mase
Niigata University
S. Ruffino
Telecom Italia
S. Singh
Samsung
April 3, 2007
Address Autoconfiguration for MANET: Terminology and Problem Statement
draft-baccelli-autoconf-statement-03
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Abstract
Traditional dynamic IPv6 address assignment solutions are not adapted
to mobile ad hoc networks. This document elaborates on this problem,
states the need for new solutions, and requirements to these
solutions.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Deployment Scenarios . . . . . . . . . . . . . . . . . . . . . 5
3.1. Standalone MANET . . . . . . . . . . . . . . . . . . . . . 5
3.2. Connected MANET . . . . . . . . . . . . . . . . . . . . . 5
3.3. Deployment Scenarios Selection . . . . . . . . . . . . . . 5
4. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 6
4.1. MANET Autoconfiguration Goals . . . . . . . . . . . . . . 6
4.2. Existing Solutions' Shortcomings . . . . . . . . . . . . . 6
4.2.1. Lack of Multi-hop Support . . . . . . . . . . . . . . 6
4.2.2. Lack of Dynamic Topology Support . . . . . . . . . . . 7
4.2.3. Lack of Network Merging Support . . . . . . . . . . . 7
4.2.4. Lack of Network Partitionning Support . . . . . . . . 7
4.3. MANET Autoconfiguration Issues . . . . . . . . . . . . . . 8
4.3.1. Address and Prefix Generation . . . . . . . . . . . . 8
4.3.2. Address Uniqueness Requirements . . . . . . . . . . . 8
4.3.3. MANET Border Routers Related Issues . . . . . . . . . 9
5. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
7. Informative References . . . . . . . . . . . . . . . . . . . . 13
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
Intellectual Property and Copyright Statements . . . . . . . . . . 16
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1. Introduction
Mobile ad hoc networks (also known as MANETs [2] [1]) are networks
composed of mobile devices that communicate over wireless media,
which dynamically self-organize multi-hop IP communication between
each other, and such regardless of the availability of a connection
to any infrastructure.
However, prior to participation in IP communication, each MANET
interface that does not benefit from appropriate static configuration
needs to automatically acquire at least one IP address, that may be
required to be unique within a given scope.
Standard automatic IPv6 address/prefix assignment solutions [5], [3]
[4] do not work "as-is" on MANETs due to ad hoc networks' unique
characteristics [2], and new mechanisms are therefore needed. This
document thus details and categorizes the issues that need to be
addressed.
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2. Terminology
In this document, several words are used to signify the requirements
of the specification. These words are often capitalized. 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].
In addition, this document uses the MANET architecture terminology
defined in [2], as well as the following terms :
Local address - An IP address configured on an interface of a router
in a MANET and valid for communication inside this MANET. A local
address MUST NOT be used for communication including routers
outside the MANET.
Global address - An IP address configured on a MANET router and
valid for communication with routers in the Internet, as well as
internally within the MANET.
Standalone MANET - An independent ad hoc network, which does not
contain a border router through which it is connected to the
Internet.
Network merger - The process by which two or more previously
disjoint ad hoc networks get connected.
Network partitioning - The process by which an ad hoc network splits
into two or more disconnected ad hoc networks.
Address generation - The process of selecting a tentative address in
view to configure an interface.
Address assignment - The process of configuring a generated address
on an interface.
Pre-service address uniqueness - The property of an address which is
assigned at most once at this given point in time, within a given
scope.
In-service address uniqueness - The property of an address which was
assigned at most once within a given scope, and which remains
unique over time, as the address is being used.
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3. Deployment Scenarios
Automatic configuration of IP addresses and/or prefixes on MANET
interfaces is necessary in a number of deployment scenarios. This
section outlines the different categories of scenarios that are
considered.
3.1. Standalone MANET
Standalone MANETs are not connected to any external network: all
traffic is generated by MANET nodes and destined to nodes in the same
MANET.
Routers joining a standalone MANET may either have (i) no previous
configuration, or (ii) pre-configured local or global IP addresses
(or prefixes). Due to potential network partitions and mergers,
standalone MANETs may be composed of routers of either either types.
Typical instances of this scenario include private or temporary
networks, set-up in areas where neither wireless coverage nor network
infrastructure exist (e.g. emergency networks for disaster recovery,
or conference-room networks).
3.2. Connected MANET
Connected MANETs have, contrary to standalone MANETs, connectivity to
one or more external networks, typically the Internet, by means of
one or more MBR (Manet Border Router, see [2]). MANET routers may
generate traffic destined to remote hosts accross these external
networks, as well as to destination inside the MANET.
Again, routers joining a connected MANET may either (i) have no
previous configuration, or (i) already own pre-configured local or
global IP addresses (or prefixes).
Typical instances of this scenario include public wireless networks
of scattered fixed WLAN Access Points participating in a MANET of
mobile users, and acting as MBRs. Another example of such a scenario
is coverage extension of a fixed wide-area wireless network, where
one or more mobile routers in the MANET are connected to the Internet
through technologies such as UMTS or WiMAX.
3.3. Deployment Scenarios Selection
Both "Standalone MANET" scenario and "Connected MANET" scenarii are
to be addressed by solutions for MANET autoconfiguration.
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4. Problem Statement
This section details the goals of MANET autoconfiguration, and
highlights the shortcomings of existing autoconfiguration solutions.
A taxonomy of autoconfiguration issues on MANETs is then elaborated.
4.1. MANET Autoconfiguration Goals
A MANET router needs to configure an IPv6 prefix(es) on its host
interface and/or an IPv6 address on its loopback interface. Besides,
it needs to configure a /128 and/or a link local address on its MANET
interface. A MANET router may also configure a prefix shorter than
/128 on its MANET interface provided prefix uniqueness is guaranteed
[2].
The primary goal of MANET autoconfiguration is thus to provide
mechanisms for IPv6 prefix allocation and address assignment, that
are suited for mobile ad hoc environments.
These mechanisms must address the distributed, multi-hop nature of
MANETs [2], and be able to follow topology and connectivity changes
by (re)configuring addresses and/or prefixes accordingly.
Solutions must achieve their task with (i) low overhead, due to
scarse bandwidth, and (ii) low delay, due to the dynamicity of the
topology.
4.2. Existing Solutions' Shortcomings
Traditional dynamic IP address assignment solutions, such as [5], [3]
or [4], do not work as-is on MANETs due to these networks' unique
properties. This section overviews the shortcomings of these
solutions in mobile ad hoc environments.
4.2.1. Lack of Multi-hop Support
Traditional solutions assume that a broadcast directly reaches every
router or host on the network, whereas this generally is not the case
in MANETs (see [2]). Some routers in the MANET will typically assume
multihop broadcast, and expect to receive through several
intermediate relayings by peer MANET routers. For example, in Fig.
1, the MANET router MR3 cannot communicate directly with a DHCP
server [4] that would be available through an MBR.
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----- MR1...MR3
/ .
+-------------+ +------------+ / .
| | p2p | MANET |/ .
| ISP Edge | Link | Border | .
| Router +---------+ Router |\ .
| | | (MBR) | \ .
+-------------+ +------------+ \----- MR2
Fig. 1. Connected MANET router topology.
4.2.2. Lack of Dynamic Topology Support
A significant proportion of the routers in the MANET may be mobile
with wireless interface(s), leading to ever changing neighbor sets
for most MANET routers (see [1]). Therefore, network topology may
change rather dynamically compared to traditional networks, which
invalidates traditional delegation solutions that were developed for
infrastructure-based networks, which assume the existence of a
permanent hierarchy among devices and the permanent reachability of a
configuration server. For instance, in Fig. 1, even if MR1 would be
able to delegate prefixes to MR3 with DHCP [4], it cannot be assumed
that MR1 and MR3 will not move and become unable to communicate
directly.
4.2.3. Lack of Network Merging Support
Network merging is a potential event that was not considered in the
design of traditional solutions, and that may greatly disrupt the
autoconfiguration mechanisms in use (see [2]). Examples of network
merging related issues include cases where a MANET A may feature
routers and hosts that use IP addresses that are locally unique
within MANET A, but this uniqueness is not guaranteed anymore if
MANET A merges with another MANET B. If address uniqueness is
required within the MANET (see Section 4.3.2), issues arise that were
not accounted for in traditional networks and solutions.
4.2.4. Lack of Network Partitionning Support
Network partinionning is a potential event that was not considered in
the design of traditional solutions, and that may invalidate usual
autoconfiguration mechanisms (see [2]). Examples of related issues
include cases such as a standalone MANET, whereby connection to the
infrastructure is not available, possibly due to network
partitnionning and loss of connectivity to an MBR. The MANET must
thus function without traditional server availability. While
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stateless protocols such as [5] and [3] could provide IP address
configuration (for MANET interfaces, loopback interfaces), these
solutions do not provide any mechanism for allocating "unique
prefix(es)" to routers in order to enable the configuration of host
interfaces. Moreover, [5] and [3] test address uniqueness via
messages that are sent to neighbors only, and as such cannot detect
the presence of duplicate addresses configured within the network but
located several hops away. However, since MANETs are generally
multi-hop, detection of duplicate addresses over several hops is a
feature that is required in most cases of MANET interface address
assignment (see Section 4.3.2).
----- MR1...MR3...MR5
/ .
/ .
/ .
MR4 .
\ .
\ .
\----- MR2
Fig. 2. Standalone MANET router topology.
4.3. MANET Autoconfiguration Issues
Taking into account the shortcomings of traditional solutions, this
section categorizes general issues with regards to MANET
autoconfiguration.
4.3.1. Address and Prefix Generation
The distributed nature of MANETs brings the need for address
generation algorithms that are not always based on traditional
central server schemes and hierarchies to provide MANET routers with
addresses and prefixes. In addition, the multi-hop aspect of mobile
ad hoc networking makes it difficult to totally avoid address and
prefix duplication a priori over all the MANET.
4.3.2. Address Uniqueness Requirements
If address uniqueness is required within a specific scope, and if the
address/prefix generation mechanism in use does not totally avoid
address/prefix duplication, then additional issues arise. This
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section overviews these problems.
Pre-service Issues -- One category of problems due to address
uniqueness requirements are called pre-service issues. Conceptually,
they relate to the fact that before a generated address is assigned
and used, it should be verified that it will not create an address
conflict within the specified scope. This is essential in the
context of routing, where it is desireable to reduce the risks of
loops due to routing table pollution with duplicate addresses.
In-Service Issues -- Another category of problems due to address
uniqueness are called in-service issues. They come from the fact
that even if an assigned address is currently unique within the
specified scope, it cannot be ensured that it will indeed remain
unique over time.
Phenomena such as MANET merging and MANET partitionning can bring the
need for checking the uniqueness (within the specified scope) of
addresses that are already assigned and used, if in-service address
uniqueness is required.
4.3.3. MANET Border Routers Related Issues
Another category of problems concern MBR management.
MBR Mobility -- Some addresses may be configured by servers available
through MBRs that may themselves be mobile and that may therefore
leave the MANET. In this case, global addresses used by routers in
the MANET may no longer be valid.
MBR Multiplicity -- In the case where multiple MBRs are available in
the MANET, providing access to multiple address configuration
servers, specific problems arise. One problem is the way in which
global prefixes are managed within the MANET. If one prefix is used
for the whole MANET, partitioning of the MANET may invalid routes in
the Internet towards MANET routers. On the other hand, use of
multiple network prefixes guarantees traffic is unambiguously routed
towards the MBR responsible for one particular prefix, but asymmetry
in the routers' choice of ingress/egress MBR can lead to non-optimal
paths followed by inbound/outbound data traffic. When a device
changes its MBR attachment, some routes may be broken, affecting
MANET packet forwarding performance and applications.
IPv6 Specifications -- Additional problems come from issues with
current IPv6 specifications. For example, the strict application of
[5] may lead to check every IPv6 unicast address for uniqueness: in a
multiple-MBR / multiple-prefixes MANET, this could bring to a large
amount of control signalling, due to frequent reconfiguration.
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Moreover, IPv6 does not currently specify an address scope that is
appropriate to fit the scope of a MANET, which could lead to
undesireable behavior such as MBRs leaking MANET local traffic
outside the MANET.
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5. Security Considerations
Address configuration in MANET could be prone to security attacks, as
in other type of IPv6 networks. Security threats to IPv6 neighbor
discovery are discussed in [6]: in particular, analysis includes
trust model and threats for a specific ad hoc network scenario, where
all the routers share a common link (i.e. they are one hop away from
each other, full-meshed connectivity is available). Although the
document does not explicitly address MANETs, where routers can be
multiple hop away from each other, the trust model it provides could
be valid also in the context of MANET autoconfiguration. It is also
worth noting that, in case of MANET connected to the Internet, other
threats defined in [6] could apply here, e.g. attacks involving
routers and DoS attacks on Duplicate Address Detection procedures.
The security analysis has to be further extended to include threats,
specific to multi-hop networks and related to the address
configuration process in particular. However, general security
issues of ad hoc routing protocols' operations are not in the scope
of MANET autoconfiguration.
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6. IANA Considerations
This document does currently not specify IANA considerations.
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7. Informative References
[1] Macker, J. and S. Corson, "MANET Routing Protocol Performance
Issues and Evaluation Considerations", RFC 2501, January 1999.
[2] Macker, J., Chakeres, I., and T. Clausen, "Mobile Ad hoc Network
Architecture", ID draft-ietf-autoconf-manetarch, February 2007.
[3] Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery
for IPv6", RFC 2461, December 1998.
[4] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M.
Carney, "Dynamic Host Configuration Protocol for IPv6",
RFC 3315, July 2003.
[5] Narten, T. and S. Thomson, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[6] Nikander, P., Kempf, J., and E. Nordmark, "IPv6 Neighbor
Discovery (ND) Trust Models and Threats", RFC 3756, May 2004.
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Contributors
This document is the result of joint efforts, including those of the
following contributers, listed in alphabetical order: C. Adjih
(INRIA), T. Clausen (Ecole Polytechnique), C. Perkins (Nokia), P.
Ruiz (University of Murcia), P. Stupar (Telecom Italia), D. Thaler
(Microsoft).
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Authors' Addresses
Emmanuel Baccelli
INRIA
Phone: +33 1 69 33 55 11
Email: Emmanuel.Baccelli@inria.fr
Kenichi Mase
Niigata University
Phone: +81 25 262 7446
Email: Mase@ie.niigata-u.ac.jp
Simone Ruffino
Telecom Italia
Phone: +39 011 228 7566
Email: Simone.Ruffino@telecomitalia.it
Shubhranshu Singh
Samsung
Phone: +82 31 280 9569
Email: Shubranshu@gmail.com
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