MANET Autoconfiguration (Autoconf) E. Baccelli (Ed.)
Internet-Draft INRIA
Expires: February 2, 2008 K. Mase
Niigata University
S. Ruffino
Telecom Italia
S. Singh
Samsung
August 2007
Address Autoconfiguration for MANET: Terminology and Problem Statement
draft-ietf-autoconf-statement-01
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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 . . . . . . . . . . . . . . . . . . . . . . 7
4.1. MANET Autoconfiguration Goals . . . . . . . . . . . . . . 7
4.2. Existing Protocols' Shortcomings . . . . . . . . . . . . . 7
4.2.1. Lack of Multi-hop Support . . . . . . . . . . . . . . 7
4.2.2. Lack of Dynamic Topology Support . . . . . . . . . . . 8
4.2.3. Lack of Network Merging Support . . . . . . . . . . . 8
4.2.4. Lack of Network Partitioning Support . . . . . . . . . 9
4.3. MANET Autoconfiguration Issues . . . . . . . . . . . . . . 9
4.3.1. Address and Prefix Generation . . . . . . . . . . . . 9
4.3.2. Prefix and Address Uniqueness Requirements . . . . . . 10
4.3.3. MANET Border Routers Related Issues . . . . . . . . . 10
5. Solutions Considerations . . . . . . . . . . . . . . . . . . . 12
6. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
8. Informative References . . . . . . . . . . . . . . . . . . . . 15
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
Intellectual Property and Copyright Statements . . . . . . . . . . 18
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1. Introduction
A Mobile Ad hoc NETwork (also known as a MANET [2] [1]) consists of a
loosely connected set of MANET routers. Each MANET router embodies
IP routing/forwarding functionality and may also incorporate host
functionality. These routers dynamically self-organize and maintain
a routing structure among themselves, regardless of the availability
of a connection to any infrastructure. MANET routers may be mobile
and may communicate over symmetric or assymetric wireless links.
They may thus join and leave the MANET at any time.
However, prior to participation in IP communication, each MANET
router 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, or to be topologically
appropriate.
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], therefore new or modified mechanisms are needed.
This document thus details and categorizes the issues that need to be
addressed.
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2. Terminology
This document uses the MANET architecture terminology defined in [2],
as well as the following terms :
MANET Local address (MLA) - An IP address configured on an interface
of a router in a MANET and valid for communication inside this
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 within a given scope, and which is unique,
before it is being used.
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, after the address has started 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 routers and hosts in the MANET and destined
to routers or hosts 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 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 (leaf networks, or other networks that
provide Internet connectivity) by means of one or more MANET border
router [2]. MANET routers may generate traffic destined to remote
hosts across 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 (ii) 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 MANET border routers. 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" and "Connected MANET" scenarios are to be
addressed by solutions for MANET autoconfiguration. Note that
solutions should also aim at addressing cases where a MANET transits
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from one scenario to an other.
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4. Problem Statement
This section details the goals of MANET autoconfiguration, and
highlights the shortcomings of existing autoconfiguration protocols.
A taxonomy of autoconfiguration issues on MANETs is then elaborated.
4.1. MANET Autoconfiguration Goals
A MANET router needs to configure IP addresses and/or prefixes on its
non-MANET interfaces. In addition, it needs to configure a link
local address, a /128 and/or an MLA on its MANET interface. A MANET
router may also configure a IP 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. Note that this task is
distinct from that of propagating knowledge about address or prefix
location, as a routing protocol does (see for example [8], [9]), or
as described in [7].
The mechanisms employed by solutions to be designed 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.
4.2. Existing Protocols' Shortcomings
Traditional dynamic IP address assignment protocols, 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 subnetwork, 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 a MANET border router,
since the server and the MANET router are not located on the same
logical link. While some DHCP extensions (such as the relay-agent
[11]) overcome this issue in a static network, it is not the case in
a dynamic topology, as explained below.
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----- MR1...MR3
/ .
+-------------+ +------------+ / .
| | p2p | MANET |/ .
| ISP Edge | Link | Border | .
| Router +---------+ Router |\ .
| | | | \ .
+-------------+ +------------+ \----- 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, such as [11], which do not assume
intermittent reachability of configuration server(s), and a
potentially ever changing hierarchy among devices. 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. For
instance, [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 may be
required for MANET interface address assignment (see Section 4.3.2).
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4.2.4. Lack of Network Partitioning Support
Network partitioning 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 partitioning
and loss of connectivity to a MANET border router. The MANET must
thus function without traditional address allocation server
availability. While 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.
----- 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
"client-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.
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4.3.2. Prefix and Address Uniqueness Requirements
If prefix or 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 section overviews these problems.
Pre-service Issues -- One category of problems due to address or
prefix uniqueness requirements are called pre-service issues.
Conceptually, they relate to the fact that before a generated address
or prefix 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 and
prefix uniqueness are called in-service issues. They come from the
fact that even if an assigned address or prefix 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 partitioning may bring the
need for checking the uniqueness (within the specified scope) of
addresses or prefixes that are already assigned and used. This need
may depend on (i) the probability of address conflicts, (ii) the
amount of the overhead for checking uniqueness of addresses, and
(iii) address/prefix uniqueness requirements from applications.
For instance, if (i) is extremely low and (ii) significant, checking
uniqueness of addresses and prefixes may not be used. If on the
other hand (i) is not extremely low, checking uniqueness of addresses
and prefixes should be used. In any case, if the application has a
hard requirement for address uniqueness assurance, checking
uniqueness of addresses and prefixes should always be used, no matter
how unlikely is the event of address conflict.
4.3.3. MANET Border Routers Related Issues
Another category of problems concern MANET border router(s)
management.
In the case where multiple MANET border routers 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 result in invalid routes
towards MANET routers, over the Internet. On the other hand, the use
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of multiple network prefixes guarantees traffic is unambiguously
routed from the hosts/routers in the Internet towards the MANET
border router responsible for one particular prefix. However,
asymmetry in the routers' choice of ingress/egress MANET border
router can lead to non-optimal paths followed by inbound/outbound
data traffic, or to broken connectivity, if egress filtering is being
done.
When a device changes its MANET border router attachment, some routes
may be broken, affecting MANET packet forwarding performance and
applications. In a multiple border router / multiple-prefixes MANET,
frequent reconfiguration could cause a large amount of control
signalling (for instance if [5] is used "as-is").
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5. Solutions Considerations
Solutions must achieve their task with (i) low overhead, due to
scarse bandwidth, and (ii) low delay/convergence time, due to the
dynamicity of the topology. The evaluation of such criteria may
depend on the targeted network properties, which include (but are not
limited to) node cardinality, node mobility characteristics, etc.
Solutions are to be designed to work at the network layer and thus to
apply to all link types. However, in situations where link-layer
multicast is needed it is possible that on some link types (e.g.
NBMA links), alternative mechanisms or protocols specifying operation
over a particular link type would be required.
Solutions must interact with existing protocols in a way that
leverages as much as possible appropriate mechanisms that are
deployed. For instance, besides the possible use of the well-known
IPv6 multicast addresses defined for neighbor discovery in [3] (e.g.
for Duplicate Address Detection), solutions may as well use some
addresses defined in [10] for auto-configuration purposes.
Solutions must also take into account the security and trust issues
that are specific to ad hoc networking (see Section 6).
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6. Security Considerations
Address configuration in MANET could be prone to security attacks, as
in other types of IPv6 networks. Security threats to IPv6 neighbor
discovery were discussed in SEND WG and described in [6]: three
different trust models are specified, with varying levels of trust
among network nodes and routers. Among them, the model by which no
trust exists among nodes may be suitable a priori for most ad hoc
networks. However, the other two models may be applicable in some
cases, for example when a trust relationship exists between an
operator and some MANET routers, or between military devices that are
in the same unit. Although [6] does not explicitly address MANETs,
the trust models it provides for ad hoc networks can be valid also in
the context of MANET autoconfiguration.
It is worth noting that analysis of [6] is strictly related to
Neighbor Discovery, Neighbor Unreachability Detection and Duplicate
Address Detection procedures, as defined in [3] and [5]. As
explained in the present document, current standard procedures cannot
be used as-is in MANET context to achieve autoconfiguration of MANET
routers and, therefore, design of new mechanisms can be foreseen.
In this case, although security threats and attacks defined in [6]
could also apply in presence of new solutions, additional threats and
attacks could be possible (e.g., non-cooperation in message
forwarding in multi-hop communications). Therefore, the security
analysis has to be further extended to include threats, specific to
multi-hop networks and related to the particular address
configuration solution.
General security issues of ad hoc routing protocols' operations are
not in the scope of MANET autoconfiguration.
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7. IANA Considerations
This document does currently not specify IANA considerations.
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8. 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.
[7] Draves, R. and D. Thaler, "Default Router Preferences and More-
Specific Routes", RFC 4191, 2005.
[8] Moy, J., "OSPF version 2", RFC 2328, 1998.
[9] Moy, J., Coltun, R., and D. Ferguson, "OSPF for IPv6",
RFC 2740, 1999.
[10] Chakeres, I., "Internet Assigned Numbers Authority (IANA)
Allocations for the Mobile Ad hoc Networks (MANET) Working
Group", ID draft-ietf-manet-iana, May 2007.
[11] Patrick, M., "DHCP Relay Agent Information Option", RFC 3046,
2001.
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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, C.
Bernardos, T. Boot, T. Clausen, C. Dearlove, H. Moustafa, C. Perkins,
A. Petrescu, P. Ruiz, P. Stupar, F. Templin, D. Thaler, K. Weniger.
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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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