IETF MIP6 Working Group N. Montavont
Internet-Draft LSIIT - ULP
Expires: January 17, 2005 R. Wakikawa
Keio University
T. Ernst
WIDE at Keio University
T. Noel
LSIIT - ULP
C. Ng
Panasonic Singapore Labs
July 19, 2004
Analysis of Multihoming in Mobile IPv6
draft-montavont-mobileip-multihoming-pb-statement-01.txt
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Abstract
Individual solutions have been proposed to extend Mobile IPv6 in
order to allow mobile nodes to be multihomed, but all issues have not
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been addressed by a single document. In this document, we thus
propose a taxonomy to classify the situations where a mobile node may
be multihomed. This taxonomy is then used to describe all multihomed
scenarios. Issues preventing mobile nodes to be multihomed while
operating Mobile IPv6 are highlighted. This document doesn't aim at
proposing solutions, however, it is expected to raise discussion in
order to make sure forthcoming solutions will address all the issues.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Taxonomy . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1 Issues Related to Mobile IPv6 . . . . . . . . . . . . . . 8
4.2 Issues Not Related to Mobile IPv6 . . . . . . . . . . . . 8
4.3 Issues Related to a Host Connected to Home Link . . . . . 9
5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . . 12
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1. Introduction
Mobile IPv6 [4],[5] is designed to allow a mobile node to maintain
its IPv6 communications while moving between IPv6 subnets. However,
the current specification does not give hints nor requirements to
deal with mobile nodes with multiple points of attachement, i.e. a
multihomed mobile node. We are thus proposing the current document
to fill this gap.
This document has two goals. The first goal is to define a taxonomy
which helps to represent the different situations where a mobile host
is multihomed. For each case, we show the configuration a multihomed
host may have (number of interfaces, number of Home Addresses or
number of Care-of Addresses). We also give a concrete illustration
for each scenario.
The second goal of this document is to define the requirements needed
to manage multihomed hosts. Different issues will be raised in order
to provide full support of multihomed hosts in Mobile IPv6. The
potentially needed solutions to support new features will be
described in a separate document.
The reader is assumed to have read our companion document [1] which
outlines the goals and benefits of multihoming for both fixed and
mobile nodes (i.e. generic IPv6 nodes). Real-life scenarios as
illustrated in that document are the based motivations of this
present study of multihomed issues peculiar to mobile nodes. The
terms used in this memo are the same as the ones used in Mobile IPv6
[4].
The document is organized as follows: in the first section, we
propose a taxonomy to classify the different cases where mobile hosts
are multihomed. Then this taxonomy is used to describe the
multihoming scenarios specific to Mobile IPv6. In the next section,
an analysis of each case is given in order to select the most
interesting scenarios highlighted in the previous section. The last
section summarizes the different features needed in Mobile IPv6 to
reach the goal defined in [1].
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2. Taxonomy
As detailed in [1], multihoming can provide a number of benefits:
ubiquitous access, redundancy/fault recovery, load sharing, load
balancing, bicasting and preferences settings. In that document, the
multihoming study is split into two main axes: either the node has
only one interface (and several IPv6 addresses) or the node has
several interfaces. In this memo, we follow the same guidelines, but
we conduct this study from the pespective of mobile nodes operating
Mobile IPv6 specifically. However, two more parameters are necessary
to study the feasability of each goal: the multihoming management
will be different according to the number of Home Addresses and the
number of Care-of Addresses the mobile node has. We then proposes
the following taxonomy:
o x = number of active interfaces
o y = number of Home Addresses (HoAs)
o z = number of Care-of Addresses (CoAs)
A value of '1' implies there is a single instance of the parameter,
whereas a value of 'n' indicates that there are multiple instances of
the parameter. An illustration of this taxonomy is given in Figure
1.
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Mobile Node
HoA1 HoA2 ... HoAn --> Mobile IP layer (x)
| | |
+-----+--------+ | |
| | | | |
CoA1 +--CoA2 +---CoA3 ... CoAn --> IP layer (y)
| | | |
Link1 Link2 Link3 ... Linkn --> IPv6 Link (n/a *)
| | | |
+-----+----+ | |
| | |
IF1 IF2 ... IFn --> Physical layer (z)
(z = the number of active interfaces)
HoA1 ::= {CoA1, 2, 3} [IF1 and IF2]
HoA2 ::= {CoA3} [IF2]
Mobile Node(x = 2, y = 3, z = 2)
* because number of IPv6 link is equal to the number of CoAs, equal to y
Figure 1: Illustration of the chosen taxonomy
The variable y indicates the number of HoAs allocated to a host. A
host may have multiple HoAs (x=n) when either:
o The host has only one home link, and all its HoAs are based on the
same IPv6 prefix (e.g. the host may have multiple interfaces).
o The host has only one home link, and multiple HoAs with distinct
prefixes because there are several IPv6 prefixes advertised on the
home link.
o The host has several home links, and thus has at least two HoAs
with different IPv6 prefixes.
As the taxonomy suggests, the fact that the mobile node has several
HoAs is independent from the fact that the mobile node has multiple
interfaces. The fact that the mobile node has multiple interfaces
does not imply that it has multiple HoAs and vice-versa.
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3. Scenarios
o x = 1: only one interface on the host
1. One HoA, one CoA (1,1,1)
The host is not multihomed. The host has only one interface,
with one HoA and is currently away from its home link (one CoA
on the foreign link).
2. Several HoAs, one CoA (1,n,1)
The host is multihomed, since it has several HoAs. This case
may happen when a host is getting access to Internet through
different ISPs and each offers a Mobile IPv6 service to the
host. That way, the host will have a HoA per ISP. Once the
host is connected to a visited IPv6 subnet, it gets one CoA.
This CoA may be registered with all the Home Agents provided
by the ISPs, in order to remain simulteneously reachable
through all its HoAs.
3. One HoA, several CoAs (1,1,n)
The host is multihomed since it has several CoAs. This case
may occur when the interface of the host is connected to a
link where multiple IPv6 prefixes are advertised.
4. Several HoAs, several CoAs (1,n,n)
The host is multihomed, since it has multiple addresses. This
case can be viewed as a combination of the two cases described
above: the host has several HoAs (e.g. given by different
ISPs) and several CoAs (e.g. because the host is receiving
multiple IPv6 prefixes).
o x = n: the host has multiple interfaces
1. One HoA, one CoA (n,1,1)
The host is multihomed: this is a special case of a host with
two interfaces connected to different IPv6 subnets; one of the
subnet is the home network of the host and allows the host to
use its HoA. The host can build a temporary IPv6 address on
its other interface but it cannot register the temporary
address with its Home Agent (unless the host stops using its
HoA, i.e. its interface connected to the home link).
2. One HoA, several CoAs (n,1,n)
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The host is multihomed: the host has several addresses to
choose from. For example, consider a host with several
interfaces, each connected to an IPv6 network (the same or
not). In this example, at least one IPv6 address is
configured on each interface. The host has only one home
link, and only one Home Agent.
3. Several HoA, one CoA (n,n,1)
The host is multihomed. This case extends the case (n,1,1)
when the host has several HoAs, for example from multiple
ISPs.
4. Several HoAs, several CoAs (n,n,n)
The host is multihomed. Many scenarios may lead to this case.
For example, consider a host with three interfaces, two of
them connected to their home link(two different HoAs) and the
last one connected to a visited link where two IPv6 prefixes
are advertised.
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4. Open Issues
In this section we highlight open issues which have to be taken into
account to handle a multihomed host using Mobile IPv6 and we list the
requirements for a Mobile IPv6 node to benefit from its multihomed
configuration in an optimized fashion. To meet some of these
requirements, specific procedures in the Mobile IPv6 specification
will be required. It's not the purpose of this document to provide
solutions to meet these requirements but we give some hints.
Solutions to meet these requirements will be defined in a separate
document.
4.1 Issues Related to Mobile IPv6
1. In the (*,n,*) cases when the mobile host otains a new CoA, it's
not clear to which HoA the new CoA would be bound to. There is
thus a need to define a relationship between HoAs and CoAs.
2. In the (*,1,n) case, several CoAs may be simultaneously used by a
mobile node. In this case, the host must be able to register all
CoAs with a single HoA on a distant node (Correspondent Node or
Home Agent). This questions how to manage multiple CoAs bound to
a single HoA and how to identify an entry in the Binding Cache.
Solutions like [10] may be used.
4.2 Issues Not Related to Mobile IPv6
1. In the (n,*,*) cases, the solution should bring support to allow
a mobile host to simultaneously use several interfaces,
regardless the number of HoAs and CoAs the mobile node may have.
2. In the (*,n,*) case, a mechanism should be defined to detail how
to bind multiple HoAs to a host.
3. In the (n,*,*) cases, a mechanism is needed to redirect flows
from one interface to another: this functionality would allow a
mobile node to pursue all communication flows that were initiated
over the failed interface before it is down.
4. In the (n,1,1) case again, the node may want to use each
interface differently according to some policies and preferences
that would define which flow would be mapped to which interface
and/or which flow should not be used over a given interface. In
order to optimize the global connectivity of a multihomed host, a
solution may be defined to allow multihomed hosts to set filters
on flows on distant nodes (Correspondent Node or Home Agent),
such as mechanisms proposed by [7], [8] and [9].
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4.3 Issues Related to a Host Connected to Home Link
In the (n,*,*) cases listed in Section 3, the host may have one of
its interfaces directly connected to a home link. This may have an
impact on the multihoming management.
For example, if we consider the case (n,n,n) with a host having three
interfaces, three HoAs and two CoAs (connected to two visited IPv6
subnets), the CoAs cannot be registered with the Home Agent serving
the host on the home link it is connected to.
Otherwise, the case (n,n,n) can translate into either case (n,n,1) or
(n,n,0) according to the way the host is connected to the Internet.
Case (n,n,1) only happens when the host is connected to a visited
link with only one interface and obtain only one CoA. Other
interfaces are connected to the home link(s). In the case (n,n,0),
i.e. several interfaces, several HoAs, and no CoA, all interfaces of
the host are connected to their respective home links.
Some Mobile IPv6 features cannot be used when the host is connected
to the same link as its Home Agent (e.g. home registration). So,
such specific scenrarios must be considered by the solutions.
5 References
[1] Ernst, T., "Goals and Benefits of Multihoming",
draft-multihoming-generic-goals-and-benefits-00 (work in
progress), February 2004.
[2] Manner, J. and M. Kojo, "Mobility Related Terminology", RFC
3753, June 2004.
[3] Ernst, T. and H. Lach, "Network Mobility Support Terminology",
draft-ietf-nemo-terminology-01 (work in progress), February
2004.
[4] Johnson, D., Perkins, C. and J. Arkko, "Mobility Support in
IPv6", RFC 3775, June 2004.
[5] Arkko, J., Devarapalli, V. and F. Dupont, "Using IPsec to
Protect Mobile IPv6 Signaling Between Mobile Nodes and Home
Agents", RFC 3776, June 2004.
[6] Montavont, N., Noel, T. and M. Kassi-Lahlou, "MIPv6 for
Multiple Interfaces", draft-montavont-mobileip-mmi-00 (work in
progress), July 2002.
[7] Soliman, H., Malki, K. and C. Castelluccia, "Per-flow movement
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in MIPv6", draft-soliman-mobileip-flow-move-02 (work in
progress), July 2002.
[8] Montavont, N. and T. Noel, "Home Agent Filtering for Mobile
IPv6", draft-montavont-mobileip-ha-filtering-v6-00 (work in
progress), January 2004.
[9] Kuladinithi, K., "Filters for Mobile IPv6 Bindings (NOMADv6)",
draft-nomadv6-mobileip-filters-02 (work in progress), June
2004.
[10] Wakikawa, R., "Multiple Care-of Addresses Registration",
draft-wakikawa-mobileip-multiplecoa-02 (work in progress),
September 2003.
[11] Stemm, M. and R. Katz, "Vertical Handoffs in Wireless Overlay
Networks", Journal Mobile Networks and Applications, vol. 3,
number 4, pages 335-350, 1998.
Authors' Addresses
Nicolas Montavont
LSIIT - Univerity Louis Pasteur
Pole API, bureau C444
Boulevard Sebastien Brant
Illkirch 67400
FRANCE
Phone: (33) 3 90 24 45 87
EMail: montavont@dpt-info.u-strasbg.fr
URI: http://www-r2.u-strasbg.fr/~montavont/
Wakikawa Ryuji
Keio University
Jun Murai Lab., Keio University.
5322 Endo
Fujisawa, Kanagawa 252-8520
Japan
Phone: +81-466-49-1100
Fax: +81-466-49-1395
EMail: ryuji@sfc.wide.ad.jp
URI: http://www.mobileip.jp/
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Ernst Thierry
WIDE at Keio University
Jun Murai Lab., Keio University.
K-square Town Campus, 1488-8 Ogura, Saiwa-Ku
Kawasaki, Kanagawa 212-0054
Japan
Phone: +81-44-580-1600
Fax: +81-44-580-1437
EMail: ernst@sfc.wide.ad.jp
URI: http://www.sfc.wide.ad.jp/~ernst/
Thomas Noel
LSIIT - Univerity Louis Pasteur
Pole API, bureau C444
Boulevard Sebastien Brant
Illkirch 67400
FRANCE
Phone: (33) 3 90 24 45 92
EMail: noel@dpt-info.u-strasbg.fr
URI: http://www-r2.u-strasbg.fr/~noel/
Chan-Wah Ng
Panasonic Singapore Laboratories Pte Ltd
Blk 1022 Tai Seng Ave #06-3530
Tai Seng Industrial Estate
Singapore 534415
SG
Phone: +65 65505420
EMail: cwng@psl.com.sg
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